Empty commit to test performance

## Summary

Previously, we panicked on expressions like `f"{v:{f'0.2f'}}"` because
we did not infer types for expressions nested inside format spec
elements.

## Test Plan

```
cargo nextest run -p red_knot_workspace -- --ignored linter_af linter_gz
```

.editorconfig

@@ -17,4 +17,7 @@ indent_size = 4
 trim_trailing_whitespace = false
 
 [*.md]
-max_line_length = 100
+max_line_length = 100
+
+[*.toml]
+indent_size = 4

.github/workflows/ci.yaml

@@ -268,6 +268,7 @@ jobs:
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: "fuzz -> target"
+          cache-all-crates: "true"
       - name: "Install cargo-binstall"
         uses: cargo-bins/cargo-binstall@main
         with:

.pre-commit-config.yaml

@@ -17,7 +17,7 @@ exclude: |
 
 repos:
   - repo: https://github.com/abravalheri/validate-pyproject
-    rev: v0.22
+    rev: v0.23
     hooks:
       - id: validate-pyproject
 
@@ -73,7 +73,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.7.3
+    rev: v0.7.4
     hooks:
       - id: ruff-format
       - id: ruff

CHANGELOG.md

@@ -1,5 +1,54 @@
 # Changelog
 
+## 0.7.4
+
+### Preview features
+
+- \[`flake8-datetimez`\] Detect usages of `datetime.max`/`datetime.min` (`DTZ901`) ([#14288](https://github.com/astral-sh/ruff/pull/14288))
+- \[`flake8-logging`\] Implement `root-logger-calls` (`LOG015`) ([#14302](https://github.com/astral-sh/ruff/pull/14302))
+- \[`flake8-no-pep420`\] Detect empty implicit namespace packages (`INP001`) ([#14236](https://github.com/astral-sh/ruff/pull/14236))
+- \[`flake8-pyi`\] Add "replace with `Self`" fix (`PYI019`) ([#14238](https://github.com/astral-sh/ruff/pull/14238))
+- \[`perflint`\] Implement quick-fix for `manual-list-comprehension` (`PERF401`) ([#13919](https://github.com/astral-sh/ruff/pull/13919))
+- \[`pylint`\] Implement `shallow-copy-environ` (`W1507`) ([#14241](https://github.com/astral-sh/ruff/pull/14241))
+- \[`ruff`\] Implement `none-not-at-end-of-union` (`RUF036`) ([#14314](https://github.com/astral-sh/ruff/pull/14314))
+- \[`ruff`\] Implementation `unsafe-markup-call` from `flake8-markupsafe` plugin (`RUF035`) ([#14224](https://github.com/astral-sh/ruff/pull/14224))
+- \[`ruff`\] Report problems for `attrs` dataclasses (`RUF008`, `RUF009`) ([#14327](https://github.com/astral-sh/ruff/pull/14327))
+
+### Rule changes
+
+- \[`flake8-boolean-trap`\] Exclude dunder methods that define operators (`FBT001`) ([#14203](https://github.com/astral-sh/ruff/pull/14203))
+- \[`flake8-pyi`\] Add "replace with `Self`" fix (`PYI034`) ([#14217](https://github.com/astral-sh/ruff/pull/14217))
+- \[`flake8-pyi`\] Always autofix `duplicate-union-members` (`PYI016`) ([#14270](https://github.com/astral-sh/ruff/pull/14270))
+- \[`flake8-pyi`\] Improve autofix for nested and mixed type unions for `unnecessary-type-union` (`PYI055`) ([#14272](https://github.com/astral-sh/ruff/pull/14272))
+- \[`flake8-pyi`\] Mark fix as unsafe when type annotation contains comments for `duplicate-literal-member` (`PYI062`) ([#14268](https://github.com/astral-sh/ruff/pull/14268))
+
+### Server
+
+- Use the current working directory to resolve settings from `ruff.configuration` ([#14352](https://github.com/astral-sh/ruff/pull/14352))
+
+### Bug fixes
+
+- Avoid conflicts between `PLC014` (`useless-import-alias`) and `I002` (`missing-required-import`) by considering `lint.isort.required-imports` for `PLC014` ([#14287](https://github.com/astral-sh/ruff/pull/14287))
+- \[`flake8-type-checking`\] Skip quoting annotation if it becomes invalid syntax (`TCH001`)
+- \[`flake8-pyi`\] Avoid using `typing.Self` in stub files pre-Python 3.11 (`PYI034`) ([#14230](https://github.com/astral-sh/ruff/pull/14230))
+- \[`flake8-pytest-style`\] Flag `pytest.raises` call with keyword argument `expected_exception` (`PT011`) ([#14298](https://github.com/astral-sh/ruff/pull/14298))
+- \[`flake8-simplify`\] Infer "unknown" truthiness for literal iterables whose items are all unpacks (`SIM222`) ([#14263](https://github.com/astral-sh/ruff/pull/14263))
+- \[`flake8-type-checking`\] Fix false positives for `typing.Annotated` (`TCH001`) ([#14311](https://github.com/astral-sh/ruff/pull/14311))
+- \[`pylint`\] Allow `await` at the top-level scope of a notebook (`PLE1142`) ([#14225](https://github.com/astral-sh/ruff/pull/14225))
+- \[`pylint`\] Fix miscellaneous issues in `await-outside-async` detection (`PLE1142`) ([#14218](https://github.com/astral-sh/ruff/pull/14218))
+- \[`pyupgrade`\] Avoid applying PEP 646 rewrites in invalid contexts (`UP044`) ([#14234](https://github.com/astral-sh/ruff/pull/14234))
+- \[`pyupgrade`\] Detect permutations in redundant open modes (`UP015`) ([#14255](https://github.com/astral-sh/ruff/pull/14255))
+- \[`refurb`\] Avoid triggering `hardcoded-string-charset` for reordered sets (`FURB156`) ([#14233](https://github.com/astral-sh/ruff/pull/14233))
+- \[`refurb`\] Further special cases added to `verbose-decimal-constructor` (`FURB157`) ([#14216](https://github.com/astral-sh/ruff/pull/14216))
+- \[`refurb`\] Use `UserString` instead of non-existent `UserStr` (`FURB189`) ([#14209](https://github.com/astral-sh/ruff/pull/14209))
+- \[`ruff`\] Avoid treating lowercase letters as `# noqa` codes (`RUF100`) ([#14229](https://github.com/astral-sh/ruff/pull/14229))
+- \[`ruff`\] Do not report when `Optional` has no type arguments (`RUF013`) ([#14181](https://github.com/astral-sh/ruff/pull/14181))
+
+### Documentation
+
+- Add "Notebook behavior" section for `F704`, `PLE1142` ([#14266](https://github.com/astral-sh/ruff/pull/14266))
+- Document comment policy around fix safety ([#14300](https://github.com/astral-sh/ruff/pull/14300))
+
 ## 0.7.3
 
 ### Preview features

Cargo.lock

@@ -170,6 +170,12 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f1fdabc7756949593fe60f30ec81974b613357de856987752631dea1e3394c80"
 
+[[package]]
+name = "base64"
+version = "0.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9e1b586273c5702936fe7b7d6896644d8be71e6314cfe09d3167c95f712589e8"
+
 [[package]]
 name = "base64"
 version = "0.22.0"
@@ -208,9 +214,9 @@ dependencies = [
 
 [[package]]
 name = "bstr"
-version = "1.10.0"
+version = "1.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "40723b8fb387abc38f4f4a37c09073622e41dd12327033091ef8950659e6dc0c"
+checksum = "1a68f1f47cdf0ec8ee4b941b2eee2a80cb796db73118c0dd09ac63fbe405be22"
 dependencies = [
  "memchr",
  "regex-automata 0.4.8",
@@ -341,9 +347,9 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "4.5.20"
+version = "4.5.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b97f376d85a664d5837dbae44bf546e6477a679ff6610010f17276f686d867e8"
+checksum = "fb3b4b9e5a7c7514dfa52869339ee98b3156b0bfb4e8a77c4ff4babb64b1604f"
 dependencies = [
  "clap_builder",
  "clap_derive",
@@ -351,9 +357,9 @@ dependencies = [
 
 [[package]]
 name = "clap_builder"
-version = "4.5.20"
+version = "4.5.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "19bc80abd44e4bed93ca373a0704ccbd1b710dc5749406201bb018272808dc54"
+checksum = "b17a95aa67cc7b5ebd32aa5370189aa0d79069ef1c64ce893bd30fb24bff20ec"
 dependencies = [
  "anstream",
  "anstyle",
@@ -829,6 +835,12 @@ version = "0.1.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9bda8e21c04aca2ae33ffc2fd8c23134f3cac46db123ba97bd9d3f3b8a4a85e1"
 
+[[package]]
+name = "dunce"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "92773504d58c093f6de2459af4af33faa518c13451eb8f2b5698ed3d36e7c813"
+
 [[package]]
 name = "dyn-clone"
 version = "1.0.17"
@@ -1307,16 +1319,16 @@ dependencies = [
 
 [[package]]
 name = "indicatif"
-version = "0.17.8"
+version = "0.17.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "763a5a8f45087d6bcea4222e7b72c291a054edf80e4ef6efd2a4979878c7bea3"
+checksum = "cbf675b85ed934d3c67b5c5469701eec7db22689d0a2139d856e0925fa28b281"
 dependencies = [
  "console",
- "instant",
  "number_prefix",
  "portable-atomic",
- "unicode-width 0.1.13",
+ "unicode-width 0.2.0",
  "vt100",
+ "web-time",
 ]
 
 [[package]]
@@ -1358,6 +1370,7 @@ dependencies = [
  "pest",
  "pest_derive",
  "regex",
+ "ron",
  "serde",
  "similar",
  "walkdir",
@@ -1501,9 +1514,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.162"
+version = "0.2.164"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "18d287de67fe55fd7e1581fe933d965a5a9477b38e949cfa9f8574ef01506398"
+checksum = "433bfe06b8c75da9b2e3fbea6e5329ff87748f0b144ef75306e674c3f6f7c13f"
 
 [[package]]
 name = "libcst"
@@ -2269,6 +2282,7 @@ dependencies = [
  "ruff_text_size",
  "rustc-hash 2.0.0",
  "salsa",
+ "serde",
  "smallvec",
  "static_assertions",
  "tempfile",
@@ -2353,7 +2367,10 @@ version = "0.0.0"
 dependencies = [
  "anyhow",
  "crossbeam",
+ "glob",
+ "insta",
  "notify",
+ "pep440_rs 0.7.2",
  "rayon",
  "red_knot_python_semantic",
  "red_knot_vendored",
@@ -2363,7 +2380,9 @@ dependencies = [
  "ruff_text_size",
  "rustc-hash 2.0.0",
  "salsa",
- "tempfile",
+ "serde",
+ "thiserror 2.0.3",
+ "toml",
  "tracing",
 ]
 
@@ -2455,9 +2474,20 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "ron"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "88073939a61e5b7680558e6be56b419e208420c2adb92be54921fa6b72283f1a"
+dependencies = [
+ "base64 0.13.1",
+ "bitflags 1.3.2",
+ "serde",
+]
+
 [[package]]
 name = "ruff"
-version = "0.7.3"
+version = "0.7.4"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2556,7 +2586,9 @@ dependencies = [
  "camino",
  "countme",
  "dashmap 6.1.0",
+ "dunce",
  "filetime",
+ "glob",
  "ignore",
  "insta",
  "matchit",
@@ -2674,7 +2706,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.7.3"
+version = "0.7.4"
 dependencies = [
  "aho-corasick",
  "annotate-snippets 0.9.2",
@@ -2778,7 +2810,6 @@ dependencies = [
  "ruff_source_file",
  "ruff_text_size",
  "rustc-hash 2.0.0",
- "salsa",
  "schemars",
  "serde",
 ]
@@ -2990,7 +3021,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_wasm"
-version = "0.7.3"
+version = "0.7.4"
 dependencies = [
  "console_error_panic_hook",
  "console_log",
@@ -3218,9 +3249,9 @@ checksum = "1c107b6f4780854c8b126e228ea8869f4d7b71260f962fefb57b996b8959ba6b"
 
 [[package]]
 name = "serde"
-version = "1.0.214"
+version = "1.0.215"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f55c3193aca71c12ad7890f1785d2b73e1b9f63a0bbc353c08ef26fe03fc56b5"
+checksum = "6513c1ad0b11a9376da888e3e0baa0077f1aed55c17f50e7b2397136129fb88f"
 dependencies = [
  "serde_derive",
 ]
@@ -3238,9 +3269,9 @@ dependencies = [
 
 [[package]]
 name = "serde_derive"
-version = "1.0.214"
+version = "1.0.215"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "de523f781f095e28fa605cdce0f8307e451cc0fd14e2eb4cd2e98a355b147766"
+checksum = "ad1e866f866923f252f05c889987993144fb74e722403468a4ebd70c3cd756c0"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3260,9 +3291,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.132"
+version = "1.0.133"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d726bfaff4b320266d395898905d0eba0345aae23b54aee3a737e260fd46db03"
+checksum = "c7fceb2473b9166b2294ef05efcb65a3db80803f0b03ef86a5fc88a2b85ee377"
 dependencies = [
  "itoa",
  "memchr",
@@ -3907,7 +3938,7 @@ version = "2.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b74fc6b57825be3373f7054754755f03ac3a8f5d70015ccad699ba2029956f4a"
 dependencies = [
- "base64",
+ "base64 0.22.0",
  "flate2",
  "log",
  "once_cell",

Cargo.toml

@@ -66,6 +66,7 @@ criterion = { version = "0.5.1", default-features = false }
 crossbeam = { version = "0.8.4" }
 dashmap = { version = "6.0.1" }
 dir-test = { version = "0.3.0" }
+dunce = { version = "1.0.5" }
 drop_bomb = { version = "0.1.5" }
 env_logger = { version = "0.11.0" }
 etcetera = { version = "0.8.0" }
@@ -81,7 +82,7 @@ hashbrown = { version = "0.15.0", default-features = false, features = [
 ignore = { version = "0.4.22" }
 imara-diff = { version = "0.1.5" }
 imperative = { version = "1.0.4" }
-indexmap = {version = "2.6.0" }
+indexmap = { version = "2.6.0" }
 indicatif = { version = "0.17.8" }
 indoc = { version = "2.0.4" }
 insta = { version = "1.35.1" }

README.md

@@ -136,8 +136,8 @@ curl -LsSf https://astral.sh/ruff/install.sh | sh
 powershell -c "irm https://astral.sh/ruff/install.ps1 | iex"
 
 # For a specific version.
-curl -LsSf https://astral.sh/ruff/0.7.3/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.7.3/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.7.4/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.7.4/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -170,7 +170,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.7.3
+  rev: v0.7.4
   hooks:
     # Run the linter.
     - id: ruff

_typos.toml

@@ -1,6 +1,11 @@
 [files]
 # https://github.com/crate-ci/typos/issues/868
-extend-exclude = ["crates/red_knot_vendored/vendor/**/*", "**/resources/**/*", "**/snapshots/**/*"]
+extend-exclude = [
+  "crates/red_knot_vendored/vendor/**/*",
+  "**/resources/**/*",
+  "**/snapshots/**/*",
+  "crates/red_knot_workspace/src/workspace/pyproject/package_name.rs"
+]
 
 [default.extend-words]
 "arange" = "arange"  # e.g. `numpy.arange`

crates/red_knot/Cargo.toml

@@ -34,6 +34,7 @@ tracing-tree = { workspace = true }
 [dev-dependencies]
 filetime = { workspace = true }
 tempfile = { workspace = true }
+ruff_db = { workspace = true, features = ["testing"] }
 
 [lints]
 workspace = true

crates/red_knot/src/main.rs

@@ -183,10 +183,10 @@ fn run() -> anyhow::Result<ExitStatus> {
 
     let system = OsSystem::new(cwd.clone());
     let cli_configuration = args.to_configuration(&cwd);
-    let workspace_metadata = WorkspaceMetadata::from_path(
+    let workspace_metadata = WorkspaceMetadata::discover(
         system.current_directory(),
         &system,
-        Some(cli_configuration.clone()),
+        Some(&cli_configuration),
     )?;
 
     // TODO: Use the `program_settings` to compute the key for the database's persistent

crates/red_knot/src/target_version.rs

@@ -4,8 +4,8 @@
 #[derive(Copy, Clone, Hash, Debug, PartialEq, Eq, PartialOrd, Ord, Default, clap::ValueEnum)]
 pub enum TargetVersion {
     Py37,
-    #[default]
     Py38,
+    #[default]
     Py39,
     Py310,
     Py311,
@@ -46,3 +46,17 @@ impl From<TargetVersion> for red_knot_python_semantic::PythonVersion {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::target_version::TargetVersion;
+    use red_knot_python_semantic::PythonVersion;
+
+    #[test]
+    fn same_default_as_python_version() {
+        assert_eq!(
+            PythonVersion::from(TargetVersion::default()),
+            PythonVersion::default()
+        );
+    }
+}

crates/red_knot/tests/file_watching.rs

@@ -6,7 +6,7 @@ use std::time::Duration;
 use anyhow::{anyhow, Context};
 
 use red_knot_python_semantic::{resolve_module, ModuleName, Program, PythonVersion, SitePackages};
-use red_knot_workspace::db::RootDatabase;
+use red_knot_workspace::db::{Db, RootDatabase};
 use red_knot_workspace::watch;
 use red_knot_workspace::watch::{directory_watcher, WorkspaceWatcher};
 use red_knot_workspace::workspace::settings::{Configuration, SearchPathConfiguration};
@@ -14,6 +14,7 @@ use red_knot_workspace::workspace::WorkspaceMetadata;
 use ruff_db::files::{system_path_to_file, File, FileError};
 use ruff_db::source::source_text;
 use ruff_db::system::{OsSystem, SystemPath, SystemPathBuf};
+use ruff_db::testing::setup_logging;
 use ruff_db::Upcast;
 
 struct TestCase {
@@ -69,7 +70,6 @@ impl TestCase {
         Some(all_events)
     }
 
-    #[cfg(unix)]
     fn take_watch_changes(&self) -> Vec<watch::ChangeEvent> {
         self.try_take_watch_changes(Duration::from_secs(10))
             .expect("Expected watch changes but observed none")
@@ -110,8 +110,8 @@ impl TestCase {
     ) -> anyhow::Result<()> {
         let program = Program::get(self.db());
 
-        self.configuration.search_paths = configuration.clone();
-        let new_settings = configuration.into_settings(self.db.workspace().root(&self.db));
+        let new_settings = configuration.to_settings(self.db.workspace().root(&self.db));
+        self.configuration.search_paths = configuration;
 
         program.update_search_paths(&mut self.db, &new_settings)?;
 
@@ -204,7 +204,9 @@ where
             .as_utf8_path()
             .canonicalize_utf8()
             .with_context(|| "Failed to canonicalize root path.")?,
-    );
+    )
+    .simplified()
+    .to_path_buf();
 
     let workspace_path = root_path.join("workspace");
 
@@ -241,8 +243,7 @@ where
         search_paths,
     };
 
-    let workspace =
-        WorkspaceMetadata::from_path(&workspace_path, &system, Some(configuration.clone()))?;
+    let workspace = WorkspaceMetadata::discover(&workspace_path, &system, Some(&configuration))?;
 
     let db = RootDatabase::new(workspace, system)?;
 
@@ -1311,3 +1312,138 @@ mod unix {
         Ok(())
     }
 }
+
+#[test]
+fn nested_packages_delete_root() -> anyhow::Result<()> {
+    let mut case = setup(|root: &SystemPath, workspace_root: &SystemPath| {
+        std::fs::write(
+            workspace_root.join("pyproject.toml").as_std_path(),
+            r#"
+            [project]
+            name = "inner"
+            "#,
+        )?;
+
+        std::fs::write(
+            root.join("pyproject.toml").as_std_path(),
+            r#"
+            [project]
+            name = "outer"
+            "#,
+        )?;
+
+        Ok(())
+    })?;
+
+    assert_eq!(
+        case.db().workspace().root(case.db()),
+        &*case.workspace_path("")
+    );
+
+    std::fs::remove_file(case.workspace_path("pyproject.toml").as_std_path())?;
+
+    let changes = case.stop_watch();
+
+    case.apply_changes(changes);
+
+    // It should now pick up the outer workspace.
+    assert_eq!(case.db().workspace().root(case.db()), case.root_path());
+
+    Ok(())
+}
+
+#[test]
+fn added_package() -> anyhow::Result<()> {
+    let _ = setup_logging();
+    let mut case = setup([
+        (
+            "pyproject.toml",
+            r#"
+            [project]
+            name = "inner"
+
+            [tool.knot.workspace]
+            members = ["packages/*"]
+            "#,
+        ),
+        (
+            "packages/a/pyproject.toml",
+            r#"
+            [project]
+            name = "a"
+            "#,
+        ),
+    ])?;
+
+    assert_eq!(case.db().workspace().packages(case.db()).len(), 2);
+
+    std::fs::create_dir(case.workspace_path("packages/b").as_std_path())
+        .context("failed to create folder for package 'b'")?;
+
+    // It seems that the file watcher won't pick up on file changes shortly after the folder
+    // was created... I suspect this is because most file watchers don't support recursive
+    // file watching. Instead, file-watching libraries manually implement recursive file watching
+    // by setting a watcher for each directory. But doing this obviously "lags" behind.
+    case.take_watch_changes();
+
+    std::fs::write(
+        case.workspace_path("packages/b/pyproject.toml")
+            .as_std_path(),
+        r#"
+            [project]
+            name = "b"
+            "#,
+    )
+    .context("failed to write pyproject.toml for package b")?;
+
+    let changes = case.stop_watch();
+
+    case.apply_changes(changes);
+
+    assert_eq!(case.db().workspace().packages(case.db()).len(), 3);
+
+    Ok(())
+}
+
+#[test]
+fn removed_package() -> anyhow::Result<()> {
+    let mut case = setup([
+        (
+            "pyproject.toml",
+            r#"
+            [project]
+            name = "inner"
+
+            [tool.knot.workspace]
+            members = ["packages/*"]
+            "#,
+        ),
+        (
+            "packages/a/pyproject.toml",
+            r#"
+            [project]
+            name = "a"
+            "#,
+        ),
+        (
+            "packages/b/pyproject.toml",
+            r#"
+            [project]
+            name = "b"
+            "#,
+        ),
+    ])?;
+
+    assert_eq!(case.db().workspace().packages(case.db()).len(), 3);
+
+    std::fs::remove_dir_all(case.workspace_path("packages/b").as_std_path())
+        .context("failed to remove package 'b'")?;
+
+    let changes = case.stop_watch();
+
+    case.apply_changes(changes);
+
+    assert_eq!(case.db().workspace().packages(case.db()).len(), 2);
+
+    Ok(())
+}

crates/red_knot_python_semantic/Cargo.toml

@@ -13,7 +13,8 @@ license = { workspace = true }
 [dependencies]
 ruff_db = { workspace = true }
 ruff_index = { workspace = true }
-ruff_python_ast = { workspace = true, features = ["salsa"] }
+ruff_python_ast = { workspace = true }
+ruff_python_parser = { workspace = true }
 ruff_python_stdlib = { workspace = true }
 ruff_source_file = { workspace = true }
 ruff_text_size = { workspace = true }
@@ -32,6 +33,7 @@ thiserror = { workspace = true }
 tracing = { workspace = true }
 rustc-hash = { workspace = true }
 hashbrown = { workspace = true }
+serde = { workspace = true, optional = true }
 smallvec = { workspace = true }
 static_assertions = { workspace = true }
 test-case = { workspace = true }

crates/red_knot_python_semantic/resources/mdtest/annotations/optional.md

@@ -0,0 +1,47 @@
+# Optional
+
+## Annotation
+
+`typing.Optional` is equivalent to using the type with a None in a Union.
+
+```py
+from typing import Optional
+
+a: Optional[int]
+a1: Optional[bool]
+a2: Optional[Optional[bool]]
+a3: Optional[None]
+
+def f():
+    # revealed: int | None
+    reveal_type(a)
+    # revealed: bool | None
+    reveal_type(a1)
+    # revealed: bool | None
+    reveal_type(a2)
+    # revealed: None
+    reveal_type(a3)
+```
+
+## Assignment
+
+```py
+from typing import Optional
+
+a: Optional[int] = 1
+a = None
+# error: [invalid-assignment] "Object of type `Literal[""]` is not assignable to `int | None`"
+a = ""
+```
+
+## Typing Extensions
+
+```py
+from typing_extensions import Optional
+
+a: Optional[int]
+
+def f():
+    # revealed: int | None
+    reveal_type(a)
+```

crates/red_knot_python_semantic/resources/mdtest/annotations/string.md

@@ -1,9 +1,191 @@
 # String annotations
 
+## Simple
+
 ```py
 def f() -> "int":
     return 1
 
-# TODO: We do not support string annotations, but we should not panic if we encounter them
-reveal_type(f())  # revealed: @Todo
+reveal_type(f())  # revealed: int
 ```
+
+## Nested
+
+```py
+def f() -> "'int'":
+    return 1
+
+reveal_type(f())  # revealed: int
+```
+
+## Type expression
+
+```py
+def f1() -> "int | str":
+    return 1
+
+def f2() -> "tuple[int, str]":
+    return 1
+
+reveal_type(f1())  # revealed: int | str
+reveal_type(f2())  # revealed: tuple[int, str]
+```
+
+## Partial
+
+```py
+def f() -> tuple[int, "str"]:
+    return 1
+
+reveal_type(f())  # revealed: tuple[int, str]
+```
+
+## Deferred
+
+```py
+def f() -> "Foo":
+    return Foo()
+
+class Foo:
+    pass
+
+reveal_type(f())  # revealed: Foo
+```
+
+## Deferred (undefined)
+
+```py
+# error: [unresolved-reference]
+def f() -> "Foo":
+    pass
+
+reveal_type(f())  # revealed: Unknown
+```
+
+## Partial deferred
+
+```py
+def f() -> int | "Foo":
+    return 1
+
+class Foo:
+    pass
+
+reveal_type(f())  # revealed: int | Foo
+```
+
+## `typing.Literal`
+
+```py
+from typing import Literal
+
+def f1() -> Literal["Foo", "Bar"]:
+    return "Foo"
+
+def f2() -> 'Literal["Foo", "Bar"]':
+    return "Foo"
+
+class Foo:
+    pass
+
+reveal_type(f1())  # revealed: Literal["Foo", "Bar"]
+reveal_type(f2())  # revealed: Literal["Foo", "Bar"]
+```
+
+## Various string kinds
+
+```py
+# error: [annotation-raw-string] "Type expressions cannot use raw string literal"
+def f1() -> r"int":
+    return 1
+
+# error: [annotation-f-string] "Type expressions cannot use f-strings"
+def f2() -> f"int":
+    return 1
+
+# error: [annotation-byte-string] "Type expressions cannot use bytes literal"
+def f3() -> b"int":
+    return 1
+
+def f4() -> "int":
+    return 1
+
+# error: [annotation-implicit-concat] "Type expressions cannot span multiple string literals"
+def f5() -> "in" "t":
+    return 1
+
+# error: [annotation-escape-character] "Type expressions cannot contain escape characters"
+def f6() -> "\N{LATIN SMALL LETTER I}nt":
+    return 1
+
+# error: [annotation-escape-character] "Type expressions cannot contain escape characters"
+def f7() -> "\x69nt":
+    return 1
+
+def f8() -> """int""":
+    return 1
+
+# error: [annotation-byte-string] "Type expressions cannot use bytes literal"
+def f9() -> "b'int'":
+    return 1
+
+reveal_type(f1())  # revealed: Unknown
+reveal_type(f2())  # revealed: Unknown
+reveal_type(f3())  # revealed: Unknown
+reveal_type(f4())  # revealed: int
+reveal_type(f5())  # revealed: Unknown
+reveal_type(f6())  # revealed: Unknown
+reveal_type(f7())  # revealed: Unknown
+reveal_type(f8())  # revealed: int
+reveal_type(f9())  # revealed: Unknown
+```
+
+## Various string kinds in `typing.Literal`
+
+```py
+from typing import Literal
+
+def f() -> Literal["a", r"b", b"c", "d" "e", "\N{LATIN SMALL LETTER F}", "\x67", """h"""]:
+    return "normal"
+
+reveal_type(f())  # revealed: Literal["a", "b", "de", "f", "g", "h"] | Literal[b"c"]
+```
+
+## Class variables
+
+```py
+MyType = int
+
+class Aliases:
+    MyType = str
+
+    forward: "MyType"
+    not_forward: MyType
+
+reveal_type(Aliases.forward)  # revealed: str
+reveal_type(Aliases.not_forward)  # revealed: str
+```
+
+## Annotated assignment
+
+```py
+a: "int" = 1
+b: "'int'" = 1
+c: "Foo"
+# error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to `Foo`"
+d: "Foo" = 1
+
+class Foo:
+    pass
+
+c = Foo()
+
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[1]
+reveal_type(c)  # revealed: Foo
+reveal_type(d)  # revealed: Foo
+```
+
+## Parameter
+
+TODO: Add tests once parameter inference is supported

crates/red_knot_python_semantic/resources/mdtest/assignment/annotations.md

@@ -110,3 +110,29 @@ c: builtins.tuple[builtins.tuple[builtins.int, builtins.int], builtins.int] = ((
 # error: [invalid-assignment] "Object of type `Literal["foo"]` is not assignable to `tuple[tuple[int, int], int]`"
 c: builtins.tuple[builtins.tuple[builtins.int, builtins.int], builtins.int] = "foo"
 ```
+
+## Future annotations are deferred
+
+```py
+from __future__ import annotations
+
+x: Foo
+
+class Foo:
+    pass
+
+x = Foo()
+reveal_type(x)  # revealed: Foo
+```
+
+## Annotations in stub files are deferred
+
+```pyi path=main.pyi
+x: Foo
+
+class Foo:
+    pass
+
+x = Foo()
+reveal_type(x)  # revealed: Foo
+```

crates/red_knot_python_semantic/resources/mdtest/call/function.md

@@ -19,6 +19,15 @@ async def get_int_async() -> int:
 reveal_type(get_int_async())  # revealed: @Todo
 ```
 
+## Generic
+
+```py
+def get_int[T]() -> int:
+    return 42
+
+reveal_type(get_int())  # revealed: int
+```
+
 ## Decorated
 
 ```py

crates/red_knot_python_semantic/resources/mdtest/exception/basic.md

@@ -41,11 +41,10 @@ except EXCEPTIONS as f:
 ## Dynamic exception types
 
 ```py
-# TODO: we should not emit these `call-possibly-unbound-method` errors for `tuple.__class_getitem__`
 def foo(
     x: type[AttributeError],
-    y: tuple[type[OSError], type[RuntimeError]],  # error: [call-possibly-unbound-method]
-    z: tuple[type[BaseException], ...],  # error: [call-possibly-unbound-method]
+    y: tuple[type[OSError], type[RuntimeError]],
+    z: tuple[type[BaseException], ...],
 ):
     try:
         help()

crates/red_knot_python_semantic/resources/mdtest/generics.md

@@ -65,31 +65,31 @@ A PEP695 type variable defines a value of type `typing.TypeVar` with attributes
 
 ```py
 def f[T, U: A, V: (A, B), W = A, X: A = A1]():
-    reveal_type(T)  # revealed: TypeVar
+    reveal_type(T)  # revealed: T
     reveal_type(T.__name__)  # revealed: Literal["T"]
     reveal_type(T.__bound__)  # revealed: None
     reveal_type(T.__constraints__)  # revealed: tuple[()]
     reveal_type(T.__default__)  # revealed: NoDefault
 
-    reveal_type(U)  # revealed: TypeVar
+    reveal_type(U)  # revealed: U
     reveal_type(U.__name__)  # revealed: Literal["U"]
     reveal_type(U.__bound__)  # revealed: type[A]
     reveal_type(U.__constraints__)  # revealed: tuple[()]
     reveal_type(U.__default__)  # revealed: NoDefault
 
-    reveal_type(V)  # revealed: TypeVar
+    reveal_type(V)  # revealed: V
     reveal_type(V.__name__)  # revealed: Literal["V"]
     reveal_type(V.__bound__)  # revealed: None
     reveal_type(V.__constraints__)  # revealed: tuple[type[A], type[B]]
     reveal_type(V.__default__)  # revealed: NoDefault
 
-    reveal_type(W)  # revealed: TypeVar
+    reveal_type(W)  # revealed: W
     reveal_type(W.__name__)  # revealed: Literal["W"]
     reveal_type(W.__bound__)  # revealed: None
     reveal_type(W.__constraints__)  # revealed: tuple[()]
     reveal_type(W.__default__)  # revealed: type[A]
 
-    reveal_type(X)  # revealed: TypeVar
+    reveal_type(X)  # revealed: X
     reveal_type(X.__name__)  # revealed: Literal["X"]
     reveal_type(X.__bound__)  # revealed: type[A]
     reveal_type(X.__constraints__)  # revealed: tuple[()]

crates/red_knot_python_semantic/resources/mdtest/literal/literal.md

@@ -51,6 +51,8 @@ invalid1: Literal[3 + 4]
 invalid2: Literal[4 + 3j]
 # error: [invalid-literal-parameter]
 invalid3: Literal[(3, 4)]
+
+hello = "hello"
 invalid4: Literal[
     1 + 2,  # error: [invalid-literal-parameter]
     "foo",

crates/red_knot_python_semantic/resources/mdtest/narrow/type.md

@@ -0,0 +1,152 @@
+# Narrowing for checks involving `type(x)`
+
+## `type(x) is C`
+
+```py
+class A: ...
+class B: ...
+
+def get_a_or_b() -> A | B:
+    return A()
+
+x = get_a_or_b()
+
+if type(x) is A:
+    reveal_type(x)  # revealed: A
+else:
+    # It would be wrong to infer `B` here. The type
+    # of `x` could be a subclass of `A`, so we need
+    # to infer the full union type:
+    reveal_type(x)  # revealed: A | B
+```
+
+## `type(x) is not C`
+
+```py
+class A: ...
+class B: ...
+
+def get_a_or_b() -> A | B:
+    return A()
+
+x = get_a_or_b()
+
+if type(x) is not A:
+    # Same reasoning as above: no narrowing should occur here.
+    reveal_type(x)  # revealed: A | B
+else:
+    reveal_type(x)  # revealed: A
+```
+
+## `type(x) == C`, `type(x) != C`
+
+No narrowing can occur for equality comparisons, since there might be a custom `__eq__`
+implementation on the metaclass.
+
+TODO: Narrowing might be possible in some cases where the classes themselves are `@final` or their
+metaclass is `@final`.
+
+```py
+class IsEqualToEverything(type):
+    def __eq__(cls, other):
+        return True
+
+class A(metaclass=IsEqualToEverything): ...
+class B(metaclass=IsEqualToEverything): ...
+
+def get_a_or_b() -> A | B:
+    return B()
+
+x = get_a_or_b()
+
+if type(x) == A:
+    reveal_type(x)  # revealed: A | B
+
+if type(x) != A:
+    reveal_type(x)  # revealed: A | B
+```
+
+## No narrowing for custom `type` callable
+
+```py
+class A: ...
+class B: ...
+
+def type(x):
+    return int
+
+def get_a_or_b() -> A | B:
+    return A()
+
+x = get_a_or_b()
+
+if type(x) is A:
+    reveal_type(x)  # revealed: A | B
+else:
+    reveal_type(x)  # revealed: A | B
+```
+
+## No narrowing for multiple arguments
+
+No narrowing should occur if `type` is used to dynamically create a class:
+
+```py
+def get_str_or_int() -> str | int:
+    return "test"
+
+x = get_str_or_int()
+
+if type(x, (), {}) is str:
+    reveal_type(x)  # revealed: str | int
+else:
+    reveal_type(x)  # revealed: str | int
+```
+
+## No narrowing for keyword arguments
+
+`type` can't be used with a keyword argument:
+
+```py
+def get_str_or_int() -> str | int:
+    return "test"
+
+x = get_str_or_int()
+
+# TODO: we could issue a diagnostic here
+if type(object=x) is str:
+    reveal_type(x)  # revealed: str | int
+```
+
+## Narrowing if `type` is aliased
+
+```py
+class A: ...
+class B: ...
+
+alias_for_type = type
+
+def get_a_or_b() -> A | B:
+    return A()
+
+x = get_a_or_b()
+
+if alias_for_type(x) is A:
+    reveal_type(x)  # revealed: A
+```
+
+## Limitations
+
+```py
+class Base: ...
+class Derived(Base): ...
+
+def get_base() -> Base:
+    return Base()
+
+x = get_base()
+
+if type(x) is Base:
+    # Ideally, this could be narrower, but there is now way to
+    # express a constraint like `Base & ~ProperSubtypeOf[Base]`.
+    reveal_type(x)  # revealed: Base
+```

crates/red_knot_python_semantic/resources/mdtest/regression/14334_diagnostics_in_wrong_file.md

@@ -0,0 +1,13 @@
+# Regression test for #14334
+
+Regression test for [this issue](https://github.com/astral-sh/ruff/issues/14334).
+
+```py path=base.py
+# error: [invalid-base]
+class Base(2): ...
+```
+
+```py path=a.py
+# No error here
+from base import Base
+```

crates/red_knot_python_semantic/resources/mdtest/sys_version_info.md

@@ -22,23 +22,23 @@ type:
 ```py
 import sys
 
-reveal_type(sys.version_info >= (3, 8))  # revealed: Literal[True]
-reveal_type((3, 8) <= sys.version_info)  # revealed: Literal[True]
+reveal_type(sys.version_info >= (3, 9))  # revealed: Literal[True]
+reveal_type((3, 9) <= sys.version_info)  # revealed: Literal[True]
 
-reveal_type(sys.version_info > (3, 8))  # revealed: Literal[True]
-reveal_type((3, 8) < sys.version_info)  # revealed: Literal[True]
+reveal_type(sys.version_info > (3, 9))  # revealed: Literal[True]
+reveal_type((3, 9) < sys.version_info)  # revealed: Literal[True]
 
-reveal_type(sys.version_info < (3, 8))  # revealed: Literal[False]
-reveal_type((3, 8) > sys.version_info)  # revealed: Literal[False]
+reveal_type(sys.version_info < (3, 9))  # revealed: Literal[False]
+reveal_type((3, 9) > sys.version_info)  # revealed: Literal[False]
 
-reveal_type(sys.version_info <= (3, 8))  # revealed: Literal[False]
-reveal_type((3, 8) >= sys.version_info)  # revealed: Literal[False]
+reveal_type(sys.version_info <= (3, 9))  # revealed: Literal[False]
+reveal_type((3, 9) >= sys.version_info)  # revealed: Literal[False]
 
-reveal_type(sys.version_info == (3, 8))  # revealed: Literal[False]
-reveal_type((3, 8) == sys.version_info)  # revealed: Literal[False]
+reveal_type(sys.version_info == (3, 9))  # revealed: Literal[False]
+reveal_type((3, 9) == sys.version_info)  # revealed: Literal[False]
 
-reveal_type(sys.version_info != (3, 8))  # revealed: Literal[True]
-reveal_type((3, 8) != sys.version_info)  # revealed: Literal[True]
+reveal_type(sys.version_info != (3, 9))  # revealed: Literal[True]
+reveal_type((3, 9) != sys.version_info)  # revealed: Literal[True]
 ```
 
 ## Non-literal types from comparisons
@@ -49,15 +49,17 @@ sometimes not:
 ```py
 import sys
 
-reveal_type(sys.version_info >= (3, 8, 1))  # revealed: bool
-reveal_type(sys.version_info >= (3, 8, 1, "final", 0))  # revealed: bool
+reveal_type(sys.version_info >= (3, 9, 1))  # revealed: bool
+reveal_type(sys.version_info >= (3, 9, 1, "final", 0))  # revealed: bool
 
-# TODO: this is an invalid comparison (`sys.version_info` is a tuple of length 5)
-# Should we issue a diagnostic here?
-reveal_type(sys.version_info >= (3, 8, 1, "final", 0, 5))  # revealed: bool
+# TODO: While this won't fail at runtime, the user has probably made a mistake
+# if they're comparing a tuple of length >5 with `sys.version_info`
+# (`sys.version_info` is a tuple of length 5). It might be worth
+# emitting a lint diagnostic of some kind warning them about the probable error?
+reveal_type(sys.version_info >= (3, 9, 1, "final", 0, 5))  # revealed: bool
 
 # TODO: this should be `Literal[False]`; see #14279
-reveal_type(sys.version_info == (3, 8, 1, "finallllll", 0))  # revealed: bool
+reveal_type(sys.version_info == (3, 9, 1, "finallllll", 0))  # revealed: bool
 ```
 
 ## Imports and aliases
@@ -69,11 +71,11 @@ another name:
 from sys import version_info
 from sys import version_info as foo
 
-reveal_type(version_info >= (3, 8))  # revealed: Literal[True]
-reveal_type(foo >= (3, 8))  # revealed: Literal[True]
+reveal_type(version_info >= (3, 9))  # revealed: Literal[True]
+reveal_type(foo >= (3, 9))  # revealed: Literal[True]
 
 bar = version_info
-reveal_type(bar >= (3, 8))  # revealed: Literal[True]
+reveal_type(bar >= (3, 9))  # revealed: Literal[True]
 ```
 
 ## Non-stdlib modules named `sys`
@@ -90,7 +92,7 @@ version_info: tuple[int, int] = (4, 2)
 ```py path=package/script.py
 from .sys import version_info
 
-reveal_type(version_info >= (3, 8))  # revealed: bool
+reveal_type(version_info >= (3, 9))  # revealed: bool
 ```
 
 ## Accessing fields by name
@@ -101,8 +103,8 @@ The fields of `sys.version_info` can be accessed by name:
 import sys
 
 reveal_type(sys.version_info.major >= 3)  # revealed: Literal[True]
-reveal_type(sys.version_info.minor >= 8)  # revealed: Literal[True]
-reveal_type(sys.version_info.minor >= 9)  # revealed: Literal[False]
+reveal_type(sys.version_info.minor >= 9)  # revealed: Literal[True]
+reveal_type(sys.version_info.minor >= 10)  # revealed: Literal[False]
 ```
 
 But the `micro`, `releaselevel` and `serial` fields are inferred as `@Todo` until we support
@@ -124,14 +126,14 @@ The fields of `sys.version_info` can be accessed by index or by slice:
 import sys
 
 reveal_type(sys.version_info[0] < 3)  # revealed: Literal[False]
-reveal_type(sys.version_info[1] > 8)  # revealed: Literal[False]
+reveal_type(sys.version_info[1] > 9)  # revealed: Literal[False]
 
-# revealed: tuple[Literal[3], Literal[8], int, Literal["alpha", "beta", "candidate", "final"], int]
+# revealed: tuple[Literal[3], Literal[9], int, Literal["alpha", "beta", "candidate", "final"], int]
 reveal_type(sys.version_info[:5])
 
-reveal_type(sys.version_info[:2] >= (3, 8))  # revealed: Literal[True]
-reveal_type(sys.version_info[0:2] >= (3, 9))  # revealed: Literal[False]
-reveal_type(sys.version_info[:3] >= (3, 9, 1))  # revealed: Literal[False]
+reveal_type(sys.version_info[:2] >= (3, 9))  # revealed: Literal[True]
+reveal_type(sys.version_info[0:2] >= (3, 10))  # revealed: Literal[False]
+reveal_type(sys.version_info[:3] >= (3, 10, 1))  # revealed: Literal[False]
 reveal_type(sys.version_info[3] == "final")  # revealed: bool
 reveal_type(sys.version_info[3] == "finalllllll")  # revealed: Literal[False]
 ```

crates/red_knot_python_semantic/resources/mdtest/unary/invert_add_usub.md

@@ -1,4 +1,6 @@
-# Unary Operations
+# Invert, UAdd, USub
+
+## Instance
 
 ```py
 from typing import Literal

crates/red_knot_python_semantic/resources/mdtest/unary/not.md

@@ -113,3 +113,101 @@ reveal_type(not ())  # revealed: Literal[True]
 reveal_type(not ("hello",))  # revealed: Literal[False]
 reveal_type(not (1, "hello"))  # revealed: Literal[False]
 ```
+
+## Instance
+
+Not operator is inferred based on
+<https://docs.python.org/3/library/stdtypes.html#truth-value-testing>. An instance is True or False
+if the `__bool__` method says so.
+
+At runtime, the `__len__` method is a fallback for `__bool__`, but we can't make use of that. If we
+have a class that defines `__len__` but not `__bool__`, it is possible that any subclass could add a
+`__bool__` method that would invalidate whatever conclusion we drew from `__len__`. So instances of
+classes without a `__bool__` method, with or without `__len__`, must be inferred as unknown
+truthiness.
+
+```py
+class AlwaysTrue:
+    def __bool__(self) -> Literal[True]:
+        return True
+
+# revealed: Literal[False]
+reveal_type(not AlwaysTrue())
+
+class AlwaysFalse:
+    def __bool__(self) -> Literal[False]:
+        return False
+
+# revealed: Literal[True]
+reveal_type(not AlwaysFalse())
+
+# We don't get into a cycle if someone sets their `__bool__` method to the `bool` builtin:
+class BoolIsBool:
+    __bool__ = bool
+
+# revealed: bool
+reveal_type(not BoolIsBool())
+
+# At runtime, no `__bool__` and no `__len__` means truthy, but we can't rely on that, because
+# a subclass could add a `__bool__` method.
+class NoBoolMethod: ...
+
+# revealed: bool
+reveal_type(not NoBoolMethod())
+
+# And we can't rely on `__len__` for the same reason: a subclass could add `__bool__`.
+class LenZero:
+    def __len__(self) -> Literal[0]:
+        return 0
+
+# revealed: bool
+reveal_type(not LenZero())
+
+class LenNonZero:
+    def __len__(self) -> Literal[1]:
+        return 1
+
+# revealed: bool
+reveal_type(not LenNonZero())
+
+class WithBothLenAndBool1:
+    def __bool__(self) -> Literal[False]:
+        return False
+
+    def __len__(self) -> Literal[2]:
+        return 2
+
+# revealed: Literal[True]
+reveal_type(not WithBothLenAndBool1())
+
+class WithBothLenAndBool2:
+    def __bool__(self) -> Literal[True]:
+        return True
+
+    def __len__(self) -> Literal[0]:
+        return 0
+
+# revealed: Literal[False]
+reveal_type(not WithBothLenAndBool2())
+
+# TODO: raise diagnostic when __bool__ method is not valid: [unsupported-operator] "Method __bool__ for type `MethodBoolInvalid` should return `bool`, returned type `int`"
+# https://docs.python.org/3/reference/datamodel.html#object.__bool__
+class MethodBoolInvalid:
+    def __bool__(self) -> int:
+        return 0
+
+# revealed: bool
+reveal_type(not MethodBoolInvalid())
+
+# Don't trust a possibly-unbound `__bool__` method:
+def get_flag() -> bool:
+    return True
+
+class PossiblyUnboundBool:
+    if get_flag():
+        def __bool__(self) -> Literal[False]:
+            return False
+
+# revealed: bool
+reveal_type(not PossiblyUnboundBool())
+```

crates/red_knot_python_semantic/src/module_resolver/typeshed.rs

@@ -459,11 +459,11 @@ foo: 3.8-   # trailing comment
 ";
         let parsed_versions = TypeshedVersions::from_str(VERSIONS).unwrap();
         assert_eq!(parsed_versions.len(), 3);
-        assert_snapshot!(parsed_versions.to_string(), @r###"
+        assert_snapshot!(parsed_versions.to_string(), @r"
         bar: 2.7-3.10
         bar.baz: 3.1-3.9
         foo: 3.8-
-        "###
+        "
         );
     }
 

crates/red_knot_python_semantic/src/node_key.rs

@@ -1,14 +1,14 @@
-use ruff_python_ast::{AnyNodeRef, NodeKind};
-use ruff_text_size::{Ranged, TextRange};
+use ruff_python_ast::AnyNodeRef;
 
 /// Compact key for a node for use in a hash map.
 ///
-/// Compares two nodes by their kind and text range.
+/// Stores the memory address of the node, because using the range and the kind
+/// of the node is not enough to uniquely identify them in ASTs resulting from
+/// invalid syntax. For example, parsing the input `for` results in a `StmtFor`
+/// AST node where both the `target` and the `iter` field are `ExprName` nodes
+/// with the same (empty) range `3..3`.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
-pub(super) struct NodeKey {
-    kind: NodeKind,
-    range: TextRange,
-}
+pub(super) struct NodeKey(usize);
 
 impl NodeKey {
     pub(super) fn from_node<'a, N>(node: N) -> Self
@@ -16,9 +16,6 @@ impl NodeKey {
         N: Into<AnyNodeRef<'a>>,
     {
         let node = node.into();
-        NodeKey {
-            kind: node.kind(),
-            range: node.range(),
-        }
+        NodeKey(node.as_ptr().as_ptr() as usize)
     }
 }

crates/red_knot_python_semantic/src/program.rs

@@ -54,6 +54,7 @@ impl Program {
 }
 
 #[derive(Clone, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize))]
 pub struct ProgramSettings {
     pub target_version: PythonVersion,
     pub search_paths: SearchPathSettings,
@@ -61,6 +62,7 @@ pub struct ProgramSettings {
 
 /// Configures the search paths for module resolution.
 #[derive(Eq, PartialEq, Debug, Clone)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize))]
 pub struct SearchPathSettings {
     /// List of user-provided paths that should take first priority in the module resolution.
     /// Examples in other type checkers are mypy's MYPYPATH environment variable,
@@ -91,6 +93,7 @@ impl SearchPathSettings {
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize))]
 pub enum SitePackages {
     Derived {
         venv_path: SystemPathBuf,

crates/red_knot_python_semantic/src/python_version.rs

@@ -5,6 +5,7 @@ use std::fmt;
 /// Unlike the `TargetVersion` enums in the CLI crates,
 /// this does not necessarily represent a Python version that we actually support.
 #[derive(Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize))]
 pub struct PythonVersion {
     pub major: u8,
     pub minor: u8,
@@ -38,7 +39,7 @@ impl PythonVersion {
 
 impl Default for PythonVersion {
     fn default() -> Self {
-        Self::PY38
+        Self::PY39
     }
 }
 

crates/red_knot_python_semantic/src/semantic_index/ast_ids.rs

@@ -49,64 +49,50 @@ fn ast_ids<'db>(db: &'db dyn Db, scope: ScopeId) -> &'db AstIds {
     semantic_index(db, scope.file(db)).ast_ids(scope.file_scope_id(db))
 }
 
-pub trait HasScopedUseId {
-    /// The type of the ID uniquely identifying the use.
-    type Id: Copy;
-
-    /// Returns the ID that uniquely identifies the use in `scope`.
-    fn scoped_use_id(&self, db: &dyn Db, scope: ScopeId) -> Self::Id;
-}
-
 /// Uniquely identifies a use of a name in a [`crate::semantic_index::symbol::FileScopeId`].
 #[newtype_index]
 pub struct ScopedUseId;
 
-impl HasScopedUseId for ast::ExprName {
-    type Id = ScopedUseId;
+pub trait HasScopedUseId {
+    /// Returns the ID that uniquely identifies the use in `scope`.
+    fn scoped_use_id(&self, db: &dyn Db, scope: ScopeId) -> ScopedUseId;
+}
 
-    fn scoped_use_id(&self, db: &dyn Db, scope: ScopeId) -> Self::Id {
+impl HasScopedUseId for ast::ExprName {
+    fn scoped_use_id(&self, db: &dyn Db, scope: ScopeId) -> ScopedUseId {
         let expression_ref = ExpressionRef::from(self);
         expression_ref.scoped_use_id(db, scope)
     }
 }
 
 impl HasScopedUseId for ast::ExpressionRef<'_> {
-    type Id = ScopedUseId;
-
-    fn scoped_use_id(&self, db: &dyn Db, scope: ScopeId) -> Self::Id {
+    fn scoped_use_id(&self, db: &dyn Db, scope: ScopeId) -> ScopedUseId {
         let ast_ids = ast_ids(db, scope);
         ast_ids.use_id(*self)
     }
 }
 
-pub trait HasScopedAstId {
-    /// The type of the ID uniquely identifying the node.
-    type Id: Copy;
-
-    /// Returns the ID that uniquely identifies the node in `scope`.
-    fn scoped_ast_id(&self, db: &dyn Db, scope: ScopeId) -> Self::Id;
-}
-
-impl<T: HasScopedAstId> HasScopedAstId for Box<T> {
-    type Id = <T as HasScopedAstId>::Id;
-
-    fn scoped_ast_id(&self, db: &dyn Db, scope: ScopeId) -> Self::Id {
-        self.as_ref().scoped_ast_id(db, scope)
-    }
-}
-
 /// Uniquely identifies an [`ast::Expr`] in a [`crate::semantic_index::symbol::FileScopeId`].
 #[newtype_index]
 pub struct ScopedExpressionId;
 
+pub trait HasScopedExpressionId {
+    /// Returns the ID that uniquely identifies the node in `scope`.
+    fn scoped_expression_id(&self, db: &dyn Db, scope: ScopeId) -> ScopedExpressionId;
+}
+
+impl<T: HasScopedExpressionId> HasScopedExpressionId for Box<T> {
+    fn scoped_expression_id(&self, db: &dyn Db, scope: ScopeId) -> ScopedExpressionId {
+        self.as_ref().scoped_expression_id(db, scope)
+    }
+}
+
 macro_rules! impl_has_scoped_expression_id {
     ($ty: ty) => {
-        impl HasScopedAstId for $ty {
-            type Id = ScopedExpressionId;
-
-            fn scoped_ast_id(&self, db: &dyn Db, scope: ScopeId) -> Self::Id {
+        impl HasScopedExpressionId for $ty {
+            fn scoped_expression_id(&self, db: &dyn Db, scope: ScopeId) -> ScopedExpressionId {
                 let expression_ref = ExpressionRef::from(self);
-                expression_ref.scoped_ast_id(db, scope)
+                expression_ref.scoped_expression_id(db, scope)
             }
         }
     };
@@ -146,29 +132,20 @@ impl_has_scoped_expression_id!(ast::ExprSlice);
 impl_has_scoped_expression_id!(ast::ExprIpyEscapeCommand);
 impl_has_scoped_expression_id!(ast::Expr);
 
-impl HasScopedAstId for ast::ExpressionRef<'_> {
-    type Id = ScopedExpressionId;
-
-    fn scoped_ast_id(&self, db: &dyn Db, scope: ScopeId) -> Self::Id {
+impl HasScopedExpressionId for ast::ExpressionRef<'_> {
+    fn scoped_expression_id(&self, db: &dyn Db, scope: ScopeId) -> ScopedExpressionId {
         let ast_ids = ast_ids(db, scope);
         ast_ids.expression_id(*self)
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub(super) struct AstIdsBuilder {
     expressions_map: FxHashMap<ExpressionNodeKey, ScopedExpressionId>,
     uses_map: FxHashMap<ExpressionNodeKey, ScopedUseId>,
 }
 
 impl AstIdsBuilder {
-    pub(super) fn new() -> Self {
-        Self {
-            expressions_map: FxHashMap::default(),
-            uses_map: FxHashMap::default(),
-        }
-    }
-
     /// Adds `expr` to the expression ids map and returns its id.
     pub(super) fn record_expression(&mut self, expr: &ast::Expr) -> ScopedExpressionId {
         let expression_id = self.expressions_map.len().into();

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -124,9 +124,9 @@ impl<'db> SemanticIndexBuilder<'db> {
         self.try_node_context_stack_manager.enter_nested_scope();
 
         let file_scope_id = self.scopes.push(scope);
-        self.symbol_tables.push(SymbolTableBuilder::new());
-        self.use_def_maps.push(UseDefMapBuilder::new());
-        let ast_id_scope = self.ast_ids.push(AstIdsBuilder::new());
+        self.symbol_tables.push(SymbolTableBuilder::default());
+        self.use_def_maps.push(UseDefMapBuilder::default());
+        let ast_id_scope = self.ast_ids.push(AstIdsBuilder::default());
 
         let scope_id = ScopeId::new(self.db, self.file, file_scope_id, countme::Count::default());
 
@@ -589,27 +589,6 @@ where
                     },
                 );
             }
-            ast::Stmt::TypeAlias(type_alias) => {
-                let symbol = self.add_symbol(
-                    type_alias
-                        .name
-                        .as_name_expr()
-                        .expect("type alias name is a name expr")
-                        .id
-                        .clone(),
-                );
-                self.add_definition(symbol, type_alias);
-
-                self.with_type_params(
-                    NodeWithScopeRef::TypeAliasTypeParameters(type_alias),
-                    type_alias.type_params.as_ref(),
-                    |builder| {
-                        builder.push_scope(NodeWithScopeRef::TypeAliasTypeParameters(type_alias));
-                        builder.visit_expr(&type_alias.value);
-                        builder.pop_scope()
-                    },
-                );
-            }
             ast::Stmt::Import(node) => {
                 for alias in &node.names {
                     let symbol_name = if let Some(asname) = &alias.asname {
@@ -697,9 +676,18 @@ where
                 if let Some(value) = &node.value {
                     self.visit_expr(value);
                 }
-                self.push_assignment(node.into());
-                self.visit_expr(&node.target);
-                self.pop_assignment();
+
+                // See https://docs.python.org/3/library/ast.html#ast.AnnAssign
+                if matches!(
+                    *node.target,
+                    ast::Expr::Attribute(_) | ast::Expr::Subscript(_) | ast::Expr::Name(_)
+                ) {
+                    self.push_assignment(node.into());
+                    self.visit_expr(&node.target);
+                    self.pop_assignment();
+                } else {
+                    self.visit_expr(&node.target);
+                }
             }
             ast::Stmt::AugAssign(
                 aug_assign @ ast::StmtAugAssign {
@@ -711,9 +699,18 @@ where
             ) => {
                 debug_assert_eq!(&self.current_assignments, &[]);
                 self.visit_expr(value);
-                self.push_assignment(aug_assign.into());
-                self.visit_expr(target);
-                self.pop_assignment();
+
+                // See https://docs.python.org/3/library/ast.html#ast.AugAssign
+                if matches!(
+                    **target,
+                    ast::Expr::Attribute(_) | ast::Expr::Subscript(_) | ast::Expr::Name(_)
+                ) {
+                    self.push_assignment(aug_assign.into());
+                    self.visit_expr(target);
+                    self.pop_assignment();
+                } else {
+                    self.visit_expr(target);
+                }
             }
             ast::Stmt::If(node) => {
                 self.visit_expr(&node.test);
@@ -1093,9 +1090,15 @@ where
             ast::Expr::Named(node) => {
                 // TODO walrus in comprehensions is implicitly nonlocal
                 self.visit_expr(&node.value);
-                self.push_assignment(node.into());
-                self.visit_expr(&node.target);
-                self.pop_assignment();
+
+                // See https://peps.python.org/pep-0572/#differences-between-assignment-expressions-and-assignment-statements
+                if node.target.is_name_expr() {
+                    self.push_assignment(node.into());
+                    self.visit_expr(&node.target);
+                    self.pop_assignment();
+                } else {
+                    self.visit_expr(&node.target);
+                }
             }
             ast::Expr::Lambda(lambda) => {
                 if let Some(parameters) = &lambda.parameters {

crates/red_knot_python_semantic/src/semantic_index/definition.rs

@@ -83,7 +83,6 @@ pub(crate) enum DefinitionNodeRef<'a> {
     For(ForStmtDefinitionNodeRef<'a>),
     Function(&'a ast::StmtFunctionDef),
     Class(&'a ast::StmtClassDef),
-    TypeAlias(&'a ast::StmtTypeAlias),
     NamedExpression(&'a ast::ExprNamed),
     Assignment(AssignmentDefinitionNodeRef<'a>),
     AnnotatedAssignment(&'a ast::StmtAnnAssign),
@@ -110,12 +109,6 @@ impl<'a> From<&'a ast::StmtClassDef> for DefinitionNodeRef<'a> {
     }
 }
 
-impl<'a> From<&'a ast::StmtTypeAlias> for DefinitionNodeRef<'a> {
-    fn from(node: &'a ast::StmtTypeAlias) -> Self {
-        Self::TypeAlias(node)
-    }
-}
-
 impl<'a> From<&'a ast::ExprNamed> for DefinitionNodeRef<'a> {
     fn from(node: &'a ast::ExprNamed) -> Self {
         Self::NamedExpression(node)
@@ -272,9 +265,6 @@ impl<'db> DefinitionNodeRef<'db> {
             DefinitionNodeRef::Class(class) => {
                 DefinitionKind::Class(AstNodeRef::new(parsed, class))
             }
-            DefinitionNodeRef::TypeAlias(type_alias) => {
-                DefinitionKind::TypeAlias(AstNodeRef::new(parsed, type_alias))
-            }
             DefinitionNodeRef::NamedExpression(named) => {
                 DefinitionKind::NamedExpression(AstNodeRef::new(parsed, named))
             }
@@ -368,7 +358,6 @@ impl<'db> DefinitionNodeRef<'db> {
             }
             Self::Function(node) => node.into(),
             Self::Class(node) => node.into(),
-            Self::TypeAlias(node) => node.into(),
             Self::NamedExpression(node) => node.into(),
             Self::Assignment(AssignmentDefinitionNodeRef {
                 value: _,
@@ -445,7 +434,6 @@ pub enum DefinitionKind<'db> {
     ImportFrom(ImportFromDefinitionKind),
     Function(AstNodeRef<ast::StmtFunctionDef>),
     Class(AstNodeRef<ast::StmtClassDef>),
-    TypeAlias(AstNodeRef<ast::StmtTypeAlias>),
     NamedExpression(AstNodeRef<ast::ExprNamed>),
     Assignment(AssignmentDefinitionKind<'db>),
     AnnotatedAssignment(AstNodeRef<ast::StmtAnnAssign>),
@@ -468,7 +456,6 @@ impl DefinitionKind<'_> {
             // functions, classes, and imports always bind, and we consider them declarations
             DefinitionKind::Function(_)
             | DefinitionKind::Class(_)
-            | DefinitionKind::TypeAlias(_)
             | DefinitionKind::Import(_)
             | DefinitionKind::ImportFrom(_)
             | DefinitionKind::TypeVar(_)
@@ -695,12 +682,6 @@ impl From<&ast::StmtClassDef> for DefinitionNodeKey {
     }
 }
 
-impl From<&ast::StmtTypeAlias> for DefinitionNodeKey {
-    fn from(node: &ast::StmtTypeAlias) -> Self {
-        Self(NodeKey::from_node(node))
-    }
-}
-
 impl From<&ast::ExprName> for DefinitionNodeKey {
     fn from(node: &ast::ExprName) -> Self {
         Self(NodeKey::from_node(node))

crates/red_knot_python_semantic/src/semantic_index/symbol.rs

@@ -142,11 +142,6 @@ impl<'db> ScopeId<'db> {
             NodeWithScopeKind::Class(class) | NodeWithScopeKind::ClassTypeParameters(class) => {
                 class.name.as_str()
             }
-            NodeWithScopeKind::TypeAliasTypeParameters(type_alias) => type_alias
-                .name
-                .as_name_expr()
-                .map(|name| name.id.as_str())
-                .unwrap_or("<type alias>"),
             NodeWithScopeKind::Function(function)
             | NodeWithScopeKind::FunctionTypeParameters(function) => function.name.as_str(),
             NodeWithScopeKind::Lambda(_) => "<lambda>",
@@ -215,7 +210,7 @@ impl ScopeKind {
 }
 
 /// Symbol table for a specific [`Scope`].
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub struct SymbolTable {
     /// The symbols in this scope.
     symbols: IndexVec<ScopedSymbolId, Symbol>,
@@ -225,13 +220,6 @@ pub struct SymbolTable {
 }
 
 impl SymbolTable {
-    fn new() -> Self {
-        Self {
-            symbols: IndexVec::new(),
-            symbols_by_name: SymbolMap::default(),
-        }
-    }
-
     fn shrink_to_fit(&mut self) {
         self.symbols.shrink_to_fit();
     }
@@ -283,18 +271,12 @@ impl PartialEq for SymbolTable {
 
 impl Eq for SymbolTable {}
 
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub(super) struct SymbolTableBuilder {
     table: SymbolTable,
 }
 
 impl SymbolTableBuilder {
-    pub(super) fn new() -> Self {
-        Self {
-            table: SymbolTable::new(),
-        }
-    }
-
     pub(super) fn add_symbol(&mut self, name: Name) -> (ScopedSymbolId, bool) {
         let hash = SymbolTable::hash_name(&name);
         let entry = self
@@ -344,7 +326,6 @@ pub(crate) enum NodeWithScopeRef<'a> {
     Lambda(&'a ast::ExprLambda),
     FunctionTypeParameters(&'a ast::StmtFunctionDef),
     ClassTypeParameters(&'a ast::StmtClassDef),
-    TypeAliasTypeParameters(&'a ast::StmtTypeAlias),
     ListComprehension(&'a ast::ExprListComp),
     SetComprehension(&'a ast::ExprSetComp),
     DictComprehension(&'a ast::ExprDictComp),
@@ -366,9 +347,6 @@ impl NodeWithScopeRef<'_> {
             NodeWithScopeRef::Function(function) => {
                 NodeWithScopeKind::Function(AstNodeRef::new(module, function))
             }
-            NodeWithScopeRef::TypeAliasTypeParameters(type_alias) => {
-                NodeWithScopeKind::TypeAliasTypeParameters(AstNodeRef::new(module, type_alias))
-            }
             NodeWithScopeRef::Lambda(lambda) => {
                 NodeWithScopeKind::Lambda(AstNodeRef::new(module, lambda))
             }
@@ -409,9 +387,6 @@ impl NodeWithScopeRef<'_> {
             NodeWithScopeRef::ClassTypeParameters(class) => {
                 NodeWithScopeKey::ClassTypeParameters(NodeKey::from_node(class))
             }
-            NodeWithScopeRef::TypeAliasTypeParameters(type_alias) => {
-                NodeWithScopeKey::TypeAliasTypeParameters(NodeKey::from_node(type_alias))
-            }
             NodeWithScopeRef::ListComprehension(comprehension) => {
                 NodeWithScopeKey::ListComprehension(NodeKey::from_node(comprehension))
             }
@@ -436,7 +411,6 @@ pub enum NodeWithScopeKind {
     ClassTypeParameters(AstNodeRef<ast::StmtClassDef>),
     Function(AstNodeRef<ast::StmtFunctionDef>),
     FunctionTypeParameters(AstNodeRef<ast::StmtFunctionDef>),
-    TypeAliasTypeParameters(AstNodeRef<ast::StmtTypeAlias>),
     Lambda(AstNodeRef<ast::ExprLambda>),
     ListComprehension(AstNodeRef<ast::ExprListComp>),
     SetComprehension(AstNodeRef<ast::ExprSetComp>),
@@ -451,9 +425,7 @@ impl NodeWithScopeKind {
             Self::Class(_) => ScopeKind::Class,
             Self::Function(_) => ScopeKind::Function,
             Self::Lambda(_) => ScopeKind::Function,
-            Self::FunctionTypeParameters(_)
-            | Self::ClassTypeParameters(_)
-            | Self::TypeAliasTypeParameters(_) => ScopeKind::Annotation,
+            Self::FunctionTypeParameters(_) | Self::ClassTypeParameters(_) => ScopeKind::Annotation,
             Self::ListComprehension(_)
             | Self::SetComprehension(_)
             | Self::DictComprehension(_)
@@ -483,7 +455,6 @@ pub(crate) enum NodeWithScopeKey {
     ClassTypeParameters(NodeKey),
     Function(NodeKey),
     FunctionTypeParameters(NodeKey),
-    TypeAliasTypeParameters(NodeKey),
     Lambda(NodeKey),
     ListComprehension(NodeKey),
     SetComprehension(NodeKey),

crates/red_knot_python_semantic/src/semantic_index/use_def.rs

@@ -459,10 +459,6 @@ pub(super) struct UseDefMapBuilder<'db> {
 }
 
 impl<'db> UseDefMapBuilder<'db> {
-    pub(super) fn new() -> Self {
-        Self::default()
-    }
-
     pub(super) fn add_symbol(&mut self, symbol: ScopedSymbolId) {
         let new_symbol = self.symbol_states.push(SymbolState::undefined());
         debug_assert_eq!(symbol, new_symbol);

crates/red_knot_python_semantic/src/semantic_model.rs

@@ -6,7 +6,7 @@ use ruff_source_file::LineIndex;
 
 use crate::module_name::ModuleName;
 use crate::module_resolver::{resolve_module, Module};
-use crate::semantic_index::ast_ids::HasScopedAstId;
+use crate::semantic_index::ast_ids::HasScopedExpressionId;
 use crate::semantic_index::semantic_index;
 use crate::types::{binding_ty, infer_scope_types, Type};
 use crate::Db;
@@ -54,7 +54,7 @@ impl HasTy for ast::ExpressionRef<'_> {
         let file_scope = index.expression_scope_id(*self);
         let scope = file_scope.to_scope_id(model.db, model.file);
 
-        let expression_id = self.scoped_ast_id(model.db, scope);
+        let expression_id = self.scoped_expression_id(model.db, scope);
         infer_scope_types(model.db, scope).expression_ty(expression_id)
     }
 }

crates/red_knot_python_semantic/src/site_packages.rs

@@ -732,7 +732,20 @@ mod tests {
         let system = TestSystem::default();
         assert!(matches!(
             VirtualEnvironment::new("/.venv", &system),
-            Err(SitePackagesDiscoveryError::VenvDirIsNotADirectory(_))
+            Err(SitePackagesDiscoveryError::VenvDirCanonicalizationError(..))
+        ));
+    }
+
+    #[test]
+    fn reject_venv_that_is_not_a_directory() {
+        let system = TestSystem::default();
+        system
+            .memory_file_system()
+            .write_file("/.venv", "")
+            .unwrap();
+        assert!(matches!(
+            VirtualEnvironment::new("/.venv", &system),
+            Err(SitePackagesDiscoveryError::VenvDirIsNotADirectory(..))
         ));
     }
 

crates/red_knot_python_semantic/src/types.rs

@@ -6,7 +6,15 @@ use itertools::Itertools;
 use ruff_db::files::File;
 use ruff_python_ast as ast;
 
-use crate::semantic_index::ast_ids::HasScopedAstId;
+pub(crate) use self::builder::{IntersectionBuilder, UnionBuilder};
+pub use self::diagnostic::{TypeCheckDiagnostic, TypeCheckDiagnostics};
+pub(crate) use self::display::TypeArrayDisplay;
+pub(crate) use self::infer::{
+    infer_deferred_types, infer_definition_types, infer_expression_types, infer_scope_types,
+};
+pub(crate) use self::signatures::Signature;
+use crate::module_resolver::file_to_module;
+use crate::semantic_index::ast_ids::HasScopedExpressionId;
 use crate::semantic_index::definition::Definition;
 use crate::semantic_index::symbol::{self as symbol, ScopeId, ScopedSymbolId};
 use crate::semantic_index::{
@@ -20,14 +28,7 @@ use crate::symbol::{Boundness, Symbol};
 use crate::types::diagnostic::TypeCheckDiagnosticsBuilder;
 use crate::types::mro::{ClassBase, Mro, MroError, MroIterator};
 use crate::types::narrow::narrowing_constraint;
-use crate::{Db, FxOrderSet, HasTy, Module, Program, SemanticModel};
-
-pub(crate) use self::builder::{IntersectionBuilder, UnionBuilder};
-pub use self::diagnostic::{TypeCheckDiagnostic, TypeCheckDiagnostics};
-pub(crate) use self::display::TypeArrayDisplay;
-pub(crate) use self::infer::{
-    infer_deferred_types, infer_definition_types, infer_expression_types, infer_scope_types,
-};
+use crate::{Db, FxOrderSet, Module, Program};
 
 mod builder;
 mod diagnostic;
@@ -35,6 +36,8 @@ mod display;
 mod infer;
 mod mro;
 mod narrow;
+mod signatures;
+mod string_annotation;
 mod unpacker;
 
 #[salsa::tracked(return_ref)]
@@ -44,7 +47,7 @@ pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
     tracing::debug!("Checking file '{path}'", path = file.path(db));
 
     let index = semantic_index(db, file);
-    let mut diagnostics = TypeCheckDiagnostics::new();
+    let mut diagnostics = TypeCheckDiagnostics::default();
 
     for scope_id in index.scope_ids() {
         let result = infer_scope_types(db, scope_id);
@@ -56,7 +59,7 @@ pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
 
 /// Infer the public type of a symbol (its type as seen from outside its scope).
 fn symbol_by_id<'db>(db: &'db dyn Db, scope: ScopeId<'db>, symbol: ScopedSymbolId) -> Symbol<'db> {
-    let _span = tracing::trace_span!("symbol_ty_by_id", ?symbol).entered();
+    let _span = tracing::trace_span!("symbol_by_id", ?symbol).entered();
 
     let use_def = use_def_map(db, scope);
 
@@ -191,6 +194,8 @@ fn declaration_ty<'db>(db: &'db dyn Db, definition: Definition<'db>) -> Type<'db
 
 /// Infer the type of a (possibly deferred) sub-expression of a [`Definition`].
 ///
+/// Supports expressions that are evaluated within a type-params sub-scope.
+///
 /// ## Panics
 /// If the given expression is not a sub-expression of the given [`Definition`].
 fn definition_expression_ty<'db>(
@@ -198,12 +203,22 @@ fn definition_expression_ty<'db>(
     definition: Definition<'db>,
     expression: &ast::Expr,
 ) -> Type<'db> {
-    let expr_id = expression.scoped_ast_id(db, definition.scope(db));
-    let inference = infer_definition_types(db, definition);
-    if let Some(ty) = inference.try_expression_ty(expr_id) {
-        ty
+    let file = definition.file(db);
+    let index = semantic_index(db, file);
+    let file_scope = index.expression_scope_id(expression);
+    let scope = file_scope.to_scope_id(db, file);
+    let expr_id = expression.scoped_expression_id(db, scope);
+    if scope == definition.scope(db) {
+        // expression is in the definition scope
+        let inference = infer_definition_types(db, definition);
+        if let Some(ty) = inference.try_expression_ty(expr_id) {
+            ty
+        } else {
+            infer_deferred_types(db, definition).expression_ty(expr_id)
+        }
     } else {
-        infer_deferred_types(db, definition).expression_ty(expr_id)
+        // expression is in a type-params sub-scope
+        infer_scope_types(db, scope).expression_ty(expr_id)
     }
 }
 
@@ -1185,14 +1200,40 @@ impl<'db> Type<'db> {
                 // TODO: see above
                 Truthiness::Ambiguous
             }
-            Type::Instance(InstanceType { class }) => {
-                // TODO: lookup `__bool__` and `__len__` methods on the instance's class
-                // More info in https://docs.python.org/3/library/stdtypes.html#truth-value-testing
-                // For now, we only special-case some builtin classes
+            instance_ty @ Type::Instance(InstanceType { class }) => {
                 if class.is_known(db, KnownClass::NoneType) {
                     Truthiness::AlwaysFalse
                 } else {
-                    Truthiness::Ambiguous
+                    // We only check the `__bool__` method for truth testing, even though at
+                    // runtime there is a fallback to `__len__`, since `__bool__` takes precedence
+                    // and a subclass could add a `__bool__` method. We don't use
+                    // `Type::call_dunder` here because of the need to check for `__bool__ = bool`.
+
+                    // Don't trust a maybe-unbound `__bool__` method.
+                    let Symbol::Type(bool_method, Boundness::Bound) =
+                        instance_ty.to_meta_type(db).member(db, "__bool__")
+                    else {
+                        return Truthiness::Ambiguous;
+                    };
+
+                    // Check if the class has `__bool__ = bool` and avoid infinite recursion, since
+                    // `Type::call` on `bool` will call `Type::bool` on the argument.
+                    if bool_method
+                        .into_class_literal()
+                        .is_some_and(|ClassLiteralType { class }| {
+                            class.is_known(db, KnownClass::Bool)
+                        })
+                    {
+                        return Truthiness::Ambiguous;
+                    }
+
+                    if let Some(Type::BooleanLiteral(bool_val)) =
+                        bool_method.call(db, &[*instance_ty]).return_ty(db)
+                    {
+                        bool_val.into()
+                    } else {
+                        Truthiness::Ambiguous
+                    }
                 }
             }
             Type::KnownInstance(known_instance) => known_instance.bool(),
@@ -1233,11 +1274,11 @@ impl<'db> Type<'db> {
             Type::FunctionLiteral(function_type) => {
                 if function_type.is_known(db, KnownFunction::RevealType) {
                     CallOutcome::revealed(
-                        function_type.return_ty(db),
+                        function_type.signature(db).return_ty,
                         *arg_types.first().unwrap_or(&Type::Unknown),
                     )
                 } else {
-                    CallOutcome::callable(function_type.return_ty(db))
+                    CallOutcome::callable(function_type.signature(db).return_ty)
                 }
             }
 
@@ -1423,6 +1464,24 @@ impl<'db> Type<'db> {
         }
     }
 
+    /// If we see a value of this type used as a type expression, what type does it name?
+    ///
+    /// For example, the builtin `int` as a value expression is of type
+    /// `Type::ClassLiteral(builtins.int)`, that is, it is the `int` class itself. As a type
+    /// expression, it names the type `Type::Instance(builtins.int)`, that is, all objects whose
+    /// `__class__` is `int`.
+    #[must_use]
+    pub fn in_type_expression(&self, db: &'db dyn Db) -> Type<'db> {
+        match self {
+            Type::ClassLiteral(_) | Type::SubclassOf(_) => self.to_instance(db),
+            Type::Union(union) => union.map(db, |element| element.in_type_expression(db)),
+            Type::Unknown => Type::Unknown,
+            // TODO map this to a new `Type::TypeVar` variant
+            Type::KnownInstance(KnownInstanceType::TypeVar(_)) => *self,
+            _ => Type::Todo,
+        }
+    }
+
     /// The type `NoneType` / `None`
     pub fn none(db: &'db dyn Db) -> Type<'db> {
         KnownClass::NoneType.to_instance(db)
@@ -1682,7 +1741,7 @@ impl<'db> KnownClass {
         }
     }
 
-    pub fn try_from_module(module: &Module, class_name: &str) -> Option<Self> {
+    pub fn try_from_file(db: &dyn Db, file: File, class_name: &str) -> Option<Self> {
         // Note: if this becomes hard to maintain (as rust can't ensure at compile time that all
         // variants of `Self` are covered), we might use a macro (in-house or dependency)
         // See: https://stackoverflow.com/q/39070244
@@ -1709,7 +1768,8 @@ impl<'db> KnownClass {
             _ => return None,
         };
 
-        candidate.check_module(module).then_some(candidate)
+        let module = file_to_module(db, file)?;
+        candidate.check_module(&module).then_some(candidate)
     }
 
     /// Return `true` if the module of `self` matches `module_name`
@@ -1747,6 +1807,8 @@ impl<'db> KnownClass {
 pub enum KnownInstanceType<'db> {
     /// The symbol `typing.Literal` (which can also be found as `typing_extensions.Literal`)
     Literal,
+    /// The symbol `typing.Optional` (which can also be found as `typing_extensions.Optional`)
+    Optional,
     /// A single instance of `typing.TypeVar`
     TypeVar(TypeVarInstance<'db>),
     // TODO: fill this enum out with more special forms, etc.
@@ -1756,6 +1818,7 @@ impl<'db> KnownInstanceType<'db> {
     pub const fn as_str(self) -> &'static str {
         match self {
             KnownInstanceType::Literal => "Literal",
+            KnownInstanceType::Optional => "Optional",
             KnownInstanceType::TypeVar(_) => "TypeVar",
         }
     }
@@ -1763,8 +1826,7 @@ impl<'db> KnownInstanceType<'db> {
     /// Evaluate the known instance in boolean context
     pub const fn bool(self) -> Truthiness {
         match self {
-            Self::Literal => Truthiness::AlwaysTrue,
-            Self::TypeVar(_) => Truthiness::AlwaysTrue,
+            Self::Literal | Self::Optional | Self::TypeVar(_) => Truthiness::AlwaysTrue,
         }
     }
 
@@ -1772,6 +1834,7 @@ impl<'db> KnownInstanceType<'db> {
     pub fn repr(self, db: &'db dyn Db) -> &'db str {
         match self {
             Self::Literal => "typing.Literal",
+            Self::Optional => "typing.Optional",
             Self::TypeVar(typevar) => typevar.name(db),
         }
     }
@@ -1780,6 +1843,7 @@ impl<'db> KnownInstanceType<'db> {
     pub const fn class(self) -> KnownClass {
         match self {
             Self::Literal => KnownClass::SpecialForm,
+            Self::Optional => KnownClass::SpecialForm,
             Self::TypeVar(_) => KnownClass::TypeVar,
         }
     }
@@ -1799,6 +1863,7 @@ impl<'db> KnownInstanceType<'db> {
         }
         match (module.name().as_str(), instance_name) {
             ("typing" | "typing_extensions", "Literal") => Some(Self::Literal),
+            ("typing" | "typing_extensions", "Optional") => Some(Self::Optional),
             _ => None,
         }
     }
@@ -2283,7 +2348,10 @@ impl<'db> FunctionType<'db> {
         self.decorators(db).contains(&decorator)
     }
 
-    /// inferred return type for this function
+    /// Typed externally-visible signature for this function.
+    ///
+    /// This is the signature as seen by external callers, possibly modified by decorators and/or
+    /// overloaded.
     ///
     /// ## Why is this a salsa query?
     ///
@@ -2292,34 +2360,32 @@ impl<'db> FunctionType<'db> {
     ///
     /// Were this not a salsa query, then the calling query
     /// would depend on the function's AST and rerun for every change in that file.
-    #[salsa::tracked]
-    pub fn return_ty(self, db: &'db dyn Db) -> Type<'db> {
+    #[salsa::tracked(return_ref)]
+    pub fn signature(self, db: &'db dyn Db) -> Signature<'db> {
+        let function_stmt_node = self.body_scope(db).node(db).expect_function();
+        let internal_signature = self.internal_signature(db);
+        if function_stmt_node.decorator_list.is_empty() {
+            return internal_signature;
+        }
+        // TODO process the effect of decorators on the signature
+        Signature::todo()
+    }
+
+    /// Typed internally-visible signature for this function.
+    ///
+    /// This represents the annotations on the function itself, unmodified by decorators and
+    /// overloads.
+    ///
+    /// These are the parameter and return types that should be used for type checking the body of
+    /// the function.
+    ///
+    /// Don't call this when checking any other file; only when type-checking the function body
+    /// scope.
+    fn internal_signature(self, db: &'db dyn Db) -> Signature<'db> {
         let scope = self.body_scope(db);
         let function_stmt_node = scope.node(db).expect_function();
-
-        // TODO if a function `bar` is decorated by `foo`,
-        // where `foo` is annotated as returning a type `X` that is a subtype of `Callable`,
-        // we need to infer the return type from `X`'s return annotation
-        // rather than from `bar`'s return annotation
-        // in order to determine the type that `bar` returns
-        if !function_stmt_node.decorator_list.is_empty() {
-            return Type::Todo;
-        }
-
-        function_stmt_node
-            .returns
-            .as_ref()
-            .map(|returns| {
-                if function_stmt_node.is_async {
-                    // TODO: generic `types.CoroutineType`!
-                    Type::Todo
-                } else {
-                    let definition =
-                        semantic_index(db, scope.file(db)).definition(function_stmt_node);
-                    definition_expression_ty(db, definition, returns.as_ref())
-                }
-            })
-            .unwrap_or(Type::Unknown)
+        let definition = semantic_index(db, scope.file(db)).definition(function_stmt_node);
+        Signature::from_function(db, definition, function_stmt_node)
     }
 
     pub fn is_known(self, db: &'db dyn Db, known_function: KnownFunction) -> bool {
@@ -2422,26 +2488,13 @@ impl<'db> Class<'db> {
     fn explicit_bases_query(self, db: &'db dyn Db) -> Box<[Type<'db>]> {
         let class_stmt = self.node(db);
 
-        if class_stmt.type_params.is_some() {
-            // when we have a specialized scope, we'll look up the inference
-            // within that scope
-            let model = SemanticModel::new(db, self.file(db));
+        let class_definition = semantic_index(db, self.file(db)).definition(class_stmt);
 
-            class_stmt
-                .bases()
-                .iter()
-                .map(|base| base.ty(&model))
-                .collect()
-        } else {
-            // Otherwise, we can do the lookup based on the definition scope
-            let class_definition = semantic_index(db, self.file(db)).definition(class_stmt);
-
-            class_stmt
-                .bases()
-                .iter()
-                .map(|base_node| definition_expression_ty(db, class_definition, base_node))
-                .collect()
-        }
+        class_stmt
+            .bases()
+            .iter()
+            .map(|base_node| definition_expression_ty(db, class_definition, base_node))
+            .collect()
     }
 
     fn file(self, db: &dyn Db) -> File {
@@ -2502,16 +2555,9 @@ impl<'db> Class<'db> {
             .as_ref()?
             .find_keyword("metaclass")?
             .value;
-        Some(if class_stmt.type_params.is_some() {
-            // when we have a specialized scope, we'll look up the inference
-            // within that scope
-            let model = SemanticModel::new(db, self.file(db));
-            metaclass_node.ty(&model)
-        } else {
-            // Otherwise, we can do the lookup based on the definition scope
-            let class_definition = semantic_index(db, self.file(db)).definition(class_stmt);
-            definition_expression_ty(db, class_definition, metaclass_node)
-        })
+        let class_definition = semantic_index(db, self.file(db)).definition(class_stmt);
+        let metaclass_ty = definition_expression_ty(db, class_definition, metaclass_node);
+        Some(metaclass_ty)
     }
 
     /// Return the metaclass of this class, or `Unknown` if the metaclass cannot be inferred.

crates/red_knot_python_semantic/src/types/builder.rs

@@ -128,7 +128,7 @@ impl<'db> IntersectionBuilder<'db> {
     pub(crate) fn new(db: &'db dyn Db) -> Self {
         Self {
             db,
-            intersections: vec![InnerIntersectionBuilder::new()],
+            intersections: vec![InnerIntersectionBuilder::default()],
         }
     }
 
@@ -231,10 +231,6 @@ struct InnerIntersectionBuilder<'db> {
 }
 
 impl<'db> InnerIntersectionBuilder<'db> {
-    fn new() -> Self {
-        Self::default()
-    }
-
     /// Adds a positive type to this intersection.
     fn add_positive(&mut self, db: &'db dyn Db, new_positive: Type<'db>) {
         if let Type::Intersection(other) = new_positive {
@@ -253,7 +249,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
                         .iter()
                         .find(|element| element.is_boolean_literal())
                     {
-                        *self = Self::new();
+                        *self = Self::default();
                         self.positive.insert(Type::BooleanLiteral(!value));
                         return;
                     }
@@ -272,7 +268,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
                 }
                 // A & B = Never    if A and B are disjoint
                 if new_positive.is_disjoint_from(db, *existing_positive) {
-                    *self = Self::new();
+                    *self = Self::default();
                     self.positive.insert(Type::Never);
                     return;
                 }
@@ -285,7 +281,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
             for (index, existing_negative) in self.negative.iter().enumerate() {
                 // S & ~T = Never    if S <: T
                 if new_positive.is_subtype_of(db, *existing_negative) {
-                    *self = Self::new();
+                    *self = Self::default();
                     self.positive.insert(Type::Never);
                     return;
                 }
@@ -326,7 +322,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
                     .iter()
                     .any(|pos| *pos == KnownClass::Bool.to_instance(db)) =>
             {
-                *self = Self::new();
+                *self = Self::default();
                 self.positive.insert(Type::BooleanLiteral(!bool));
             }
             _ => {
@@ -348,7 +344,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
                 for existing_positive in &self.positive {
                     // S & ~T = Never    if S <: T
                     if existing_positive.is_subtype_of(db, new_negative) {
-                        *self = Self::new();
+                        *self = Self::default();
                         self.positive.insert(Type::Never);
                         return;
                     }

crates/red_knot_python_semantic/src/types/diagnostic.rs

@@ -73,10 +73,6 @@ pub struct TypeCheckDiagnostics {
 }
 
 impl TypeCheckDiagnostics {
-    pub fn new() -> Self {
-        Self { inner: Vec::new() }
-    }
-
     pub(super) fn push(&mut self, diagnostic: TypeCheckDiagnostic) {
         self.inner.push(Arc::new(diagnostic));
     }
@@ -148,7 +144,7 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
         Self {
             db,
             file,
-            diagnostics: TypeCheckDiagnostics::new(),
+            diagnostics: TypeCheckDiagnostics::default(),
         }
     }
 

crates/red_knot_python_semantic/src/types/display.rs

@@ -1,13 +1,14 @@
 //! Display implementations for types.
 
-use std::fmt::{self, Display, Formatter};
+use std::fmt::{self, Display, Formatter, Write};
 
 use ruff_db::display::FormatterJoinExtension;
 use ruff_python_ast::str::Quote;
 use ruff_python_literal::escape::AsciiEscape;
 
 use crate::types::{
-    ClassLiteralType, InstanceType, IntersectionType, KnownClass, SubclassOfType, Type, UnionType,
+    ClassLiteralType, InstanceType, IntersectionType, KnownClass, StringLiteralType,
+    SubclassOfType, Type, UnionType,
 };
 use crate::Db;
 use rustc_hash::FxHashMap;
@@ -85,15 +86,13 @@ impl Display for DisplayRepresentation<'_> {
             Type::SubclassOf(SubclassOfType { class }) => {
                 write!(f, "type[{}]", class.name(self.db))
             }
-            Type::KnownInstance(known_instance) => f.write_str(known_instance.as_str()),
+            Type::KnownInstance(known_instance) => f.write_str(known_instance.repr(self.db)),
             Type::FunctionLiteral(function) => f.write_str(function.name(self.db)),
             Type::Union(union) => union.display(self.db).fmt(f),
             Type::Intersection(intersection) => intersection.display(self.db).fmt(f),
             Type::IntLiteral(n) => n.fmt(f),
             Type::BooleanLiteral(boolean) => f.write_str(if boolean { "True" } else { "False" }),
-            Type::StringLiteral(string) => {
-                write!(f, r#""{}""#, string.value(self.db).replace('"', r#"\""#))
-            }
+            Type::StringLiteral(string) => string.display(self.db).fmt(f),
             Type::LiteralString => f.write_str("LiteralString"),
             Type::BytesLiteral(bytes) => {
                 let escape =
@@ -328,13 +327,40 @@ impl<'db> Display for DisplayTypeArray<'_, 'db> {
     }
 }
 
+impl<'db> StringLiteralType<'db> {
+    fn display(&'db self, db: &'db dyn Db) -> DisplayStringLiteralType<'db> {
+        DisplayStringLiteralType { db, ty: self }
+    }
+}
+
+struct DisplayStringLiteralType<'db> {
+    ty: &'db StringLiteralType<'db>,
+    db: &'db dyn Db,
+}
+
+impl Display for DisplayStringLiteralType<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        let value = self.ty.value(self.db);
+        f.write_char('"')?;
+        for ch in value.chars() {
+            match ch {
+                // `escape_debug` will escape even single quotes, which is not necessary for our
+                // use case as we are already using double quotes to wrap the string.
+                '\'' => f.write_char('\'')?,
+                _ => write!(f, "{}", ch.escape_debug())?,
+            }
+        }
+        f.write_char('"')
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use ruff_db::files::system_path_to_file;
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
 
     use crate::db::tests::TestDb;
-    use crate::types::{global_symbol, SliceLiteralType, Type, UnionType};
+    use crate::types::{global_symbol, SliceLiteralType, StringLiteralType, Type, UnionType};
     use crate::{Program, ProgramSettings, PythonVersion, SearchPathSettings};
 
     fn setup_db() -> TestDb {
@@ -451,4 +477,28 @@ mod tests {
             "slice[None, None, Literal[2]]"
         );
     }
+
+    #[test]
+    fn string_literal_display() {
+        let db = setup_db();
+
+        assert_eq!(
+            Type::StringLiteral(StringLiteralType::new(&db, r"\n"))
+                .display(&db)
+                .to_string(),
+            r#"Literal["\\n"]"#
+        );
+        assert_eq!(
+            Type::StringLiteral(StringLiteralType::new(&db, "'"))
+                .display(&db)
+                .to_string(),
+            r#"Literal["'"]"#
+        );
+        assert_eq!(
+            Type::StringLiteral(StringLiteralType::new(&db, r#"""#))
+                .display(&db)
+                .to_string(),
+            r#"Literal["\""]"#
+        );
+    }
 }

crates/red_knot_python_semantic/src/types/mro.rs

@@ -371,8 +371,9 @@ impl<'db> ClassBase<'db> {
             | Type::ModuleLiteral(_)
             | Type::SubclassOf(_) => None,
             Type::KnownInstance(known_instance) => match known_instance {
-                KnownInstanceType::Literal => None,
-                KnownInstanceType::TypeVar(_) => None,
+                KnownInstanceType::TypeVar(_)
+                | KnownInstanceType::Literal
+                | KnownInstanceType::Optional => None,
             },
         }
     }

crates/red_knot_python_semantic/src/types/narrow.rs

@@ -1,4 +1,4 @@
-use crate::semantic_index::ast_ids::HasScopedAstId;
+use crate::semantic_index::ast_ids::HasScopedExpressionId;
 use crate::semantic_index::constraint::{Constraint, ConstraintNode, PatternConstraint};
 use crate::semantic_index::definition::Definition;
 use crate::semantic_index::expression::Expression;
@@ -257,17 +257,26 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
         expression: Expression<'db>,
         is_positive: bool,
     ) -> Option<NarrowingConstraints<'db>> {
+        fn is_narrowing_target_candidate(expr: &ast::Expr) -> bool {
+            matches!(expr, ast::Expr::Name(_) | ast::Expr::Call(_))
+        }
+
         let ast::ExprCompare {
             range: _,
             left,
             ops,
             comparators,
         } = expr_compare;
-        if !left.is_name_expr() && comparators.iter().all(|c| !c.is_name_expr()) {
-            // If none of the comparators are name expressions,
-            // we have no symbol to narrow down the type of.
+
+        // Performance optimization: early return if there are no potential narrowing targets.
+        if !is_narrowing_target_candidate(left)
+            && comparators
+                .iter()
+                .all(|c| !is_narrowing_target_candidate(c))
+        {
             return None;
         }
+
         if !is_positive && comparators.len() > 1 {
             // We can't negate a constraint made by a multi-comparator expression, since we can't
             // know which comparison part is the one being negated.
@@ -283,42 +292,85 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
             .tuple_windows::<(&ruff_python_ast::Expr, &ruff_python_ast::Expr)>();
         let mut constraints = NarrowingConstraints::default();
         for (op, (left, right)) in std::iter::zip(&**ops, comparator_tuples) {
-            if let ast::Expr::Name(ast::ExprName {
-                range: _,
-                id,
-                ctx: _,
-            }) = left
-            {
-                // SAFETY: we should always have a symbol for every Name node.
-                let symbol = self.symbols().symbol_id_by_name(id).unwrap();
-                let rhs_ty = inference.expression_ty(right.scoped_ast_id(self.db, scope));
+            let rhs_ty = inference.expression_ty(right.scoped_expression_id(self.db, scope));
 
-                match if is_positive { *op } else { op.negate() } {
-                    ast::CmpOp::IsNot => {
-                        if rhs_ty.is_singleton(self.db) {
-                            let ty = IntersectionBuilder::new(self.db)
-                                .add_negative(rhs_ty)
-                                .build();
-                            constraints.insert(symbol, ty);
-                        } else {
-                            // Non-singletons cannot be safely narrowed using `is not`
+            match left {
+                ast::Expr::Name(ast::ExprName {
+                    range: _,
+                    id,
+                    ctx: _,
+                }) => {
+                    let symbol = self
+                        .symbols()
+                        .symbol_id_by_name(id)
+                        .expect("Should always have a symbol for every Name node");
+
+                    match if is_positive { *op } else { op.negate() } {
+                        ast::CmpOp::IsNot => {
+                            if rhs_ty.is_singleton(self.db) {
+                                let ty = IntersectionBuilder::new(self.db)
+                                    .add_negative(rhs_ty)
+                                    .build();
+                                constraints.insert(symbol, ty);
+                            } else {
+                                // Non-singletons cannot be safely narrowed using `is not`
+                            }
                         }
-                    }
-                    ast::CmpOp::Is => {
-                        constraints.insert(symbol, rhs_ty);
-                    }
-                    ast::CmpOp::NotEq => {
-                        if rhs_ty.is_single_valued(self.db) {
-                            let ty = IntersectionBuilder::new(self.db)
-                                .add_negative(rhs_ty)
-                                .build();
-                            constraints.insert(symbol, ty);
+                        ast::CmpOp::Is => {
+                            constraints.insert(symbol, rhs_ty);
+                        }
+                        ast::CmpOp::NotEq => {
+                            if rhs_ty.is_single_valued(self.db) {
+                                let ty = IntersectionBuilder::new(self.db)
+                                    .add_negative(rhs_ty)
+                                    .build();
+                                constraints.insert(symbol, ty);
+                            }
+                        }
+                        _ => {
+                            // TODO other comparison types
                         }
-                    }
-                    _ => {
-                        // TODO other comparison types
                     }
                 }
+                ast::Expr::Call(ast::ExprCall {
+                    range: _,
+                    func: callable,
+                    arguments:
+                        ast::Arguments {
+                            args,
+                            keywords,
+                            range: _,
+                        },
+                }) if rhs_ty.is_class_literal() && keywords.is_empty() => {
+                    let [ast::Expr::Name(ast::ExprName { id, .. })] = &**args else {
+                        continue;
+                    };
+
+                    let is_valid_constraint = if is_positive {
+                        op == &ast::CmpOp::Is
+                    } else {
+                        op == &ast::CmpOp::IsNot
+                    };
+
+                    if !is_valid_constraint {
+                        continue;
+                    }
+
+                    let callable_ty =
+                        inference.expression_ty(callable.scoped_expression_id(self.db, scope));
+
+                    if callable_ty
+                        .into_class_literal()
+                        .is_some_and(|c| c.class.is_known(self.db, KnownClass::Type))
+                    {
+                        let symbol = self
+                            .symbols()
+                            .symbol_id_by_name(id)
+                            .expect("Should always have a symbol for every Name node");
+                        constraints.insert(symbol, rhs_ty.to_instance(self.db));
+                    }
+                }
+                _ => {}
             }
         }
         Some(constraints)
@@ -336,7 +388,7 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
         // TODO: add support for PEP 604 union types on the right hand side of `isinstance`
         // and `issubclass`, for example `isinstance(x, str | (int | float))`.
         match inference
-            .expression_ty(expr_call.func.scoped_ast_id(self.db, scope))
+            .expression_ty(expr_call.func.scoped_expression_id(self.db, scope))
             .into_function_literal()
             .and_then(|f| f.known(self.db))
             .and_then(KnownFunction::constraint_function)
@@ -348,7 +400,7 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
                     let symbol = self.symbols().symbol_id_by_name(id).unwrap();
 
                     let class_info_ty =
-                        inference.expression_ty(class_info.scoped_ast_id(self.db, scope));
+                        inference.expression_ty(class_info.scoped_expression_id(self.db, scope));
 
                     let to_constraint = match function {
                         KnownConstraintFunction::IsInstance => {
@@ -414,7 +466,7 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
             // filter our arms with statically known truthiness
             .filter(|expr| {
                 inference
-                    .expression_ty(expr.scoped_ast_id(self.db, scope))
+                    .expression_ty(expr.scoped_expression_id(self.db, scope))
                     .bool(self.db)
                     != match expr_bool_op.op {
                         BoolOp::And => Truthiness::AlwaysTrue,

crates/red_knot_python_semantic/src/types/signatures.rs

@@ -0,0 +1,480 @@
+#![allow(dead_code)]
+use super::{definition_expression_ty, Type};
+use crate::semantic_index::definition::Definition;
+use crate::Db;
+use ruff_python_ast::{self as ast, name::Name};
+
+/// A typed callable signature.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) struct Signature<'db> {
+    parameters: Parameters<'db>,
+
+    /// Annotated return type (Unknown if no annotation.)
+    pub(crate) return_ty: Type<'db>,
+}
+
+impl<'db> Signature<'db> {
+    /// Return a todo signature: (*args: Todo, **kwargs: Todo) -> Todo
+    pub(crate) fn todo() -> Self {
+        Self {
+            parameters: Parameters::todo(),
+            return_ty: Type::Todo,
+        }
+    }
+
+    /// Return a typed signature from a function definition.
+    pub(super) fn from_function(
+        db: &'db dyn Db,
+        definition: Definition<'db>,
+        function_node: &'db ast::StmtFunctionDef,
+    ) -> Self {
+        let return_ty = function_node
+            .returns
+            .as_ref()
+            .map(|returns| {
+                if function_node.is_async {
+                    // TODO: generic `types.CoroutineType`!
+                    Type::Todo
+                } else {
+                    definition_expression_ty(db, definition, returns.as_ref())
+                }
+            })
+            .unwrap_or(Type::Unknown);
+
+        Self {
+            parameters: Parameters::from_parameters(
+                db,
+                definition,
+                function_node.parameters.as_ref(),
+            ),
+            return_ty,
+        }
+    }
+}
+
+/// The parameters portion of a typed signature.
+///
+/// The ordering of parameters is always as given in this struct: first positional-only parameters,
+/// then positional-or-keyword, then optionally the variadic parameter, then keyword-only
+/// parameters, and last, optionally the variadic keywords parameter.
+#[derive(Clone, Debug, Default, PartialEq, Eq)]
+pub(super) struct Parameters<'db> {
+    /// Parameters which may only be filled by positional arguments.
+    positional_only: Box<[ParameterWithDefault<'db>]>,
+
+    /// Parameters which may be filled by positional or keyword arguments.
+    positional_or_keyword: Box<[ParameterWithDefault<'db>]>,
+
+    /// The `*args` variadic parameter, if any.
+    variadic: Option<Parameter<'db>>,
+
+    /// Parameters which may only be filled by keyword arguments.
+    keyword_only: Box<[ParameterWithDefault<'db>]>,
+
+    /// The `**kwargs` variadic keywords parameter, if any.
+    keywords: Option<Parameter<'db>>,
+}
+
+impl<'db> Parameters<'db> {
+    /// Return todo parameters: (*args: Todo, **kwargs: Todo)
+    fn todo() -> Self {
+        Self {
+            variadic: Some(Parameter {
+                name: Some(Name::new_static("args")),
+                annotated_ty: Type::Todo,
+            }),
+            keywords: Some(Parameter {
+                name: Some(Name::new_static("kwargs")),
+                annotated_ty: Type::Todo,
+            }),
+            ..Default::default()
+        }
+    }
+
+    fn from_parameters(
+        db: &'db dyn Db,
+        definition: Definition<'db>,
+        parameters: &'db ast::Parameters,
+    ) -> Self {
+        let ast::Parameters {
+            posonlyargs,
+            args,
+            vararg,
+            kwonlyargs,
+            kwarg,
+            range: _,
+        } = parameters;
+        let positional_only = posonlyargs
+            .iter()
+            .map(|arg| ParameterWithDefault::from_node(db, definition, arg))
+            .collect();
+        let positional_or_keyword = args
+            .iter()
+            .map(|arg| ParameterWithDefault::from_node(db, definition, arg))
+            .collect();
+        let variadic = vararg
+            .as_ref()
+            .map(|arg| Parameter::from_node(db, definition, arg));
+        let keyword_only = kwonlyargs
+            .iter()
+            .map(|arg| ParameterWithDefault::from_node(db, definition, arg))
+            .collect();
+        let keywords = kwarg
+            .as_ref()
+            .map(|arg| Parameter::from_node(db, definition, arg));
+        Self {
+            positional_only,
+            positional_or_keyword,
+            variadic,
+            keyword_only,
+            keywords,
+        }
+    }
+}
+
+/// A single parameter of a typed signature, with optional default value.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(super) struct ParameterWithDefault<'db> {
+    parameter: Parameter<'db>,
+
+    /// Type of the default value, if any.
+    default_ty: Option<Type<'db>>,
+}
+
+impl<'db> ParameterWithDefault<'db> {
+    fn from_node(
+        db: &'db dyn Db,
+        definition: Definition<'db>,
+        parameter_with_default: &'db ast::ParameterWithDefault,
+    ) -> Self {
+        Self {
+            default_ty: parameter_with_default
+                .default
+                .as_deref()
+                .map(|default| definition_expression_ty(db, definition, default)),
+            parameter: Parameter::from_node(db, definition, &parameter_with_default.parameter),
+        }
+    }
+}
+
+/// A single parameter of a typed signature.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(super) struct Parameter<'db> {
+    /// Parameter name.
+    ///
+    /// It is possible for signatures to be defined in ways that leave positional-only parameters
+    /// nameless (e.g. via `Callable` annotations).
+    name: Option<Name>,
+
+    /// Annotated type of the parameter (Unknown if no annotation.)
+    annotated_ty: Type<'db>,
+}
+
+impl<'db> Parameter<'db> {
+    fn from_node(
+        db: &'db dyn Db,
+        definition: Definition<'db>,
+        parameter: &'db ast::Parameter,
+    ) -> Self {
+        Parameter {
+            name: Some(parameter.name.id.clone()),
+            annotated_ty: parameter
+                .annotation
+                .as_deref()
+                .map(|annotation| definition_expression_ty(db, definition, annotation))
+                .unwrap_or(Type::Unknown),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::db::tests::TestDb;
+    use crate::program::{Program, SearchPathSettings};
+    use crate::python_version::PythonVersion;
+    use crate::types::{global_symbol, FunctionType};
+    use crate::ProgramSettings;
+    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+
+    pub(crate) fn setup_db() -> TestDb {
+        let db = TestDb::new();
+
+        let src_root = SystemPathBuf::from("/src");
+        db.memory_file_system()
+            .create_directory_all(&src_root)
+            .unwrap();
+
+        Program::from_settings(
+            &db,
+            &ProgramSettings {
+                target_version: PythonVersion::default(),
+                search_paths: SearchPathSettings::new(src_root),
+            },
+        )
+        .expect("Valid search path settings");
+
+        db
+    }
+
+    #[track_caller]
+    fn get_function_f<'db>(db: &'db TestDb, file: &'static str) -> FunctionType<'db> {
+        let module = ruff_db::files::system_path_to_file(db, file).unwrap();
+        global_symbol(db, module, "f")
+            .expect_type()
+            .expect_function_literal()
+    }
+
+    #[track_caller]
+    fn assert_param_with_default<'db>(
+        db: &'db TestDb,
+        param_with_default: &ParameterWithDefault<'db>,
+        expected_name: &'static str,
+        expected_annotation_ty_display: &'static str,
+        expected_default_ty_display: Option<&'static str>,
+    ) {
+        assert_eq!(
+            param_with_default
+                .default_ty
+                .map(|ty| ty.display(db).to_string()),
+            expected_default_ty_display.map(ToString::to_string)
+        );
+        assert_param(
+            db,
+            &param_with_default.parameter,
+            expected_name,
+            expected_annotation_ty_display,
+        );
+    }
+
+    #[track_caller]
+    fn assert_param<'db>(
+        db: &'db TestDb,
+        param: &Parameter<'db>,
+        expected_name: &'static str,
+        expected_annotation_ty_display: &'static str,
+    ) {
+        assert_eq!(param.name.as_ref().unwrap(), expected_name);
+        assert_eq!(
+            param.annotated_ty.display(db).to_string(),
+            expected_annotation_ty_display
+        );
+    }
+
+    #[test]
+    fn empty() {
+        let mut db = setup_db();
+        db.write_dedented("/src/a.py", "def f(): ...").unwrap();
+        let func = get_function_f(&db, "/src/a.py");
+
+        let sig = func.internal_signature(&db);
+
+        assert_eq!(sig.return_ty.display(&db).to_string(), "Unknown");
+        let params = sig.parameters;
+        assert!(params.positional_only.is_empty());
+        assert!(params.positional_or_keyword.is_empty());
+        assert!(params.variadic.is_none());
+        assert!(params.keyword_only.is_empty());
+        assert!(params.keywords.is_none());
+    }
+
+    #[test]
+    #[allow(clippy::many_single_char_names)]
+    fn full() {
+        let mut db = setup_db();
+        db.write_dedented(
+            "/src/a.py",
+            "
+            def f(a, b: int, c = 1, d: int = 2, /,
+                  e = 3, f: Literal[4] = 4, *args: object,
+                  g = 5, h: Literal[6] = 6, **kwargs: str) -> bytes: ...
+            ",
+        )
+        .unwrap();
+        let func = get_function_f(&db, "/src/a.py");
+
+        let sig = func.internal_signature(&db);
+
+        assert_eq!(sig.return_ty.display(&db).to_string(), "bytes");
+        let params = sig.parameters;
+        let [a, b, c, d] = &params.positional_only[..] else {
+            panic!("expected four positional-only parameters");
+        };
+        let [e, f] = &params.positional_or_keyword[..] else {
+            panic!("expected two positional-or-keyword parameters");
+        };
+        let Some(args) = params.variadic else {
+            panic!("expected a variadic parameter");
+        };
+        let [g, h] = &params.keyword_only[..] else {
+            panic!("expected two keyword-only parameters");
+        };
+        let Some(kwargs) = params.keywords else {
+            panic!("expected a kwargs parameter");
+        };
+
+        assert_param_with_default(&db, a, "a", "Unknown", None);
+        assert_param_with_default(&db, b, "b", "int", None);
+        assert_param_with_default(&db, c, "c", "Unknown", Some("Literal[1]"));
+        assert_param_with_default(&db, d, "d", "int", Some("Literal[2]"));
+        assert_param_with_default(&db, e, "e", "Unknown", Some("Literal[3]"));
+        assert_param_with_default(&db, f, "f", "Literal[4]", Some("Literal[4]"));
+        assert_param_with_default(&db, g, "g", "Unknown", Some("Literal[5]"));
+        assert_param_with_default(&db, h, "h", "Literal[6]", Some("Literal[6]"));
+        assert_param(&db, &args, "args", "object");
+        assert_param(&db, &kwargs, "kwargs", "str");
+    }
+
+    #[test]
+    fn not_deferred() {
+        let mut db = setup_db();
+        db.write_dedented(
+            "/src/a.py",
+            "
+            class A: ...
+            class B: ...
+
+            alias = A
+
+            def f(a: alias): ...
+
+            alias = B
+            ",
+        )
+        .unwrap();
+        let func = get_function_f(&db, "/src/a.py");
+
+        let sig = func.internal_signature(&db);
+
+        let [a] = &sig.parameters.positional_or_keyword[..] else {
+            panic!("expected one positional-or-keyword parameter");
+        };
+        // Parameter resolution not deferred; we should see A not B
+        assert_param_with_default(&db, a, "a", "A", None);
+    }
+
+    #[test]
+    fn deferred_in_stub() {
+        let mut db = setup_db();
+        db.write_dedented(
+            "/src/a.pyi",
+            "
+            class A: ...
+            class B: ...
+
+            alias = A
+
+            def f(a: alias): ...
+
+            alias = B
+            ",
+        )
+        .unwrap();
+        let func = get_function_f(&db, "/src/a.pyi");
+
+        let sig = func.internal_signature(&db);
+
+        let [a] = &sig.parameters.positional_or_keyword[..] else {
+            panic!("expected one positional-or-keyword parameter");
+        };
+        // Parameter resolution deferred; we should see B
+        assert_param_with_default(&db, a, "a", "B", None);
+    }
+
+    #[test]
+    fn generic_not_deferred() {
+        let mut db = setup_db();
+        db.write_dedented(
+            "/src/a.py",
+            "
+            class A: ...
+            class B: ...
+
+            alias = A
+
+            def f[T](a: alias, b: T) -> T: ...
+
+            alias = B
+            ",
+        )
+        .unwrap();
+        let func = get_function_f(&db, "/src/a.py");
+
+        let sig = func.internal_signature(&db);
+
+        let [a, b] = &sig.parameters.positional_or_keyword[..] else {
+            panic!("expected two positional-or-keyword parameters");
+        };
+        // TODO resolution should not be deferred; we should see A not B
+        assert_param_with_default(&db, a, "a", "B", None);
+        assert_param_with_default(&db, b, "b", "T", None);
+    }
+
+    #[test]
+    fn generic_deferred_in_stub() {
+        let mut db = setup_db();
+        db.write_dedented(
+            "/src/a.pyi",
+            "
+            class A: ...
+            class B: ...
+
+            alias = A
+
+            def f[T](a: alias, b: T) -> T: ...
+
+            alias = B
+            ",
+        )
+        .unwrap();
+        let func = get_function_f(&db, "/src/a.pyi");
+
+        let sig = func.internal_signature(&db);
+
+        let [a, b] = &sig.parameters.positional_or_keyword[..] else {
+            panic!("expected two positional-or-keyword parameters");
+        };
+        // Parameter resolution deferred; we should see B
+        assert_param_with_default(&db, a, "a", "B", None);
+        assert_param_with_default(&db, b, "b", "T", None);
+    }
+
+    #[test]
+    fn external_signature_no_decorator() {
+        let mut db = setup_db();
+        db.write_dedented(
+            "/src/a.py",
+            "
+            def f(a: int) -> int: ...
+            ",
+        )
+        .unwrap();
+        let func = get_function_f(&db, "/src/a.py");
+
+        let expected_sig = func.internal_signature(&db);
+
+        // With no decorators, internal and external signature are the same
+        assert_eq!(func.signature(&db), &expected_sig);
+    }
+
+    #[test]
+    fn external_signature_decorated() {
+        let mut db = setup_db();
+        db.write_dedented(
+            "/src/a.py",
+            "
+            def deco(func): ...
+
+            @deco
+            def f(a: int) -> int: ...
+            ",
+        )
+        .unwrap();
+        let func = get_function_f(&db, "/src/a.py");
+
+        let expected_sig = Signature::todo();
+
+        // With no decorators, internal and external signature are the same
+        assert_eq!(func.signature(&db), &expected_sig);
+    }
+}

crates/red_knot_python_semantic/src/types/string_annotation.rs

@@ -0,0 +1,77 @@
+use ruff_db::files::File;
+use ruff_db::source::source_text;
+use ruff_python_ast::str::raw_contents;
+use ruff_python_ast::{self as ast, ModExpression, StringFlags};
+use ruff_python_parser::{parse_expression_range, Parsed};
+use ruff_text_size::Ranged;
+
+use crate::types::diagnostic::{TypeCheckDiagnostics, TypeCheckDiagnosticsBuilder};
+use crate::Db;
+
+type AnnotationParseResult = Result<Parsed<ModExpression>, TypeCheckDiagnostics>;
+
+/// Parses the given expression as a string annotation.
+pub(crate) fn parse_string_annotation(
+    db: &dyn Db,
+    file: File,
+    string_expr: &ast::ExprStringLiteral,
+) -> AnnotationParseResult {
+    let _span = tracing::trace_span!("parse_string_annotation", string=?string_expr.range(), file=%file.path(db)).entered();
+
+    let source = source_text(db.upcast(), file);
+    let node_text = &source[string_expr.range()];
+    let mut diagnostics = TypeCheckDiagnosticsBuilder::new(db, file);
+
+    if let [string_literal] = string_expr.value.as_slice() {
+        let prefix = string_literal.flags.prefix();
+        if prefix.is_raw() {
+            diagnostics.add(
+                string_literal.into(),
+                "annotation-raw-string",
+                format_args!("Type expressions cannot use raw string literal"),
+            );
+        // Compare the raw contents (without quotes) of the expression with the parsed contents
+        // contained in the string literal.
+        } else if raw_contents(node_text)
+            .is_some_and(|raw_contents| raw_contents == string_literal.as_str())
+        {
+            let range_excluding_quotes = string_literal
+                .range()
+                .add_start(string_literal.flags.opener_len())
+                .sub_end(string_literal.flags.closer_len());
+
+            // TODO: Support multiline strings like:
+            // ```py
+            // x: """
+            //     int
+            //     | float
+            // """ = 1
+            // ```
+            match parse_expression_range(source.as_str(), range_excluding_quotes) {
+                Ok(parsed) => return Ok(parsed),
+                Err(parse_error) => diagnostics.add(
+                    string_literal.into(),
+                    "forward-annotation-syntax-error",
+                    format_args!("Syntax error in forward annotation: {}", parse_error.error),
+                ),
+            }
+        } else {
+            // The raw contents of the string doesn't match the parsed content. This could be the
+            // case for annotations that contain escape sequences.
+            diagnostics.add(
+                string_expr.into(),
+                "annotation-escape-character",
+                format_args!("Type expressions cannot contain escape characters"),
+            );
+        }
+    } else {
+        // String is implicitly concatenated.
+        diagnostics.add(
+            string_expr.into(),
+            "annotation-implicit-concat",
+            format_args!("Type expressions cannot span multiple string literals"),
+        );
+    }
+
+    Err(diagnostics.finish())
+}

crates/red_knot_python_semantic/src/types/unpacker.rs

@@ -4,7 +4,7 @@ use ruff_db::files::File;
 use ruff_python_ast::{self as ast, AnyNodeRef};
 use rustc_hash::FxHashMap;
 
-use crate::semantic_index::ast_ids::{HasScopedAstId, ScopedExpressionId};
+use crate::semantic_index::ast_ids::{HasScopedExpressionId, ScopedExpressionId};
 use crate::semantic_index::symbol::ScopeId;
 use crate::types::{Type, TypeCheckDiagnostics, TypeCheckDiagnosticsBuilder};
 use crate::Db;
@@ -29,7 +29,7 @@ impl<'db> Unpacker<'db> {
         match target {
             ast::Expr::Name(target_name) => {
                 self.targets
-                    .insert(target_name.scoped_ast_id(self.db, scope), value_ty);
+                    .insert(target_name.scoped_expression_id(self.db, scope), value_ty);
             }
             ast::Expr::Starred(ast::ExprStarred { value, .. }) => {
                 self.unpack(value, value_ty, scope);

crates/red_knot_server/src/session.rs

@@ -68,7 +68,7 @@ impl Session {
             let system = LSPSystem::new(index.clone());
 
             // TODO(dhruvmanila): Get the values from the client settings
-            let metadata = WorkspaceMetadata::from_path(system_path, &system, None)?;
+            let metadata = WorkspaceMetadata::discover(system_path, &system, None)?;
             // TODO(micha): Handle the case where the program settings are incorrect more gracefully.
             workspaces.insert(path, RootDatabase::new(metadata, system)?);
         }

crates/red_knot_server/src/system.rs

@@ -7,8 +7,8 @@ use lsp_types::Url;
 use ruff_db::file_revision::FileRevision;
 use ruff_db::system::walk_directory::WalkDirectoryBuilder;
 use ruff_db::system::{
-    DirectoryEntry, FileType, Metadata, OsSystem, Result, System, SystemPath, SystemPathBuf,
-    SystemVirtualPath, SystemVirtualPathBuf,
+    DirectoryEntry, FileType, GlobError, Metadata, OsSystem, PatternError, Result, System,
+    SystemPath, SystemPathBuf, SystemVirtualPath, SystemVirtualPathBuf,
 };
 use ruff_notebook::{Notebook, NotebookError};
 
@@ -198,6 +198,16 @@ impl System for LSPSystem {
         self.os_system.walk_directory(path)
     }
 
+    fn glob(
+        &self,
+        pattern: &str,
+    ) -> std::result::Result<
+        Box<dyn Iterator<Item = std::result::Result<SystemPathBuf, GlobError>>>,
+        PatternError,
+    > {
+        self.os_system.glob(pattern)
+    }
+
     fn as_any(&self) -> &dyn Any {
         self
     }

crates/red_knot_vendored/vendor/typeshed/source_commit.txt

@@ -1 +1 @@
-d262beb07502cda412db2179fb406d45d1a9486f
+5052fa2f18db4493892e0f2775030683c9d06531

crates/red_knot_vendored/vendor/typeshed/stdlib/VERSIONS

@@ -24,18 +24,22 @@ _asyncio: 3.0-
 _bisect: 3.0-
 _blake2: 3.6-
 _bootlocale: 3.4-3.9
+_bz2: 3.3-
 _codecs: 3.0-
 _collections_abc: 3.3-
 _compat_pickle: 3.1-
 _compression: 3.5-
+_contextvars: 3.7-
 _csv: 3.0-
 _ctypes: 3.0-
 _curses: 3.0-
+_dbm: 3.0-
 _decimal: 3.3-
 _dummy_thread: 3.0-3.8
 _dummy_threading: 3.0-3.8
 _frozen_importlib: 3.0-
 _frozen_importlib_external: 3.5-
+_gdbm: 3.0-
 _heapq: 3.0-
 _imp: 3.0-
 _interpchannels: 3.13-
@@ -45,6 +49,7 @@ _io: 3.0-
 _json: 3.0-
 _locale: 3.0-
 _lsprof: 3.0-
+_lzma: 3.3-
 _markupbase: 3.0-
 _msi: 3.0-3.12
 _operator: 3.4-
@@ -52,12 +57,14 @@ _osx_support: 3.0-
 _posixsubprocess: 3.2-
 _py_abc: 3.7-
 _pydecimal: 3.5-
+_queue: 3.7-
 _random: 3.0-
 _sitebuiltins: 3.4-
 _socket: 3.0-  # present in 3.0 at runtime, but not in typeshed
 _sqlite3: 3.0-
 _ssl: 3.0-
 _stat: 3.4-
+_struct: 3.0-
 _thread: 3.0-
 _threading_local: 3.0-
 _tkinter: 3.0-

crates/red_knot_vendored/vendor/typeshed/stdlib/_bz2.pyi

@@ -0,0 +1,18 @@
+from _typeshed import ReadableBuffer
+from typing import final
+
+@final
+class BZ2Compressor:
+    def __init__(self, compresslevel: int = 9) -> None: ...
+    def compress(self, data: ReadableBuffer, /) -> bytes: ...
+    def flush(self) -> bytes: ...
+
+@final
+class BZ2Decompressor:
+    def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes: ...
+    @property
+    def eof(self) -> bool: ...
+    @property
+    def needs_input(self) -> bool: ...
+    @property
+    def unused_data(self) -> bytes: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_contextvars.pyi

@@ -0,0 +1,61 @@
+import sys
+from collections.abc import Callable, Iterator, Mapping
+from typing import Any, ClassVar, Generic, TypeVar, final, overload
+from typing_extensions import ParamSpec
+
+if sys.version_info >= (3, 9):
+    from types import GenericAlias
+
+_T = TypeVar("_T")
+_D = TypeVar("_D")
+_P = ParamSpec("_P")
+
+@final
+class ContextVar(Generic[_T]):
+    @overload
+    def __init__(self, name: str) -> None: ...
+    @overload
+    def __init__(self, name: str, *, default: _T) -> None: ...
+    def __hash__(self) -> int: ...
+    @property
+    def name(self) -> str: ...
+    @overload
+    def get(self) -> _T: ...
+    @overload
+    def get(self, default: _T, /) -> _T: ...
+    @overload
+    def get(self, default: _D, /) -> _D | _T: ...
+    def set(self, value: _T, /) -> Token[_T]: ...
+    def reset(self, token: Token[_T], /) -> None: ...
+    if sys.version_info >= (3, 9):
+        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
+
+@final
+class Token(Generic[_T]):
+    @property
+    def var(self) -> ContextVar[_T]: ...
+    @property
+    def old_value(self) -> Any: ...  # returns either _T or MISSING, but that's hard to express
+    MISSING: ClassVar[object]
+    if sys.version_info >= (3, 9):
+        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
+
+def copy_context() -> Context: ...
+
+# It doesn't make sense to make this generic, because for most Contexts each ContextVar will have
+# a different value.
+@final
+class Context(Mapping[ContextVar[Any], Any]):
+    def __init__(self) -> None: ...
+    @overload
+    def get(self, key: ContextVar[_T], default: None = None, /) -> _T | None: ...
+    @overload
+    def get(self, key: ContextVar[_T], default: _T, /) -> _T: ...
+    @overload
+    def get(self, key: ContextVar[_T], default: _D, /) -> _T | _D: ...
+    def run(self, callable: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs) -> _T: ...
+    def copy(self) -> Context: ...
+    def __getitem__(self, key: ContextVar[_T], /) -> _T: ...
+    def __iter__(self) -> Iterator[ContextVar[Any]]: ...
+    def __len__(self) -> int: ...
+    def __eq__(self, value: object, /) -> bool: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_dbm.pyi

@@ -0,0 +1,43 @@
+import sys
+from _typeshed import ReadOnlyBuffer, StrOrBytesPath
+from types import TracebackType
+from typing import TypeVar, overload
+from typing_extensions import Self, TypeAlias
+
+if sys.platform != "win32":
+    _T = TypeVar("_T")
+    _KeyType: TypeAlias = str | ReadOnlyBuffer
+    _ValueType: TypeAlias = str | ReadOnlyBuffer
+
+    class error(OSError): ...
+    library: str
+
+    # Actual typename dbm, not exposed by the implementation
+    class _dbm:
+        def close(self) -> None: ...
+        if sys.version_info >= (3, 13):
+            def clear(self) -> None: ...
+
+        def __getitem__(self, item: _KeyType) -> bytes: ...
+        def __setitem__(self, key: _KeyType, value: _ValueType) -> None: ...
+        def __delitem__(self, key: _KeyType) -> None: ...
+        def __len__(self) -> int: ...
+        def __del__(self) -> None: ...
+        def __enter__(self) -> Self: ...
+        def __exit__(
+            self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
+        ) -> None: ...
+        @overload
+        def get(self, k: _KeyType) -> bytes | None: ...
+        @overload
+        def get(self, k: _KeyType, default: _T) -> bytes | _T: ...
+        def keys(self) -> list[bytes]: ...
+        def setdefault(self, k: _KeyType, default: _ValueType = ...) -> bytes: ...
+        # Don't exist at runtime
+        __new__: None  # type: ignore[assignment]
+        __init__: None  # type: ignore[assignment]
+
+    if sys.version_info >= (3, 11):
+        def open(filename: StrOrBytesPath, flags: str = "r", mode: int = 0o666, /) -> _dbm: ...
+    else:
+        def open(filename: str, flags: str = "r", mode: int = 0o666, /) -> _dbm: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_frozen_importlib_external.pyi

@@ -107,9 +107,9 @@ class FileLoader:
     def get_filename(self, name: str | None = None) -> str: ...
     def load_module(self, name: str | None = None) -> types.ModuleType: ...
     if sys.version_info >= (3, 10):
-        def get_resource_reader(self, module: types.ModuleType) -> importlib.readers.FileReader: ...
+        def get_resource_reader(self, name: str | None = None) -> importlib.readers.FileReader: ...
     else:
-        def get_resource_reader(self, module: types.ModuleType) -> Self | None: ...
+        def get_resource_reader(self, name: str | None = None) -> Self | None: ...
         def open_resource(self, resource: str) -> _io.FileIO: ...
         def resource_path(self, resource: str) -> str: ...
         def is_resource(self, name: str) -> bool: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_gdbm.pyi

@@ -0,0 +1,47 @@
+import sys
+from _typeshed import ReadOnlyBuffer, StrOrBytesPath
+from types import TracebackType
+from typing import TypeVar, overload
+from typing_extensions import Self, TypeAlias
+
+if sys.platform != "win32":
+    _T = TypeVar("_T")
+    _KeyType: TypeAlias = str | ReadOnlyBuffer
+    _ValueType: TypeAlias = str | ReadOnlyBuffer
+
+    open_flags: str
+
+    class error(OSError): ...
+    # Actual typename gdbm, not exposed by the implementation
+    class _gdbm:
+        def firstkey(self) -> bytes | None: ...
+        def nextkey(self, key: _KeyType) -> bytes | None: ...
+        def reorganize(self) -> None: ...
+        def sync(self) -> None: ...
+        def close(self) -> None: ...
+        if sys.version_info >= (3, 13):
+            def clear(self) -> None: ...
+
+        def __getitem__(self, item: _KeyType) -> bytes: ...
+        def __setitem__(self, key: _KeyType, value: _ValueType) -> None: ...
+        def __delitem__(self, key: _KeyType) -> None: ...
+        def __contains__(self, key: _KeyType) -> bool: ...
+        def __len__(self) -> int: ...
+        def __enter__(self) -> Self: ...
+        def __exit__(
+            self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
+        ) -> None: ...
+        @overload
+        def get(self, k: _KeyType) -> bytes | None: ...
+        @overload
+        def get(self, k: _KeyType, default: _T) -> bytes | _T: ...
+        def keys(self) -> list[bytes]: ...
+        def setdefault(self, k: _KeyType, default: _ValueType = ...) -> bytes: ...
+        # Don't exist at runtime
+        __new__: None  # type: ignore[assignment]
+        __init__: None  # type: ignore[assignment]
+
+    if sys.version_info >= (3, 11):
+        def open(filename: StrOrBytesPath, flags: str = "r", mode: int = 0o666, /) -> _gdbm: ...
+    else:
+        def open(filename: str, flags: str = "r", mode: int = 0o666, /) -> _gdbm: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_io.pyi

@@ -33,10 +33,10 @@ class _IOBase:
     def readable(self) -> bool: ...
     read: Callable[..., Any]
     def readlines(self, hint: int = -1, /) -> list[bytes]: ...
-    def seek(self, offset: int, whence: int = ..., /) -> int: ...
+    def seek(self, offset: int, whence: int = 0, /) -> int: ...
     def seekable(self) -> bool: ...
     def tell(self) -> int: ...
-    def truncate(self, size: int | None = ..., /) -> int: ...
+    def truncate(self, size: int | None = None, /) -> int: ...
     def writable(self) -> bool: ...
     write: Callable[..., Any]
     def writelines(self, lines: Iterable[ReadableBuffer], /) -> None: ...
@@ -59,8 +59,8 @@ class _BufferedIOBase(_IOBase):
     def readinto(self, buffer: WriteableBuffer, /) -> int: ...
     def write(self, buffer: ReadableBuffer, /) -> int: ...
     def readinto1(self, buffer: WriteableBuffer, /) -> int: ...
-    def read(self, size: int | None = ..., /) -> bytes: ...
-    def read1(self, size: int = ..., /) -> bytes: ...
+    def read(self, size: int | None = -1, /) -> bytes: ...
+    def read1(self, size: int = -1, /) -> bytes: ...
 
 class FileIO(RawIOBase, _RawIOBase, BinaryIO):  # type: ignore[misc]  # incompatible definitions of writelines in the base classes
     mode: str
@@ -69,13 +69,15 @@ class FileIO(RawIOBase, _RawIOBase, BinaryIO):  # type: ignore[misc]  # incompat
     # "name" is a str. In the future, making FileIO generic might help.
     name: Any
     def __init__(
-        self, file: FileDescriptorOrPath, mode: str = ..., closefd: bool = ..., opener: _Opener | None = ...
+        self, file: FileDescriptorOrPath, mode: str = "r", closefd: bool = True, opener: _Opener | None = None
     ) -> None: ...
     @property
     def closefd(self) -> bool: ...
+    def seek(self, pos: int, whence: int = 0, /) -> int: ...
+    def read(self, size: int | None = -1, /) -> bytes | MaybeNone: ...
 
 class BytesIO(BufferedIOBase, _BufferedIOBase, BinaryIO):  # type: ignore[misc]  # incompatible definitions of methods in the base classes
-    def __init__(self, initial_bytes: ReadableBuffer = ...) -> None: ...
+    def __init__(self, initial_bytes: ReadableBuffer = b"") -> None: ...
     # BytesIO does not contain a "name" field. This workaround is necessary
     # to allow BytesIO sub-classes to add this field, as it is defined
     # as a read-only property on IO[].
@@ -83,16 +85,22 @@ class BytesIO(BufferedIOBase, _BufferedIOBase, BinaryIO):  # type: ignore[misc]
     def getvalue(self) -> bytes: ...
     def getbuffer(self) -> memoryview: ...
     def read1(self, size: int | None = -1, /) -> bytes: ...
+    def readlines(self, size: int | None = None, /) -> list[bytes]: ...
+    def seek(self, pos: int, whence: int = 0, /) -> int: ...
 
 class BufferedReader(BufferedIOBase, _BufferedIOBase, BinaryIO):  # type: ignore[misc]  # incompatible definitions of methods in the base classes
     raw: RawIOBase
     def __init__(self, raw: RawIOBase, buffer_size: int = 8192) -> None: ...
     def peek(self, size: int = 0, /) -> bytes: ...
+    def seek(self, target: int, whence: int = 0, /) -> int: ...
+    def truncate(self, pos: int | None = None, /) -> int: ...
 
 class BufferedWriter(BufferedIOBase, _BufferedIOBase, BinaryIO):  # type: ignore[misc]  # incompatible definitions of writelines in the base classes
     raw: RawIOBase
     def __init__(self, raw: RawIOBase, buffer_size: int = 8192) -> None: ...
     def write(self, buffer: ReadableBuffer, /) -> int: ...
+    def seek(self, target: int, whence: int = 0, /) -> int: ...
+    def truncate(self, pos: int | None = None, /) -> int: ...
 
 class BufferedRandom(BufferedIOBase, _BufferedIOBase, BinaryIO):  # type: ignore[misc]  # incompatible definitions of methods in the base classes
     mode: str
@@ -101,10 +109,11 @@ class BufferedRandom(BufferedIOBase, _BufferedIOBase, BinaryIO):  # type: ignore
     def __init__(self, raw: RawIOBase, buffer_size: int = 8192) -> None: ...
     def seek(self, target: int, whence: int = 0, /) -> int: ...  # stubtest needs this
     def peek(self, size: int = 0, /) -> bytes: ...
+    def truncate(self, pos: int | None = None, /) -> int: ...
 
 class BufferedRWPair(BufferedIOBase, _BufferedIOBase):
     def __init__(self, reader: RawIOBase, writer: RawIOBase, buffer_size: int = 8192) -> None: ...
-    def peek(self, size: int = ..., /) -> bytes: ...
+    def peek(self, size: int = 0, /) -> bytes: ...
 
 class _TextIOBase(_IOBase):
     encoding: str
@@ -115,9 +124,9 @@ class _TextIOBase(_IOBase):
     def detach(self) -> BinaryIO: ...
     def write(self, s: str, /) -> int: ...
     def writelines(self, lines: Iterable[str], /) -> None: ...  # type: ignore[override]
-    def readline(self, size: int = ..., /) -> str: ...  # type: ignore[override]
+    def readline(self, size: int = -1, /) -> str: ...  # type: ignore[override]
     def readlines(self, hint: int = -1, /) -> list[str]: ...  # type: ignore[override]
-    def read(self, size: int | None = ..., /) -> str: ...
+    def read(self, size: int | None = -1, /) -> str: ...
 
 @type_check_only
 class _WrappedBuffer(Protocol):
@@ -177,9 +186,10 @@ class TextIOWrapper(TextIOBase, _TextIOBase, TextIO, Generic[_BufferT_co]):  # t
     # TextIOWrapper's version of seek only supports a limited subset of
     # operations.
     def seek(self, cookie: int, whence: int = 0, /) -> int: ...
+    def truncate(self, pos: int | None = None, /) -> int: ...
 
 class StringIO(TextIOBase, _TextIOBase, TextIO):  # type: ignore[misc]  # incompatible definitions of write in the base classes
-    def __init__(self, initial_value: str | None = ..., newline: str | None = ...) -> None: ...
+    def __init__(self, initial_value: str | None = "", newline: str | None = "\n") -> None: ...
     # StringIO does not contain a "name" field. This workaround is necessary
     # to allow StringIO sub-classes to add this field, as it is defined
     # as a read-only property on IO[].
@@ -187,9 +197,11 @@ class StringIO(TextIOBase, _TextIOBase, TextIO):  # type: ignore[misc]  # incomp
     def getvalue(self) -> str: ...
     @property
     def line_buffering(self) -> bool: ...
+    def seek(self, pos: int, whence: int = 0, /) -> int: ...
+    def truncate(self, pos: int | None = None, /) -> int: ...
 
 class IncrementalNewlineDecoder:
-    def __init__(self, decoder: codecs.IncrementalDecoder | None, translate: bool, errors: str = ...) -> None: ...
+    def __init__(self, decoder: codecs.IncrementalDecoder | None, translate: bool, errors: str = "strict") -> None: ...
     def decode(self, input: ReadableBuffer | str, final: bool = False) -> str: ...
     @property
     def newlines(self) -> str | tuple[str, ...] | None: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_lzma.pyi

@@ -0,0 +1,60 @@
+from _typeshed import ReadableBuffer
+from collections.abc import Mapping, Sequence
+from typing import Any, Final, final
+from typing_extensions import TypeAlias
+
+_FilterChain: TypeAlias = Sequence[Mapping[str, Any]]
+
+FORMAT_AUTO: Final = 0
+FORMAT_XZ: Final = 1
+FORMAT_ALONE: Final = 2
+FORMAT_RAW: Final = 3
+CHECK_NONE: Final = 0
+CHECK_CRC32: Final = 1
+CHECK_CRC64: Final = 4
+CHECK_SHA256: Final = 10
+CHECK_ID_MAX: Final = 15
+CHECK_UNKNOWN: Final = 16
+FILTER_LZMA1: int  # v big number
+FILTER_LZMA2: Final = 33
+FILTER_DELTA: Final = 3
+FILTER_X86: Final = 4
+FILTER_IA64: Final = 6
+FILTER_ARM: Final = 7
+FILTER_ARMTHUMB: Final = 8
+FILTER_SPARC: Final = 9
+FILTER_POWERPC: Final = 5
+MF_HC3: Final = 3
+MF_HC4: Final = 4
+MF_BT2: Final = 18
+MF_BT3: Final = 19
+MF_BT4: Final = 20
+MODE_FAST: Final = 1
+MODE_NORMAL: Final = 2
+PRESET_DEFAULT: Final = 6
+PRESET_EXTREME: int  # v big number
+
+@final
+class LZMADecompressor:
+    def __init__(self, format: int | None = ..., memlimit: int | None = ..., filters: _FilterChain | None = ...) -> None: ...
+    def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes: ...
+    @property
+    def check(self) -> int: ...
+    @property
+    def eof(self) -> bool: ...
+    @property
+    def unused_data(self) -> bytes: ...
+    @property
+    def needs_input(self) -> bool: ...
+
+@final
+class LZMACompressor:
+    def __init__(
+        self, format: int | None = ..., check: int = ..., preset: int | None = ..., filters: _FilterChain | None = ...
+    ) -> None: ...
+    def compress(self, data: ReadableBuffer, /) -> bytes: ...
+    def flush(self) -> bytes: ...
+
+class LZMAError(Exception): ...
+
+def is_check_supported(check_id: int, /) -> bool: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_queue.pyi

@@ -0,0 +1,20 @@
+import sys
+from typing import Any, Generic, TypeVar
+
+if sys.version_info >= (3, 9):
+    from types import GenericAlias
+
+_T = TypeVar("_T")
+
+class Empty(Exception): ...
+
+class SimpleQueue(Generic[_T]):
+    def __init__(self) -> None: ...
+    def empty(self) -> bool: ...
+    def get(self, block: bool = True, timeout: float | None = None) -> _T: ...
+    def get_nowait(self) -> _T: ...
+    def put(self, item: _T, block: bool = True, timeout: float | None = None) -> None: ...
+    def put_nowait(self, item: _T) -> None: ...
+    def qsize(self) -> int: ...
+    if sys.version_info >= (3, 9):
+        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_struct.pyi

@@ -0,0 +1,22 @@
+from _typeshed import ReadableBuffer, WriteableBuffer
+from collections.abc import Iterator
+from typing import Any
+
+def pack(fmt: str | bytes, /, *v: Any) -> bytes: ...
+def pack_into(fmt: str | bytes, buffer: WriteableBuffer, offset: int, /, *v: Any) -> None: ...
+def unpack(format: str | bytes, buffer: ReadableBuffer, /) -> tuple[Any, ...]: ...
+def unpack_from(format: str | bytes, /, buffer: ReadableBuffer, offset: int = 0) -> tuple[Any, ...]: ...
+def iter_unpack(format: str | bytes, buffer: ReadableBuffer, /) -> Iterator[tuple[Any, ...]]: ...
+def calcsize(format: str | bytes, /) -> int: ...
+
+class Struct:
+    @property
+    def format(self) -> str: ...
+    @property
+    def size(self) -> int: ...
+    def __init__(self, format: str | bytes) -> None: ...
+    def pack(self, *v: Any) -> bytes: ...
+    def pack_into(self, buffer: WriteableBuffer, offset: int, *v: Any) -> None: ...
+    def unpack(self, buffer: ReadableBuffer, /) -> tuple[Any, ...]: ...
+    def unpack_from(self, buffer: ReadableBuffer, offset: int = 0) -> tuple[Any, ...]: ...
+    def iter_unpack(self, buffer: ReadableBuffer, /) -> Iterator[tuple[Any, ...]]: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_threading_local.pyi

@@ -1,5 +1,5 @@
 from typing import Any
-from typing_extensions import TypeAlias
+from typing_extensions import Self, TypeAlias
 from weakref import ReferenceType
 
 __all__ = ["local"]
@@ -12,6 +12,7 @@ class _localimpl:
     def create_dict(self) -> _LocalDict: ...
 
 class local:
+    def __new__(cls, /, *args: Any, **kw: Any) -> Self: ...
     def __getattribute__(self, name: str) -> Any: ...
     def __setattr__(self, name: str, value: Any) -> None: ...
     def __delattr__(self, name: str) -> None: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/builtins.pyi

@@ -1284,9 +1284,7 @@ class property:
 
 @final
 class _NotImplementedType(Any):
-    # A little weird, but typing the __call__ as NotImplemented makes the error message
-    # for NotImplemented() much better
-    __call__: NotImplemented  # type: ignore[valid-type]  # pyright: ignore[reportInvalidTypeForm]
+    __call__: None
 
 NotImplemented: _NotImplementedType
 
@@ -1917,7 +1915,7 @@ class StopIteration(Exception):
 
 class OSError(Exception):
     errno: int | None
-    strerror: str
+    strerror: str | None
     # filename, filename2 are actually str | bytes | None
     filename: Any
     filename2: Any

crates/red_knot_vendored/vendor/typeshed/stdlib/bz2.pyi

@@ -1,9 +1,10 @@
 import _compression
 import sys
+from _bz2 import BZ2Compressor as BZ2Compressor, BZ2Decompressor as BZ2Decompressor
 from _compression import BaseStream
 from _typeshed import ReadableBuffer, StrOrBytesPath, WriteableBuffer
 from collections.abc import Iterable
-from typing import IO, Any, Literal, Protocol, SupportsIndex, TextIO, final, overload
+from typing import IO, Any, Literal, Protocol, SupportsIndex, TextIO, overload
 from typing_extensions import Self, TypeAlias
 
 __all__ = ["BZ2File", "BZ2Compressor", "BZ2Decompressor", "open", "compress", "decompress"]
@@ -128,19 +129,3 @@ class BZ2File(BaseStream, IO[bytes]):
     def seek(self, offset: int, whence: int = 0) -> int: ...
     def write(self, data: ReadableBuffer) -> int: ...
     def writelines(self, seq: Iterable[ReadableBuffer]) -> None: ...
-
-@final
-class BZ2Compressor:
-    def __init__(self, compresslevel: int = 9) -> None: ...
-    def compress(self, data: ReadableBuffer, /) -> bytes: ...
-    def flush(self) -> bytes: ...
-
-@final
-class BZ2Decompressor:
-    def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes: ...
-    @property
-    def eof(self) -> bool: ...
-    @property
-    def needs_input(self) -> bool: ...
-    @property
-    def unused_data(self) -> bytes: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/contextvars.pyi

@@ -1,63 +1,3 @@
-import sys
-from collections.abc import Callable, Iterator, Mapping
-from typing import Any, ClassVar, Generic, TypeVar, final, overload
-from typing_extensions import ParamSpec
-
-if sys.version_info >= (3, 9):
-    from types import GenericAlias
+from _contextvars import Context as Context, ContextVar as ContextVar, Token as Token, copy_context as copy_context
 
 __all__ = ("Context", "ContextVar", "Token", "copy_context")
-
-_T = TypeVar("_T")
-_D = TypeVar("_D")
-_P = ParamSpec("_P")
-
-@final
-class ContextVar(Generic[_T]):
-    @overload
-    def __init__(self, name: str) -> None: ...
-    @overload
-    def __init__(self, name: str, *, default: _T) -> None: ...
-    def __hash__(self) -> int: ...
-    @property
-    def name(self) -> str: ...
-    @overload
-    def get(self) -> _T: ...
-    @overload
-    def get(self, default: _T, /) -> _T: ...
-    @overload
-    def get(self, default: _D, /) -> _D | _T: ...
-    def set(self, value: _T, /) -> Token[_T]: ...
-    def reset(self, token: Token[_T], /) -> None: ...
-    if sys.version_info >= (3, 9):
-        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
-
-@final
-class Token(Generic[_T]):
-    @property
-    def var(self) -> ContextVar[_T]: ...
-    @property
-    def old_value(self) -> Any: ...  # returns either _T or MISSING, but that's hard to express
-    MISSING: ClassVar[object]
-    if sys.version_info >= (3, 9):
-        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
-
-def copy_context() -> Context: ...
-
-# It doesn't make sense to make this generic, because for most Contexts each ContextVar will have
-# a different value.
-@final
-class Context(Mapping[ContextVar[Any], Any]):
-    def __init__(self) -> None: ...
-    @overload
-    def get(self, key: ContextVar[_T], default: None = None, /) -> _T | None: ...
-    @overload
-    def get(self, key: ContextVar[_T], default: _T, /) -> _T: ...
-    @overload
-    def get(self, key: ContextVar[_T], default: _D, /) -> _T | _D: ...
-    def run(self, callable: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs) -> _T: ...
-    def copy(self) -> Context: ...
-    def __getitem__(self, key: ContextVar[_T], /) -> _T: ...
-    def __iter__(self) -> Iterator[ContextVar[Any]]: ...
-    def __len__(self) -> int: ...
-    def __eq__(self, value: object, /) -> bool: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/dbm/gnu.pyi

@@ -1,47 +1 @@
-import sys
-from _typeshed import ReadOnlyBuffer, StrOrBytesPath
-from types import TracebackType
-from typing import TypeVar, overload
-from typing_extensions import Self, TypeAlias
-
-if sys.platform != "win32":
-    _T = TypeVar("_T")
-    _KeyType: TypeAlias = str | ReadOnlyBuffer
-    _ValueType: TypeAlias = str | ReadOnlyBuffer
-
-    open_flags: str
-
-    class error(OSError): ...
-    # Actual typename gdbm, not exposed by the implementation
-    class _gdbm:
-        def firstkey(self) -> bytes | None: ...
-        def nextkey(self, key: _KeyType) -> bytes | None: ...
-        def reorganize(self) -> None: ...
-        def sync(self) -> None: ...
-        def close(self) -> None: ...
-        if sys.version_info >= (3, 13):
-            def clear(self) -> None: ...
-
-        def __getitem__(self, item: _KeyType) -> bytes: ...
-        def __setitem__(self, key: _KeyType, value: _ValueType) -> None: ...
-        def __delitem__(self, key: _KeyType) -> None: ...
-        def __contains__(self, key: _KeyType) -> bool: ...
-        def __len__(self) -> int: ...
-        def __enter__(self) -> Self: ...
-        def __exit__(
-            self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
-        ) -> None: ...
-        @overload
-        def get(self, k: _KeyType) -> bytes | None: ...
-        @overload
-        def get(self, k: _KeyType, default: _T) -> bytes | _T: ...
-        def keys(self) -> list[bytes]: ...
-        def setdefault(self, k: _KeyType, default: _ValueType = ...) -> bytes: ...
-        # Don't exist at runtime
-        __new__: None  # type: ignore[assignment]
-        __init__: None  # type: ignore[assignment]
-
-    if sys.version_info >= (3, 11):
-        def open(filename: StrOrBytesPath, flags: str = "r", mode: int = 0o666, /) -> _gdbm: ...
-    else:
-        def open(filename: str, flags: str = "r", mode: int = 0o666, /) -> _gdbm: ...
+from _gdbm import *

crates/red_knot_vendored/vendor/typeshed/stdlib/dbm/ndbm.pyi

@@ -1,43 +1 @@
-import sys
-from _typeshed import ReadOnlyBuffer, StrOrBytesPath
-from types import TracebackType
-from typing import TypeVar, overload
-from typing_extensions import Self, TypeAlias
-
-if sys.platform != "win32":
-    _T = TypeVar("_T")
-    _KeyType: TypeAlias = str | ReadOnlyBuffer
-    _ValueType: TypeAlias = str | ReadOnlyBuffer
-
-    class error(OSError): ...
-    library: str
-
-    # Actual typename dbm, not exposed by the implementation
-    class _dbm:
-        def close(self) -> None: ...
-        if sys.version_info >= (3, 13):
-            def clear(self) -> None: ...
-
-        def __getitem__(self, item: _KeyType) -> bytes: ...
-        def __setitem__(self, key: _KeyType, value: _ValueType) -> None: ...
-        def __delitem__(self, key: _KeyType) -> None: ...
-        def __len__(self) -> int: ...
-        def __del__(self) -> None: ...
-        def __enter__(self) -> Self: ...
-        def __exit__(
-            self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
-        ) -> None: ...
-        @overload
-        def get(self, k: _KeyType) -> bytes | None: ...
-        @overload
-        def get(self, k: _KeyType, default: _T) -> bytes | _T: ...
-        def keys(self) -> list[bytes]: ...
-        def setdefault(self, k: _KeyType, default: _ValueType = ...) -> bytes: ...
-        # Don't exist at runtime
-        __new__: None  # type: ignore[assignment]
-        __init__: None  # type: ignore[assignment]
-
-    if sys.version_info >= (3, 11):
-        def open(filename: StrOrBytesPath, flags: str = "r", mode: int = 0o666, /) -> _dbm: ...
-    else:
-        def open(filename: str, flags: str = "r", mode: int = 0o666, /) -> _dbm: ...
+from _dbm import *

crates/red_knot_vendored/vendor/typeshed/stdlib/distutils/ccompiler.pyi

@@ -1,5 +1,5 @@
 from _typeshed import BytesPath, StrPath, Unused
-from collections.abc import Callable, Iterable
+from collections.abc import Callable, Iterable, Sequence
 from distutils.file_util import _BytesPathT, _StrPathT
 from typing import Literal, overload
 from typing_extensions import TypeAlias, TypeVarTuple, Unpack
@@ -63,7 +63,7 @@ class CCompiler:
     def set_executables(self, **args: str) -> None: ...
     def compile(
         self,
-        sources: list[str],
+        sources: Sequence[StrPath],
         output_dir: str | None = None,
         macros: list[_Macro] | None = None,
         include_dirs: list[str] | None = None,

crates/red_knot_vendored/vendor/typeshed/stdlib/fractions.pyi

@@ -2,7 +2,7 @@ import sys
 from collections.abc import Callable
 from decimal import Decimal
 from numbers import Integral, Rational, Real
-from typing import Any, Literal, SupportsIndex, overload
+from typing import Any, Literal, Protocol, SupportsIndex, overload
 from typing_extensions import Self, TypeAlias
 
 _ComparableNum: TypeAlias = int | float | Decimal | Real
@@ -20,11 +20,19 @@ else:
     @overload
     def gcd(a: Integral, b: Integral) -> Integral: ...
 
+class _ConvertibleToIntegerRatio(Protocol):
+    def as_integer_ratio(self) -> tuple[int | Rational, int | Rational]: ...
+
 class Fraction(Rational):
     @overload
     def __new__(cls, numerator: int | Rational = 0, denominator: int | Rational | None = None) -> Self: ...
     @overload
     def __new__(cls, value: float | Decimal | str, /) -> Self: ...
+
+    if sys.version_info >= (3, 14):
+        @overload
+        def __new__(cls, value: _ConvertibleToIntegerRatio) -> Self: ...
+
     @classmethod
     def from_float(cls, f: float) -> Self: ...
     @classmethod

crates/red_knot_vendored/vendor/typeshed/stdlib/getopt.pyi

@@ -1,7 +1,11 @@
+from collections.abc import Iterable
+
 __all__ = ["GetoptError", "error", "getopt", "gnu_getopt"]
 
-def getopt(args: list[str], shortopts: str, longopts: list[str] = []) -> tuple[list[tuple[str, str]], list[str]]: ...
-def gnu_getopt(args: list[str], shortopts: str, longopts: list[str] = []) -> tuple[list[tuple[str, str]], list[str]]: ...
+def getopt(args: list[str], shortopts: str, longopts: Iterable[str] | str = []) -> tuple[list[tuple[str, str]], list[str]]: ...
+def gnu_getopt(
+    args: list[str], shortopts: str, longopts: Iterable[str] | str = []
+) -> tuple[list[tuple[str, str]], list[str]]: ...
 
 class GetoptError(Exception):
     msg: str

crates/red_knot_vendored/vendor/typeshed/stdlib/ipaddress.pyi

@@ -128,19 +128,6 @@ class _BaseNetwork(_IPAddressBase, Generic[_A]):
     @property
     def hostmask(self) -> _A: ...
 
-class _BaseInterface(_BaseAddress, Generic[_A, _N]):
-    hostmask: _A
-    netmask: _A
-    network: _N
-    @property
-    def ip(self) -> _A: ...
-    @property
-    def with_hostmask(self) -> str: ...
-    @property
-    def with_netmask(self) -> str: ...
-    @property
-    def with_prefixlen(self) -> str: ...
-
 class _BaseV4:
     @property
     def version(self) -> Literal[4]: ...
@@ -154,9 +141,21 @@ class IPv4Address(_BaseV4, _BaseAddress):
 
 class IPv4Network(_BaseV4, _BaseNetwork[IPv4Address]): ...
 
-class IPv4Interface(IPv4Address, _BaseInterface[IPv4Address, IPv4Network]):
+class IPv4Interface(IPv4Address):
+    netmask: IPv4Address
+    network: IPv4Network
     def __eq__(self, other: object) -> bool: ...
     def __hash__(self) -> int: ...
+    @property
+    def hostmask(self) -> IPv4Address: ...
+    @property
+    def ip(self) -> IPv4Address: ...
+    @property
+    def with_hostmask(self) -> str: ...
+    @property
+    def with_netmask(self) -> str: ...
+    @property
+    def with_prefixlen(self) -> str: ...
 
 class _BaseV6:
     @property
@@ -184,9 +183,21 @@ class IPv6Network(_BaseV6, _BaseNetwork[IPv6Address]):
     @property
     def is_site_local(self) -> bool: ...
 
-class IPv6Interface(IPv6Address, _BaseInterface[IPv6Address, IPv6Network]):
+class IPv6Interface(IPv6Address):
+    netmask: IPv6Address
+    network: IPv6Network
     def __eq__(self, other: object) -> bool: ...
     def __hash__(self) -> int: ...
+    @property
+    def hostmask(self) -> IPv6Address: ...
+    @property
+    def ip(self) -> IPv6Address: ...
+    @property
+    def with_hostmask(self) -> str: ...
+    @property
+    def with_netmask(self) -> str: ...
+    @property
+    def with_prefixlen(self) -> str: ...
 
 def v4_int_to_packed(address: int) -> bytes: ...
 def v6_int_to_packed(address: int) -> bytes: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/logging/config.pyi

@@ -1,6 +1,6 @@
 import sys
 from _typeshed import StrOrBytesPath
-from collections.abc import Callable, Hashable, Iterable, Sequence
+from collections.abc import Callable, Hashable, Iterable, Mapping, Sequence
 from configparser import RawConfigParser
 from re import Pattern
 from threading import Thread
@@ -63,7 +63,7 @@ def dictConfig(config: _DictConfigArgs | dict[str, Any]) -> None: ...
 if sys.version_info >= (3, 10):
     def fileConfig(
         fname: StrOrBytesPath | IO[str] | RawConfigParser,
-        defaults: dict[str, str] | None = None,
+        defaults: Mapping[str, str] | None = None,
         disable_existing_loggers: bool = True,
         encoding: str | None = None,
     ) -> None: ...
@@ -71,7 +71,7 @@ if sys.version_info >= (3, 10):
 else:
     def fileConfig(
         fname: StrOrBytesPath | IO[str] | RawConfigParser,
-        defaults: dict[str, str] | None = None,
+        defaults: Mapping[str, str] | None = None,
         disable_existing_loggers: bool = True,
     ) -> None: ...
 

crates/red_knot_vendored/vendor/typeshed/stdlib/logging/handlers.pyi

@@ -260,6 +260,8 @@ class QueueHandler(Handler):
     def __init__(self, queue: _QueueLike[Any]) -> None: ...
     def prepare(self, record: LogRecord) -> Any: ...
     def enqueue(self, record: LogRecord) -> None: ...
+    if sys.version_info >= (3, 12):
+        listener: QueueListener | None
 
 class QueueListener:
     handlers: tuple[Handler, ...]  # undocumented

crates/red_knot_vendored/vendor/typeshed/stdlib/lzma.pyi

@@ -1,7 +1,41 @@
 from _compression import BaseStream
+from _lzma import (
+    CHECK_CRC32 as CHECK_CRC32,
+    CHECK_CRC64 as CHECK_CRC64,
+    CHECK_ID_MAX as CHECK_ID_MAX,
+    CHECK_NONE as CHECK_NONE,
+    CHECK_SHA256 as CHECK_SHA256,
+    CHECK_UNKNOWN as CHECK_UNKNOWN,
+    FILTER_ARM as FILTER_ARM,
+    FILTER_ARMTHUMB as FILTER_ARMTHUMB,
+    FILTER_DELTA as FILTER_DELTA,
+    FILTER_IA64 as FILTER_IA64,
+    FILTER_LZMA1 as FILTER_LZMA1,
+    FILTER_LZMA2 as FILTER_LZMA2,
+    FILTER_POWERPC as FILTER_POWERPC,
+    FILTER_SPARC as FILTER_SPARC,
+    FILTER_X86 as FILTER_X86,
+    FORMAT_ALONE as FORMAT_ALONE,
+    FORMAT_AUTO as FORMAT_AUTO,
+    FORMAT_RAW as FORMAT_RAW,
+    FORMAT_XZ as FORMAT_XZ,
+    MF_BT2 as MF_BT2,
+    MF_BT3 as MF_BT3,
+    MF_BT4 as MF_BT4,
+    MF_HC3 as MF_HC3,
+    MF_HC4 as MF_HC4,
+    MODE_FAST as MODE_FAST,
+    MODE_NORMAL as MODE_NORMAL,
+    PRESET_DEFAULT as PRESET_DEFAULT,
+    PRESET_EXTREME as PRESET_EXTREME,
+    LZMACompressor as LZMACompressor,
+    LZMADecompressor as LZMADecompressor,
+    LZMAError as LZMAError,
+    _FilterChain,
+    is_check_supported as is_check_supported,
+)
 from _typeshed import ReadableBuffer, StrOrBytesPath
-from collections.abc import Mapping, Sequence
-from typing import IO, Any, Final, Literal, TextIO, final, overload
+from typing import IO, Literal, TextIO, overload
 from typing_extensions import Self, TypeAlias
 
 __all__ = [
@@ -48,62 +82,6 @@ _OpenTextWritingMode: TypeAlias = Literal["wt", "xt", "at"]
 
 _PathOrFile: TypeAlias = StrOrBytesPath | IO[bytes]
 
-_FilterChain: TypeAlias = Sequence[Mapping[str, Any]]
-
-FORMAT_AUTO: Final = 0
-FORMAT_XZ: Final = 1
-FORMAT_ALONE: Final = 2
-FORMAT_RAW: Final = 3
-CHECK_NONE: Final = 0
-CHECK_CRC32: Final = 1
-CHECK_CRC64: Final = 4
-CHECK_SHA256: Final = 10
-CHECK_ID_MAX: Final = 15
-CHECK_UNKNOWN: Final = 16
-FILTER_LZMA1: int  # v big number
-FILTER_LZMA2: Final = 33
-FILTER_DELTA: Final = 3
-FILTER_X86: Final = 4
-FILTER_IA64: Final = 6
-FILTER_ARM: Final = 7
-FILTER_ARMTHUMB: Final = 8
-FILTER_SPARC: Final = 9
-FILTER_POWERPC: Final = 5
-MF_HC3: Final = 3
-MF_HC4: Final = 4
-MF_BT2: Final = 18
-MF_BT3: Final = 19
-MF_BT4: Final = 20
-MODE_FAST: Final = 1
-MODE_NORMAL: Final = 2
-PRESET_DEFAULT: Final = 6
-PRESET_EXTREME: int  # v big number
-
-# from _lzma.c
-@final
-class LZMADecompressor:
-    def __init__(self, format: int | None = ..., memlimit: int | None = ..., filters: _FilterChain | None = ...) -> None: ...
-    def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes: ...
-    @property
-    def check(self) -> int: ...
-    @property
-    def eof(self) -> bool: ...
-    @property
-    def unused_data(self) -> bytes: ...
-    @property
-    def needs_input(self) -> bool: ...
-
-# from _lzma.c
-@final
-class LZMACompressor:
-    def __init__(
-        self, format: int | None = ..., check: int = ..., preset: int | None = ..., filters: _FilterChain | None = ...
-    ) -> None: ...
-    def compress(self, data: ReadableBuffer, /) -> bytes: ...
-    def flush(self) -> bytes: ...
-
-class LZMAError(Exception): ...
-
 class LZMAFile(BaseStream, IO[bytes]):  # type: ignore[misc]  # incompatible definitions of writelines in the base classes
     def __init__(
         self,
@@ -194,4 +172,3 @@ def compress(
 def decompress(
     data: ReadableBuffer, format: int = 0, memlimit: int | None = None, filters: _FilterChain | None = None
 ) -> bytes: ...
-def is_check_supported(check_id: int, /) -> bool: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/mmap.pyi

@@ -34,9 +34,22 @@ class mmap:
     if sys.platform == "win32":
         def __init__(self, fileno: int, length: int, tagname: str | None = ..., access: int = ..., offset: int = ...) -> None: ...
     else:
-        def __init__(
-            self, fileno: int, length: int, flags: int = ..., prot: int = ..., access: int = ..., offset: int = ...
-        ) -> None: ...
+        if sys.version_info >= (3, 13):
+            def __init__(
+                self,
+                fileno: int,
+                length: int,
+                flags: int = ...,
+                prot: int = ...,
+                access: int = ...,
+                offset: int = ...,
+                *,
+                trackfd: bool = True,
+            ) -> None: ...
+        else:
+            def __init__(
+                self, fileno: int, length: int, flags: int = ..., prot: int = ..., access: int = ..., offset: int = ...
+            ) -> None: ...
 
     def close(self) -> None: ...
     def flush(self, offset: int = ..., size: int = ...) -> None: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/multiprocessing/managers.pyi

@@ -10,6 +10,7 @@ from typing_extensions import Self, TypeAlias
 from .connection import Connection
 from .context import BaseContext
 from .shared_memory import _SLT, ShareableList as _ShareableList, SharedMemory as _SharedMemory
+from .util import Finalize as _Finalize
 
 __all__ = ["BaseManager", "SyncManager", "BaseProxy", "Token", "SharedMemoryManager"]
 
@@ -60,31 +61,58 @@ class ValueProxy(BaseProxy, Generic[_T]):
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
 
-class DictProxy(BaseProxy, MutableMapping[_KT, _VT]):
-    __builtins__: ClassVar[dict[str, Any]]
-    def __len__(self) -> int: ...
-    def __getitem__(self, key: _KT, /) -> _VT: ...
-    def __setitem__(self, key: _KT, value: _VT, /) -> None: ...
-    def __delitem__(self, key: _KT, /) -> None: ...
-    def __iter__(self) -> Iterator[_KT]: ...
-    def copy(self) -> dict[_KT, _VT]: ...
-    @overload  # type: ignore[override]
-    def get(self, key: _KT, /) -> _VT | None: ...
-    @overload
-    def get(self, key: _KT, default: _VT, /) -> _VT: ...
-    @overload
-    def get(self, key: _KT, default: _T, /) -> _VT | _T: ...
-    @overload
-    def pop(self, key: _KT, /) -> _VT: ...
-    @overload
-    def pop(self, key: _KT, default: _VT, /) -> _VT: ...
-    @overload
-    def pop(self, key: _KT, default: _T, /) -> _VT | _T: ...
-    def keys(self) -> list[_KT]: ...  # type: ignore[override]
-    def items(self) -> list[tuple[_KT, _VT]]: ...  # type: ignore[override]
-    def values(self) -> list[_VT]: ...  # type: ignore[override]
-    if sys.version_info >= (3, 13):
-        def __class_getitem__(cls, args: Any, /) -> Any: ...
+if sys.version_info >= (3, 13):
+    class _BaseDictProxy(BaseProxy, MutableMapping[_KT, _VT]):
+        __builtins__: ClassVar[dict[str, Any]]
+        def __len__(self) -> int: ...
+        def __getitem__(self, key: _KT, /) -> _VT: ...
+        def __setitem__(self, key: _KT, value: _VT, /) -> None: ...
+        def __delitem__(self, key: _KT, /) -> None: ...
+        def __iter__(self) -> Iterator[_KT]: ...
+        def copy(self) -> dict[_KT, _VT]: ...
+        @overload  # type: ignore[override]
+        def get(self, key: _KT, /) -> _VT | None: ...
+        @overload
+        def get(self, key: _KT, default: _VT, /) -> _VT: ...
+        @overload
+        def get(self, key: _KT, default: _T, /) -> _VT | _T: ...
+        @overload
+        def pop(self, key: _KT, /) -> _VT: ...
+        @overload
+        def pop(self, key: _KT, default: _VT, /) -> _VT: ...
+        @overload
+        def pop(self, key: _KT, default: _T, /) -> _VT | _T: ...
+        def keys(self) -> list[_KT]: ...  # type: ignore[override]
+        def items(self) -> list[tuple[_KT, _VT]]: ...  # type: ignore[override]
+        def values(self) -> list[_VT]: ...  # type: ignore[override]
+
+    class DictProxy(_BaseDictProxy[_KT, _VT]):
+        def __class_getitem__(cls, args: Any, /) -> GenericAlias: ...
+
+else:
+    class DictProxy(BaseProxy, MutableMapping[_KT, _VT]):
+        __builtins__: ClassVar[dict[str, Any]]
+        def __len__(self) -> int: ...
+        def __getitem__(self, key: _KT, /) -> _VT: ...
+        def __setitem__(self, key: _KT, value: _VT, /) -> None: ...
+        def __delitem__(self, key: _KT, /) -> None: ...
+        def __iter__(self) -> Iterator[_KT]: ...
+        def copy(self) -> dict[_KT, _VT]: ...
+        @overload  # type: ignore[override]
+        def get(self, key: _KT, /) -> _VT | None: ...
+        @overload
+        def get(self, key: _KT, default: _VT, /) -> _VT: ...
+        @overload
+        def get(self, key: _KT, default: _T, /) -> _VT | _T: ...
+        @overload
+        def pop(self, key: _KT, /) -> _VT: ...
+        @overload
+        def pop(self, key: _KT, default: _VT, /) -> _VT: ...
+        @overload
+        def pop(self, key: _KT, default: _T, /) -> _VT | _T: ...
+        def keys(self) -> list[_KT]: ...  # type: ignore[override]
+        def items(self) -> list[tuple[_KT, _VT]]: ...  # type: ignore[override]
+        def values(self) -> list[_VT]: ...  # type: ignore[override]
 
 class BaseListProxy(BaseProxy, MutableSequence[_T]):
     __builtins__: ClassVar[dict[str, Any]]
@@ -156,7 +184,7 @@ class BaseManager:
     def get_server(self) -> Server: ...
     def connect(self) -> None: ...
     def start(self, initializer: Callable[..., object] | None = None, initargs: Iterable[Any] = ()) -> None: ...
-    def shutdown(self) -> None: ...  # only available after start() was called
+    shutdown: _Finalize  # only available after start() was called
     def join(self, timeout: float | None = None) -> None: ...  # undocumented
     @property
     def address(self) -> Any: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/multiprocessing/spawn.pyi

@@ -23,7 +23,7 @@ def get_command_line(**kwds: Any) -> list[str]: ...
 def spawn_main(pipe_handle: int, parent_pid: int | None = None, tracker_fd: int | None = None) -> None: ...
 
 # undocumented
-def _main(fd: int) -> Any: ...
+def _main(fd: int, parent_sentinel: int) -> int: ...
 def get_preparation_data(name: str) -> dict[str, Any]: ...
 
 old_main_modules: list[ModuleType]

crates/red_knot_vendored/vendor/typeshed/stdlib/queue.pyi

@@ -1,4 +1,5 @@
 import sys
+from _queue import Empty as Empty, SimpleQueue as SimpleQueue
 from threading import Condition, Lock
 from typing import Any, Generic, TypeVar
 
@@ -11,7 +12,6 @@ if sys.version_info >= (3, 13):
 
 _T = TypeVar("_T")
 
-class Empty(Exception): ...
 class Full(Exception): ...
 
 if sys.version_info >= (3, 13):
@@ -55,14 +55,3 @@ class PriorityQueue(Queue[_T]):
 
 class LifoQueue(Queue[_T]):
     queue: list[_T]
-
-class SimpleQueue(Generic[_T]):
-    def __init__(self) -> None: ...
-    def empty(self) -> bool: ...
-    def get(self, block: bool = True, timeout: float | None = None) -> _T: ...
-    def get_nowait(self) -> _T: ...
-    def put(self, item: _T, block: bool = True, timeout: float | None = None) -> None: ...
-    def put_nowait(self, item: _T) -> None: ...
-    def qsize(self) -> int: ...
-    if sys.version_info >= (3, 9):
-        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/struct.pyi

@@ -1,26 +1,5 @@
-from _typeshed import ReadableBuffer, WriteableBuffer
-from collections.abc import Iterator
-from typing import Any
+from _struct import *
 
 __all__ = ["calcsize", "pack", "pack_into", "unpack", "unpack_from", "iter_unpack", "Struct", "error"]
 
 class error(Exception): ...
-
-def pack(fmt: str | bytes, /, *v: Any) -> bytes: ...
-def pack_into(fmt: str | bytes, buffer: WriteableBuffer, offset: int, /, *v: Any) -> None: ...
-def unpack(format: str | bytes, buffer: ReadableBuffer, /) -> tuple[Any, ...]: ...
-def unpack_from(format: str | bytes, /, buffer: ReadableBuffer, offset: int = 0) -> tuple[Any, ...]: ...
-def iter_unpack(format: str | bytes, buffer: ReadableBuffer, /) -> Iterator[tuple[Any, ...]]: ...
-def calcsize(format: str | bytes, /) -> int: ...
-
-class Struct:
-    @property
-    def format(self) -> str: ...
-    @property
-    def size(self) -> int: ...
-    def __init__(self, format: str | bytes) -> None: ...
-    def pack(self, *v: Any) -> bytes: ...
-    def pack_into(self, buffer: WriteableBuffer, offset: int, *v: Any) -> None: ...
-    def unpack(self, buffer: ReadableBuffer, /) -> tuple[Any, ...]: ...
-    def unpack_from(self, buffer: ReadableBuffer, offset: int = 0) -> tuple[Any, ...]: ...
-    def iter_unpack(self, buffer: ReadableBuffer, /) -> Iterator[tuple[Any, ...]]: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/tarfile.pyi

@@ -1,7 +1,7 @@
 import bz2
 import io
 import sys
-from _typeshed import StrOrBytesPath, StrPath
+from _typeshed import StrOrBytesPath, StrPath, SupportsRead
 from builtins import list as _list  # aliases to avoid name clashes with fields named "type" or "list"
 from collections.abc import Callable, Iterable, Iterator, Mapping
 from gzip import _ReadableFileobj as _GzipReadableFileobj, _WritableFileobj as _GzipWritableFileobj
@@ -481,7 +481,7 @@ class TarFile:
         *,
         filter: Callable[[TarInfo], TarInfo | None] | None = None,
     ) -> None: ...
-    def addfile(self, tarinfo: TarInfo, fileobj: IO[bytes] | None = None) -> None: ...
+    def addfile(self, tarinfo: TarInfo, fileobj: SupportsRead[bytes] | None = None) -> None: ...
     def gettarinfo(
         self, name: StrOrBytesPath | None = None, arcname: str | None = None, fileobj: IO[bytes] | None = None
     ) -> TarInfo: ...

crates/red_knot_wasm/src/lib.rs

@@ -3,15 +3,15 @@ use std::any::Any;
 use js_sys::Error;
 use wasm_bindgen::prelude::*;
 
-use red_knot_workspace::db::RootDatabase;
+use red_knot_workspace::db::{Db, RootDatabase};
 use red_knot_workspace::workspace::settings::Configuration;
 use red_knot_workspace::workspace::WorkspaceMetadata;
 use ruff_db::diagnostic::Diagnostic;
 use ruff_db::files::{system_path_to_file, File};
 use ruff_db::system::walk_directory::WalkDirectoryBuilder;
 use ruff_db::system::{
-    DirectoryEntry, MemoryFileSystem, Metadata, System, SystemPath, SystemPathBuf,
-    SystemVirtualPath,
+    DirectoryEntry, GlobError, MemoryFileSystem, Metadata, PatternError, System, SystemPath,
+    SystemPathBuf, SystemVirtualPath,
 };
 use ruff_notebook::Notebook;
 
@@ -42,10 +42,10 @@ impl Workspace {
     #[wasm_bindgen(constructor)]
     pub fn new(root: &str, settings: &Settings) -> Result<Workspace, Error> {
         let system = WasmSystem::new(SystemPath::new(root));
-        let workspace = WorkspaceMetadata::from_path(
+        let workspace = WorkspaceMetadata::discover(
             SystemPath::new(root),
             &system,
-            Some(Configuration {
+            Some(&Configuration {
                 target_version: Some(settings.target_version.into()),
                 ..Configuration::default()
             }),
@@ -184,8 +184,8 @@ impl Settings {
 #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Default)]
 pub enum TargetVersion {
     Py37,
-    #[default]
     Py38,
+    #[default]
     Py39,
     Py310,
     Py311,
@@ -226,7 +226,7 @@ impl System for WasmSystem {
     }
 
     fn canonicalize_path(&self, path: &SystemPath) -> ruff_db::system::Result<SystemPathBuf> {
-        Ok(self.fs.canonicalize(path))
+        self.fs.canonicalize(path)
     }
 
     fn read_to_string(&self, path: &SystemPath) -> ruff_db::system::Result<String> {
@@ -272,6 +272,13 @@ impl System for WasmSystem {
         self.fs.walk_directory(path)
     }
 
+    fn glob(
+        &self,
+        pattern: &str,
+    ) -> Result<Box<dyn Iterator<Item = Result<SystemPathBuf, GlobError>>>, PatternError> {
+        Ok(Box::new(self.fs.glob(pattern)?))
+    }
+
     fn as_any(&self) -> &dyn Any {
         self
     }
@@ -284,3 +291,17 @@ impl System for WasmSystem {
 fn not_found() -> std::io::Error {
     std::io::Error::new(std::io::ErrorKind::NotFound, "No such file or directory")
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::TargetVersion;
+    use red_knot_python_semantic::PythonVersion;
+
+    #[test]
+    fn same_default_as_python_version() {
+        assert_eq!(
+            PythonVersion::from(TargetVersion::default()),
+            PythonVersion::default()
+        );
+    }
+}

crates/red_knot_workspace/Cargo.toml

@@ -15,22 +15,29 @@ license.workspace = true
 red_knot_python_semantic = { workspace = true }
 
 ruff_cache = { workspace = true }
-ruff_db = { workspace = true, features = ["os", "cache"] }
-ruff_python_ast = { workspace = true }
+ruff_db = { workspace = true, features = ["os", "cache", "serde"] }
+ruff_python_ast = { workspace = true, features = ["serde"] }
 ruff_text_size = { workspace = true }
 red_knot_vendored = { workspace = true }
 
 anyhow = { workspace = true }
 crossbeam = { workspace = true }
+glob = { workspace = true }
 notify = { workspace = true }
+pep440_rs = { workspace = true }
 rayon = { workspace = true }
 rustc-hash = { workspace = true }
 salsa = { workspace = true }
+serde = { workspace = true }
+thiserror = { workspace = true }
+toml = { workspace = true }
 tracing = { workspace = true }
 
 [dev-dependencies]
+red_knot_python_semantic = { workspace = true, features = ["serde"] }
 ruff_db = { workspace = true, features = ["testing"] }
-tempfile = { workspace = true }
+glob = { workspace = true }
+insta = { workspace = true, features = ["redactions", "ron"] }
 
 [features]
 default = ["zstd"]

crates/red_knot_workspace/resources/test/corpus/04_assign_invalid_target.py

@@ -0,0 +1 @@
+../../../../ruff_python_parser/resources/invalid/statements/invalid_assignment_targets.py

crates/red_knot_workspace/resources/test/corpus/04_assign_named_expr_invalid_target.py

@@ -0,0 +1 @@
+../../../../ruff_python_parser/resources/invalid/expressions/named/invalid_target.py

crates/red_knot_workspace/resources/test/corpus/04_aug_assign_invalid_target.py

@@ -0,0 +1 @@
+../../../../ruff_python_parser/resources/invalid/statements/invalid_augmented_assignment_target.py

crates/red_knot_workspace/resources/test/corpus/10_if_invalid.py

@@ -0,0 +1 @@
+x if $z

crates/red_knot_workspace/resources/test/corpus/16_for_invalid.py

@@ -0,0 +1 @@
+for

crates/red_knot_workspace/resources/test/corpus/83_jupyter_notebook_ipython_magic.ipynb

@@ -0,0 +1 @@
+../../../../ruff_notebook/resources/test/fixtures/jupyter/unused_variable.ipynb

crates/red_knot_workspace/resources/test/corpus/85_match_invalid.py

@@ -0,0 +1,3 @@
+match some_int:
+    case x:=2:
+        pass

crates/red_knot_workspace/resources/test/corpus/94_strformat_conversion.py

@@ -0,0 +1,3 @@
+msg = "hello"
+
+f"{msg!r:>{10+10}}"

crates/red_knot_workspace/resources/test/corpus/98_ann_assign_invalid_target.py

@@ -0,0 +1 @@
+../../../../ruff_python_parser/resources/inline/err/ann_assign_stmt_invalid_target.py

crates/red_knot_workspace/src/db.rs

@@ -15,7 +15,9 @@ use ruff_db::{Db as SourceDb, Upcast};
 mod changes;
 
 #[salsa::db]
-pub trait Db: SemanticDb + Upcast<dyn SemanticDb> {}
+pub trait Db: SemanticDb + Upcast<dyn SemanticDb> {
+    fn workspace(&self) -> Workspace;
+}
 
 #[salsa::db]
 pub struct RootDatabase {
@@ -45,11 +47,6 @@ impl RootDatabase {
         Ok(db)
     }
 
-    pub fn workspace(&self) -> Workspace {
-        // SAFETY: The workspace is always initialized in `new`.
-        self.workspace.unwrap()
-    }
-
     /// Checks all open files in the workspace and its dependencies.
     pub fn check(&self) -> Result<Vec<Box<dyn Diagnostic>>, Cancelled> {
         self.with_db(|db| db.workspace().check(db))
@@ -153,7 +150,11 @@ impl salsa::Database for RootDatabase {
 }
 
 #[salsa::db]
-impl Db for RootDatabase {}
+impl Db for RootDatabase {
+    fn workspace(&self) -> Workspace {
+        self.workspace.unwrap()
+    }
+}
 
 #[cfg(test)]
 pub(crate) mod tests {
@@ -168,6 +169,7 @@ pub(crate) mod tests {
     use ruff_db::{Db as SourceDb, Upcast};
 
     use crate::db::Db;
+    use crate::workspace::{Workspace, WorkspaceMetadata};
 
     #[salsa::db]
     pub(crate) struct TestDb {
@@ -176,17 +178,23 @@ pub(crate) mod tests {
         files: Files,
         system: TestSystem,
         vendored: VendoredFileSystem,
+        workspace: Option<Workspace>,
     }
 
     impl TestDb {
-        pub(crate) fn new() -> Self {
-            Self {
+        pub(crate) fn new(workspace: WorkspaceMetadata) -> Self {
+            let mut db = Self {
                 storage: salsa::Storage::default(),
                 system: TestSystem::default(),
                 vendored: red_knot_vendored::file_system().clone(),
                 files: Files::default(),
                 events: Arc::default(),
-            }
+                workspace: None,
+            };
+
+            let workspace = Workspace::from_metadata(&db, workspace);
+            db.workspace = Some(workspace);
+            db
         }
     }
 
@@ -254,7 +262,11 @@ pub(crate) mod tests {
     }
 
     #[salsa::db]
-    impl Db for TestDb {}
+    impl Db for TestDb {
+        fn workspace(&self) -> Workspace {
+            self.workspace.unwrap()
+        }
+    }
 
     #[salsa::db]
     impl salsa::Database for TestDb {

crates/red_knot_workspace/src/db/changes.rs

@@ -1,16 +1,15 @@
+use crate::db::{Db, RootDatabase};
+use crate::watch;
+use crate::watch::{ChangeEvent, CreatedKind, DeletedKind};
+use crate::workspace::settings::Configuration;
+use crate::workspace::{Workspace, WorkspaceMetadata};
 use red_knot_python_semantic::Program;
 use ruff_db::files::{system_path_to_file, File, Files};
 use ruff_db::system::walk_directory::WalkState;
 use ruff_db::system::SystemPath;
-use ruff_db::Db;
+use ruff_db::Db as _;
 use rustc_hash::FxHashSet;
 
-use crate::db::RootDatabase;
-use crate::watch;
-use crate::watch::{CreatedKind, DeletedKind};
-use crate::workspace::settings::Configuration;
-use crate::workspace::WorkspaceMetadata;
-
 impl RootDatabase {
     #[tracing::instrument(level = "debug", skip(self, changes, base_configuration))]
     pub fn apply_changes(
@@ -18,7 +17,7 @@ impl RootDatabase {
         changes: Vec<watch::ChangeEvent>,
         base_configuration: Option<&Configuration>,
     ) {
-        let workspace = self.workspace();
+        let mut workspace = self.workspace();
         let workspace_path = workspace.root(self).to_path_buf();
         let program = Program::get(self);
         let custom_stdlib_versions_path = program
@@ -58,6 +57,12 @@ impl RootDatabase {
                     // Changes to ignore files or settings can change the workspace structure or add/remove files
                     // from packages.
                     if let Some(package) = workspace.package(self, path) {
+                        if package.root(self) == workspace.root(self)
+                            || matches!(change, ChangeEvent::Deleted { .. })
+                        {
+                            workspace_change = true;
+                        }
+
                         changed_packages.insert(package);
                     } else {
                         workspace_change = true;
@@ -151,18 +156,22 @@ impl RootDatabase {
         }
 
         if workspace_change {
-            match WorkspaceMetadata::from_path(
-                &workspace_path,
-                self.system(),
-                base_configuration.cloned(),
-            ) {
+            match WorkspaceMetadata::discover(&workspace_path, self.system(), base_configuration) {
                 Ok(metadata) => {
-                    tracing::debug!("Reloading workspace after structural change");
-                    // TODO: Handle changes in the program settings.
-                    workspace.reload(self, metadata);
+                    if metadata.root() == workspace.root(self) {
+                        tracing::debug!("Reloading workspace after structural change");
+                        // TODO: Handle changes in the program settings.
+                        workspace.reload(self, metadata);
+                    } else {
+                        tracing::debug!("Replace workspace after structural change");
+                        workspace = Workspace::from_metadata(self, metadata);
+                        self.workspace = Some(workspace);
+                    }
                 }
                 Err(error) => {
-                    tracing::error!("Failed to load workspace, keep old workspace: {error}");
+                    tracing::error!(
+                        "Failed to load workspace, keeping old workspace configuration: {error}"
+                    );
                 }
             }
 
@@ -227,6 +236,3 @@ impl RootDatabase {
         }
     }
 }
-
-#[cfg(test)]
-mod tests {}

crates/red_knot_workspace/src/watch/watcher.rs

@@ -210,7 +210,15 @@ impl Debouncer {
         }
 
         let kind = event.kind;
-        let path = match SystemPathBuf::from_path_buf(event.paths.into_iter().next().unwrap()) {
+
+        // There are cases where paths can be empty.
+        // https://github.com/astral-sh/ruff/issues/14222
+        let Some(path) = event.paths.into_iter().next() else {
+            tracing::debug!("Ignoring change event with kind '{kind:?}' without a path",);
+            return;
+        };
+
+        let path = match SystemPathBuf::from_path_buf(path) {
             Ok(path) => path,
             Err(path) => {
                 tracing::debug!(

crates/red_knot_workspace/src/watch/workspace_watcher.rs

@@ -6,9 +6,9 @@ use tracing::info;
 use red_knot_python_semantic::system_module_search_paths;
 use ruff_cache::{CacheKey, CacheKeyHasher};
 use ruff_db::system::{SystemPath, SystemPathBuf};
-use ruff_db::Upcast;
+use ruff_db::{Db as _, Upcast};
 
-use crate::db::RootDatabase;
+use crate::db::{Db, RootDatabase};
 use crate::watch::Watcher;
 
 /// Wrapper around a [`Watcher`] that watches the relevant paths of a workspace.
@@ -68,10 +68,9 @@ impl WorkspaceWatcher {
 
         self.has_errored_paths = false;
 
-        let workspace_path = workspace_path
-            .as_utf8_path()
-            .canonicalize_utf8()
-            .map(SystemPathBuf::from_utf8_path_buf)
+        let workspace_path = db
+            .system()
+            .canonicalize_path(&workspace_path)
             .unwrap_or(workspace_path);
 
         // Find the non-overlapping module search paths and filter out paths that are already covered by the workspace.

crates/red_knot_workspace/src/workspace.rs

@@ -1,26 +1,28 @@
-use rustc_hash::{FxBuildHasher, FxHashSet};
-use salsa::{Durability, Setter as _};
-use std::borrow::Cow;
-use std::{collections::BTreeMap, sync::Arc};
-
 use crate::db::Db;
 use crate::db::RootDatabase;
 use crate::workspace::files::{Index, Indexed, IndexedIter, PackageFiles};
-pub use metadata::{PackageMetadata, WorkspaceMetadata};
+pub use metadata::{PackageMetadata, WorkspaceDiscoveryError, WorkspaceMetadata};
 use red_knot_python_semantic::types::check_types;
 use red_knot_python_semantic::SearchPathSettings;
 use ruff_db::diagnostic::{Diagnostic, ParseDiagnostic, Severity};
 use ruff_db::parsed::parsed_module;
 use ruff_db::source::{source_text, SourceTextError};
+use ruff_db::system::FileType;
 use ruff_db::{
     files::{system_path_to_file, File},
     system::{walk_directory::WalkState, SystemPath, SystemPathBuf},
 };
 use ruff_python_ast::{name::Name, PySourceType};
 use ruff_text_size::TextRange;
+use rustc_hash::{FxBuildHasher, FxHashSet};
+use salsa::{Durability, Setter as _};
+use std::borrow::Cow;
+use std::iter::FusedIterator;
+use std::{collections::BTreeMap, sync::Arc};
 
 mod files;
 mod metadata;
+mod pyproject;
 pub mod settings;
 
 /// The project workspace as a Salsa ingredient.
@@ -81,7 +83,7 @@ pub struct Workspace {
 
     /// The (first-party) packages in this workspace.
     #[return_ref]
-    package_tree: BTreeMap<SystemPathBuf, Package>,
+    package_tree: PackageTree,
 
     /// The unresolved search path configuration.
     #[return_ref]
@@ -106,7 +108,6 @@ pub struct Package {
 }
 
 impl Workspace {
-    /// Discovers the closest workspace at `path` and returns its metadata.
     pub fn from_metadata(db: &dyn Db, metadata: WorkspaceMetadata) -> Self {
         let mut packages = BTreeMap::new();
 
@@ -114,10 +115,12 @@ impl Workspace {
             packages.insert(package.root.clone(), Package::from_metadata(db, package));
         }
 
+        let program_settings = metadata.settings.program;
+
         Workspace::builder(
             metadata.root,
-            packages,
-            metadata.settings.program.search_paths,
+            PackageTree(packages),
+            program_settings.search_paths,
         )
         .durability(Durability::MEDIUM)
         .open_fileset_durability(Durability::LOW)
@@ -128,15 +131,11 @@ impl Workspace {
         self.root_buf(db)
     }
 
-    pub fn packages(self, db: &dyn Db) -> impl Iterator<Item = Package> + '_ {
-        self.package_tree(db).values().copied()
-    }
-
     pub fn reload(self, db: &mut dyn Db, metadata: WorkspaceMetadata) {
         tracing::debug!("Reloading workspace");
         assert_eq!(self.root(db), metadata.root());
 
-        let mut old_packages = self.package_tree(db).clone();
+        let mut old_packages = self.package_tree(db).0.clone();
         let mut new_packages = BTreeMap::new();
 
         for package_metadata in metadata.packages {
@@ -157,13 +156,13 @@ impl Workspace {
                 .to(metadata.settings.program.search_paths);
         }
 
-        self.set_package_tree(db).to(new_packages);
+        self.set_package_tree(db).to(PackageTree(new_packages));
     }
 
     pub fn update_package(self, db: &mut dyn Db, metadata: PackageMetadata) -> anyhow::Result<()> {
         let path = metadata.root().to_path_buf();
 
-        if let Some(package) = self.package_tree(db).get(&path).copied() {
+        if let Some(package) = self.package_tree(db).get(&path) {
             package.update(db, metadata);
             Ok(())
         } else {
@@ -171,20 +170,17 @@ impl Workspace {
         }
     }
 
+    pub fn packages(self, db: &dyn Db) -> &PackageTree {
+        self.package_tree(db)
+    }
+
     /// Returns the closest package to which the first-party `path` belongs.
     ///
     /// Returns `None` if the `path` is outside of any package or if `file` isn't a first-party file
     /// (e.g. third-party dependencies or `excluded`).
-    pub fn package(self, db: &dyn Db, path: &SystemPath) -> Option<Package> {
+    pub fn package(self, db: &dyn Db, path: impl AsRef<SystemPath>) -> Option<Package> {
         let packages = self.package_tree(db);
-
-        let (package_path, package) = packages.range(..=path.to_path_buf()).next_back()?;
-
-        if path.starts_with(package_path) {
-            Some(*package)
-        } else {
-            None
-        }
+        packages.get(path.as_ref())
     }
 
     /// Checks all open files in the workspace and its dependencies.
@@ -342,7 +338,7 @@ impl Package {
                 let _entered =
                     tracing::debug_span!("index_package_files", package = %self.name(db)).entered();
 
-                let files = discover_package_files(db, self.root(db));
+                let files = discover_package_files(db, self);
                 tracing::info!("Found {} files in package `{}`", files.len(), self.name(db));
                 vacant.set(files)
             }
@@ -407,23 +403,33 @@ pub(super) fn check_file(db: &dyn Db, file: File) -> Vec<Box<dyn Diagnostic>> {
     diagnostics
 }
 
-fn discover_package_files(db: &dyn Db, path: &SystemPath) -> FxHashSet<File> {
+fn discover_package_files(db: &dyn Db, package: Package) -> FxHashSet<File> {
     let paths = std::sync::Mutex::new(Vec::new());
+    let packages = db.workspace().packages(db);
 
-    db.system().walk_directory(path).run(|| {
+    db.system().walk_directory(package.root(db)).run(|| {
         Box::new(|entry| {
             match entry {
                 Ok(entry) => {
                     // Skip over any non python files to avoid creating too many entries in `Files`.
-                    if entry.file_type().is_file()
-                        && entry
-                            .path()
-                            .extension()
-                            .and_then(PySourceType::try_from_extension)
-                            .is_some()
-                    {
-                        let mut paths = paths.lock().unwrap();
-                        paths.push(entry.into_path());
+                    match entry.file_type() {
+                        FileType::File => {
+                            if entry
+                                .path()
+                                .extension()
+                                .and_then(PySourceType::try_from_extension)
+                                .is_some()
+                            {
+                                let mut paths = paths.lock().unwrap();
+                                paths.push(entry.into_path());
+                            }
+                        }
+                        FileType::Directory | FileType::Symlink => {
+                            // Don't traverse into nested packages (the workspace-package is an ancestor of all other packages)
+                            if packages.get(entry.path()) != Some(package) {
+                                return WalkState::Skip;
+                            }
+                        }
                     }
                 }
                 Err(error) => {
@@ -464,6 +470,7 @@ impl<'a> WorkspaceFiles<'a> {
             WorkspaceFiles::PackageFiles(
                 workspace
                     .packages(db)
+                    .iter()
                     .map(|package| package.files(db))
                     .collect(),
             )
@@ -545,20 +552,78 @@ impl Diagnostic for IOErrorDiagnostic {
     }
 }
 
+#[derive(Debug, Eq, PartialEq, Clone)]
+pub struct PackageTree(BTreeMap<SystemPathBuf, Package>);
+
+impl PackageTree {
+    pub fn get(&self, path: &SystemPath) -> Option<Package> {
+        let (package_path, package) = self.0.range(..=path.to_path_buf()).next_back()?;
+
+        if path.starts_with(package_path) {
+            Some(*package)
+        } else {
+            None
+        }
+    }
+
+    // The package table should never be empty, that's why `is_empty` makes little sense
+    #[allow(clippy::len_without_is_empty)]
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    pub fn iter(&self) -> PackageTreeIter {
+        PackageTreeIter(self.0.values())
+    }
+}
+
+impl<'a> IntoIterator for &'a PackageTree {
+    type Item = Package;
+    type IntoIter = PackageTreeIter<'a>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+pub struct PackageTreeIter<'a>(std::collections::btree_map::Values<'a, SystemPathBuf, Package>);
+
+impl Iterator for PackageTreeIter<'_> {
+    type Item = Package;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.next().copied()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
+
+    fn last(mut self) -> Option<Self::Item> {
+        self.0.next_back().copied()
+    }
+}
+
+impl ExactSizeIterator for PackageTreeIter<'_> {}
+impl FusedIterator for PackageTreeIter<'_> {}
+
 #[cfg(test)]
 mod tests {
     use crate::db::tests::TestDb;
-    use crate::workspace::check_file;
+    use crate::workspace::{check_file, WorkspaceMetadata};
     use red_knot_python_semantic::types::check_types;
     use ruff_db::diagnostic::Diagnostic;
     use ruff_db::files::system_path_to_file;
     use ruff_db::source::source_text;
-    use ruff_db::system::{DbWithTestSystem, SystemPath};
+    use ruff_db::system::{DbWithTestSystem, SystemPath, SystemPathBuf};
     use ruff_db::testing::assert_function_query_was_not_run;
+    use ruff_python_ast::name::Name;
 
     #[test]
     fn check_file_skips_type_checking_when_file_cant_be_read() -> ruff_db::system::Result<()> {
-        let mut db = TestDb::new();
+        let workspace =
+            WorkspaceMetadata::single_package(Name::new_static("test"), SystemPathBuf::from("/"));
+        let mut db = TestDb::new(workspace);
         let path = SystemPath::new("test.py");
 
         db.write_file(path, "x = 10")?;

crates/red_knot_workspace/src/workspace/files.rs

@@ -232,21 +232,28 @@ impl Drop for IndexedMut<'_> {
 mod tests {
     use rustc_hash::FxHashSet;
 
+    use crate::db::tests::TestDb;
+    use crate::db::Db;
+    use crate::workspace::files::Index;
+    use crate::workspace::WorkspaceMetadata;
     use ruff_db::files::system_path_to_file;
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
     use ruff_python_ast::name::Name;
 
-    use crate::db::tests::TestDb;
-    use crate::workspace::files::Index;
-    use crate::workspace::Package;
-
     #[test]
     fn re_entrance() -> anyhow::Result<()> {
-        let mut db = TestDb::new();
+        let metadata = WorkspaceMetadata::single_package(
+            Name::new_static("test"),
+            SystemPathBuf::from("/test"),
+        );
+        let mut db = TestDb::new(metadata);
 
         db.write_file("test.py", "")?;
 
-        let package = Package::new(&db, Name::new("test"), SystemPathBuf::from("/test"));
+        let package = db
+            .workspace()
+            .package(&db, "/test")
+            .expect("test package to exist");
 
         let file = system_path_to_file(&db, "test.py").unwrap();
 

crates/red_knot_workspace/src/workspace/metadata.rs

@@ -1,67 +1,191 @@
-use crate::workspace::settings::{Configuration, WorkspaceSettings};
-use ruff_db::system::{System, SystemPath, SystemPathBuf};
+use ruff_db::system::{GlobError, System, SystemPath, SystemPathBuf};
 use ruff_python_ast::name::Name;
+use rustc_hash::{FxBuildHasher, FxHashMap, FxHashSet};
+use thiserror::Error;
 
-#[derive(Debug)]
+use crate::workspace::pyproject::{PyProject, PyProjectError, Workspace};
+use crate::workspace::settings::{Configuration, WorkspaceSettings};
+
+#[derive(Debug, PartialEq, Eq)]
+#[cfg_attr(test, derive(serde::Serialize))]
 pub struct WorkspaceMetadata {
     pub(super) root: SystemPathBuf,
 
     /// The (first-party) packages in this workspace.
     pub(super) packages: Vec<PackageMetadata>,
 
+    /// The resolved settings for this workspace.
     pub(super) settings: WorkspaceSettings,
 }
 
 /// A first-party package in a workspace.
-#[derive(Debug)]
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[cfg_attr(test, derive(serde::Serialize))]
 pub struct PackageMetadata {
     pub(super) name: Name,
 
     /// The path to the root directory of the package.
     pub(super) root: SystemPathBuf,
-    // TODO: Add the loaded package configuration (not the nested ruff settings)
+
+    pub(super) configuration: Configuration,
 }
 
 impl WorkspaceMetadata {
+    /// Creates a workspace that consists of a single package located at `root`.
+    pub fn single_package(name: Name, root: SystemPathBuf) -> Self {
+        let package = PackageMetadata {
+            name,
+            root: root.clone(),
+            configuration: Configuration::default(),
+        };
+
+        let packages = vec![package];
+        let settings = packages[0]
+            .configuration
+            .to_workspace_settings(&root, &packages);
+
+        Self {
+            root,
+            packages,
+            settings,
+        }
+    }
+
     /// Discovers the closest workspace at `path` and returns its metadata.
-    pub fn from_path(
+    ///
+    /// 1. Traverse upwards in the `path`'s ancestor chain and find the first `pyproject.toml`.
+    /// 1. If the `pyproject.toml` contains no `knot.workspace` table, then keep traversing the `path`'s ancestor
+    ///    chain until we find one or reach the root.
+    /// 1. If we've found a workspace, then resolve the workspace's members and assert that the closest
+    ///    package (the first found package without a `knot.workspace` table is a member. If not, create
+    ///    a single package workspace for the closest package.
+    /// 1. If there's no `pyrpoject.toml` with a `knot.workspace` table, then create a single-package workspace.
+    /// 1. If no ancestor directory contains any `pyproject.toml`, create an ad-hoc workspace for `path`
+    ///    that consists of a single package and uses the default settings.
+    pub fn discover(
         path: &SystemPath,
         system: &dyn System,
-        base_configuration: Option<Configuration>,
-    ) -> anyhow::Result<WorkspaceMetadata> {
-        assert!(
-            system.is_directory(path),
-            "Workspace root path must be a directory"
-        );
-        tracing::debug!("Searching for workspace in '{path}'");
+        base_configuration: Option<&Configuration>,
+    ) -> Result<WorkspaceMetadata, WorkspaceDiscoveryError> {
+        tracing::debug!("Searching for a workspace in '{path}'");
 
-        let root = path.to_path_buf();
-
-        // TODO: Discover package name from `pyproject.toml`.
-        let package_name: Name = path.file_name().unwrap_or("<root>").into();
-
-        let package = PackageMetadata {
-            name: package_name,
-            root: root.clone(),
-        };
-
-        // TODO: Load the configuration from disk.
-        let mut configuration = Configuration::default();
-
-        if let Some(base_configuration) = base_configuration {
-            configuration.extend(base_configuration);
+        if !system.is_directory(path) {
+            return Err(WorkspaceDiscoveryError::NotADirectory(path.to_path_buf()));
         }
 
-        // TODO: Respect the package configurations when resolving settings (e.g. for the target version).
-        let settings = configuration.into_workspace_settings(&root);
+        let mut closest_package: Option<PackageMetadata> = None;
 
-        let workspace = WorkspaceMetadata {
-            root,
-            packages: vec![package],
-            settings,
+        for ancestor in path.ancestors() {
+            let pyproject_path = ancestor.join("pyproject.toml");
+            if let Ok(pyproject_str) = system.read_to_string(&pyproject_path) {
+                let pyproject = PyProject::from_str(&pyproject_str).map_err(|error| {
+                    WorkspaceDiscoveryError::InvalidPyProject {
+                        path: pyproject_path,
+                        source: Box::new(error),
+                    }
+                })?;
+
+                let workspace_table = pyproject.workspace().cloned();
+                let package = PackageMetadata::from_pyproject(
+                    pyproject,
+                    ancestor.to_path_buf(),
+                    base_configuration,
+                );
+
+                if let Some(workspace_table) = workspace_table {
+                    let workspace_root = ancestor;
+                    tracing::debug!("Found workspace at '{}'", workspace_root);
+
+                    match collect_packages(
+                        package,
+                        &workspace_table,
+                        closest_package,
+                        base_configuration,
+                        system,
+                    )? {
+                        CollectedPackagesOrStandalone::Packages(mut packages) => {
+                            let mut by_name =
+                                FxHashMap::with_capacity_and_hasher(packages.len(), FxBuildHasher);
+
+                            let mut workspace_package = None;
+
+                            for package in &packages {
+                                if let Some(conflicting) = by_name.insert(package.name(), package) {
+                                    return Err(WorkspaceDiscoveryError::DuplicatePackageNames {
+                                        name: package.name().clone(),
+                                        first: conflicting.root().to_path_buf(),
+                                        second: package.root().to_path_buf(),
+                                    });
+                                }
+
+                                if package.root() == workspace_root {
+                                    workspace_package = Some(package);
+                                } else if !package.root().starts_with(workspace_root) {
+                                    return Err(WorkspaceDiscoveryError::PackageOutsideWorkspace {
+                                        package_name: package.name().clone(),
+                                        package_root: package.root().to_path_buf(),
+                                        workspace_root: workspace_root.to_path_buf(),
+                                    });
+                                }
+                            }
+
+                            let workspace_package = workspace_package
+                                .expect("workspace package to be part of the workspace's packages");
+
+                            let settings = workspace_package
+                                .configuration
+                                .to_workspace_settings(workspace_root, &packages);
+
+                            packages.sort_unstable_by(|a, b| a.root().cmp(b.root()));
+
+                            return Ok(Self {
+                                root: workspace_root.to_path_buf(),
+                                packages,
+                                settings,
+                            });
+                        }
+                        CollectedPackagesOrStandalone::Standalone(package) => {
+                            closest_package = Some(package);
+                            break;
+                        }
+                    }
+                }
+
+                // Not a workspace itself, keep looking for an enclosing workspace.
+                if closest_package.is_none() {
+                    closest_package = Some(package);
+                }
+            }
+        }
+
+        // No workspace found, but maybe a pyproject.toml was found.
+        let package = if let Some(enclosing_package) = closest_package {
+            tracing::debug!("Single package workspace at '{}'", enclosing_package.root());
+
+            enclosing_package
+        } else {
+            tracing::debug!("The ancestor directories contain no `pyproject.toml`. Falling back to a virtual project.");
+
+            // Create a package with a default configuration
+            PackageMetadata {
+                name: path.file_name().unwrap_or("root").into(),
+                root: path.to_path_buf(),
+                // TODO create the configuration from the pyproject toml
+                configuration: base_configuration.cloned().unwrap_or_default(),
+            }
         };
 
-        Ok(workspace)
+        let root = package.root().to_path_buf();
+        let packages = vec![package];
+        let settings = packages[0]
+            .configuration
+            .to_workspace_settings(&root, &packages);
+
+        Ok(Self {
+            root,
+            packages,
+            settings,
+        })
     }
 
     pub fn root(&self) -> &SystemPath {
@@ -78,6 +202,30 @@ impl WorkspaceMetadata {
 }
 
 impl PackageMetadata {
+    pub(crate) fn from_pyproject(
+        pyproject: PyProject,
+        root: SystemPathBuf,
+        base_configuration: Option<&Configuration>,
+    ) -> Self {
+        let name = pyproject.project.and_then(|project| project.name);
+        let name = name
+            .map(|name| Name::new(&*name))
+            .unwrap_or_else(|| Name::new(root.file_name().unwrap_or("root")));
+
+        // TODO: load configuration from pyrpoject.toml
+        let mut configuration = Configuration::default();
+
+        if let Some(base_configuration) = base_configuration {
+            configuration.extend(base_configuration.clone());
+        }
+
+        PackageMetadata {
+            name,
+            root,
+            configuration,
+        }
+    }
+
     pub fn name(&self) -> &Name {
         &self.name
     }
@@ -86,3 +234,577 @@ impl PackageMetadata {
         &self.root
     }
 }
+
+fn collect_packages(
+    workspace_package: PackageMetadata,
+    workspace_table: &Workspace,
+    closest_package: Option<PackageMetadata>,
+    base_configuration: Option<&Configuration>,
+    system: &dyn System,
+) -> Result<CollectedPackagesOrStandalone, WorkspaceDiscoveryError> {
+    let workspace_root = workspace_package.root().to_path_buf();
+    let mut member_paths = FxHashSet::default();
+
+    for glob in workspace_table.members() {
+        let full_glob = workspace_package.root().join(glob);
+
+        let matches = system.glob(full_glob.as_str()).map_err(|error| {
+            WorkspaceDiscoveryError::InvalidMembersPattern {
+                raw_glob: glob.clone(),
+                source: error,
+            }
+        })?;
+
+        for result in matches {
+            let path = result?;
+            let normalized = SystemPath::absolute(path, &workspace_root);
+
+            // Skip over non-directory entry. E.g.finder might end up creating a `.DS_STORE` file
+            // that ends up matching `/projects/*`.
+            if system.is_directory(&normalized) {
+                member_paths.insert(normalized);
+            } else {
+                tracing::debug!("Ignoring non-directory workspace member '{normalized}'");
+            }
+        }
+    }
+
+    // The workspace root is always a member. Don't re-add it
+    let mut packages = vec![workspace_package];
+    member_paths.remove(&workspace_root);
+
+    // Add the package that is closest to the current working directory except
+    // if that package isn't a workspace member, then fallback to creating a single
+    // package workspace.
+    if let Some(closest_package) = closest_package {
+        // the closest `pyproject.toml` isn't a member of this workspace because it is
+        // explicitly included or simply not listed.
+        // Create a standalone workspace.
+        if !member_paths.remove(closest_package.root())
+            || workspace_table.is_excluded(closest_package.root(), &workspace_root)?
+        {
+            tracing::debug!(
+                "Ignoring workspace '{workspace_root}' because package '{package}' is not a member",
+                package = closest_package.name()
+            );
+            return Ok(CollectedPackagesOrStandalone::Standalone(closest_package));
+        }
+
+        tracing::debug!("adding package '{}'", closest_package.name());
+        packages.push(closest_package);
+    }
+
+    // Add all remaining member paths
+    for member_path in member_paths {
+        if workspace_table.is_excluded(&member_path, workspace_root.as_path())? {
+            tracing::debug!("Ignoring excluded member '{member_path}'");
+            continue;
+        }
+
+        let pyproject_path = member_path.join("pyproject.toml");
+
+        let pyproject_str = match system.read_to_string(&pyproject_path) {
+            Ok(pyproject_str) => pyproject_str,
+
+            Err(error) => {
+                if error.kind() == std::io::ErrorKind::NotFound
+                    && member_path
+                        .file_name()
+                        .is_some_and(|name| name.starts_with('.'))
+                {
+                    tracing::debug!(
+                        "Ignore member '{member_path}' because it has no pyproject.toml and is hidden",
+                    );
+                    continue;
+                }
+
+                return Err(WorkspaceDiscoveryError::MemberFailedToReadPyProject {
+                    package_root: member_path,
+                    source: error,
+                });
+            }
+        };
+
+        let pyproject = PyProject::from_str(&pyproject_str).map_err(|error| {
+            WorkspaceDiscoveryError::InvalidPyProject {
+                source: Box::new(error),
+                path: pyproject_path,
+            }
+        })?;
+
+        if pyproject.workspace().is_some() {
+            return Err(WorkspaceDiscoveryError::NestedWorkspaces {
+                package_root: member_path,
+            });
+        }
+
+        let package = PackageMetadata::from_pyproject(pyproject, member_path, base_configuration);
+
+        tracing::debug!(
+            "Adding package '{}' at '{}'",
+            package.name(),
+            package.root()
+        );
+
+        packages.push(package);
+    }
+
+    Ok(CollectedPackagesOrStandalone::Packages(packages))
+}
+
+enum CollectedPackagesOrStandalone {
+    Packages(Vec<PackageMetadata>),
+    Standalone(PackageMetadata),
+}
+
+#[derive(Debug, Error)]
+pub enum WorkspaceDiscoveryError {
+    #[error("workspace path '{0}' is not a directory")]
+    NotADirectory(SystemPathBuf),
+
+    #[error("nested workspaces aren't supported but the package located at '{package_root}' defines a `knot.workspace` table")]
+    NestedWorkspaces { package_root: SystemPathBuf },
+
+    #[error("the workspace contains two packages named '{name}': '{first}' and '{second}'")]
+    DuplicatePackageNames {
+        name: Name,
+        first: SystemPathBuf,
+        second: SystemPathBuf,
+    },
+
+    #[error("the package '{package_name}' located at '{package_root}' is outside the workspace's root directory '{workspace_root}'")]
+    PackageOutsideWorkspace {
+        workspace_root: SystemPathBuf,
+        package_name: Name,
+        package_root: SystemPathBuf,
+    },
+
+    #[error(
+        "failed to read the `pyproject.toml` for the package located at '{package_root}': {source}"
+    )]
+    MemberFailedToReadPyProject {
+        package_root: SystemPathBuf,
+        source: std::io::Error,
+    },
+
+    #[error("{path} is not a valid `pyproject.toml`: {source}")]
+    InvalidPyProject {
+        source: Box<PyProjectError>,
+        path: SystemPathBuf,
+    },
+
+    #[error("invalid glob '{raw_glob}' in `tool.knot.workspace.members`: {source}")]
+    InvalidMembersPattern {
+        source: glob::PatternError,
+        raw_glob: String,
+    },
+
+    #[error("failed to match member glob: {error}")]
+    FailedToMatchGlob {
+        #[from]
+        error: GlobError,
+    },
+}
+
+#[cfg(test)]
+mod tests {
+    //! Integration tests for workspace discovery
+
+    use crate::snapshot_workspace;
+    use anyhow::Context;
+    use insta::assert_ron_snapshot;
+    use ruff_db::system::{SystemPathBuf, TestSystem};
+
+    use crate::workspace::{WorkspaceDiscoveryError, WorkspaceMetadata};
+
+    #[test]
+    fn package_without_pyproject() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([(root.join("foo.py"), ""), (root.join("bar.py"), "")])
+            .context("Failed to write files")?;
+
+        let workspace = WorkspaceMetadata::discover(&root, &system, None)
+            .context("Failed to discover workspace")?;
+
+        assert_eq!(workspace.root(), &*root);
+
+        snapshot_workspace!(workspace);
+
+        Ok(())
+    }
+
+    #[test]
+    fn single_package() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "backend"
+                    "#,
+                ),
+                (root.join("db/__init__.py"), ""),
+            ])
+            .context("Failed to write files")?;
+
+        let workspace = WorkspaceMetadata::discover(&root, &system, None)
+            .context("Failed to discover workspace")?;
+
+        assert_eq!(workspace.root(), &*root);
+        snapshot_workspace!(workspace);
+
+        // Discovering the same package from a subdirectory should give the same result
+        let from_src = WorkspaceMetadata::discover(&root.join("db"), &system, None)
+            .context("Failed to discover workspace from src sub-directory")?;
+
+        assert_eq!(from_src, workspace);
+
+        Ok(())
+    }
+
+    #[test]
+    fn workspace_members() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "workspace-root"
+
+                    [tool.knot.workspace]
+                    members = ["packages/*"]
+                    exclude = ["packages/excluded"]
+                    "#,
+                ),
+                (
+                    root.join("packages/a/pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "member-a"
+                    "#,
+                ),
+                (
+                    root.join("packages/x/pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "member-x"
+                    "#,
+                ),
+            ])
+            .context("Failed to write files")?;
+
+        let workspace = WorkspaceMetadata::discover(&root, &system, None)
+            .context("Failed to discover workspace")?;
+
+        assert_eq!(workspace.root(), &*root);
+
+        snapshot_workspace!(workspace);
+
+        // Discovering the same package from a member should give the same result
+        let from_src = WorkspaceMetadata::discover(&root.join("packages/a"), &system, None)
+            .context("Failed to discover workspace from src sub-directory")?;
+
+        assert_eq!(from_src, workspace);
+
+        Ok(())
+    }
+
+    #[test]
+    fn workspace_excluded() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "workspace-root"
+
+                    [tool.knot.workspace]
+                    members = ["packages/*"]
+                    exclude = ["packages/excluded"]
+                    "#,
+                ),
+                (
+                    root.join("packages/a/pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "member-a"
+                    "#,
+                ),
+                (
+                    root.join("packages/excluded/pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "member-x"
+                    "#,
+                ),
+            ])
+            .context("Failed to write files")?;
+
+        let workspace = WorkspaceMetadata::discover(&root, &system, None)
+            .context("Failed to discover workspace")?;
+
+        assert_eq!(workspace.root(), &*root);
+        snapshot_workspace!(workspace);
+
+        // Discovering the `workspace` for `excluded` should discover a single-package workspace
+        let excluded_workspace =
+            WorkspaceMetadata::discover(&root.join("packages/excluded"), &system, None)
+                .context("Failed to discover workspace from src sub-directory")?;
+
+        assert_ne!(excluded_workspace, workspace);
+
+        Ok(())
+    }
+
+    #[test]
+    fn workspace_non_unique_member_names() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "workspace-root"
+
+                    [tool.knot.workspace]
+                    members = ["packages/*"]
+                    "#,
+                ),
+                (
+                    root.join("packages/a/pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "a"
+                    "#,
+                ),
+                (
+                    root.join("packages/b/pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "a"
+                    "#,
+                ),
+            ])
+            .context("Failed to write files")?;
+
+        let error = WorkspaceMetadata::discover(&root, &system, None).expect_err(
+            "Discovery should error because the workspace contains two packages with the same names.",
+        );
+
+        assert_error_eq(&error, "the workspace contains two packages named 'a': '/app/packages/a' and '/app/packages/b'");
+
+        Ok(())
+    }
+
+    #[test]
+    fn nested_workspaces() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "workspace-root"
+
+                    [tool.knot.workspace]
+                    members = ["packages/*"]
+                    "#,
+                ),
+                (
+                    root.join("packages/a/pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "nested-workspace"
+
+                    [tool.knot.workspace]
+                    members = ["packages/*"]
+                    "#,
+                ),
+            ])
+            .context("Failed to write files")?;
+
+        let error = WorkspaceMetadata::discover(&root, &system, None).expect_err(
+            "Discovery should error because the workspace has a package that itself is a workspace",
+        );
+
+        assert_error_eq(&error, "nested workspaces aren't supported but the package located at '/app/packages/a' defines a `knot.workspace` table");
+
+        Ok(())
+    }
+
+    #[test]
+    fn member_missing_pyproject_toml() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "workspace-root"
+
+                    [tool.knot.workspace]
+                    members = ["packages/*"]
+                    "#,
+                ),
+                (root.join("packages/a/test.py"), ""),
+            ])
+            .context("Failed to write files")?;
+
+        let error = WorkspaceMetadata::discover(&root, &system, None)
+            .expect_err("Discovery should error because member `a` has no `pypyroject.toml`");
+
+        assert_error_eq(&error, "failed to read the `pyproject.toml` for the package located at '/app/packages/a': No such file or directory");
+
+        Ok(())
+    }
+
+    /// Folders that match the members pattern but don't have a pyproject.toml
+    /// aren't valid members and discovery fails. However, don't fail
+    /// if the folder name indicates that it is a hidden folder that might
+    /// have been crated by another tool
+    #[test]
+    fn member_pattern_matching_hidden_folder() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "workspace-root"
+
+                    [tool.knot.workspace]
+                    members = ["packages/*"]
+                    "#,
+                ),
+                (root.join("packages/.hidden/a.py"), ""),
+            ])
+            .context("Failed to write files")?;
+
+        let workspace = WorkspaceMetadata::discover(&root, &system, None)?;
+
+        snapshot_workspace!(workspace);
+
+        Ok(())
+    }
+
+    #[test]
+    fn member_pattern_matching_file() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "workspace-root"
+
+                    [tool.knot.workspace]
+                    members = ["packages/*"]
+                    "#,
+                ),
+                (root.join("packages/.DS_STORE"), ""),
+            ])
+            .context("Failed to write files")?;
+
+        let workspace = WorkspaceMetadata::discover(&root, &system, None)?;
+
+        snapshot_workspace!(&workspace);
+
+        Ok(())
+    }
+
+    #[test]
+    fn workspace_root_not_an_ancestor_of_member() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_files([
+                (
+                    root.join("pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "workspace-root"
+
+                    [tool.knot.workspace]
+                    members = ["../packages/*"]
+                    "#,
+                ),
+                (
+                    root.join("../packages/a/pyproject.toml"),
+                    r#"
+                    [project]
+                    name = "a"
+                    "#,
+                ),
+            ])
+            .context("Failed to write files")?;
+
+        let error = WorkspaceMetadata::discover(&root, &system, None).expect_err(
+            "Discovery should error because member `a` is outside the workspace's directory`",
+        );
+
+        assert_error_eq(&error, "the package 'a' located at '/packages/a' is outside the workspace's root directory '/app'");
+
+        Ok(())
+    }
+
+    #[track_caller]
+    fn assert_error_eq(error: &WorkspaceDiscoveryError, message: &str) {
+        assert_eq!(error.to_string().replace('\\', "/"), message);
+    }
+
+    /// Snapshots a workspace but with all paths using unix separators.
+    #[macro_export]
+    macro_rules! snapshot_workspace {
+    ($workspace:expr) => {{
+        assert_ron_snapshot!($workspace,{
+            ".root" => insta::dynamic_redaction(|content, _content_path| {
+                content.as_str().unwrap().replace("\\", "/")
+            }),
+            ".packages[].root" => insta::dynamic_redaction(|content, _content_path| {
+                content.as_str().unwrap().replace("\\", "/")
+            }),
+        });
+    }};
+}
+}

crates/red_knot_workspace/src/workspace/pyproject.rs

@@ -0,0 +1,108 @@
+mod package_name;
+
+use pep440_rs::{Version, VersionSpecifiers};
+use serde::Deserialize;
+use thiserror::Error;
+
+use crate::workspace::metadata::WorkspaceDiscoveryError;
+pub(crate) use package_name::PackageName;
+use ruff_db::system::SystemPath;
+
+/// A `pyproject.toml` as specified in PEP 517.
+#[derive(Deserialize, Debug, Default, Clone)]
+#[serde(rename_all = "kebab-case")]
+pub(crate) struct PyProject {
+    /// PEP 621-compliant project metadata.
+    pub project: Option<Project>,
+    /// Tool-specific metadata.
+    pub tool: Option<Tool>,
+}
+
+impl PyProject {
+    pub(crate) fn workspace(&self) -> Option<&Workspace> {
+        self.tool
+            .as_ref()
+            .and_then(|tool| tool.knot.as_ref())
+            .and_then(|knot| knot.workspace.as_ref())
+    }
+}
+
+#[derive(Error, Debug)]
+pub enum PyProjectError {
+    #[error(transparent)]
+    TomlSyntax(#[from] toml::de::Error),
+}
+
+impl PyProject {
+    pub(crate) fn from_str(content: &str) -> Result<Self, PyProjectError> {
+        toml::from_str(content).map_err(PyProjectError::TomlSyntax)
+    }
+}
+
+/// PEP 621 project metadata (`project`).
+///
+/// See <https://packaging.python.org/en/latest/specifications/pyproject-toml>.
+#[derive(Deserialize, Debug, Clone, PartialEq)]
+#[cfg_attr(test, derive(serde::Serialize))]
+#[serde(rename_all = "kebab-case")]
+pub(crate) struct Project {
+    /// The name of the project
+    ///
+    /// Note: Intentionally option to be more permissive during deserialization.
+    /// `PackageMetadata::from_pyproject` reports missing names.
+    pub name: Option<PackageName>,
+    /// The version of the project
+    pub version: Option<Version>,
+    /// The Python versions this project is compatible with.
+    pub requires_python: Option<VersionSpecifiers>,
+}
+
+#[derive(Deserialize, Debug, Clone, PartialEq, Eq)]
+pub(crate) struct Tool {
+    pub knot: Option<Knot>,
+}
+
+#[derive(Deserialize, Debug, Clone, PartialEq, Eq)]
+#[serde(rename_all = "kebab-case", deny_unknown_fields)]
+pub(crate) struct Knot {
+    pub(crate) workspace: Option<Workspace>,
+}
+
+#[derive(Deserialize, Debug, Clone, PartialEq, Eq)]
+#[serde(rename_all = "kebab-case", deny_unknown_fields)]
+pub(crate) struct Workspace {
+    pub(crate) members: Option<Vec<String>>,
+    pub(crate) exclude: Option<Vec<String>>,
+}
+
+impl Workspace {
+    pub(crate) fn members(&self) -> &[String] {
+        self.members.as_deref().unwrap_or_default()
+    }
+
+    pub(crate) fn exclude(&self) -> &[String] {
+        self.exclude.as_deref().unwrap_or_default()
+    }
+
+    pub(crate) fn is_excluded(
+        &self,
+        path: &SystemPath,
+        workspace_root: &SystemPath,
+    ) -> Result<bool, WorkspaceDiscoveryError> {
+        for exclude in self.exclude() {
+            let full_glob =
+                glob::Pattern::new(workspace_root.join(exclude).as_str()).map_err(|error| {
+                    WorkspaceDiscoveryError::InvalidMembersPattern {
+                        raw_glob: exclude.clone(),
+                        source: error,
+                    }
+                })?;
+
+            if full_glob.matches_path(path.as_std_path()) {
+                return Ok(true);
+            }
+        }
+
+        Ok(false)
+    }
+}

crates/red_knot_workspace/src/workspace/pyproject/package_name.rs

@@ -0,0 +1,140 @@
+use serde::{Deserialize, Deserializer, Serialize};
+use std::ops::Deref;
+use thiserror::Error;
+
+/// The normalized name of a package.
+///
+/// Converts the name to lowercase and collapses runs of `-`, `_`, and `.` down to a single `-`.
+/// For example, `---`, `.`, and `__` are all converted to a single `-`.
+///
+/// See: <https://packaging.python.org/en/latest/specifications/name-normalization/>
+#[derive(Debug, Default, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize)]
+pub(crate) struct PackageName(String);
+
+impl PackageName {
+    /// Create a validated, normalized package name.
+    pub(crate) fn new(name: String) -> Result<Self, InvalidPackageNameError> {
+        if name.is_empty() {
+            return Err(InvalidPackageNameError::Empty);
+        }
+
+        if name.starts_with(['-', '_', '.']) {
+            return Err(InvalidPackageNameError::NonAlphanumericStart(
+                name.chars().next().unwrap(),
+            ));
+        }
+
+        if name.ends_with(['-', '_', '.']) {
+            return Err(InvalidPackageNameError::NonAlphanumericEnd(
+                name.chars().last().unwrap(),
+            ));
+        }
+
+        let Some(start) = name.find(|c: char| {
+            !c.is_ascii() || c.is_ascii_uppercase() || matches!(c, '-' | '_' | '.')
+        }) else {
+            return Ok(Self(name));
+        };
+
+        let (already_normalized, maybe_normalized) = name.split_at(start);
+
+        let mut normalized = String::with_capacity(name.len());
+        normalized.push_str(already_normalized);
+        let mut last = None;
+
+        for c in maybe_normalized.chars() {
+            if !c.is_ascii() {
+                return Err(InvalidPackageNameError::InvalidCharacter(c));
+            }
+
+            if c.is_ascii_uppercase() {
+                normalized.push(c.to_ascii_lowercase());
+            } else if matches!(c, '-' | '_' | '.') {
+                if matches!(last, Some('-' | '_' | '.')) {
+                    // Only keep a single instance of `-`, `_` and `.`
+                } else {
+                    normalized.push('-');
+                }
+            } else {
+                normalized.push(c);
+            }
+
+            last = Some(c);
+        }
+
+        Ok(Self(normalized))
+    }
+
+    /// Returns the underlying package name.
+    pub(crate) fn as_str(&self) -> &str {
+        &self.0
+    }
+}
+
+impl From<PackageName> for String {
+    fn from(value: PackageName) -> Self {
+        value.0
+    }
+}
+
+impl<'de> Deserialize<'de> for PackageName {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let s = String::deserialize(deserializer)?;
+        Self::new(s).map_err(serde::de::Error::custom)
+    }
+}
+
+impl std::fmt::Display for PackageName {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl Deref for PackageName {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.as_str()
+    }
+}
+
+#[derive(Error, Debug)]
+pub(crate) enum InvalidPackageNameError {
+    #[error("name must start with letter or number but it starts with '{0}'")]
+    NonAlphanumericStart(char),
+    #[error("name must end with letter or number but it ends with '{0}'")]
+    NonAlphanumericEnd(char),
+    #[error("valid name consists only of ASCII letters and numbers, period, underscore and hyphen but name contains '{0}'"
+    )]
+    InvalidCharacter(char),
+    #[error("name must not be empty")]
+    Empty,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::PackageName;
+
+    #[test]
+    fn normalize() {
+        let inputs = [
+            "friendly-bard",
+            "Friendly-Bard",
+            "FRIENDLY-BARD",
+            "friendly.bard",
+            "friendly_bard",
+            "friendly--bard",
+            "friendly-.bard",
+            "FrIeNdLy-._.-bArD",
+        ];
+
+        for input in inputs {
+            assert_eq!(
+                PackageName::new(input.to_string()).unwrap(),
+                PackageName::new("friendly-bard".to_string()).unwrap(),
+            );
+        }
+    }
+}

crates/red_knot_workspace/src/workspace/settings.rs

@@ -1,10 +1,12 @@
+use crate::workspace::PackageMetadata;
 use red_knot_python_semantic::{ProgramSettings, PythonVersion, SearchPathSettings, SitePackages};
 use ruff_db::system::{SystemPath, SystemPathBuf};
 
 /// The resolved configurations.
 ///
 /// The main difference to [`Configuration`] is that default values are filled in.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[cfg_attr(test, derive(serde::Serialize))]
 pub struct WorkspaceSettings {
     pub(super) program: ProgramSettings,
 }
@@ -16,7 +18,8 @@ impl WorkspaceSettings {
 }
 
 /// The configuration for the workspace or a package.
-#[derive(Debug, Default, Clone)]
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+#[cfg_attr(test, derive(serde::Serialize))]
 pub struct Configuration {
     pub target_version: Option<PythonVersion>,
     pub search_paths: SearchPathConfiguration,
@@ -29,17 +32,22 @@ impl Configuration {
         self.search_paths.extend(with.search_paths);
     }
 
-    pub fn into_workspace_settings(self, workspace_root: &SystemPath) -> WorkspaceSettings {
+    pub fn to_workspace_settings(
+        &self,
+        workspace_root: &SystemPath,
+        _packages: &[PackageMetadata],
+    ) -> WorkspaceSettings {
         WorkspaceSettings {
             program: ProgramSettings {
                 target_version: self.target_version.unwrap_or_default(),
-                search_paths: self.search_paths.into_settings(workspace_root),
+                search_paths: self.search_paths.to_settings(workspace_root),
             },
         }
     }
 }
 
 #[derive(Debug, Default, Clone, Eq, PartialEq)]
+#[cfg_attr(test, derive(serde::Serialize))]
 pub struct SearchPathConfiguration {
     /// List of user-provided paths that should take first priority in the module resolution.
     /// Examples in other type checkers are mypy's MYPYPATH environment variable,
@@ -59,15 +67,19 @@ pub struct SearchPathConfiguration {
 }
 
 impl SearchPathConfiguration {
-    pub fn into_settings(self, workspace_root: &SystemPath) -> SearchPathSettings {
-        let site_packages = self.site_packages.unwrap_or(SitePackages::Known(vec![]));
+    pub fn to_settings(&self, workspace_root: &SystemPath) -> SearchPathSettings {
+        let site_packages = self
+            .site_packages
+            .clone()
+            .unwrap_or(SitePackages::Known(vec![]));
 
         SearchPathSettings {
-            extra_paths: self.extra_paths.unwrap_or_default(),
+            extra_paths: self.extra_paths.clone().unwrap_or_default(),
             src_root: self
+                .clone()
                 .src_root
                 .unwrap_or_else(|| workspace_root.to_path_buf()),
-            custom_typeshed: self.custom_typeshed,
+            custom_typeshed: self.custom_typeshed.clone(),
             site_packages,
         }
     }

crates/red_knot_workspace/src/workspace/snapshots/red_knot_workspace__workspace__metadata__tests__member_pattern_matching_file.snap

@@ -0,0 +1,37 @@
+---
+source: crates/red_knot_workspace/src/workspace/metadata.rs
+expression: "&workspace"
+snapshot_kind: text
+---
+WorkspaceMetadata(
+  root: "/app",
+  packages: [
+    PackageMetadata(
+      name: Name("workspace-root"),
+      root: "/app",
+      configuration: Configuration(
+        target_version: None,
+        search_paths: SearchPathConfiguration(
+          extra_paths: None,
+          src_root: None,
+          custom_typeshed: None,
+          site_packages: None,
+        ),
+      ),
+    ),
+  ],
+  settings: WorkspaceSettings(
+    program: ProgramSettings(
+      target_version: PythonVersion(
+        major: 3,
+        minor: 9,
+      ),
+      search_paths: SearchPathSettings(
+        extra_paths: [],
+        src_root: "/app",
+        custom_typeshed: None,
+        site_packages: Known([]),
+      ),
+    ),
+  ),
+)