Bump 0.12.3 (#19279)

Summary
--

Fixes the test failures in #19279. This is the same variable used to
construct the SARIF output:


350d563c88/crates/ruff_linter/src/message/sarif.rs (L39-L44)

Test Plan
--

Existing tests with the modified filter

.github/workflows/ci.yaml

@@ -385,8 +385,8 @@ jobs:
       - name: "Build"
         run: cargo build --release --locked
 
-  cargo-test-msrv:
-    name: "cargo test (msrv)"
+  cargo-build-msrv:
+    name: "cargo build (msrv)"
     runs-on: depot-ubuntu-latest-8
     needs: determine_changes
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}

CHANGELOG.md

@@ -1,5 +1,33 @@
 # Changelog
 
+## 0.12.3
+
+### Preview features
+
+- \[`flake8-bugbear`\] Support non-context-manager calls in `B017` ([#19063](https://github.com/astral-sh/ruff/pull/19063))
+- \[`flake8-use-pathlib`\] Add autofixes for `PTH100`, `PTH106`, `PTH107`, `PTH108`, `PTH110`, `PTH111`, `PTH112`, `PTH113`, `PTH114`, `PTH115`, `PTH117`, `PTH119`, `PTH120` ([#19213](https://github.com/astral-sh/ruff/pull/19213))
+- \[`flake8-use-pathlib`\] Add autofixes for `PTH203`, `PTH204`, `PTH205` ([#18922](https://github.com/astral-sh/ruff/pull/18922))
+
+### Bug fixes
+
+- \[`flake8-return`\] Fix false-positive for variables used inside nested functions in `RET504` ([#18433](https://github.com/astral-sh/ruff/pull/18433))
+- Treat form feed as valid whitespace before a line continuation ([#19220](https://github.com/astral-sh/ruff/pull/19220))
+- \[`flake8-type-checking`\] Fix syntax error introduced by fix (`TC008`) ([#19150](https://github.com/astral-sh/ruff/pull/19150))
+- \[`pyupgrade`\] Keyword arguments in `super` should suppress the `UP008` fix ([#19131](https://github.com/astral-sh/ruff/pull/19131))
+
+### Documentation
+
+- \[`flake8-pyi`\] Make example error out-of-the-box (`PYI007`, `PYI008`) ([#19103](https://github.com/astral-sh/ruff/pull/19103))
+- \[`flake8-simplify`\] Make example error out-of-the-box (`SIM116`) ([#19111](https://github.com/astral-sh/ruff/pull/19111))
+- \[`flake8-type-checking`\] Make example error out-of-the-box (`TC001`) ([#19151](https://github.com/astral-sh/ruff/pull/19151))
+- \[`flake8-use-pathlib`\] Make example error out-of-the-box (`PTH210`) ([#19189](https://github.com/astral-sh/ruff/pull/19189))
+- \[`pycodestyle`\] Make example error out-of-the-box (`E272`) ([#19191](https://github.com/astral-sh/ruff/pull/19191))
+- \[`pycodestyle`\] Make example not raise unnecessary `SyntaxError` (`E114`) ([#19190](https://github.com/astral-sh/ruff/pull/19190))
+- \[`pydoclint`\] Make example error out-of-the-box (`DOC501`) ([#19218](https://github.com/astral-sh/ruff/pull/19218))
+- \[`pylint`, `pyupgrade`\] Fix syntax errors in examples (`PLW1501`, `UP028`) ([#19127](https://github.com/astral-sh/ruff/pull/19127))
+- \[`pylint`\] Update `missing-maxsplit-arg` docs and error to suggest proper usage (`PLC0207`) ([#18949](https://github.com/astral-sh/ruff/pull/18949))
+- \[`flake8-bandit`\] Make example error out-of-the-box (`S412`) ([#19241](https://github.com/astral-sh/ruff/pull/19241))
+
 ## 0.12.2
 
 ### Preview features

Cargo.lock

@@ -2711,7 +2711,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.12.2"
+version = "0.12.3"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2961,7 +2961,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.12.2"
+version = "0.12.3"
 dependencies = [
  "aho-corasick",
  "anyhow",
@@ -3294,7 +3294,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_wasm"
-version = "0.12.2"
+version = "0.12.3"
 dependencies = [
  "console_error_panic_hook",
  "console_log",
@@ -4152,9 +4152,12 @@ version = "0.0.0"
 dependencies = [
  "bitflags 2.9.1",
  "insta",
+ "regex",
  "ruff_db",
  "ruff_python_ast",
  "ruff_python_parser",
+ "ruff_python_trivia",
+ "ruff_source_file",
  "ruff_text_size",
  "rustc-hash",
  "salsa",

README.md

@@ -148,8 +148,8 @@ 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/0.12.2/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.12.2/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.12.3/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.12.3/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -182,7 +182,7 @@ 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: v0.12.2
+  rev: v0.12.3
   hooks:
     # Run the linter.
     - id: ruff-check

crates/ruff/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff"
-version = "0.12.2"
+version = "0.12.3"
 publish = true
 authors = { workspace = true }
 edition = { workspace = true }

crates/ruff/tests/lint.rs

@@ -5692,3 +5692,57 @@ class Foo:
     "
     );
 }
+
+#[test_case::test_case("concise")]
+#[test_case::test_case("full")]
+#[test_case::test_case("json")]
+#[test_case::test_case("json-lines")]
+#[test_case::test_case("junit")]
+#[test_case::test_case("grouped")]
+#[test_case::test_case("github")]
+#[test_case::test_case("gitlab")]
+#[test_case::test_case("pylint")]
+#[test_case::test_case("rdjson")]
+#[test_case::test_case("azure")]
+#[test_case::test_case("sarif")]
+fn output_format(output_format: &str) -> Result<()> {
+    const CONTENT: &str = "\
+import os  # F401
+x = y      # F821
+match 42:  # invalid-syntax
+    case _: ...
+";
+
+    let tempdir = TempDir::new()?;
+    let input = tempdir.path().join("input.py");
+    fs::write(&input, CONTENT)?;
+
+    let snapshot = format!("output_format_{output_format}");
+
+    insta::with_settings!({
+        filters => vec![
+            (tempdir_filter(&tempdir).as_str(), "[TMP]/"),
+            (r#""[^"]+\\?/?input.py"#, r#""[TMP]/input.py"#),
+            (ruff_linter::VERSION, "[VERSION]"),
+        ]
+    }, {
+        assert_cmd_snapshot!(
+            snapshot,
+            Command::new(get_cargo_bin(BIN_NAME))
+                .args([
+                    "check",
+                    "--no-cache",
+                    "--output-format",
+                    output_format,
+                    "--select",
+                    "F401,F821",
+                    "--target-version",
+                    "py39",
+                    "input.py",
+                ])
+                .current_dir(&tempdir),
+        );
+    });
+
+    Ok(())
+}

crates/ruff/tests/snapshots/lint__output_format_azure.snap

@@ -0,0 +1,23 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - azure
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+##vso[task.logissue type=error;sourcepath=[TMP]/input.py;linenumber=1;columnnumber=8;code=F401;]`os` imported but unused
+##vso[task.logissue type=error;sourcepath=[TMP]/input.py;linenumber=2;columnnumber=5;code=F821;]Undefined name `y`
+##vso[task.logissue type=error;sourcepath=[TMP]/input.py;linenumber=3;columnnumber=1;]SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
+
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_concise.snap

@@ -0,0 +1,25 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - concise
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+input.py:1:8: F401 [*] `os` imported but unused
+input.py:2:5: F821 Undefined name `y`
+input.py:3:1: SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
+Found 3 errors.
+[*] 1 fixable with the `--fix` option.
+
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_full.snap

@@ -0,0 +1,49 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - full
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+input.py:1:8: F401 [*] `os` imported but unused
+  |
+1 | import os  # F401
+  |        ^^ F401
+2 | x = y      # F821
+3 | match 42:  # invalid-syntax
+  |
+  = help: Remove unused import: `os`
+
+input.py:2:5: F821 Undefined name `y`
+  |
+1 | import os  # F401
+2 | x = y      # F821
+  |     ^ F821
+3 | match 42:  # invalid-syntax
+4 |     case _: ...
+  |
+
+input.py:3:1: SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
+  |
+1 | import os  # F401
+2 | x = y      # F821
+3 | match 42:  # invalid-syntax
+  | ^^^^^
+4 |     case _: ...
+  |
+
+Found 3 errors.
+[*] 1 fixable with the `--fix` option.
+
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_github.snap

@@ -0,0 +1,23 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - github
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+::error title=Ruff (F401),file=[TMP]/input.py,line=1,col=8,endLine=1,endColumn=10::input.py:1:8: F401 `os` imported but unused
+::error title=Ruff (F821),file=[TMP]/input.py,line=2,col=5,endLine=2,endColumn=6::input.py:2:5: F821 Undefined name `y`
+::error title=Ruff,file=[TMP]/input.py,line=3,col=1,endLine=3,endColumn=6::input.py:3:1: SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
+
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_gitlab.snap

@@ -0,0 +1,60 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - gitlab
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+[
+  {
+    "check_name": "F401",
+    "description": "`os` imported but unused",
+    "fingerprint": "4dbad37161e65c72",
+    "location": {
+      "lines": {
+        "begin": 1,
+        "end": 1
+      },
+      "path": "input.py"
+    },
+    "severity": "major"
+  },
+  {
+    "check_name": "F821",
+    "description": "Undefined name `y`",
+    "fingerprint": "7af59862a085230",
+    "location": {
+      "lines": {
+        "begin": 2,
+        "end": 2
+      },
+      "path": "input.py"
+    },
+    "severity": "major"
+  },
+  {
+    "check_name": "syntax-error",
+    "description": "Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)",
+    "fingerprint": "e558cec859bb66e8",
+    "location": {
+      "lines": {
+        "begin": 3,
+        "end": 3
+      },
+      "path": "input.py"
+    },
+    "severity": "major"
+  }
+]
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_grouped.snap

@@ -0,0 +1,27 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - grouped
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+input.py:
+  1:8 F401 [*] `os` imported but unused
+  2:5 F821 Undefined name `y`
+  3:1 SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
+
+Found 3 errors.
+[*] 1 fixable with the `--fix` option.
+
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_json-lines.snap

@@ -0,0 +1,23 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - json-lines
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+{"cell":null,"code":"F401","end_location":{"column":10,"row":1},"filename":"[TMP]/input.py","fix":{"applicability":"safe","edits":[{"content":"","end_location":{"column":1,"row":2},"location":{"column":1,"row":1}}],"message":"Remove unused import: `os`"},"location":{"column":8,"row":1},"message":"`os` imported but unused","noqa_row":1,"url":"https://docs.astral.sh/ruff/rules/unused-import"}
+{"cell":null,"code":"F821","end_location":{"column":6,"row":2},"filename":"[TMP]/input.py","fix":null,"location":{"column":5,"row":2},"message":"Undefined name `y`","noqa_row":2,"url":"https://docs.astral.sh/ruff/rules/undefined-name"}
+{"cell":null,"code":null,"end_location":{"column":6,"row":3},"filename":"[TMP]/input.py","fix":null,"location":{"column":1,"row":3},"message":"SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)","noqa_row":null,"url":null}
+
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_json.snap

@@ -0,0 +1,88 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - json
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+[
+  {
+    "cell": null,
+    "code": "F401",
+    "end_location": {
+      "column": 10,
+      "row": 1
+    },
+    "filename": "[TMP]/input.py",
+    "fix": {
+      "applicability": "safe",
+      "edits": [
+        {
+          "content": "",
+          "end_location": {
+            "column": 1,
+            "row": 2
+          },
+          "location": {
+            "column": 1,
+            "row": 1
+          }
+        }
+      ],
+      "message": "Remove unused import: `os`"
+    },
+    "location": {
+      "column": 8,
+      "row": 1
+    },
+    "message": "`os` imported but unused",
+    "noqa_row": 1,
+    "url": "https://docs.astral.sh/ruff/rules/unused-import"
+  },
+  {
+    "cell": null,
+    "code": "F821",
+    "end_location": {
+      "column": 6,
+      "row": 2
+    },
+    "filename": "[TMP]/input.py",
+    "fix": null,
+    "location": {
+      "column": 5,
+      "row": 2
+    },
+    "message": "Undefined name `y`",
+    "noqa_row": 2,
+    "url": "https://docs.astral.sh/ruff/rules/undefined-name"
+  },
+  {
+    "cell": null,
+    "code": null,
+    "end_location": {
+      "column": 6,
+      "row": 3
+    },
+    "filename": "[TMP]/input.py",
+    "fix": null,
+    "location": {
+      "column": 1,
+      "row": 3
+    },
+    "message": "SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)",
+    "noqa_row": null,
+    "url": null
+  }
+]
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_junit.snap

@@ -0,0 +1,34 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - junit
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+<?xml version="1.0" encoding="UTF-8"?>
+<testsuites name="ruff" tests="3" failures="3" errors="0">
+    <testsuite name="[TMP]/input.py" tests="3" disabled="0" errors="0" failures="3" package="org.ruff">
+        <testcase name="org.ruff.F401" classname="[TMP]/input" line="1" column="8">
+            <failure message="`os` imported but unused">line 1, col 8, `os` imported but unused</failure>
+        </testcase>
+        <testcase name="org.ruff.F821" classname="[TMP]/input" line="2" column="5">
+            <failure message="Undefined name `y`">line 2, col 5, Undefined name `y`</failure>
+        </testcase>
+        <testcase name="org.ruff" classname="[TMP]/input" line="3" column="1">
+            <failure message="SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)">line 3, col 1, SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)</failure>
+        </testcase>
+    </testsuite>
+</testsuites>
+
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_pylint.snap

@@ -0,0 +1,23 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - pylint
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+input.py:1: [F401] `os` imported but unused
+input.py:2: [F821] Undefined name `y`
+input.py:3: SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
+
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_rdjson.snap

@@ -0,0 +1,103 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - rdjson
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+{
+  "diagnostics": [
+    {
+      "code": {
+        "url": "https://docs.astral.sh/ruff/rules/unused-import",
+        "value": "F401"
+      },
+      "location": {
+        "path": "[TMP]/input.py",
+        "range": {
+          "end": {
+            "column": 10,
+            "line": 1
+          },
+          "start": {
+            "column": 8,
+            "line": 1
+          }
+        }
+      },
+      "message": "`os` imported but unused",
+      "suggestions": [
+        {
+          "range": {
+            "end": {
+              "column": 1,
+              "line": 2
+            },
+            "start": {
+              "column": 1,
+              "line": 1
+            }
+          },
+          "text": ""
+        }
+      ]
+    },
+    {
+      "code": {
+        "url": "https://docs.astral.sh/ruff/rules/undefined-name",
+        "value": "F821"
+      },
+      "location": {
+        "path": "[TMP]/input.py",
+        "range": {
+          "end": {
+            "column": 6,
+            "line": 2
+          },
+          "start": {
+            "column": 5,
+            "line": 2
+          }
+        }
+      },
+      "message": "Undefined name `y`"
+    },
+    {
+      "code": {
+        "url": null,
+        "value": null
+      },
+      "location": {
+        "path": "[TMP]/input.py",
+        "range": {
+          "end": {
+            "column": 6,
+            "line": 3
+          },
+          "start": {
+            "column": 1,
+            "line": 3
+          }
+        }
+      },
+      "message": "SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)"
+    }
+  ],
+  "severity": "warning",
+  "source": {
+    "name": "ruff",
+    "url": "https://docs.astral.sh/ruff"
+  }
+}
+----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_sarif.snap

@@ -0,0 +1,142 @@
+---
+source: crates/ruff/tests/lint.rs
+info:
+  program: ruff
+  args:
+    - check
+    - "--no-cache"
+    - "--output-format"
+    - sarif
+    - "--select"
+    - "F401,F821"
+    - "--target-version"
+    - py39
+    - input.py
+---
+success: false
+exit_code: 1
+----- stdout -----
+{
+  "$schema": "https://json.schemastore.org/sarif-2.1.0.json",
+  "runs": [
+    {
+      "results": [
+        {
+          "level": "error",
+          "locations": [
+            {
+              "physicalLocation": {
+                "artifactLocation": {
+                  "uri": "[TMP]/input.py"
+                },
+                "region": {
+                  "endColumn": 10,
+                  "endLine": 1,
+                  "startColumn": 8,
+                  "startLine": 1
+                }
+              }
+            }
+          ],
+          "message": {
+            "text": "`os` imported but unused"
+          },
+          "ruleId": "F401"
+        },
+        {
+          "level": "error",
+          "locations": [
+            {
+              "physicalLocation": {
+                "artifactLocation": {
+                  "uri": "[TMP]/input.py"
+                },
+                "region": {
+                  "endColumn": 6,
+                  "endLine": 2,
+                  "startColumn": 5,
+                  "startLine": 2
+                }
+              }
+            }
+          ],
+          "message": {
+            "text": "Undefined name `y`"
+          },
+          "ruleId": "F821"
+        },
+        {
+          "level": "error",
+          "locations": [
+            {
+              "physicalLocation": {
+                "artifactLocation": {
+                  "uri": "[TMP]/input.py"
+                },
+                "region": {
+                  "endColumn": 6,
+                  "endLine": 3,
+                  "startColumn": 1,
+                  "startLine": 3
+                }
+              }
+            }
+          ],
+          "message": {
+            "text": "SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)"
+          },
+          "ruleId": null
+        }
+      ],
+      "tool": {
+        "driver": {
+          "informationUri": "https://github.com/astral-sh/ruff",
+          "name": "ruff",
+          "rules": [
+            {
+              "fullDescription": {
+                "text": "## What it does\nChecks for unused imports.\n\n## Why is this bad?\nUnused imports add a performance overhead at runtime, and risk creating\nimport cycles. They also increase the cognitive load of reading the code.\n\nIf an import statement is used to check for the availability or existence\nof a module, consider using `importlib.util.find_spec` instead.\n\nIf an import statement is used to re-export a symbol as part of a module's\npublic interface, consider using a \"redundant\" import alias, which\ninstructs Ruff (and other tools) to respect the re-export, and avoid\nmarking it as unused, as in:\n\n```python\nfrom module import member as member\n```\n\nAlternatively, you can use `__all__` to declare a symbol as part of the module's\ninterface, as in:\n\n```python\n# __init__.py\nimport some_module\n\n__all__ = [\"some_module\"]\n```\n\n## Fix safety\n\nFixes to remove unused imports are safe, except in `__init__.py` files.\n\nApplying fixes to `__init__.py` files is currently in preview. The fix offered depends on the\ntype of the unused import. Ruff will suggest a safe fix to export first-party imports with\neither a redundant alias or, if already present in the file, an `__all__` entry. If multiple\n`__all__` declarations are present, Ruff will not offer a fix. Ruff will suggest an unsafe fix\nto remove third-party and standard library imports -- the fix is unsafe because the module's\ninterface changes.\n\n## Example\n\n```python\nimport numpy as np  # unused import\n\n\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nUse instead:\n\n```python\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nTo check the availability of a module, use `importlib.util.find_spec`:\n\n```python\nfrom importlib.util import find_spec\n\nif find_spec(\"numpy\") is not None:\n    print(\"numpy is installed\")\nelse:\n    print(\"numpy is not installed\")\n```\n\n## Preview\nWhen [preview](https://docs.astral.sh/ruff/preview/) is enabled,\nthe criterion for determining whether an import is first-party\nis stricter, which could affect the suggested fix. See [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc) for more details.\n\n## Options\n- `lint.ignore-init-module-imports`\n- `lint.pyflakes.allowed-unused-imports`\n\n## References\n- [Python documentation: `import`](https://docs.python.org/3/reference/simple_stmts.html#the-import-statement)\n- [Python documentation: `importlib.util.find_spec`](https://docs.python.org/3/library/importlib.html#importlib.util.find_spec)\n- [Typing documentation: interface conventions](https://typing.python.org/en/latest/source/libraries.html#library-interface-public-and-private-symbols)\n"
+              },
+              "help": {
+                "text": "`{name}` imported but unused; consider using `importlib.util.find_spec` to test for availability"
+              },
+              "helpUri": "https://docs.astral.sh/ruff/rules/unused-import",
+              "id": "F401",
+              "properties": {
+                "id": "F401",
+                "kind": "Pyflakes",
+                "name": "unused-import",
+                "problem.severity": "error"
+              },
+              "shortDescription": {
+                "text": "`{name}` imported but unused; consider using `importlib.util.find_spec` to test for availability"
+              }
+            },
+            {
+              "fullDescription": {
+                "text": "## What it does\nChecks for uses of undefined names.\n\n## Why is this bad?\nAn undefined name is likely to raise `NameError` at runtime.\n\n## Example\n```python\ndef double():\n    return n * 2  # raises `NameError` if `n` is undefined when `double` is called\n```\n\nUse instead:\n```python\ndef double(n):\n    return n * 2\n```\n\n## Options\n- [`target-version`]: Can be used to configure which symbols Ruff will understand\n  as being available in the `builtins` namespace.\n\n## References\n- [Python documentation: Naming and binding](https://docs.python.org/3/reference/executionmodel.html#naming-and-binding)\n"
+              },
+              "help": {
+                "text": "Undefined name `{name}`. {tip}"
+              },
+              "helpUri": "https://docs.astral.sh/ruff/rules/undefined-name",
+              "id": "F821",
+              "properties": {
+                "id": "F821",
+                "kind": "Pyflakes",
+                "name": "undefined-name",
+                "problem.severity": "error"
+              },
+              "shortDescription": {
+                "text": "Undefined name `{name}`. {tip}"
+              }
+            }
+          ],
+          "version": "[VERSION]"
+        }
+      }
+    }
+  ],
+  "version": "2.1.0"
+}
+----- stderr -----

crates/ruff_linter/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff_linter"
-version = "0.12.2"
+version = "0.12.3"
 publish = false
 authors = { workspace = true }
 edition = { workspace = true }

crates/ruff_linter/resources/test/fixtures/flake8_return/RET504.py

@@ -422,6 +422,35 @@ def func(a: dict[str, int]) -> list[dict[str, int]]:
         services = a["services"]
         return services
 
+
+# See: https://github.com/astral-sh/ruff/issues/14052
+def outer() -> list[object]:
+    @register
+    async def inner() -> None:
+        print(layout)
+
+    layout = [...]
+    return layout
+
+def outer() -> list[object]:
+    with open("") as f:
+        async def inner() -> None:
+            print(layout)
+
+    layout = [...]
+    return layout
+
+
+def outer() -> list[object]:
+    def inner():
+        with open("") as f:
+            async def inner_inner() -> None:
+                print(layout)
+
+    layout = [...]
+    return layout
+
+
 # See: https://github.com/astral-sh/ruff/issues/18411
 def f():
     (#=

crates/ruff_linter/resources/test/fixtures/flake8_type_checking/whitespace.py

@@ -0,0 +1,6 @@
+# Regression test for: https://github.com/astral-sh/ruff/issues/19175
+# there is a (potentially invisible) unicode formfeed character (000C) between `TYPE_CHECKING` and the backslash
+from typing import TYPE_CHECKING\
+
+if TYPE_CHECKING: import builtins
+builtins.print("!")

crates/ruff_linter/src/checkers/ast/analyze/bindings.rs

@@ -4,8 +4,8 @@ use crate::Fix;
 use crate::checkers::ast::Checker;
 use crate::codes::Rule;
 use crate::rules::{
-    flake8_import_conventions, flake8_pyi, flake8_pytest_style, flake8_type_checking, pyflakes,
-    pylint, pyupgrade, refurb, ruff,
+    flake8_import_conventions, flake8_pyi, flake8_pytest_style, flake8_return,
+    flake8_type_checking, pyflakes, pylint, pyupgrade, refurb, ruff,
 };
 
 /// Run lint rules over the [`Binding`]s.
@@ -25,11 +25,20 @@ pub(crate) fn bindings(checker: &Checker) {
         Rule::ForLoopWrites,
         Rule::CustomTypeVarForSelf,
         Rule::PrivateTypeParameter,
+        Rule::UnnecessaryAssign,
     ]) {
         return;
     }
 
     for (binding_id, binding) in checker.semantic.bindings.iter_enumerated() {
+        if checker.is_rule_enabled(Rule::UnnecessaryAssign) {
+            if binding.kind.is_function_definition() {
+                flake8_return::rules::unnecessary_assign(
+                    checker,
+                    binding.statement(checker.semantic()).unwrap(),
+                );
+            }
+        }
         if checker.is_rule_enabled(Rule::UnusedVariable) {
             if binding.kind.is_bound_exception()
                 && binding.is_unused()

crates/ruff_linter/src/checkers/ast/analyze/statement.rs

@@ -207,7 +207,6 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                 Rule::UnnecessaryReturnNone,
                 Rule::ImplicitReturnValue,
                 Rule::ImplicitReturn,
-                Rule::UnnecessaryAssign,
                 Rule::SuperfluousElseReturn,
                 Rule::SuperfluousElseRaise,
                 Rule::SuperfluousElseContinue,

crates/ruff_linter/src/importer/insertion.rs

@@ -5,6 +5,7 @@ use ruff_python_ast::Stmt;
 use ruff_python_ast::helpers::is_docstring_stmt;
 use ruff_python_codegen::Stylist;
 use ruff_python_parser::{TokenKind, Tokens};
+use ruff_python_trivia::is_python_whitespace;
 use ruff_python_trivia::{PythonWhitespace, textwrap::indent};
 use ruff_source_file::{LineRanges, UniversalNewlineIterator};
 use ruff_text_size::{Ranged, TextSize};
@@ -306,7 +307,7 @@ fn match_semicolon(s: &str) -> Option<TextSize> {
 fn match_continuation(s: &str) -> Option<TextSize> {
     for (offset, c) in s.char_indices() {
         match c {
-            ' ' | '\t' => continue,
+            _ if is_python_whitespace(c) => continue,
             '\\' => return Some(TextSize::try_from(offset).unwrap()),
             _ => break,
         }

crates/ruff_linter/src/rules/flake8_return/rules/function.rs

@@ -539,7 +539,21 @@ fn implicit_return(checker: &Checker, function_def: &ast::StmtFunctionDef, stmt:
 }
 
 /// RET504
-fn unnecessary_assign(checker: &Checker, stack: &Stack) {
+pub(crate) fn unnecessary_assign(checker: &Checker, function_stmt: &Stmt) {
+    let Stmt::FunctionDef(function_def) = function_stmt else {
+        return;
+    };
+    let Some(stack) = create_stack(checker, function_def) else {
+        return;
+    };
+
+    if !result_exists(&stack.returns) {
+        return;
+    }
+
+    let Some(function_scope) = checker.semantic().function_scope(function_def) else {
+        return;
+    };
     for (assign, return_, stmt) in &stack.assignment_return {
         // Identify, e.g., `return x`.
         let Some(value) = return_.value.as_ref() else {
@@ -583,6 +597,22 @@ fn unnecessary_assign(checker: &Checker, stack: &Stack) {
             continue;
         }
 
+        let Some(assigned_binding) = function_scope
+            .get(assigned_id)
+            .map(|binding_id| checker.semantic().binding(binding_id))
+        else {
+            continue;
+        };
+        // Check if there's any reference made to `assigned_binding` in another scope, e.g, nested
+        // functions. If there is, ignore them.
+        if assigned_binding
+            .references()
+            .map(|reference_id| checker.semantic().reference(reference_id))
+            .any(|reference| reference.scope_id() != assigned_binding.scope)
+        {
+            continue;
+        }
+
         let mut diagnostic = checker.report_diagnostic(
             UnnecessaryAssign {
                 name: assigned_id.to_string(),
@@ -665,24 +695,21 @@ fn superfluous_elif_else(checker: &Checker, stack: &Stack) {
     }
 }
 
-/// Run all checks from the `flake8-return` plugin.
-pub(crate) fn function(checker: &Checker, function_def: &ast::StmtFunctionDef) {
-    let ast::StmtFunctionDef {
-        decorator_list,
-        returns,
-        body,
-        ..
-    } = function_def;
+fn create_stack<'a>(
+    checker: &'a Checker,
+    function_def: &'a ast::StmtFunctionDef,
+) -> Option<Stack<'a>> {
+    let ast::StmtFunctionDef { body, .. } = function_def;
 
     // Find the last statement in the function.
     let Some(last_stmt) = body.last() else {
         // Skip empty functions.
-        return;
+        return None;
     };
 
     // Skip functions that consist of a single return statement.
     if body.len() == 1 && matches!(last_stmt, Stmt::Return(_)) {
-        return;
+        return None;
     }
 
     // Traverse the function body, to collect the stack.
@@ -696,9 +723,29 @@ pub(crate) fn function(checker: &Checker, function_def: &ast::StmtFunctionDef) {
 
     // Avoid false positives for generators.
     if stack.is_generator {
-        return;
+        return None;
     }
 
+    Some(stack)
+}
+
+/// Run all checks from the `flake8-return` plugin, but `RET504` which is ran
+/// after the semantic model is fully built.
+pub(crate) fn function(checker: &Checker, function_def: &ast::StmtFunctionDef) {
+    let ast::StmtFunctionDef {
+        decorator_list,
+        returns,
+        body,
+        ..
+    } = function_def;
+
+    let Some(stack) = create_stack(checker, function_def) else {
+        return;
+    };
+    let Some(last_stmt) = body.last() else {
+        return;
+    };
+
     if checker.any_rule_enabled(&[
         Rule::SuperfluousElseReturn,
         Rule::SuperfluousElseRaise,
@@ -721,10 +768,6 @@ pub(crate) fn function(checker: &Checker, function_def: &ast::StmtFunctionDef) {
         if checker.is_rule_enabled(Rule::ImplicitReturn) {
             implicit_return(checker, function_def, last_stmt);
         }
-
-        if checker.is_rule_enabled(Rule::UnnecessaryAssign) {
-            unnecessary_assign(checker, &stack);
-        }
     } else {
         if checker.is_rule_enabled(Rule::UnnecessaryReturnNone) {
             // Skip functions that have a return annotation that is not `None`.

crates/ruff_linter/src/rules/flake8_return/snapshots/ruff_linter__rules__flake8_return__tests__RET504_RET504.py.snap

@@ -247,8 +247,6 @@ RET504.py:423:16: RET504 [*] Unnecessary assignment to `services` before `return
 422 |         services = a["services"]
 423 |         return services
     |                ^^^^^^^^ RET504
-424 |
-425 | # See: https://github.com/astral-sh/ruff/issues/18411
     |
     = help: Remove unnecessary assignment
 
@@ -260,46 +258,46 @@ RET504.py:423:16: RET504 [*] Unnecessary assignment to `services` before `return
 423     |-        return services
     422 |+        return a["services"]
 424 423 | 
-425 424 | # See: https://github.com/astral-sh/ruff/issues/18411
-426 425 | def f():
+425 424 | 
+426 425 | # See: https://github.com/astral-sh/ruff/issues/14052
 
-RET504.py:429:12: RET504 [*] Unnecessary assignment to `x` before `return` statement
+RET504.py:458:12: RET504 [*] Unnecessary assignment to `x` before `return` statement
     |
-427 |     (#=
-428 |     x) = 1
-429 |     return x
+456 |     (#=
+457 |     x) = 1
+458 |     return x
     |            ^ RET504
-430 |
-431 | def f():
+459 |
+460 | def f():
     |
     = help: Remove unnecessary assignment
 
 ℹ Unsafe fix
-424 424 | 
-425 425 | # See: https://github.com/astral-sh/ruff/issues/18411
-426 426 | def f():
-427     |-    (#=
-428     |-    x) = 1
-429     |-    return x
-    427 |+    return 1
-430 428 | 
-431 429 | def f():
-432 430 |     x = (1
+453 453 | 
+454 454 | # See: https://github.com/astral-sh/ruff/issues/18411
+455 455 | def f():
+456     |-    (#=
+457     |-    x) = 1
+458     |-    return x
+    456 |+    return 1
+459 457 | 
+460 458 | def f():
+461 459 |     x = (1
 
-RET504.py:434:12: RET504 [*] Unnecessary assignment to `x` before `return` statement
+RET504.py:463:12: RET504 [*] Unnecessary assignment to `x` before `return` statement
     |
-432 |     x = (1
-433 |               )
-434 |     return x
+461 |     x = (1
+462 |               )
+463 |     return x
     |            ^ RET504
     |
     = help: Remove unnecessary assignment
 
 ℹ Unsafe fix
-429 429 |     return x
-430 430 | 
-431 431 | def f():
-432     |-    x = (1
-    432 |+    return (1
-433 433 |               )
-434     |-    return x
+458 458 |     return x
+459 459 | 
+460 460 | def f():
+461     |-    x = (1
+    461 |+    return (1
+462 462 |               )
+463     |-    return x

crates/ruff_linter/src/rules/flake8_type_checking/mod.rs

@@ -36,6 +36,7 @@ mod tests {
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("TC004_8.py"))]
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("TC004_9.py"))]
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("quote.py"))]
+    #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("whitespace.py"))]
     #[test_case(Rule::RuntimeStringUnion, Path::new("TC010_1.py"))]
     #[test_case(Rule::RuntimeStringUnion, Path::new("TC010_2.py"))]
     #[test_case(Rule::TypingOnlyFirstPartyImport, Path::new("TC001.py"))]

crates/ruff_linter/src/rules/flake8_type_checking/snapshots/ruff_linter__rules__flake8_type_checking__tests__runtime-import-in-type-checking-block_whitespace.py.snap

@@ -0,0 +1,22 @@
+---
+source: crates/ruff_linter/src/rules/flake8_type_checking/mod.rs
+---
+whitespace.py:5:26: TC004 [*] Move import `builtins` out of type-checking block. Import is used for more than type hinting.
+  |
+3 | from typing import TYPE_CHECKING\
+4 |
+5 | if TYPE_CHECKING: import builtins
+  |                          ^^^^^^^^ TC004
+6 | builtins.print("!")
+  |
+  = help: Move out of type-checking block
+
+ℹ Unsafe fix
+1 1 | # Regression test for: https://github.com/astral-sh/ruff/issues/19175
+2 2 | # there is a (potentially invisible) unicode formfeed character (000C) between `TYPE_CHECKING` and the backslash
+3   |-from typing import TYPE_CHECKING\
+  3 |+from typing import TYPE_CHECKING; import builtins\
+4 4 | 
+5   |-if TYPE_CHECKING: import builtins
+  5 |+if TYPE_CHECKING: pass
+6 6 | builtins.print("!")

crates/ruff_python_semantic/src/model.rs

@@ -2094,6 +2094,20 @@ impl<'a> SemanticModel<'a> {
             None
         })
     }
+
+    /// Finds and returns the [`Scope`] corresponding to a given [`ast::StmtFunctionDef`].
+    ///
+    /// This method searches all scopes created by a function definition, comparing the
+    /// [`TextRange`] of the provided `function_def` with the the range of the function
+    /// associated with the scope.
+    pub fn function_scope(&self, function_def: &ast::StmtFunctionDef) -> Option<&Scope> {
+        self.scopes.iter().find(|scope| {
+            let Some(function) = scope.kind.as_function() else {
+                return false;
+            };
+            function.range() == function_def.range()
+        })
+    }
 }
 
 pub struct ShadowedBinding {

crates/ruff_wasm/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff_wasm"
-version = "0.12.2"
+version = "0.12.3"
 publish = false
 authors = { workspace = true }
 edition = { workspace = true }

crates/ty/docs/cli.md

@@ -84,7 +84,8 @@ over all configuration files.</p>
 <li><code>3.11</code></li>
 <li><code>3.12</code></li>
 <li><code>3.13</code></li>
-</ul></dd><dt id="ty-check--respect-ignore-files"><a href="#ty-check--respect-ignore-files"><code>--respect-ignore-files</code></a></dt><dd><p>Respect file exclusions via <code>.gitignore</code> and other standard ignore files. Use <code>--no-respect-gitignore</code> to disable</p>
+</ul></dd><dt id="ty-check--quiet"><a href="#ty-check--quiet"><code>--quiet</code></a></dt><dd><p>Use quiet output</p>
+</dd><dt id="ty-check--respect-ignore-files"><a href="#ty-check--respect-ignore-files"><code>--respect-ignore-files</code></a></dt><dd><p>Respect file exclusions via <code>.gitignore</code> and other standard ignore files. Use <code>--no-respect-gitignore</code> to disable</p>
 </dd><dt id="ty-check--typeshed"><a href="#ty-check--typeshed"><code>--typeshed</code></a>, <code>--custom-typeshed-dir</code> <i>path</i></dt><dd><p>Custom directory to use for stdlib typeshed stubs</p>
 </dd><dt id="ty-check--verbose"><a href="#ty-check--verbose"><code>--verbose</code></a>, <code>-v</code></dt><dd><p>Use verbose output (or <code>-vv</code> and <code>-vvv</code> for more verbose output)</p>
 </dd><dt id="ty-check--warn"><a href="#ty-check--warn"><code>--warn</code></a> <i>rule</i></dt><dd><p>Treat the given rule as having severity 'warn'. Can be specified multiple times.</p>

crates/ty/src/lib.rs

@@ -1,12 +1,13 @@
 mod args;
 mod logging;
+mod printer;
 mod python_version;
 mod version;
 
 pub use args::Cli;
 use ty_static::EnvVars;
 
-use std::io::{self, BufWriter, Write, stdout};
+use std::fmt::Write;
 use std::process::{ExitCode, Termination};
 
 use anyhow::Result;
@@ -14,6 +15,7 @@ use std::sync::Mutex;
 
 use crate::args::{CheckCommand, Command, TerminalColor};
 use crate::logging::setup_tracing;
+use crate::printer::Printer;
 use anyhow::{Context, anyhow};
 use clap::{CommandFactory, Parser};
 use colored::Colorize;
@@ -25,7 +27,7 @@ use ruff_db::system::{OsSystem, SystemPath, SystemPathBuf};
 use salsa::plumbing::ZalsaDatabase;
 use ty_project::metadata::options::ProjectOptionsOverrides;
 use ty_project::watch::ProjectWatcher;
-use ty_project::{Db, DummyReporter, Reporter, watch};
+use ty_project::{Db, watch};
 use ty_project::{ProjectDatabase, ProjectMetadata};
 use ty_server::run_server;
 
@@ -42,6 +44,8 @@ pub fn run() -> anyhow::Result<ExitStatus> {
         Command::Check(check_args) => run_check(check_args),
         Command::Version => version().map(|()| ExitStatus::Success),
         Command::GenerateShellCompletion { shell } => {
+            use std::io::stdout;
+
             shell.generate(&mut Cli::command(), &mut stdout());
             Ok(ExitStatus::Success)
         }
@@ -49,7 +53,7 @@ pub fn run() -> anyhow::Result<ExitStatus> {
 }
 
 pub(crate) fn version() -> Result<()> {
-    let mut stdout = BufWriter::new(io::stdout().lock());
+    let mut stdout = Printer::default().stream_for_requested_summary().lock();
     let version_info = crate::version::version();
     writeln!(stdout, "ty {}", &version_info)?;
     Ok(())
@@ -61,6 +65,8 @@ fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
     let verbosity = args.verbosity.level();
     let _guard = setup_tracing(verbosity, args.color.unwrap_or_default())?;
 
+    let printer = Printer::default().with_verbosity(verbosity);
+
     tracing::warn!(
         "ty is pre-release software and not ready for production use. \
             Expect to encounter bugs, missing features, and fatal errors.",
@@ -125,7 +131,8 @@ fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
     }
 
     let project_options_overrides = ProjectOptionsOverrides::new(config_file, options);
-    let (main_loop, main_loop_cancellation_token) = MainLoop::new(project_options_overrides);
+    let (main_loop, main_loop_cancellation_token) =
+        MainLoop::new(project_options_overrides, printer);
 
     // Listen to Ctrl+C and abort the watch mode.
     let main_loop_cancellation_token = Mutex::new(Some(main_loop_cancellation_token));
@@ -143,7 +150,7 @@ fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
         main_loop.run(&mut db)?
     };
 
-    let mut stdout = stdout().lock();
+    let mut stdout = printer.stream_for_requested_summary().lock();
     match std::env::var(EnvVars::TY_MEMORY_REPORT).as_deref() {
         Ok("short") => write!(stdout, "{}", db.salsa_memory_dump().display_short())?,
         Ok("mypy_primer") => write!(stdout, "{}", db.salsa_memory_dump().display_mypy_primer())?,
@@ -192,12 +199,16 @@ struct MainLoop {
     /// The file system watcher, if running in watch mode.
     watcher: Option<ProjectWatcher>,
 
+    /// Interface for displaying information to the user.
+    printer: Printer,
+
     project_options_overrides: ProjectOptionsOverrides,
 }
 
 impl MainLoop {
     fn new(
         project_options_overrides: ProjectOptionsOverrides,
+        printer: Printer,
     ) -> (Self, MainLoopCancellationToken) {
         let (sender, receiver) = crossbeam_channel::bounded(10);
 
@@ -207,6 +218,7 @@ impl MainLoop {
                 receiver,
                 watcher: None,
                 project_options_overrides,
+                printer,
             },
             MainLoopCancellationToken { sender },
         )
@@ -223,32 +235,24 @@ impl MainLoop {
 
         // Do not show progress bars with `--watch`, indicatif does not seem to
         // handle cancelling independent progress bars very well.
-        self.run_with_progress::<DummyReporter>(db)?;
+        // TODO(zanieb): We can probably use `MultiProgress` to handle this case in the future.
+        self.printer = self.printer.with_no_progress();
+        self.run(db)?;
 
         Ok(ExitStatus::Success)
     }
 
     fn run(self, db: &mut ProjectDatabase) -> Result<ExitStatus> {
-        self.run_with_progress::<IndicatifReporter>(db)
-    }
-
-    fn run_with_progress<R>(mut self, db: &mut ProjectDatabase) -> Result<ExitStatus>
-    where
-        R: Reporter + Default + 'static,
-    {
         self.sender.send(MainLoopMessage::CheckWorkspace).unwrap();
 
-        let result = self.main_loop::<R>(db);
+        let result = self.main_loop(db);
 
         tracing::debug!("Exiting main loop");
 
         result
     }
 
-    fn main_loop<R>(&mut self, db: &mut ProjectDatabase) -> Result<ExitStatus>
-    where
-        R: Reporter + Default + 'static,
-    {
+    fn main_loop(mut self, db: &mut ProjectDatabase) -> Result<ExitStatus> {
         // Schedule the first check.
         tracing::debug!("Starting main loop");
 
@@ -264,7 +268,7 @@ impl MainLoop {
                     // to prevent blocking the main loop here.
                     rayon::spawn(move || {
                         match salsa::Cancelled::catch(|| {
-                            let mut reporter = R::default();
+                            let mut reporter = IndicatifReporter::from(self.printer);
                             db.check_with_reporter(&mut reporter)
                         }) {
                             Ok(result) => {
@@ -299,10 +303,12 @@ impl MainLoop {
                             return Ok(ExitStatus::Success);
                         }
 
-                        let mut stdout = stdout().lock();
-
                         if result.is_empty() {
-                            writeln!(stdout, "{}", "All checks passed!".green().bold())?;
+                            writeln!(
+                                self.printer.stream_for_success_summary(),
+                                "{}",
+                                "All checks passed!".green().bold()
+                            )?;
 
                             if self.watcher.is_none() {
                                 return Ok(ExitStatus::Success);
@@ -311,14 +317,19 @@ impl MainLoop {
                             let mut max_severity = Severity::Info;
                             let diagnostics_count = result.len();
 
+                            let mut stdout = self.printer.stream_for_details().lock();
                             for diagnostic in result {
-                                write!(stdout, "{}", diagnostic.display(db, &display_config))?;
+                                // Only render diagnostics if they're going to be displayed, since doing
+                                // so is expensive.
+                                if stdout.is_enabled() {
+                                    write!(stdout, "{}", diagnostic.display(db, &display_config))?;
+                                }
 
                                 max_severity = max_severity.max(diagnostic.severity());
                             }
 
                             writeln!(
-                                stdout,
+                                self.printer.stream_for_failure_summary(),
                                 "Found {} diagnostic{}",
                                 diagnostics_count,
                                 if diagnostics_count > 1 { "s" } else { "" }
@@ -378,27 +389,53 @@ impl MainLoop {
 }
 
 /// A progress reporter for `ty check`.
-#[derive(Default)]
-struct IndicatifReporter(Option<indicatif::ProgressBar>);
+enum IndicatifReporter {
+    /// A constructed reporter that is not yet ready, contains the target for the progress bar.
+    Pending(indicatif::ProgressDrawTarget),
+    /// A reporter that is ready, containing a progress bar to report to.
+    ///
+    /// Initialization of the bar is deferred to [`ty_project::ProgressReporter::set_files`] so we
+    /// do not initialize the bar too early as it may take a while to collect the number of files to
+    /// process and we don't want to display an empty "0/0" bar.
+    Initialized(indicatif::ProgressBar),
+}
 
-impl ty_project::Reporter for IndicatifReporter {
+impl From<Printer> for IndicatifReporter {
+    fn from(printer: Printer) -> Self {
+        Self::Pending(printer.progress_target())
+    }
+}
+
+impl ty_project::ProgressReporter for IndicatifReporter {
     fn set_files(&mut self, files: usize) {
-        let progress = indicatif::ProgressBar::new(files as u64);
-        progress.set_style(
+        let target = match std::mem::replace(
+            self,
+            IndicatifReporter::Pending(indicatif::ProgressDrawTarget::hidden()),
+        ) {
+            Self::Pending(target) => target,
+            Self::Initialized(_) => panic!("The progress reporter should only be initialized once"),
+        };
+
+        let bar = indicatif::ProgressBar::with_draw_target(Some(files as u64), target);
+        bar.set_style(
             indicatif::ProgressStyle::with_template(
                 "{msg:8.dim} {bar:60.green/dim} {pos}/{len} files",
             )
             .unwrap()
             .progress_chars("--"),
         );
-        progress.set_message("Checking");
-
-        self.0 = Some(progress);
+        bar.set_message("Checking");
+        *self = Self::Initialized(bar);
     }
 
     fn report_file(&self, _file: &ruff_db::files::File) {
-        if let Some(ref progress_bar) = self.0 {
-            progress_bar.inc(1);
+        match self {
+            IndicatifReporter::Initialized(progress_bar) => {
+                progress_bar.inc(1);
+            }
+            IndicatifReporter::Pending(_) => {
+                panic!("`report_file` called before `set_files`")
+            }
         }
     }
 }

crates/ty/src/logging.rs

@@ -24,15 +24,32 @@ pub(crate) struct Verbosity {
         help = "Use verbose output (or `-vv` and `-vvv` for more verbose output)",
         action = clap::ArgAction::Count,
         global = true,
+        overrides_with = "quiet",
     )]
     verbose: u8,
+
+    #[arg(
+        long,
+        help = "Use quiet output",
+        action = clap::ArgAction::Count,
+        global = true,
+        overrides_with = "verbose",
+    )]
+    quiet: u8,
 }
 
 impl Verbosity {
-    /// Returns the verbosity level based on the number of `-v` flags.
+    /// Returns the verbosity level based on the number of `-v` and `-q` flags.
     ///
     /// Returns `None` if the user did not specify any verbosity flags.
     pub(crate) fn level(&self) -> VerbosityLevel {
+        // `--quiet` and `--verbose` are mutually exclusive in Clap, so we can just check one first.
+        match self.quiet {
+            0 => {}
+            _ => return VerbosityLevel::Quiet,
+            // TODO(zanieb): Add support for `-qq` with a "silent" mode
+        }
+
         match self.verbose {
             0 => VerbosityLevel::Default,
             1 => VerbosityLevel::Verbose,
@@ -42,9 +59,14 @@ impl Verbosity {
     }
 }
 
-#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Default)]
 pub(crate) enum VerbosityLevel {
+    /// Quiet output.  Only shows Ruff and ty events up to the [`ERROR`](tracing::Level::ERROR).
+    /// Silences output except for summary information.
+    Quiet,
+
     /// Default output level. Only shows Ruff and ty events up to the [`WARN`](tracing::Level::WARN).
+    #[default]
     Default,
 
     /// Enables verbose output. Emits Ruff and ty events up to the [`INFO`](tracing::Level::INFO).
@@ -62,6 +84,7 @@ pub(crate) enum VerbosityLevel {
 impl VerbosityLevel {
     const fn level_filter(self) -> LevelFilter {
         match self {
+            VerbosityLevel::Quiet => LevelFilter::ERROR,
             VerbosityLevel::Default => LevelFilter::WARN,
             VerbosityLevel::Verbose => LevelFilter::INFO,
             VerbosityLevel::ExtraVerbose => LevelFilter::DEBUG,

crates/ty/src/printer.rs

@@ -0,0 +1,172 @@
+use std::io::StdoutLock;
+
+use indicatif::ProgressDrawTarget;
+
+use crate::logging::VerbosityLevel;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub(crate) struct Printer {
+    verbosity: VerbosityLevel,
+    no_progress: bool,
+}
+
+impl Printer {
+    #[must_use]
+    pub(crate) fn with_no_progress(self) -> Self {
+        Self {
+            verbosity: self.verbosity,
+            no_progress: true,
+        }
+    }
+
+    #[must_use]
+    pub(crate) fn with_verbosity(self, verbosity: VerbosityLevel) -> Self {
+        Self {
+            verbosity,
+            no_progress: self.no_progress,
+        }
+    }
+
+    /// Return the [`ProgressDrawTarget`] for this printer.
+    pub(crate) fn progress_target(self) -> ProgressDrawTarget {
+        if self.no_progress {
+            return ProgressDrawTarget::hidden();
+        }
+
+        match self.verbosity {
+            VerbosityLevel::Quiet => ProgressDrawTarget::hidden(),
+            VerbosityLevel::Default => ProgressDrawTarget::stderr(),
+            // Hide the progress bar when in verbose mode.
+            // Otherwise, it gets interleaved with log messages.
+            VerbosityLevel::Verbose => ProgressDrawTarget::hidden(),
+            VerbosityLevel::ExtraVerbose => ProgressDrawTarget::hidden(),
+            VerbosityLevel::Trace => ProgressDrawTarget::hidden(),
+        }
+    }
+
+    /// Return the [`Stdout`] stream for important messages.
+    ///
+    /// Unlike [`Self::stdout_general`], the returned stream will be enabled when
+    /// [`VerbosityLevel::Quiet`] is used.
+    fn stdout_important(self) -> Stdout {
+        match self.verbosity {
+            VerbosityLevel::Quiet => Stdout::enabled(),
+            VerbosityLevel::Default => Stdout::enabled(),
+            VerbosityLevel::Verbose => Stdout::enabled(),
+            VerbosityLevel::ExtraVerbose => Stdout::enabled(),
+            VerbosityLevel::Trace => Stdout::enabled(),
+        }
+    }
+
+    /// Return the [`Stdout`] stream for general messages.
+    ///
+    /// The returned stream will be disabled when [`VerbosityLevel::Quiet`] is used.
+    fn stdout_general(self) -> Stdout {
+        match self.verbosity {
+            VerbosityLevel::Quiet => Stdout::disabled(),
+            VerbosityLevel::Default => Stdout::enabled(),
+            VerbosityLevel::Verbose => Stdout::enabled(),
+            VerbosityLevel::ExtraVerbose => Stdout::enabled(),
+            VerbosityLevel::Trace => Stdout::enabled(),
+        }
+    }
+
+    /// Return the [`Stdout`] stream for a summary message that was explicitly requested by the
+    /// user.
+    ///
+    /// For example, in `ty version` the user has requested the version information and we should
+    /// display it even if [`VerbosityLevel::Quiet`] is used. Or, in `ty check`, if the
+    /// `TY_MEMORY_REPORT` variable has been set, we should display the memory report because the
+    /// user has opted-in to display.
+    pub(crate) fn stream_for_requested_summary(self) -> Stdout {
+        self.stdout_important()
+    }
+
+    /// Return the [`Stdout`] stream for a summary message on failure.
+    ///
+    /// For example, in `ty check`, this would be used for the message indicating the number of
+    /// diagnostics found. The failure summary should capture information that is not reflected in
+    /// the exit code.
+    pub(crate) fn stream_for_failure_summary(self) -> Stdout {
+        self.stdout_important()
+    }
+
+    /// Return the [`Stdout`] stream for a summary message on success.
+    ///
+    /// For example, in `ty check`, this would be used for the message indicating that no diagnostic
+    /// were found. The success summary does not capture important information for users that have
+    /// opted-in to [`VerbosityLevel::Quiet`].
+    pub(crate) fn stream_for_success_summary(self) -> Stdout {
+        self.stdout_general()
+    }
+
+    /// Return the [`Stdout`] stream for detailed messages.
+    ///
+    /// For example, in `ty check`, this would be used for the diagnostic output.
+    pub(crate) fn stream_for_details(self) -> Stdout {
+        self.stdout_general()
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum StreamStatus {
+    Enabled,
+    Disabled,
+}
+
+#[derive(Debug)]
+pub(crate) struct Stdout {
+    status: StreamStatus,
+    lock: Option<StdoutLock<'static>>,
+}
+
+impl Stdout {
+    fn enabled() -> Self {
+        Self {
+            status: StreamStatus::Enabled,
+            lock: None,
+        }
+    }
+
+    fn disabled() -> Self {
+        Self {
+            status: StreamStatus::Disabled,
+            lock: None,
+        }
+    }
+
+    pub(crate) fn lock(mut self) -> Self {
+        match self.status {
+            StreamStatus::Enabled => {
+                // Drop the previous lock first, to avoid deadlocking
+                self.lock.take();
+                self.lock = Some(std::io::stdout().lock());
+            }
+            StreamStatus::Disabled => self.lock = None,
+        }
+        self
+    }
+
+    fn handle(&mut self) -> Box<dyn std::io::Write + '_> {
+        match self.lock.as_mut() {
+            Some(lock) => Box::new(lock),
+            None => Box::new(std::io::stdout()),
+        }
+    }
+
+    pub(crate) fn is_enabled(&self) -> bool {
+        matches!(self.status, StreamStatus::Enabled)
+    }
+}
+
+impl std::fmt::Write for Stdout {
+    fn write_str(&mut self, s: &str) -> std::fmt::Result {
+        match self.status {
+            StreamStatus::Enabled => {
+                let _ = write!(self.handle(), "{s}");
+                Ok(())
+            }
+            StreamStatus::Disabled => Ok(()),
+        }
+    }
+}

crates/ty/tests/cli/main.rs

@@ -14,6 +14,64 @@ use std::{
 };
 use tempfile::TempDir;
 
+#[test]
+fn test_quiet_output() -> anyhow::Result<()> {
+    let case = CliTest::with_file("test.py", "x: int = 1")?;
+
+    // By default, we emit an "all checks passed" message
+    assert_cmd_snapshot!(case.command(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    All checks passed!
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // With `quiet`, the message is not displayed
+    assert_cmd_snapshot!(case.command().arg("--quiet"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    ");
+
+    let case = CliTest::with_file("test.py", "x: int = 'foo'")?;
+
+    // By default, we emit a diagnostic
+    assert_cmd_snapshot!(case.command(), @r#"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[invalid-assignment]: Object of type `Literal["foo"]` is not assignable to `int`
+     --> test.py:1:1
+      |
+    1 | x: int = 'foo'
+      | ^
+      |
+    info: rule `invalid-assignment` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    "#);
+
+    // With `quiet`, the diagnostic is not displayed, just the summary message
+    assert_cmd_snapshot!(case.command().arg("--quiet"), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    Found 1 diagnostic
+
+    ----- stderr -----
+    ");
+
+    Ok(())
+}
+
 #[test]
 fn test_run_in_sub_directory() -> anyhow::Result<()> {
     let case = CliTest::with_files([("test.py", "~"), ("subdir/nothing", "")])?;

crates/ty_ide/Cargo.toml

@@ -15,9 +15,12 @@ bitflags = { workspace = true }
 ruff_db = { workspace = true }
 ruff_python_ast = { workspace = true }
 ruff_python_parser = { workspace = true }
+ruff_python_trivia = { workspace = true }
+ruff_source_file = { workspace = true }
 ruff_text_size = { workspace = true }
 ty_python_semantic = { workspace = true }
 
+regex = { workspace = true }
 rustc-hash = { workspace = true }
 salsa = { workspace = true }
 smallvec = { workspace = true }

crates/ty_ide/src/docstring.rs

@@ -0,0 +1,664 @@
+//! Docstring parsing utilities for language server features.
+//!
+//! This module provides functionality for extracting structured information from
+//! Python docstrings, including parameter documentation for signature help.
+//! Supports Google-style, NumPy-style, and reST/Sphinx-style docstrings.
+//! There are no formal specifications for any of these formats, so the parsing
+//! logic needs to be tolerant of variations.
+
+use regex::Regex;
+use ruff_python_trivia::leading_indentation;
+use ruff_source_file::UniversalNewlines;
+use std::collections::HashMap;
+use std::sync::LazyLock;
+
+// Static regex instances to avoid recompilation
+static GOOGLE_SECTION_REGEX: LazyLock<Regex> = LazyLock::new(|| {
+    Regex::new(r"(?i)^\s*(Args|Arguments|Parameters)\s*:\s*$")
+        .expect("Google section regex should be valid")
+});
+
+static GOOGLE_PARAM_REGEX: LazyLock<Regex> = LazyLock::new(|| {
+    Regex::new(r"^\s*(\*?\*?\w+)\s*(\(.*?\))?\s*:\s*(.+)")
+        .expect("Google parameter regex should be valid")
+});
+
+static NUMPY_SECTION_REGEX: LazyLock<Regex> = LazyLock::new(|| {
+    Regex::new(r"(?i)^\s*Parameters\s*$").expect("NumPy section regex should be valid")
+});
+
+static NUMPY_UNDERLINE_REGEX: LazyLock<Regex> =
+    LazyLock::new(|| Regex::new(r"^\s*-+\s*$").expect("NumPy underline regex should be valid"));
+
+static REST_PARAM_REGEX: LazyLock<Regex> = LazyLock::new(|| {
+    Regex::new(r"^\s*:param\s+(?:(\w+)\s+)?(\w+)\s*:\s*(.+)")
+        .expect("reST parameter regex should be valid")
+});
+
+/// Extract parameter documentation from popular docstring formats.
+/// Returns a map of parameter names to their documentation.
+pub fn get_parameter_documentation(docstring: &str) -> HashMap<String, String> {
+    let mut param_docs = HashMap::new();
+
+    // Google-style docstrings
+    param_docs.extend(extract_google_style_params(docstring));
+
+    // NumPy-style docstrings
+    param_docs.extend(extract_numpy_style_params(docstring));
+
+    // reST/Sphinx-style docstrings
+    param_docs.extend(extract_rest_style_params(docstring));
+
+    param_docs
+}
+
+/// Extract parameter documentation from Google-style docstrings.
+fn extract_google_style_params(docstring: &str) -> HashMap<String, String> {
+    let mut param_docs = HashMap::new();
+
+    let mut in_args_section = false;
+    let mut current_param: Option<String> = None;
+    let mut current_doc = String::new();
+
+    for line_obj in docstring.universal_newlines() {
+        let line = line_obj.as_str();
+        if GOOGLE_SECTION_REGEX.is_match(line) {
+            in_args_section = true;
+            continue;
+        }
+
+        if in_args_section {
+            // Check if we hit another section (starts with a word followed by colon at line start)
+            if !line.starts_with(' ') && !line.starts_with('\t') && line.contains(':') {
+                if let Some(colon_pos) = line.find(':') {
+                    let section_name = line[..colon_pos].trim();
+                    // If this looks like another section, stop processing args
+                    if !section_name.is_empty()
+                        && section_name
+                            .chars()
+                            .all(|c| c.is_alphabetic() || c.is_whitespace())
+                    {
+                        // Check if this is a known section name
+                        let known_sections = [
+                            "Returns", "Return", "Raises", "Yields", "Yield", "Examples",
+                            "Example", "Note", "Notes", "Warning", "Warnings",
+                        ];
+                        if known_sections.contains(&section_name) {
+                            if let Some(param_name) = current_param.take() {
+                                param_docs.insert(param_name, current_doc.trim().to_string());
+                                current_doc.clear();
+                            }
+                            in_args_section = false;
+                            continue;
+                        }
+                    }
+                }
+            }
+
+            if let Some(captures) = GOOGLE_PARAM_REGEX.captures(line) {
+                // Save previous parameter if exists
+                if let Some(param_name) = current_param.take() {
+                    param_docs.insert(param_name, current_doc.trim().to_string());
+                    current_doc.clear();
+                }
+
+                // Start new parameter
+                if let (Some(param), Some(desc)) = (captures.get(1), captures.get(3)) {
+                    current_param = Some(param.as_str().to_string());
+                    current_doc = desc.as_str().to_string();
+                }
+            } else if line.starts_with(' ') || line.starts_with('\t') {
+                // This is a continuation of the current parameter documentation
+                if current_param.is_some() {
+                    if !current_doc.is_empty() {
+                        current_doc.push('\n');
+                    }
+                    current_doc.push_str(line.trim());
+                }
+            } else {
+                // This is a line that doesn't start with whitespace and isn't a parameter
+                // It might be a section or other content, so stop processing args
+                if let Some(param_name) = current_param.take() {
+                    param_docs.insert(param_name, current_doc.trim().to_string());
+                    current_doc.clear();
+                }
+                in_args_section = false;
+            }
+        }
+    }
+
+    // Don't forget the last parameter
+    if let Some(param_name) = current_param {
+        param_docs.insert(param_name, current_doc.trim().to_string());
+    }
+
+    param_docs
+}
+
+/// Calculate the indentation level of a line (number of leading whitespace characters)
+fn get_indentation_level(line: &str) -> usize {
+    leading_indentation(line).len()
+}
+
+/// Extract parameter documentation from NumPy-style docstrings.
+fn extract_numpy_style_params(docstring: &str) -> HashMap<String, String> {
+    let mut param_docs = HashMap::new();
+
+    let mut lines = docstring
+        .universal_newlines()
+        .map(|line| line.as_str())
+        .peekable();
+    let mut in_params_section = false;
+    let mut found_underline = false;
+    let mut current_param: Option<String> = None;
+    let mut current_doc = String::new();
+    let mut base_param_indent: Option<usize> = None;
+    let mut base_content_indent: Option<usize> = None;
+
+    while let Some(line) = lines.next() {
+        if NUMPY_SECTION_REGEX.is_match(line) {
+            // Check if the next line is an underline
+            if let Some(next_line) = lines.peek() {
+                if NUMPY_UNDERLINE_REGEX.is_match(next_line) {
+                    in_params_section = true;
+                    found_underline = false;
+                    base_param_indent = None;
+                    base_content_indent = None;
+                    continue;
+                }
+            }
+        }
+
+        if in_params_section && !found_underline {
+            if NUMPY_UNDERLINE_REGEX.is_match(line) {
+                found_underline = true;
+                continue;
+            }
+        }
+
+        if in_params_section && found_underline {
+            let current_indent = get_indentation_level(line);
+            let trimmed = line.trim();
+
+            // Skip empty lines
+            if trimmed.is_empty() {
+                continue;
+            }
+
+            // Check if we hit another section
+            if current_indent == 0 {
+                if let Some(next_line) = lines.peek() {
+                    if NUMPY_UNDERLINE_REGEX.is_match(next_line) {
+                        // This is another section
+                        if let Some(param_name) = current_param.take() {
+                            param_docs.insert(param_name, current_doc.trim().to_string());
+                            current_doc.clear();
+                        }
+                        in_params_section = false;
+                        continue;
+                    }
+                }
+            }
+
+            // Determine if this could be a parameter line
+            let could_be_param = if let Some(base_indent) = base_param_indent {
+                // We've seen parameters before - check if this matches the expected parameter indentation
+                current_indent == base_indent
+            } else {
+                // First potential parameter - check if it has reasonable indentation and content
+                current_indent > 0
+                    && (trimmed.contains(':')
+                        || trimmed.chars().all(|c| c.is_alphanumeric() || c == '_'))
+            };
+
+            if could_be_param {
+                // Check if this could be a section header by looking at the next line
+                if let Some(next_line) = lines.peek() {
+                    if NUMPY_UNDERLINE_REGEX.is_match(next_line) {
+                        // This is a section header, not a parameter
+                        if let Some(param_name) = current_param.take() {
+                            param_docs.insert(param_name, current_doc.trim().to_string());
+                            current_doc.clear();
+                        }
+                        in_params_section = false;
+                        continue;
+                    }
+                }
+
+                // Set base indentation levels on first parameter
+                if base_param_indent.is_none() {
+                    base_param_indent = Some(current_indent);
+                }
+
+                // Handle parameter with type annotation (param : type)
+                if trimmed.contains(':') {
+                    // Save previous parameter if exists
+                    if let Some(param_name) = current_param.take() {
+                        param_docs.insert(param_name, current_doc.trim().to_string());
+                        current_doc.clear();
+                    }
+
+                    // Extract parameter name and description
+                    let parts: Vec<&str> = trimmed.splitn(2, ':').collect();
+                    if parts.len() == 2 {
+                        let param_name = parts[0].trim();
+
+                        // Extract just the parameter name (before any type info)
+                        let param_name = param_name.split_whitespace().next().unwrap_or(param_name);
+                        current_param = Some(param_name.to_string());
+                        current_doc.clear(); // Description comes on following lines, not on this line
+                    }
+                } else {
+                    // Handle parameter without type annotation
+                    // Save previous parameter if exists
+                    if let Some(param_name) = current_param.take() {
+                        param_docs.insert(param_name, current_doc.trim().to_string());
+                        current_doc.clear();
+                    }
+
+                    // This line is the parameter name
+                    current_param = Some(trimmed.to_string());
+                    current_doc.clear();
+                }
+            } else if current_param.is_some() {
+                // Determine if this is content for the current parameter
+                let is_content = if let Some(base_content) = base_content_indent {
+                    // We've seen content before - check if this matches expected content indentation
+                    current_indent >= base_content
+                } else {
+                    // First potential content line - should be more indented than parameter
+                    if let Some(base_param) = base_param_indent {
+                        current_indent > base_param
+                    } else {
+                        // Fallback: any indented content
+                        current_indent > 0
+                    }
+                };
+
+                if is_content {
+                    // Set base content indentation on first content line
+                    if base_content_indent.is_none() {
+                        base_content_indent = Some(current_indent);
+                    }
+
+                    // This is a continuation of the current parameter documentation
+                    if !current_doc.is_empty() {
+                        current_doc.push('\n');
+                    }
+                    current_doc.push_str(trimmed);
+                } else {
+                    // This line doesn't match our expected indentation patterns
+                    // Save current parameter and stop processing
+                    if let Some(param_name) = current_param.take() {
+                        param_docs.insert(param_name, current_doc.trim().to_string());
+                        current_doc.clear();
+                    }
+                    in_params_section = false;
+                }
+            }
+        }
+    }
+
+    // Don't forget the last parameter
+    if let Some(param_name) = current_param {
+        param_docs.insert(param_name, current_doc.trim().to_string());
+    }
+
+    param_docs
+}
+
+/// Extract parameter documentation from reST/Sphinx-style docstrings.
+fn extract_rest_style_params(docstring: &str) -> HashMap<String, String> {
+    let mut param_docs = HashMap::new();
+
+    let mut current_param: Option<String> = None;
+    let mut current_doc = String::new();
+
+    for line_obj in docstring.universal_newlines() {
+        let line = line_obj.as_str();
+        if let Some(captures) = REST_PARAM_REGEX.captures(line) {
+            // Save previous parameter if exists
+            if let Some(param_name) = current_param.take() {
+                param_docs.insert(param_name, current_doc.trim().to_string());
+                current_doc.clear();
+            }
+
+            // Extract parameter name and description
+            if let (Some(param_match), Some(desc_match)) = (captures.get(2), captures.get(3)) {
+                current_param = Some(param_match.as_str().to_string());
+                current_doc = desc_match.as_str().to_string();
+            }
+        } else if current_param.is_some() {
+            let trimmed = line.trim();
+
+            // Check if this is a new section - stop processing if we hit section headers
+            if trimmed == "Parameters" || trimmed == "Args" || trimmed == "Arguments" {
+                // Save current param and stop processing
+                if let Some(param_name) = current_param.take() {
+                    param_docs.insert(param_name, current_doc.trim().to_string());
+                    current_doc.clear();
+                }
+                break;
+            }
+
+            // Check if this is another directive line starting with ':'
+            if trimmed.starts_with(':') {
+                // This is a new directive, save current param
+                if let Some(param_name) = current_param.take() {
+                    param_docs.insert(param_name, current_doc.trim().to_string());
+                    current_doc.clear();
+                }
+                // Let the next iteration handle this directive
+                continue;
+            }
+
+            // Check if this is a continuation line (indented)
+            if line.starts_with("    ") && !trimmed.is_empty() {
+                // This is a continuation line
+                if !current_doc.is_empty() {
+                    current_doc.push('\n');
+                }
+                current_doc.push_str(trimmed);
+            } else if !trimmed.is_empty() && !line.starts_with(' ') && !line.starts_with('\t') {
+                // This is a non-indented line - likely end of the current parameter
+                if let Some(param_name) = current_param.take() {
+                    param_docs.insert(param_name, current_doc.trim().to_string());
+                    current_doc.clear();
+                }
+                break;
+            }
+        }
+    }
+
+    // Don't forget the last parameter
+    if let Some(param_name) = current_param {
+        param_docs.insert(param_name, current_doc.trim().to_string());
+    }
+
+    param_docs
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_google_style_parameter_documentation() {
+        let docstring = r#"
+        This is a function description.
+
+        Args:
+            param1 (str): The first parameter description
+            param2 (int): The second parameter description
+                This is a continuation of param2 description.
+            param3: A parameter without type annotation
+
+        Returns:
+            str: The return value description
+        "#;
+
+        let param_docs = get_parameter_documentation(docstring);
+
+        assert_eq!(param_docs.len(), 3);
+        assert_eq!(&param_docs["param1"], "The first parameter description");
+        assert_eq!(
+            &param_docs["param2"],
+            "The second parameter description\nThis is a continuation of param2 description."
+        );
+        assert_eq!(&param_docs["param3"], "A parameter without type annotation");
+    }
+
+    #[test]
+    fn test_numpy_style_parameter_documentation() {
+        let docstring = r#"
+        This is a function description.
+
+        Parameters
+        ----------
+        param1 : str
+            The first parameter description
+        param2 : int
+            The second parameter description
+            This is a continuation of param2 description.
+        param3
+            A parameter without type annotation
+
+        Returns
+        -------
+        str
+            The return value description
+        "#;
+
+        let param_docs = get_parameter_documentation(docstring);
+
+        assert_eq!(param_docs.len(), 3);
+        assert_eq!(
+            param_docs.get("param1").expect("param1 should exist"),
+            "The first parameter description"
+        );
+        assert_eq!(
+            param_docs.get("param2").expect("param2 should exist"),
+            "The second parameter description\nThis is a continuation of param2 description."
+        );
+        assert_eq!(
+            param_docs.get("param3").expect("param3 should exist"),
+            "A parameter without type annotation"
+        );
+    }
+
+    #[test]
+    fn test_no_parameter_documentation() {
+        let docstring = r#"
+        This is a simple function description without parameter documentation.
+        "#;
+
+        let param_docs = get_parameter_documentation(docstring);
+        assert!(param_docs.is_empty());
+    }
+
+    #[test]
+    fn test_mixed_style_parameter_documentation() {
+        let docstring = r#"
+        This is a function description.
+
+        Args:
+            param1 (str): Google-style parameter
+            param2 (int): Another Google-style parameter
+
+        Parameters
+        ----------
+        param3 : bool
+            NumPy-style parameter
+        "#;
+
+        let param_docs = get_parameter_documentation(docstring);
+
+        assert_eq!(param_docs.len(), 3);
+        assert_eq!(
+            param_docs.get("param1").expect("param1 should exist"),
+            "Google-style parameter"
+        );
+        assert_eq!(
+            param_docs.get("param2").expect("param2 should exist"),
+            "Another Google-style parameter"
+        );
+        assert_eq!(
+            param_docs.get("param3").expect("param3 should exist"),
+            "NumPy-style parameter"
+        );
+    }
+
+    #[test]
+    fn test_rest_style_parameter_documentation() {
+        let docstring = r#"
+        This is a function description.
+
+        :param str param1: The first parameter description
+        :param int param2: The second parameter description
+            This is a continuation of param2 description.
+        :param param3: A parameter without type annotation
+        :returns: The return value description
+        :rtype: str
+        "#;
+
+        let param_docs = get_parameter_documentation(docstring);
+
+        assert_eq!(param_docs.len(), 3);
+        assert_eq!(
+            param_docs.get("param1").expect("param1 should exist"),
+            "The first parameter description"
+        );
+        assert_eq!(
+            param_docs.get("param2").expect("param2 should exist"),
+            "The second parameter description\nThis is a continuation of param2 description."
+        );
+        assert_eq!(
+            param_docs.get("param3").expect("param3 should exist"),
+            "A parameter without type annotation"
+        );
+    }
+
+    #[test]
+    fn test_mixed_style_with_rest_parameter_documentation() {
+        let docstring = r#"
+        This is a function description.
+
+        Args:
+            param1 (str): Google-style parameter
+
+        :param int param2: reST-style parameter
+        :param param3: Another reST-style parameter
+
+        Parameters
+        ----------
+        param4 : bool
+            NumPy-style parameter
+        "#;
+
+        let param_docs = get_parameter_documentation(docstring);
+
+        assert_eq!(param_docs.len(), 4);
+        assert_eq!(
+            param_docs.get("param1").expect("param1 should exist"),
+            "Google-style parameter"
+        );
+        assert_eq!(
+            param_docs.get("param2").expect("param2 should exist"),
+            "reST-style parameter"
+        );
+        assert_eq!(
+            param_docs.get("param3").expect("param3 should exist"),
+            "Another reST-style parameter"
+        );
+        assert_eq!(
+            param_docs.get("param4").expect("param4 should exist"),
+            "NumPy-style parameter"
+        );
+    }
+
+    #[test]
+    fn test_numpy_style_with_different_indentation() {
+        let docstring = r#"
+        This is a function description.
+
+        Parameters
+        ----------
+        param1 : str
+            The first parameter description
+        param2 : int
+            The second parameter description
+            This is a continuation of param2 description.
+        param3
+            A parameter without type annotation
+
+        Returns
+        -------
+        str
+            The return value description
+        "#;
+
+        let param_docs = get_parameter_documentation(docstring);
+
+        assert_eq!(param_docs.len(), 3);
+        assert_eq!(
+            param_docs.get("param1").expect("param1 should exist"),
+            "The first parameter description"
+        );
+        assert_eq!(
+            param_docs.get("param2").expect("param2 should exist"),
+            "The second parameter description\nThis is a continuation of param2 description."
+        );
+        assert_eq!(
+            param_docs.get("param3").expect("param3 should exist"),
+            "A parameter without type annotation"
+        );
+    }
+
+    #[test]
+    fn test_numpy_style_with_tabs_and_mixed_indentation() {
+        // Using raw strings to avoid tab/space conversion issues in the test
+        let docstring = "
+        This is a function description.
+
+        Parameters
+        ----------
+\tparam1 : str
+\t\tThe first parameter description
+\tparam2 : int
+\t\tThe second parameter description
+\t\tThis is a continuation of param2 description.
+\tparam3
+\t\tA parameter without type annotation
+        ";
+
+        let param_docs = get_parameter_documentation(docstring);
+
+        assert_eq!(param_docs.len(), 3);
+        assert_eq!(
+            param_docs.get("param1").expect("param1 should exist"),
+            "The first parameter description"
+        );
+        assert_eq!(
+            param_docs.get("param2").expect("param2 should exist"),
+            "The second parameter description\nThis is a continuation of param2 description."
+        );
+        assert_eq!(
+            param_docs.get("param3").expect("param3 should exist"),
+            "A parameter without type annotation"
+        );
+    }
+
+    #[test]
+    fn test_universal_newlines() {
+        // Test with Windows-style line endings (\r\n)
+        let docstring_windows = "This is a function description.\r\n\r\nArgs:\r\n    param1 (str): The first parameter\r\n    param2 (int): The second parameter\r\n";
+
+        // Test with old Mac-style line endings (\r)
+        let docstring_mac = "This is a function description.\r\rArgs:\r    param1 (str): The first parameter\r    param2 (int): The second parameter\r";
+
+        // Test with Unix-style line endings (\n) - should work the same
+        let docstring_unix = "This is a function description.\n\nArgs:\n    param1 (str): The first parameter\n    param2 (int): The second parameter\n";
+
+        let param_docs_windows = get_parameter_documentation(docstring_windows);
+        let param_docs_mac = get_parameter_documentation(docstring_mac);
+        let param_docs_unix = get_parameter_documentation(docstring_unix);
+
+        // All should produce the same results
+        assert_eq!(param_docs_windows.len(), 2);
+        assert_eq!(param_docs_mac.len(), 2);
+        assert_eq!(param_docs_unix.len(), 2);
+
+        assert_eq!(
+            param_docs_windows.get("param1"),
+            Some(&"The first parameter".to_string())
+        );
+        assert_eq!(
+            param_docs_mac.get("param1"),
+            Some(&"The first parameter".to_string())
+        );
+        assert_eq!(
+            param_docs_unix.get("param1"),
+            Some(&"The first parameter".to_string())
+        );
+    }
+}

crates/ty_ide/src/lib.rs

@@ -1,14 +1,17 @@
 mod completion;
 mod db;
+mod docstring;
 mod find_node;
 mod goto;
 mod hover;
 mod inlay_hints;
 mod markup;
 mod semantic_tokens;
+mod signature_help;
 
 pub use completion::completion;
 pub use db::Db;
+pub use docstring::get_parameter_documentation;
 pub use goto::goto_type_definition;
 pub use hover::hover;
 pub use inlay_hints::inlay_hints;
@@ -16,6 +19,7 @@ pub use markup::MarkupKind;
 pub use semantic_tokens::{
     SemanticToken, SemanticTokenModifier, SemanticTokenType, SemanticTokens, semantic_tokens,
 };
+pub use signature_help::{ParameterDetails, SignatureDetails, SignatureHelpInfo, signature_help};
 
 use ruff_db::files::{File, FileRange};
 use ruff_text_size::{Ranged, TextRange};

crates/ty_ide/src/signature_help.rs

@@ -0,0 +1,687 @@
+//! This module handles the "signature help" request in the language server
+//! protocol. This request is typically issued by a client when the user types
+//! an open parenthesis and starts to enter arguments for a function call.
+//! The signature help provides information that the editor displays to the
+//! user about the target function signature including parameter names,
+//! types, and documentation. It supports multiple signatures for union types
+//! and overloads.
+
+use crate::{Db, docstring::get_parameter_documentation, find_node::covering_node};
+use ruff_db::files::File;
+use ruff_db::parsed::parsed_module;
+use ruff_python_ast::{self as ast, AnyNodeRef};
+use ruff_text_size::{Ranged, TextRange, TextSize};
+use ty_python_semantic::semantic_index::definition::Definition;
+use ty_python_semantic::types::{CallSignatureDetails, call_signature_details};
+
+// Limitations of the current implementation:
+
+// TODO - If the target function is declared in a stub file but defined (implemented)
+// in a source file, the documentation will not reflect the a docstring that appears
+// only in the implementation. To do this, we'll need to map the function or
+// method in the stub to the implementation and extract the docstring from there.
+
+/// Information about a function parameter
+#[derive(Debug, Clone)]
+pub struct ParameterDetails {
+    /// The parameter name (e.g., "param1")
+    pub name: String,
+    /// The parameter label in the signature (e.g., "param1: str")
+    pub label: String,
+    /// Documentation specific to the parameter, typically extracted from the
+    /// function's docstring
+    pub documentation: Option<String>,
+}
+
+/// Information about a function signature
+#[derive(Debug, Clone)]
+pub struct SignatureDetails {
+    /// Text representation of the full signature (including input parameters and return type).
+    pub label: String,
+    /// Documentation for the signature, typically from the function's docstring.
+    pub documentation: Option<String>,
+    /// Information about each of the parameters in left-to-right order.
+    pub parameters: Vec<ParameterDetails>,
+    /// Index of the parameter that corresponds to the argument where the
+    /// user's cursor is currently positioned.
+    pub active_parameter: Option<usize>,
+}
+
+/// Signature help information for function calls
+#[derive(Debug, Clone)]
+pub struct SignatureHelpInfo {
+    /// Information about each of the signatures for the function call. We
+    /// need to handle multiple because of unions, overloads, and composite
+    /// calls like constructors (which invoke both __new__ and __init__).
+    pub signatures: Vec<SignatureDetails>,
+    /// Index of the "active signature" which is the first signature where
+    /// all arguments that are currently present in the code map to parameters.
+    pub active_signature: Option<usize>,
+}
+
+/// Signature help information for function calls at the given position
+pub fn signature_help(db: &dyn Db, file: File, offset: TextSize) -> Option<SignatureHelpInfo> {
+    let parsed = parsed_module(db, file).load(db);
+
+    // Get the call expression at the given position.
+    let (call_expr, current_arg_index) = get_call_expr(&parsed, offset)?;
+
+    // Get signature details from the semantic analyzer.
+    let signature_details: Vec<CallSignatureDetails<'_>> =
+        call_signature_details(db, file, call_expr);
+
+    if signature_details.is_empty() {
+        return None;
+    }
+
+    // Find the active signature - the first signature where all arguments map to parameters.
+    let active_signature_index = find_active_signature_from_details(&signature_details);
+
+    // Convert to SignatureDetails objects.
+    let signatures: Vec<SignatureDetails> = signature_details
+        .into_iter()
+        .map(|details| {
+            create_signature_details_from_call_signature_details(db, &details, current_arg_index)
+        })
+        .collect();
+
+    Some(SignatureHelpInfo {
+        signatures,
+        active_signature: active_signature_index,
+    })
+}
+
+/// Returns the innermost call expression that contains the specified offset
+/// and the index of the argument that the offset maps to.
+fn get_call_expr(
+    parsed: &ruff_db::parsed::ParsedModuleRef,
+    offset: TextSize,
+) -> Option<(&ast::ExprCall, usize)> {
+    // Create a range from the offset for the covering_node function.
+    let range = TextRange::new(offset, offset);
+
+    // Find the covering node at the given position that is a function call.
+    let covering_node = covering_node(parsed.syntax().into(), range)
+        .find_first(|node| matches!(node, AnyNodeRef::ExprCall(_)))
+        .ok()?;
+
+    // Get the function call expression.
+    let AnyNodeRef::ExprCall(call_expr) = covering_node.node() else {
+        return None;
+    };
+
+    // Determine which argument corresponding to the current cursor location.
+    let current_arg_index = get_argument_index(call_expr, offset);
+
+    Some((call_expr, current_arg_index))
+}
+
+/// Determine which argument is associated with the specified offset.
+/// Returns zero if not within any argument.
+fn get_argument_index(call_expr: &ast::ExprCall, offset: TextSize) -> usize {
+    let mut current_arg = 0;
+
+    for (i, arg) in call_expr.arguments.arguments_source_order().enumerate() {
+        if offset <= arg.end() {
+            return i;
+        }
+        current_arg = i + 1;
+    }
+
+    current_arg
+}
+
+/// Create signature details from `CallSignatureDetails`.
+fn create_signature_details_from_call_signature_details(
+    db: &dyn crate::Db,
+    details: &CallSignatureDetails,
+    current_arg_index: usize,
+) -> SignatureDetails {
+    let signature_label = details.label.clone();
+
+    let documentation = get_callable_documentation(db, details.definition);
+
+    // Translate the argument index to parameter index using the mapping.
+    let active_parameter =
+        if details.argument_to_parameter_mapping.is_empty() && current_arg_index == 0 {
+            Some(0)
+        } else {
+            details
+                .argument_to_parameter_mapping
+                .get(current_arg_index)
+                .and_then(|&param_index| param_index)
+                .or({
+                    // If we can't find a mapping for this argument, but we have a current
+                    // argument index, use that as the active parameter if it's within bounds.
+                    if current_arg_index < details.parameter_label_offsets.len() {
+                        Some(current_arg_index)
+                    } else {
+                        None
+                    }
+                })
+        };
+
+    SignatureDetails {
+        label: signature_label.clone(),
+        documentation: Some(documentation),
+        parameters: create_parameters_from_offsets(
+            &details.parameter_label_offsets,
+            &signature_label,
+            db,
+            details.definition,
+            &details.parameter_names,
+        ),
+        active_parameter,
+    }
+}
+
+/// Determine appropriate documentation for a callable type based on its original type.
+fn get_callable_documentation(db: &dyn crate::Db, definition: Option<Definition>) -> String {
+    // TODO: If the definition is located within a stub file and no docstring
+    // is present, try to map the symbol to an implementation file and extract
+    // the docstring from that location.
+    if let Some(definition) = definition {
+        definition.docstring(db).unwrap_or_default()
+    } else {
+        String::new()
+    }
+}
+
+/// Create `ParameterDetails` objects from parameter label offsets.
+fn create_parameters_from_offsets(
+    parameter_offsets: &[TextRange],
+    signature_label: &str,
+    db: &dyn crate::Db,
+    definition: Option<Definition>,
+    parameter_names: &[String],
+) -> Vec<ParameterDetails> {
+    // Extract parameter documentation from the function's docstring if available.
+    let param_docs = if let Some(definition) = definition {
+        let docstring = definition.docstring(db);
+        docstring
+            .map(|doc| get_parameter_documentation(&doc))
+            .unwrap_or_default()
+    } else {
+        std::collections::HashMap::new()
+    };
+
+    parameter_offsets
+        .iter()
+        .enumerate()
+        .map(|(i, offset)| {
+            // Extract the parameter label from the signature string.
+            let start = usize::from(offset.start());
+            let end = usize::from(offset.end());
+            let label = signature_label
+                .get(start..end)
+                .unwrap_or("unknown")
+                .to_string();
+
+            // Get the parameter name for documentation lookup.
+            let param_name = parameter_names.get(i).map(String::as_str).unwrap_or("");
+
+            ParameterDetails {
+                name: param_name.to_string(),
+                label,
+                documentation: param_docs.get(param_name).cloned(),
+            }
+        })
+        .collect()
+}
+
+/// Find the active signature index from `CallSignatureDetails`.
+/// The active signature is the first signature where all arguments present in the call
+/// have valid mappings to parameters (i.e., none of the mappings are None).
+fn find_active_signature_from_details(signature_details: &[CallSignatureDetails]) -> Option<usize> {
+    let first = signature_details.first()?;
+
+    // If there are no arguments in the mapping, just return the first signature.
+    if first.argument_to_parameter_mapping.is_empty() {
+        return Some(0);
+    }
+
+    // First, try to find a signature where all arguments have valid parameter mappings.
+    let perfect_match = signature_details.iter().position(|details| {
+        // Check if all arguments have valid parameter mappings (i.e., are not None).
+        details
+            .argument_to_parameter_mapping
+            .iter()
+            .all(Option::is_some)
+    });
+
+    if let Some(index) = perfect_match {
+        return Some(index);
+    }
+
+    // If no perfect match, find the signature with the most valid argument mappings.
+    let (best_index, _) = signature_details
+        .iter()
+        .enumerate()
+        .max_by_key(|(_, details)| {
+            details
+                .argument_to_parameter_mapping
+                .iter()
+                .filter(|mapping| mapping.is_some())
+                .count()
+        })?;
+
+    Some(best_index)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::signature_help::SignatureHelpInfo;
+    use crate::tests::{CursorTest, cursor_test};
+
+    #[test]
+    fn signature_help_basic_function_call() {
+        let test = cursor_test(
+            r#"
+        def example_function(param1: str, param2: int) -> str:
+            """This is a docstring for the example function.
+            
+            Args:
+                param1: The first parameter as a string
+                param2: The second parameter as an integer
+            
+            Returns:
+                A formatted string combining both parameters
+            """
+            return f"{param1}: {param2}"
+
+        result = example_function(<CURSOR>
+        "#,
+        );
+
+        // Test that signature help is provided
+        let result = test.signature_help().expect("Should have signature help");
+        assert_eq!(result.signatures.len(), 1);
+
+        let signature = &result.signatures[0];
+        assert!(signature.label.contains("param1") && signature.label.contains("param2"));
+
+        // Verify that the docstring is extracted and included in the documentation
+        let expected_docstring = concat!(
+            "This is a docstring for the example function.\n",
+            "            \n",
+            "            Args:\n",
+            "                param1: The first parameter as a string\n",
+            "                param2: The second parameter as an integer\n",
+            "            \n",
+            "            Returns:\n",
+            "                A formatted string combining both parameters\n",
+            "            "
+        );
+        assert_eq!(
+            signature.documentation,
+            Some(expected_docstring.to_string())
+        );
+
+        assert_eq!(result.active_signature, Some(0));
+        assert_eq!(signature.active_parameter, Some(0));
+    }
+
+    #[test]
+    fn signature_help_method_call() {
+        let test = cursor_test(
+            r#"
+        class MyClass:
+            def my_method(self, arg1: str, arg2: bool) -> None:
+                pass
+
+        obj = MyClass()
+        obj.my_method(arg2=True, arg1=<CURSOR>
+        "#,
+        );
+
+        // Test that signature help is provided for method calls
+        let result = test.signature_help().expect("Should have signature help");
+        assert_eq!(result.signatures.len(), 1);
+
+        let signature = &result.signatures[0];
+        assert!(signature.label.contains("arg1") && signature.label.contains("arg2"));
+        assert_eq!(result.active_signature, Some(0));
+
+        // Check the active parameter from the active signature
+        if let Some(active_sig_index) = result.active_signature {
+            let active_signature = &result.signatures[active_sig_index];
+            assert_eq!(active_signature.active_parameter, Some(0));
+        }
+    }
+
+    #[test]
+    fn signature_help_nested_function_calls() {
+        let test = cursor_test(
+            r#"
+        def outer(a: int) -> int:
+            return a * 2
+
+        def inner(b: str) -> str:
+            return b.upper()
+
+        result = outer(inner(<CURSOR>
+        "#,
+        );
+
+        // Test that signature help focuses on the innermost function call
+        let result = test.signature_help().expect("Should have signature help");
+        assert_eq!(result.signatures.len(), 1);
+
+        let signature = &result.signatures[0];
+        assert!(signature.label.contains("str") || signature.label.contains("->"));
+        assert_eq!(result.active_signature, Some(0));
+        assert_eq!(signature.active_parameter, Some(0));
+    }
+
+    #[test]
+    fn signature_help_union_callable() {
+        let test = cursor_test(
+            r#"
+        import random
+        def func_a(x: int) -> int:
+            return x
+
+        def func_b(y: str) -> str:
+            return y
+
+        if random.random() > 0.5:
+            f = func_a
+        else:
+            f = func_b
+        
+        f(<CURSOR>
+        "#,
+        );
+
+        let result = test.signature_help().expect("Should have signature help");
+
+        assert_eq!(result.signatures.len(), 2);
+
+        let signature = &result.signatures[0];
+        assert_eq!(signature.label, "(x: int) -> int");
+        assert_eq!(signature.parameters.len(), 1);
+
+        // Check parameter information
+        let param = &signature.parameters[0];
+        assert_eq!(param.label, "x: int");
+        assert_eq!(param.name, "x");
+
+        // Validate the second signature (from func_b)
+        let signature_b = &result.signatures[1];
+        assert_eq!(signature_b.label, "(y: str) -> str");
+        assert_eq!(signature_b.parameters.len(), 1);
+
+        // Check parameter information for the second signature
+        let param_b = &signature_b.parameters[0];
+        assert_eq!(param_b.label, "y: str");
+        assert_eq!(param_b.name, "y");
+
+        assert_eq!(result.active_signature, Some(0));
+
+        // Check the active parameter from the active signature
+        if let Some(active_sig_index) = result.active_signature {
+            let active_signature = &result.signatures[active_sig_index];
+            assert_eq!(active_signature.active_parameter, Some(0));
+        }
+    }
+
+    #[test]
+    fn signature_help_overloaded_function() {
+        let test = cursor_test(
+            r#"
+        from typing import overload
+
+        @overload
+        def process(value: int) -> str: ...
+        
+        @overload
+        def process(value: str) -> int: ...
+        
+        def process(value):
+            if isinstance(value, int):
+                return str(value)
+            else:
+                return len(value)
+
+        result = process(<CURSOR>
+        "#,
+        );
+
+        // Test that signature help is provided for overloaded functions
+        let result = test.signature_help().expect("Should have signature help");
+
+        // We should have signatures for the overloads
+        assert_eq!(result.signatures.len(), 2);
+        assert_eq!(result.active_signature, Some(0));
+
+        // Check the active parameter from the active signature
+        if let Some(active_sig_index) = result.active_signature {
+            let active_signature = &result.signatures[active_sig_index];
+            assert_eq!(active_signature.active_parameter, Some(0));
+        }
+
+        // Validate the first overload: process(value: int) -> str
+        let signature1 = &result.signatures[0];
+        assert_eq!(signature1.label, "(value: int) -> str");
+        assert_eq!(signature1.parameters.len(), 1);
+
+        let param1 = &signature1.parameters[0];
+        assert_eq!(param1.label, "value: int");
+        assert_eq!(param1.name, "value");
+
+        // Validate the second overload: process(value: str) -> int
+        let signature2 = &result.signatures[1];
+        assert_eq!(signature2.label, "(value: str) -> int");
+        assert_eq!(signature2.parameters.len(), 1);
+
+        let param2 = &signature2.parameters[0];
+        assert_eq!(param2.label, "value: str");
+        assert_eq!(param2.name, "value");
+    }
+
+    #[test]
+    fn signature_help_class_constructor() {
+        let test = cursor_test(
+            r#"
+        class Point:
+            """A simple point class representing a 2D coordinate."""
+            
+            def __init__(self, x: int, y: int):
+                """Initialize a point with x and y coordinates.
+                
+                Args:
+                    x: The x-coordinate
+                    y: The y-coordinate
+                """
+                self.x = x
+                self.y = y
+
+        point = Point(<CURSOR>
+        "#,
+        );
+
+        let result = test.signature_help().expect("Should have signature help");
+
+        // Should have exactly one signature for the constructor
+        assert_eq!(result.signatures.len(), 1);
+        let signature = &result.signatures[0];
+
+        // Validate the constructor signature
+        assert_eq!(signature.label, "(x: int, y: int) -> Point");
+        assert_eq!(signature.parameters.len(), 2);
+
+        // Validate the first parameter (x: int)
+        let param_x = &signature.parameters[0];
+        assert_eq!(param_x.label, "x: int");
+        assert_eq!(param_x.name, "x");
+        assert_eq!(param_x.documentation, Some("The x-coordinate".to_string()));
+
+        // Validate the second parameter (y: int)
+        let param_y = &signature.parameters[1];
+        assert_eq!(param_y.label, "y: int");
+        assert_eq!(param_y.name, "y");
+        assert_eq!(param_y.documentation, Some("The y-coordinate".to_string()));
+
+        // Should have the __init__ method docstring as documentation (not the class docstring)
+        let expected_docstring = "Initialize a point with x and y coordinates.\n                \n                Args:\n                    x: The x-coordinate\n                    y: The y-coordinate\n                ";
+        assert_eq!(
+            signature.documentation,
+            Some(expected_docstring.to_string())
+        );
+    }
+
+    #[test]
+    fn signature_help_callable_object() {
+        let test = cursor_test(
+            r#"
+        class Multiplier:
+            def __call__(self, x: int) -> int:
+                return x * 2
+
+        multiplier = Multiplier()
+        result = multiplier(<CURSOR>
+        "#,
+        );
+
+        let result = test.signature_help().expect("Should have signature help");
+
+        // Should have a signature for the callable object
+        assert!(!result.signatures.is_empty());
+        let signature = &result.signatures[0];
+
+        // Should provide signature help for the callable
+        assert!(signature.label.contains("int") || signature.label.contains("->"));
+    }
+
+    #[test]
+    fn signature_help_subclass_of_constructor() {
+        let test = cursor_test(
+            r#"
+        from typing import Type
+
+        def create_instance(cls: Type[list]) -> list:
+            return cls(<CURSOR>
+        "#,
+        );
+
+        let result = test.signature_help().expect("Should have signature help");
+
+        // Should have a signature
+        assert!(!result.signatures.is_empty());
+        let signature = &result.signatures[0];
+
+        // Should have empty documentation for now
+        assert_eq!(signature.documentation, Some(String::new()));
+    }
+
+    #[test]
+    fn signature_help_parameter_label_offsets() {
+        let test = cursor_test(
+            r#"
+        def test_function(param1: str, param2: int, param3: bool) -> str:
+            return f"{param1}: {param2}, {param3}"
+
+        result = test_function(<CURSOR>
+        "#,
+        );
+
+        let result = test.signature_help().expect("Should have signature help");
+        assert_eq!(result.signatures.len(), 1);
+
+        let signature = &result.signatures[0];
+        assert_eq!(signature.parameters.len(), 3);
+
+        // Check that we have parameter labels
+        for (i, param) in signature.parameters.iter().enumerate() {
+            let expected_param_spec = match i {
+                0 => "param1: str",
+                1 => "param2: int",
+                2 => "param3: bool",
+                _ => panic!("Unexpected parameter index"),
+            };
+            assert_eq!(param.label, expected_param_spec);
+        }
+    }
+
+    #[test]
+    fn signature_help_active_signature_selection() {
+        // This test verifies that the algorithm correctly selects the first signature
+        // where all arguments present in the call have valid parameter mappings.
+        let test = cursor_test(
+            r#"
+        from typing import overload
+
+        @overload  
+        def process(value: int) -> str: ...
+        
+        @overload
+        def process(value: str, flag: bool) -> int: ...
+        
+        def process(value, flag=None):
+            if isinstance(value, int):
+                return str(value)
+            elif flag is not None:
+                return len(value) if flag else 0
+            else:
+                return len(value)
+
+        # Call with two arguments - should select the second overload
+        result = process("hello", True<CURSOR>)
+        "#,
+        );
+
+        let result = test.signature_help().expect("Should have signature help");
+
+        // Should have signatures for the overloads.
+        assert!(!result.signatures.is_empty());
+
+        // Check that we have an active signature and parameter
+        if let Some(active_sig_index) = result.active_signature {
+            let active_signature = &result.signatures[active_sig_index];
+            assert_eq!(active_signature.active_parameter, Some(1));
+        }
+    }
+
+    #[test]
+    fn signature_help_parameter_documentation() {
+        let test = cursor_test(
+            r#"
+        def documented_function(param1: str, param2: int) -> str:
+            """This is a function with parameter documentation.
+            
+            Args:
+                param1: The first parameter description
+                param2: The second parameter description
+            """
+            return f"{param1}: {param2}"
+
+        result = documented_function(<CURSOR>
+        "#,
+        );
+
+        let result = test.signature_help().expect("Should have signature help");
+        assert_eq!(result.signatures.len(), 1);
+
+        let signature = &result.signatures[0];
+        assert_eq!(signature.parameters.len(), 2);
+
+        // Check that parameter documentation is extracted
+        let param1 = &signature.parameters[0];
+        assert_eq!(
+            param1.documentation,
+            Some("The first parameter description".to_string())
+        );
+
+        let param2 = &signature.parameters[1];
+        assert_eq!(
+            param2.documentation,
+            Some("The second parameter description".to_string())
+        );
+    }
+
+    impl CursorTest {
+        fn signature_help(&self) -> Option<SignatureHelpInfo> {
+            crate::signature_help::signature_help(&self.db, self.cursor.file, self.cursor.offset)
+        }
+    }
+}

crates/ty_project/src/db.rs

@@ -5,7 +5,7 @@ use std::{cmp, fmt};
 
 use crate::metadata::settings::file_settings;
 use crate::{DEFAULT_LINT_REGISTRY, DummyReporter};
-use crate::{Project, ProjectMetadata, Reporter};
+use crate::{ProgressReporter, Project, ProjectMetadata};
 use ruff_db::Db as SourceDb;
 use ruff_db::diagnostic::Diagnostic;
 use ruff_db::files::{File, Files};
@@ -87,7 +87,7 @@ impl ProjectDatabase {
     }
 
     /// Checks all open files in the project and its dependencies, using the given reporter.
-    pub fn check_with_reporter(&self, reporter: &mut dyn Reporter) -> Vec<Diagnostic> {
+    pub fn check_with_reporter(&self, reporter: &mut dyn ProgressReporter) -> Vec<Diagnostic> {
         let reporter = AssertUnwindSafe(reporter);
         self.project().check(self, CheckMode::OpenFiles, reporter)
     }
@@ -95,7 +95,7 @@ impl ProjectDatabase {
     /// Check the project with the given mode.
     pub fn check_with_mode(&self, mode: CheckMode) -> Vec<Diagnostic> {
         let mut reporter = DummyReporter;
-        let reporter = AssertUnwindSafe(&mut reporter as &mut dyn Reporter);
+        let reporter = AssertUnwindSafe(&mut reporter as &mut dyn ProgressReporter);
         self.project().check(self, mode, reporter)
     }
 

crates/ty_project/src/lib.rs

@@ -113,7 +113,7 @@ pub struct Project {
 }
 
 /// A progress reporter.
-pub trait Reporter: Send + Sync {
+pub trait ProgressReporter: Send + Sync {
     /// Initialize the reporter with the number of files.
     fn set_files(&mut self, files: usize);
 
@@ -121,11 +121,11 @@ pub trait Reporter: Send + Sync {
     fn report_file(&self, file: &File);
 }
 
-/// A no-op implementation of [`Reporter`].
+/// A no-op implementation of [`ProgressReporter`].
 #[derive(Default)]
 pub struct DummyReporter;
 
-impl Reporter for DummyReporter {
+impl ProgressReporter for DummyReporter {
     fn set_files(&mut self, _files: usize) {}
     fn report_file(&self, _file: &File) {}
 }
@@ -212,7 +212,7 @@ impl Project {
         self,
         db: &ProjectDatabase,
         mode: CheckMode,
-        mut reporter: AssertUnwindSafe<&mut dyn Reporter>,
+        mut reporter: AssertUnwindSafe<&mut dyn ProgressReporter>,
     ) -> Vec<Diagnostic> {
         let project_span = tracing::debug_span!("Project::check");
         let _span = project_span.enter();
@@ -257,8 +257,11 @@ impl Project {
                             tracing::debug_span!(parent: project_span, "check_file", ?file);
                         let _entered = check_file_span.entered();
 
-                        let result = self.check_file_impl(&db, file);
-                        file_diagnostics.lock().unwrap().extend(result);
+                        let result = check_file_impl(&db, file);
+                        file_diagnostics
+                            .lock()
+                            .unwrap()
+                            .extend(result.iter().map(Clone::clone));
 
                         reporter.report_file(&file);
                     });
@@ -285,7 +288,7 @@ impl Project {
             return Vec::new();
         }
 
-        self.check_file_impl(db, file)
+        check_file_impl(db, file).iter().map(Clone::clone).collect()
     }
 
     /// Opens a file in the project.
@@ -466,71 +469,73 @@ impl Project {
             self.set_file_set(db).to(IndexedFiles::lazy());
         }
     }
+}
 
-    fn check_file_impl(self, db: &dyn Db, file: File) -> Vec<Diagnostic> {
-        let mut diagnostics: Vec<Diagnostic> = Vec::new();
+#[salsa::tracked(returns(deref), heap_size=get_size2::GetSize::get_heap_size)]
+pub(crate) fn check_file_impl(db: &dyn Db, file: File) -> Box<[Diagnostic]> {
+    let mut diagnostics: Vec<Diagnostic> = Vec::new();
 
-        // Abort checking if there are IO errors.
-        let source = source_text(db, file);
+    // Abort checking if there are IO errors.
+    let source = source_text(db, file);
 
-        if let Some(read_error) = source.read_error() {
-            diagnostics.push(
-                IOErrorDiagnostic {
-                    file: Some(file),
-                    error: read_error.clone().into(),
-                }
-                .to_diagnostic(),
-            );
-            return diagnostics;
-        }
-
-        let parsed = parsed_module(db, file);
-
-        let parsed_ref = parsed.load(db);
-        diagnostics.extend(
-            parsed_ref
-                .errors()
-                .iter()
-                .map(|error| Diagnostic::invalid_syntax(file, &error.error, error)),
-        );
-
-        diagnostics.extend(parsed_ref.unsupported_syntax_errors().iter().map(|error| {
-            let mut error = Diagnostic::invalid_syntax(file, error, error);
-            add_inferred_python_version_hint_to_diagnostic(db, &mut error, "parsing syntax");
-            error
-        }));
-
-        {
-            let db = AssertUnwindSafe(db);
-            match catch(&**db, file, || check_types(*db, file)) {
-                Ok(Some(type_check_diagnostics)) => {
-                    diagnostics.extend(type_check_diagnostics.into_iter().cloned());
-                }
-                Ok(None) => {}
-                Err(diagnostic) => diagnostics.push(diagnostic),
+    if let Some(read_error) = source.read_error() {
+        diagnostics.push(
+            IOErrorDiagnostic {
+                file: Some(file),
+                error: read_error.clone().into(),
             }
-        }
-
-        if self
-            .open_fileset(db)
-            .is_none_or(|files| !files.contains(&file))
-        {
-            // Drop the AST now that we are done checking this file. It is not currently open,
-            // so it is unlikely to be accessed again soon. If any queries need to access the AST
-            // from across files, it will be re-parsed.
-            parsed.clear();
-        }
-
-        diagnostics.sort_unstable_by_key(|diagnostic| {
-            diagnostic
-                .primary_span()
-                .and_then(|span| span.range())
-                .unwrap_or_default()
-                .start()
-        });
-
-        diagnostics
+            .to_diagnostic(),
+        );
+        return diagnostics.into_boxed_slice();
     }
+
+    let parsed = parsed_module(db, file);
+
+    let parsed_ref = parsed.load(db);
+    diagnostics.extend(
+        parsed_ref
+            .errors()
+            .iter()
+            .map(|error| Diagnostic::invalid_syntax(file, &error.error, error)),
+    );
+
+    diagnostics.extend(parsed_ref.unsupported_syntax_errors().iter().map(|error| {
+        let mut error = Diagnostic::invalid_syntax(file, error, error);
+        add_inferred_python_version_hint_to_diagnostic(db, &mut error, "parsing syntax");
+        error
+    }));
+
+    {
+        let db = AssertUnwindSafe(db);
+        match catch(&**db, file, || check_types(*db, file)) {
+            Ok(Some(type_check_diagnostics)) => {
+                diagnostics.extend(type_check_diagnostics);
+            }
+            Ok(None) => {}
+            Err(diagnostic) => diagnostics.push(diagnostic),
+        }
+    }
+
+    if db
+        .project()
+        .open_fileset(db)
+        .is_none_or(|files| !files.contains(&file))
+    {
+        // Drop the AST now that we are done checking this file. It is not currently open,
+        // so it is unlikely to be accessed again soon. If any queries need to access the AST
+        // from across files, it will be re-parsed.
+        parsed.clear();
+    }
+
+    diagnostics.sort_unstable_by_key(|diagnostic| {
+        diagnostic
+            .primary_span()
+            .and_then(|span| span.range())
+            .unwrap_or_default()
+            .start()
+    });
+
+    diagnostics.into_boxed_slice()
 }
 
 #[derive(Debug)]
@@ -701,8 +706,8 @@ where
 
 #[cfg(test)]
 mod tests {
-    use crate::Db;
     use crate::ProjectMetadata;
+    use crate::check_file_impl;
     use crate::db::tests::TestDb;
     use ruff_db::Db as _;
     use ruff_db::files::system_path_to_file;
@@ -741,9 +746,8 @@ mod tests {
 
         assert_eq!(source_text(&db, file).as_str(), "");
         assert_eq!(
-            db.project()
-                .check_file_impl(&db, file)
-                .into_iter()
+            check_file_impl(&db, file)
+                .iter()
                 .map(|diagnostic| diagnostic.primary_message().to_string())
                 .collect::<Vec<_>>(),
             vec!["Failed to read file: No such file or directory".to_string()]
@@ -758,9 +762,8 @@ mod tests {
 
         assert_eq!(source_text(&db, file).as_str(), "");
         assert_eq!(
-            db.project()
-                .check_file_impl(&db, file)
-                .into_iter()
+            check_file_impl(&db, file)
+                .iter()
                 .map(|diagnostic| diagnostic.primary_message().to_string())
                 .collect::<Vec<_>>(),
             vec![] as Vec<String>

crates/ty_python_semantic/src/semantic_index/definition.rs

@@ -1,7 +1,7 @@
 use std::ops::Deref;
 
 use ruff_db::files::{File, FileRange};
-use ruff_db::parsed::ParsedModuleRef;
+use ruff_db::parsed::{ParsedModuleRef, parsed_module};
 use ruff_python_ast as ast;
 use ruff_text_size::{Ranged, TextRange};
 
@@ -57,6 +57,45 @@ impl<'db> Definition<'db> {
     pub fn focus_range(self, db: &'db dyn Db, module: &ParsedModuleRef) -> FileRange {
         FileRange::new(self.file(db), self.kind(db).target_range(module))
     }
+
+    /// Extract a docstring from this definition, if applicable.
+    /// This method returns a docstring for function and class definitions.
+    /// The docstring is extracted from the first statement in the body if it's a string literal.
+    pub fn docstring(self, db: &'db dyn Db) -> Option<String> {
+        let file = self.file(db);
+        let module = parsed_module(db, file).load(db);
+        let kind = self.kind(db);
+
+        match kind {
+            DefinitionKind::Function(function_def) => {
+                let function_node = function_def.node(&module);
+                docstring_from_body(&function_node.body)
+                    .map(|docstring_expr| docstring_expr.value.to_str().to_owned())
+            }
+            DefinitionKind::Class(class_def) => {
+                let class_node = class_def.node(&module);
+                docstring_from_body(&class_node.body)
+                    .map(|docstring_expr| docstring_expr.value.to_str().to_owned())
+            }
+            _ => None,
+        }
+    }
+}
+
+/// Extract a docstring from a function or class body.
+fn docstring_from_body(body: &[ast::Stmt]) -> Option<&ast::ExprStringLiteral> {
+    let stmt = body.first()?;
+    // Require the docstring to be a standalone expression.
+    let ast::Stmt::Expr(ast::StmtExpr {
+        value,
+        range: _,
+        node_index: _,
+    }) = stmt
+    else {
+        return None;
+    };
+    // Only match string literals.
+    value.as_string_literal_expr()
 }
 
 /// One or more [`Definition`]s.

crates/ty_python_semantic/src/types.rs

@@ -1,5 +1,5 @@
 use infer::nearest_enclosing_class;
-use itertools::Either;
+use itertools::{Either, Itertools};
 use ruff_db::parsed::parsed_module;
 
 use std::slice::Iter;
@@ -46,7 +46,9 @@ use crate::types::generics::{
     GenericContext, PartialSpecialization, Specialization, walk_generic_context,
     walk_partial_specialization, walk_specialization,
 };
-pub use crate::types::ide_support::{all_members, definition_kind_for_name};
+pub use crate::types::ide_support::{
+    CallSignatureDetails, all_members, call_signature_details, definition_kind_for_name,
+};
 use crate::types::infer::infer_unpack_types;
 use crate::types::mro::{Mro, MroError, MroIterator};
 pub(crate) use crate::types::narrow::infer_narrowing_constraint;
@@ -88,8 +90,7 @@ mod definition;
 #[cfg(test)]
 mod property_tests;
 
-#[salsa::tracked(returns(ref), heap_size=get_size2::GetSize::get_heap_size)]
-pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
+pub fn check_types(db: &dyn Db, file: File) -> Vec<Diagnostic> {
     let _span = tracing::trace_span!("check_types", ?file).entered();
 
     tracing::debug!("Checking file '{path}'", path = file.path(db));
@@ -111,7 +112,7 @@ pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
 
     check_suppressions(db, file, &mut diagnostics);
 
-    diagnostics
+    diagnostics.into_vec()
 }
 
 /// Infer the type of a binding.
@@ -7535,6 +7536,23 @@ impl<'db> ModuleLiteralType<'db> {
         self._importing_file(db)
     }
 
+    fn available_submodule_attributes(&self, db: &'db dyn Db) -> impl Iterator<Item = Name> {
+        self.importing_file(db)
+            .into_iter()
+            .flat_map(|file| imported_modules(db, file))
+            .filter_map(|submodule_name| submodule_name.relative_to(self.module(db).name()))
+            .filter_map(|relative_submodule| relative_submodule.components().next().map(Name::from))
+    }
+
+    fn resolve_submodule(self, db: &'db dyn Db, name: &str) -> Option<Type<'db>> {
+        let importing_file = self.importing_file(db)?;
+        let relative_submodule_name = ModuleName::new(name)?;
+        let mut absolute_submodule_name = self.module(db).name().clone();
+        absolute_submodule_name.extend(&relative_submodule_name);
+        let submodule = resolve_module(db, &absolute_submodule_name)?;
+        Some(Type::module_literal(db, importing_file, &submodule))
+    }
+
     fn static_member(self, db: &'db dyn Db, name: &str) -> PlaceAndQualifiers<'db> {
         // `__dict__` is a very special member that is never overridden by module globals;
         // we should always look it up directly as an attribute on `types.ModuleType`,
@@ -7554,17 +7572,9 @@ impl<'db> ModuleLiteralType<'db> {
         // the parent module's `__init__.py` file being evaluated. That said, we have
         // chosen to always have the submodule take priority. (This matches pyright's
         // current behavior, but is the opposite of mypy's current behavior.)
-        if let Some(importing_file) = self.importing_file(db) {
-            if let Some(submodule_name) = ModuleName::new(name) {
-                let imported_submodules = imported_modules(db, importing_file);
-                let mut full_submodule_name = self.module(db).name().clone();
-                full_submodule_name.extend(&submodule_name);
-                if imported_submodules.contains(&full_submodule_name) {
-                    if let Some(submodule) = resolve_module(db, &full_submodule_name) {
-                        return Place::bound(Type::module_literal(db, importing_file, &submodule))
-                            .into();
-                    }
-                }
+        if self.available_submodule_attributes(db).contains(name) {
+            if let Some(submodule) = self.resolve_submodule(db, name) {
+                return Place::bound(submodule).into();
             }
         }
 

crates/ty_python_semantic/src/types/call.rs

@@ -3,7 +3,7 @@ use super::{Signature, Type};
 use crate::Db;
 
 mod arguments;
-mod bind;
+pub(crate) mod bind;
 pub(super) use arguments::{Argument, CallArgumentTypes, CallArguments};
 pub(super) use bind::{Binding, Bindings, CallableBinding};
 

crates/ty_python_semantic/src/types/call/arguments.rs

@@ -2,6 +2,7 @@ use std::borrow::Cow;
 use std::ops::{Deref, DerefMut};
 
 use itertools::{Either, Itertools};
+use ruff_python_ast as ast;
 
 use crate::Db;
 use crate::types::KnownClass;
@@ -14,6 +15,26 @@ use super::Type;
 pub(crate) struct CallArguments<'a>(Vec<Argument<'a>>);
 
 impl<'a> CallArguments<'a> {
+    /// Create `CallArguments` from AST arguments
+    pub(crate) fn from_arguments(arguments: &'a ast::Arguments) -> Self {
+        arguments
+            .arguments_source_order()
+            .map(|arg_or_keyword| match arg_or_keyword {
+                ast::ArgOrKeyword::Arg(arg) => match arg {
+                    ast::Expr::Starred(ast::ExprStarred { .. }) => Argument::Variadic,
+                    _ => Argument::Positional,
+                },
+                ast::ArgOrKeyword::Keyword(ast::Keyword { arg, .. }) => {
+                    if let Some(arg) = arg {
+                        Argument::Keyword(&arg.id)
+                    } else {
+                        Argument::Keywords
+                    }
+                }
+            })
+            .collect()
+    }
+
     /// Prepend an optional extra synthetic argument (for a `self` or `cls` parameter) to the front
     /// of this argument list. (If `bound_self` is none, we return the argument list
     /// unmodified.)

crates/ty_python_semantic/src/types/call/bind.rs

@@ -2109,7 +2109,7 @@ impl<'db> Binding<'db> {
         }
     }
 
-    fn match_parameters(
+    pub(crate) fn match_parameters(
         &mut self,
         arguments: &CallArguments<'_>,
         argument_forms: &mut [Option<ParameterForm>],
@@ -2267,6 +2267,12 @@ impl<'db> Binding<'db> {
         self.parameter_tys = parameter_tys;
         self.errors = errors;
     }
+
+    /// Returns a vector where each index corresponds to an argument position,
+    /// and the value is the parameter index that argument maps to (if any).
+    pub(crate) fn argument_to_parameter_mapping(&self) -> &[Option<usize>] {
+        &self.argument_parameters
+    }
 }
 
 #[derive(Clone, Debug)]

crates/ty_python_semantic/src/types/class.rs

@@ -678,6 +678,7 @@ impl<'db> ClassType<'db> {
                 if let Some(signature) = signature {
                     let synthesized_signature = |signature: &Signature<'db>| {
                         Signature::new(signature.parameters().clone(), Some(correct_return_type))
+                            .with_definition(signature.definition())
                             .bind_self()
                     };
 

crates/ty_python_semantic/src/types/diagnostic.rs

@@ -1598,6 +1598,10 @@ impl TypeCheckDiagnostics {
         self.diagnostics.shrink_to_fit();
     }
 
+    pub(crate) fn into_vec(self) -> Vec<Diagnostic> {
+        self.diagnostics
+    }
+
     pub fn iter(&self) -> std::slice::Iter<'_, Diagnostic> {
         self.diagnostics.iter()
     }

crates/ty_python_semantic/src/types/display.rs

@@ -5,6 +5,7 @@ use std::fmt::{self, Display, Formatter, Write};
 use ruff_db::display::FormatterJoinExtension;
 use ruff_python_ast::str::{Quote, TripleQuotes};
 use ruff_python_literal::escape::AsciiEscape;
+use ruff_text_size::{TextRange, TextSize};
 
 use crate::types::class::{ClassLiteral, ClassType, GenericAlias};
 use crate::types::function::{FunctionType, OverloadLiteral};
@@ -557,46 +558,193 @@ pub(crate) struct DisplaySignature<'db> {
     db: &'db dyn Db,
 }
 
-impl Display for DisplaySignature<'_> {
-    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        f.write_char('(')?;
+impl DisplaySignature<'_> {
+    /// Get detailed display information including component ranges
+    pub(crate) fn to_string_parts(&self) -> SignatureDisplayDetails {
+        let mut writer = SignatureWriter::Details(SignatureDetailsWriter::new());
+        self.write_signature(&mut writer).unwrap();
+
+        match writer {
+            SignatureWriter::Details(details) => details.finish(),
+            SignatureWriter::Formatter(_) => unreachable!("Expected Details variant"),
+        }
+    }
+
+    /// Internal method to write signature with the signature writer
+    fn write_signature(&self, writer: &mut SignatureWriter) -> fmt::Result {
+        // Opening parenthesis
+        writer.write_char('(')?;
 
         if self.parameters.is_gradual() {
             // We represent gradual form as `...` in the signature, internally the parameters still
             // contain `(*args, **kwargs)` parameters.
-            f.write_str("...")?;
+            writer.write_str("...")?;
         } else {
             let mut star_added = false;
             let mut needs_slash = false;
-            let mut join = f.join(", ");
+            let mut first = true;
 
             for parameter in self.parameters.as_slice() {
+                // Handle special separators
                 if !star_added && parameter.is_keyword_only() {
-                    join.entry(&'*');
+                    if !first {
+                        writer.write_str(", ")?;
+                    }
+                    writer.write_char('*')?;
                     star_added = true;
+                    first = false;
                 }
                 if parameter.is_positional_only() {
                     needs_slash = true;
                 } else if needs_slash {
-                    join.entry(&'/');
+                    if !first {
+                        writer.write_str(", ")?;
+                    }
+                    writer.write_char('/')?;
                     needs_slash = false;
+                    first = false;
                 }
-                join.entry(&parameter.display(self.db));
+
+                // Add comma before parameter if not first
+                if !first {
+                    writer.write_str(", ")?;
+                }
+
+                // Write parameter with range tracking
+                let param_name = parameter.display_name();
+                writer.write_parameter(&parameter.display(self.db), param_name.as_deref())?;
+
+                first = false;
             }
+
             if needs_slash {
-                join.entry(&'/');
+                if !first {
+                    writer.write_str(", ")?;
+                }
+                writer.write_char('/')?;
             }
-            join.finish()?;
         }
 
-        write!(
-            f,
-            ") -> {}",
-            self.return_ty.unwrap_or(Type::unknown()).display(self.db)
-        )
+        // Closing parenthesis
+        writer.write_char(')')?;
+
+        // Return type
+        let return_ty = self.return_ty.unwrap_or_else(Type::unknown);
+        writer.write_return_type(&return_ty.display(self.db))?;
+
+        Ok(())
     }
 }
 
+impl Display for DisplaySignature<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        let mut writer = SignatureWriter::Formatter(f);
+        self.write_signature(&mut writer)
+    }
+}
+
+/// Writer for building signature strings with different output targets
+enum SignatureWriter<'a, 'b> {
+    /// Write directly to a formatter (for Display trait)
+    Formatter(&'a mut Formatter<'b>),
+    /// Build a string with range tracking (for `to_string_parts`)
+    Details(SignatureDetailsWriter),
+}
+
+/// Writer that builds a string with range tracking
+struct SignatureDetailsWriter {
+    label: String,
+    parameter_ranges: Vec<TextRange>,
+    parameter_names: Vec<String>,
+}
+
+impl SignatureDetailsWriter {
+    fn new() -> Self {
+        Self {
+            label: String::new(),
+            parameter_ranges: Vec::new(),
+            parameter_names: Vec::new(),
+        }
+    }
+
+    fn finish(self) -> SignatureDisplayDetails {
+        SignatureDisplayDetails {
+            label: self.label,
+            parameter_ranges: self.parameter_ranges,
+            parameter_names: self.parameter_names,
+        }
+    }
+}
+
+impl SignatureWriter<'_, '_> {
+    fn write_char(&mut self, c: char) -> fmt::Result {
+        match self {
+            SignatureWriter::Formatter(f) => f.write_char(c),
+            SignatureWriter::Details(details) => {
+                details.label.push(c);
+                Ok(())
+            }
+        }
+    }
+
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        match self {
+            SignatureWriter::Formatter(f) => f.write_str(s),
+            SignatureWriter::Details(details) => {
+                details.label.push_str(s);
+                Ok(())
+            }
+        }
+    }
+
+    fn write_parameter<T: Display>(&mut self, param: &T, param_name: Option<&str>) -> fmt::Result {
+        match self {
+            SignatureWriter::Formatter(f) => param.fmt(f),
+            SignatureWriter::Details(details) => {
+                let param_start = details.label.len();
+                let param_display = param.to_string();
+                details.label.push_str(&param_display);
+
+                // Use TextSize::try_from for safe conversion, falling back to empty range on overflow
+                let start = TextSize::try_from(param_start).unwrap_or_default();
+                let length = TextSize::try_from(param_display.len()).unwrap_or_default();
+                details.parameter_ranges.push(TextRange::at(start, length));
+
+                // Store the parameter name if available
+                if let Some(name) = param_name {
+                    details.parameter_names.push(name.to_string());
+                } else {
+                    details.parameter_names.push(String::new());
+                }
+
+                Ok(())
+            }
+        }
+    }
+
+    fn write_return_type<T: Display>(&mut self, return_ty: &T) -> fmt::Result {
+        match self {
+            SignatureWriter::Formatter(f) => write!(f, " -> {return_ty}"),
+            SignatureWriter::Details(details) => {
+                let return_display = format!(" -> {return_ty}");
+                details.label.push_str(&return_display);
+                Ok(())
+            }
+        }
+    }
+}
+
+/// Details about signature display components, including ranges for parameters and return type
+#[derive(Debug, Clone)]
+pub(crate) struct SignatureDisplayDetails {
+    /// The full signature string
+    pub label: String,
+    /// Ranges for each parameter within the label
+    pub parameter_ranges: Vec<TextRange>,
+    /// Names of the parameters in order
+    pub parameter_names: Vec<String>,
+}
+
 impl<'db> Parameter<'db> {
     fn display(&'db self, db: &'db dyn Db) -> DisplayParameter<'db> {
         DisplayParameter { param: self, db }

crates/ty_python_semantic/src/types/ide_support.rs

@@ -1,17 +1,20 @@
 use std::cmp::Ordering;
 
-use crate::module_resolver::resolve_module;
 use crate::place::{Place, imported_symbol, place_from_bindings, place_from_declarations};
+use crate::semantic_index::definition::Definition;
 use crate::semantic_index::definition::DefinitionKind;
 use crate::semantic_index::place::ScopeId;
 use crate::semantic_index::{
-    attribute_scopes, global_scope, imported_modules, place_table, semantic_index, use_def_map,
+    attribute_scopes, global_scope, place_table, semantic_index, use_def_map,
 };
+use crate::types::call::CallArguments;
+use crate::types::signatures::Signature;
 use crate::types::{ClassBase, ClassLiteral, KnownClass, KnownInstanceType, Type};
-use crate::{Db, NameKind};
+use crate::{Db, HasType, NameKind, SemanticModel};
 use ruff_db::files::File;
 use ruff_python_ast as ast;
 use ruff_python_ast::name::Name;
+use ruff_text_size::TextRange;
 use rustc_hash::FxHashSet;
 
 pub(crate) fn all_declarations_and_bindings<'db>(
@@ -197,26 +200,14 @@ impl<'db> AllMembers<'db> {
                     });
                 }
 
-                let module_name = module.name();
-                self.members.extend(
-                    literal
-                        .importing_file(db)
-                        .into_iter()
-                        .flat_map(|file| imported_modules(db, file))
-                        .filter_map(|submodule_name| {
-                            let module = resolve_module(db, submodule_name)?;
-                            let ty = Type::module_literal(db, file, &module);
-                            Some((submodule_name, ty))
-                        })
-                        .filter_map(|(submodule_name, ty)| {
-                            let relative = submodule_name.relative_to(module_name)?;
-                            Some((relative, ty))
-                        })
-                        .filter_map(|(relative_submodule_name, ty)| {
-                            let name = Name::from(relative_submodule_name.components().next()?);
+                self.members
+                    .extend(literal.available_submodule_attributes(db).filter_map(
+                        |submodule_name| {
+                            let ty = literal.resolve_submodule(db, &submodule_name)?;
+                            let name = submodule_name.clone();
                             Some(Member { name, ty })
-                        }),
-                );
+                        },
+                    ));
             }
         }
     }
@@ -366,3 +357,73 @@ pub fn definition_kind_for_name<'db>(
 
     None
 }
+
+/// Details about a callable signature for IDE support.
+#[derive(Debug, Clone)]
+pub struct CallSignatureDetails<'db> {
+    /// The signature itself
+    pub signature: Signature<'db>,
+
+    /// The display label for this signature (e.g., "(param1: str, param2: int) -> str")
+    pub label: String,
+
+    /// Label offsets for each parameter in the signature string.
+    /// Each range specifies the start position and length of a parameter label
+    /// within the full signature string.
+    pub parameter_label_offsets: Vec<TextRange>,
+
+    /// The names of the parameters in the signature, in order.
+    /// This provides easy access to parameter names for documentation lookup.
+    pub parameter_names: Vec<String>,
+
+    /// The definition where this callable was originally defined (useful for
+    /// extracting docstrings).
+    pub definition: Option<Definition<'db>>,
+
+    /// Mapping from argument indices to parameter indices. This helps
+    /// determine which parameter corresponds to which argument position.
+    pub argument_to_parameter_mapping: Vec<Option<usize>>,
+}
+
+/// Extract signature details from a function call expression.
+/// This function analyzes the callable being invoked and returns zero or more
+/// `CallSignatureDetails` objects, each representing one possible signature
+/// (in case of overloads or union types).
+pub fn call_signature_details<'db>(
+    db: &'db dyn Db,
+    file: File,
+    call_expr: &ast::ExprCall,
+) -> Vec<CallSignatureDetails<'db>> {
+    let model = SemanticModel::new(db, file);
+    let func_type = call_expr.func.inferred_type(&model);
+
+    // Use into_callable to handle all the complex type conversions
+    if let Some(callable_type) = func_type.into_callable(db) {
+        let call_arguments = CallArguments::from_arguments(&call_expr.arguments);
+        let bindings = callable_type.bindings(db).match_parameters(&call_arguments);
+
+        // Extract signature details from all callable bindings
+        bindings
+            .into_iter()
+            .flat_map(std::iter::IntoIterator::into_iter)
+            .map(|binding| {
+                let signature = &binding.signature;
+                let display_details = signature.display(db).to_string_parts();
+                let parameter_label_offsets = display_details.parameter_ranges.clone();
+                let parameter_names = display_details.parameter_names.clone();
+
+                CallSignatureDetails {
+                    signature: signature.clone(),
+                    label: display_details.label,
+                    parameter_label_offsets,
+                    parameter_names,
+                    definition: signature.definition(),
+                    argument_to_parameter_mapping: binding.argument_to_parameter_mapping().to_vec(),
+                }
+            })
+            .collect()
+    } else {
+        // Type is not callable, return empty signatures
+        vec![]
+    }
+}

crates/ty_python_semantic/src/types/infer.rs

@@ -84,9 +84,7 @@ use crate::semantic_index::place::{
 use crate::semantic_index::{
     ApplicableConstraints, EagerSnapshotResult, SemanticIndex, place_table, semantic_index,
 };
-use crate::types::call::{
-    Argument, Binding, Bindings, CallArgumentTypes, CallArguments, CallError,
-};
+use crate::types::call::{Binding, Bindings, CallArgumentTypes, CallArguments, CallError};
 use crate::types::class::{CodeGeneratorKind, MetaclassErrorKind, SliceLiteral};
 use crate::types::diagnostic::{
     self, CALL_NON_CALLABLE, CONFLICTING_DECLARATIONS, CONFLICTING_METACLASS,
@@ -1917,7 +1915,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         self.infer_type_parameters(type_params);
 
         if let Some(arguments) = class.arguments.as_deref() {
-            let call_arguments = Self::parse_arguments(arguments);
+            let call_arguments = CallArguments::from_arguments(arguments);
             let argument_forms = vec![Some(ParameterForm::Value); call_arguments.len()];
             self.infer_argument_types(arguments, call_arguments, &argument_forms);
         }
@@ -4626,29 +4624,6 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         self.infer_expression(expression)
     }
 
-    fn parse_arguments(arguments: &ast::Arguments) -> CallArguments<'_> {
-        arguments
-            .arguments_source_order()
-            .map(|arg_or_keyword| {
-                match arg_or_keyword {
-                    ast::ArgOrKeyword::Arg(arg) => match arg {
-                        ast::Expr::Starred(ast::ExprStarred { .. }) => Argument::Variadic,
-                        // TODO diagnostic if after a keyword argument
-                        _ => Argument::Positional,
-                    },
-                    ast::ArgOrKeyword::Keyword(ast::Keyword { arg, .. }) => {
-                        if let Some(arg) = arg {
-                            Argument::Keyword(&arg.id)
-                        } else {
-                            // TODO diagnostic if not last
-                            Argument::Keywords
-                        }
-                    }
-                }
-            })
-            .collect()
-    }
-
     fn infer_argument_types<'a>(
         &mut self,
         ast_arguments: &ast::Arguments,
@@ -5362,7 +5337,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         // We don't call `Type::try_call`, because we want to perform type inference on the
         // arguments after matching them to parameters, but before checking that the argument types
         // are assignable to any parameter annotations.
-        let call_arguments = Self::parse_arguments(arguments);
+        let call_arguments = CallArguments::from_arguments(arguments);
 
         let callable_type = self.infer_maybe_standalone_expression(func);
 
@@ -10035,7 +10010,7 @@ mod tests {
     }
 
     #[track_caller]
-    fn assert_diagnostic_messages(diagnostics: &TypeCheckDiagnostics, expected: &[&str]) {
+    fn assert_diagnostic_messages(diagnostics: &[Diagnostic], expected: &[&str]) {
         let messages: Vec<&str> = diagnostics
             .iter()
             .map(Diagnostic::primary_message)
@@ -10048,7 +10023,7 @@ mod tests {
         let file = system_path_to_file(db, filename).unwrap();
         let diagnostics = check_types(db, file);
 
-        assert_diagnostic_messages(diagnostics, expected);
+        assert_diagnostic_messages(&diagnostics, expected);
     }
 
     #[test]

crates/ty_python_semantic/src/types/signatures.rs

@@ -213,7 +213,7 @@ impl<'a, 'db> IntoIterator for &'a CallableSignature<'db> {
 }
 
 /// The signature of one of the overloads of a callable.
-#[derive(Clone, Debug, PartialEq, Eq, Hash, salsa::Update, get_size2::GetSize)]
+#[derive(Clone, Debug, salsa::Update, get_size2::GetSize)]
 pub struct Signature<'db> {
     /// The generic context for this overload, if it is generic.
     pub(crate) generic_context: Option<GenericContext<'db>>,
@@ -223,6 +223,10 @@ pub struct Signature<'db> {
     /// to its own generic context.
     pub(crate) inherited_generic_context: Option<GenericContext<'db>>,
 
+    /// The original definition associated with this function, if available.
+    /// This is useful for locating and extracting docstring information for the signature.
+    pub(crate) definition: Option<Definition<'db>>,
+
     /// Parameters, in source order.
     ///
     /// The ordering of parameters in a valid signature must be: first positional-only parameters,
@@ -265,6 +269,7 @@ impl<'db> Signature<'db> {
         Self {
             generic_context: None,
             inherited_generic_context: None,
+            definition: None,
             parameters,
             return_ty,
         }
@@ -278,6 +283,7 @@ impl<'db> Signature<'db> {
         Self {
             generic_context,
             inherited_generic_context: None,
+            definition: None,
             parameters,
             return_ty,
         }
@@ -288,6 +294,7 @@ impl<'db> Signature<'db> {
         Signature {
             generic_context: None,
             inherited_generic_context: None,
+            definition: None,
             parameters: Parameters::gradual_form(),
             return_ty: Some(signature_type),
         }
@@ -300,6 +307,7 @@ impl<'db> Signature<'db> {
         Signature {
             generic_context: None,
             inherited_generic_context: None,
+            definition: None,
             parameters: Parameters::todo(),
             return_ty: Some(signature_type),
         }
@@ -332,6 +340,7 @@ impl<'db> Signature<'db> {
         Self {
             generic_context: generic_context.or(legacy_generic_context),
             inherited_generic_context,
+            definition: Some(definition),
             parameters,
             return_ty,
         }
@@ -351,6 +360,7 @@ impl<'db> Signature<'db> {
         Self {
             generic_context: self.generic_context,
             inherited_generic_context: self.inherited_generic_context,
+            definition: self.definition,
             // Parameters are at contravariant position, so the variance is flipped.
             parameters: self.parameters.materialize(db, variance.flip()),
             return_ty: Some(
@@ -373,6 +383,7 @@ impl<'db> Signature<'db> {
             inherited_generic_context: self
                 .inherited_generic_context
                 .map(|ctx| ctx.normalized_impl(db, visitor)),
+            definition: self.definition,
             parameters: self
                 .parameters
                 .iter()
@@ -392,6 +403,7 @@ impl<'db> Signature<'db> {
         Self {
             generic_context: self.generic_context,
             inherited_generic_context: self.inherited_generic_context,
+            definition: self.definition,
             parameters: self.parameters.apply_type_mapping(db, type_mapping),
             return_ty: self
                 .return_ty
@@ -422,10 +434,16 @@ impl<'db> Signature<'db> {
         &self.parameters
     }
 
+    /// Return the definition associated with this signature, if any.
+    pub(crate) fn definition(&self) -> Option<Definition<'db>> {
+        self.definition
+    }
+
     pub(crate) fn bind_self(&self) -> Self {
         Self {
             generic_context: self.generic_context,
             inherited_generic_context: self.inherited_generic_context,
+            definition: self.definition,
             parameters: Parameters::new(self.parameters().iter().skip(1).cloned()),
             return_ty: self.return_ty,
         }
@@ -899,6 +917,33 @@ impl<'db> Signature<'db> {
 
         true
     }
+
+    /// Create a new signature with the given definition.
+    pub(crate) fn with_definition(self, definition: Option<Definition<'db>>) -> Self {
+        Self { definition, ..self }
+    }
+}
+
+// Manual implementations of PartialEq, Eq, and Hash that exclude the definition field
+// since the definition is not relevant for type equality/equivalence
+impl PartialEq for Signature<'_> {
+    fn eq(&self, other: &Self) -> bool {
+        self.generic_context == other.generic_context
+            && self.inherited_generic_context == other.inherited_generic_context
+            && self.parameters == other.parameters
+            && self.return_ty == other.return_ty
+    }
+}
+
+impl Eq for Signature<'_> {}
+
+impl std::hash::Hash for Signature<'_> {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.generic_context.hash(state);
+        self.inherited_generic_context.hash(state);
+        self.parameters.hash(state);
+        self.return_ty.hash(state);
+    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, salsa::Update, get_size2::GetSize)]

crates/ty_server/src/server.rs

@@ -2,14 +2,14 @@
 
 use self::schedule::spawn_main_loop;
 use crate::PositionEncoding;
-use crate::session::{AllOptions, ClientOptions, Session};
+use crate::session::{AllOptions, ClientOptions, DiagnosticMode, Session};
 use lsp_server::Connection;
 use lsp_types::{
     ClientCapabilities, DiagnosticOptions, DiagnosticServerCapabilities, HoverProviderCapability,
     InlayHintOptions, InlayHintServerCapabilities, MessageType, SemanticTokensLegend,
     SemanticTokensOptions, SemanticTokensServerCapabilities, ServerCapabilities,
-    TextDocumentSyncCapability, TextDocumentSyncKind, TextDocumentSyncOptions,
-    TypeDefinitionProviderCapability, Url, WorkDoneProgressOptions,
+    SignatureHelpOptions, TextDocumentSyncCapability, TextDocumentSyncKind,
+    TextDocumentSyncOptions, TypeDefinitionProviderCapability, Url, WorkDoneProgressOptions,
 };
 use std::num::NonZeroUsize;
 use std::panic::PanicHookInfo;
@@ -54,7 +54,8 @@ impl Server {
 
         let client_capabilities = init_params.capabilities;
         let position_encoding = Self::find_best_position_encoding(&client_capabilities);
-        let server_capabilities = Self::server_capabilities(position_encoding);
+        let server_capabilities =
+            Self::server_capabilities(position_encoding, global_options.diagnostic_mode());
 
         let connection = connection.initialize_finish(
             id,
@@ -168,13 +169,17 @@ impl Server {
             .unwrap_or_default()
     }
 
-    fn server_capabilities(position_encoding: PositionEncoding) -> ServerCapabilities {
+    fn server_capabilities(
+        position_encoding: PositionEncoding,
+        diagnostic_mode: DiagnosticMode,
+    ) -> ServerCapabilities {
         ServerCapabilities {
             position_encoding: Some(position_encoding.into()),
             diagnostic_provider: Some(DiagnosticServerCapabilities::Options(DiagnosticOptions {
                 identifier: Some(crate::DIAGNOSTIC_NAME.into()),
                 inter_file_dependencies: true,
-                workspace_diagnostics: true,
+                // TODO: Dynamically register for workspace diagnostics.
+                workspace_diagnostics: diagnostic_mode.is_workspace(),
                 ..Default::default()
             })),
             text_document_sync: Some(TextDocumentSyncCapability::Options(
@@ -186,6 +191,11 @@ impl Server {
             )),
             type_definition_provider: Some(TypeDefinitionProviderCapability::Simple(true)),
             hover_provider: Some(HoverProviderCapability::Simple(true)),
+            signature_help_provider: Some(SignatureHelpOptions {
+                trigger_characters: Some(vec!["(".to_string(), ",".to_string()]),
+                retrigger_characters: Some(vec![")".to_string()]),
+                work_done_progress_options: lsp_types::WorkDoneProgressOptions::default(),
+            }),
             inlay_hint_provider: Some(lsp_types::OneOf::Right(
                 InlayHintServerCapabilities::Options(InlayHintOptions::default()),
             )),

crates/ty_server/src/server/api.rs

@@ -58,6 +58,9 @@ pub(super) fn request(req: server::Request) -> Task {
         >(
             req, BackgroundSchedule::Worker
         ),
+        requests::SignatureHelpRequestHandler::METHOD => background_document_request_task::<
+            requests::SignatureHelpRequestHandler,
+        >(req, BackgroundSchedule::Worker),
         requests::CompletionRequestHandler::METHOD => background_document_request_task::<
             requests::CompletionRequestHandler,
         >(

crates/ty_server/src/server/api/requests.rs

@@ -6,6 +6,7 @@ mod inlay_hints;
 mod semantic_tokens;
 mod semantic_tokens_range;
 mod shutdown;
+mod signature_help;
 mod workspace_diagnostic;
 
 pub(super) use completion::CompletionRequestHandler;
@@ -16,4 +17,5 @@ pub(super) use inlay_hints::InlayHintRequestHandler;
 pub(super) use semantic_tokens::SemanticTokensRequestHandler;
 pub(super) use semantic_tokens_range::SemanticTokensRangeRequestHandler;
 pub(super) use shutdown::ShutdownHandler;
+pub(super) use signature_help::SignatureHelpRequestHandler;
 pub(super) use workspace_diagnostic::WorkspaceDiagnosticRequestHandler;

crates/ty_server/src/server/api/requests/signature_help.rs

@@ -0,0 +1,145 @@
+use std::borrow::Cow;
+
+use crate::DocumentSnapshot;
+use crate::document::{PositionEncoding, PositionExt};
+use crate::server::api::traits::{
+    BackgroundDocumentRequestHandler, RequestHandler, RetriableRequestHandler,
+};
+use crate::session::client::Client;
+use lsp_types::request::SignatureHelpRequest;
+use lsp_types::{
+    Documentation, ParameterInformation, ParameterLabel, SignatureHelp, SignatureHelpParams,
+    SignatureInformation, Url,
+};
+use ruff_db::source::{line_index, source_text};
+use ty_ide::signature_help;
+use ty_project::ProjectDatabase;
+
+pub(crate) struct SignatureHelpRequestHandler;
+
+impl RequestHandler for SignatureHelpRequestHandler {
+    type RequestType = SignatureHelpRequest;
+}
+
+impl BackgroundDocumentRequestHandler for SignatureHelpRequestHandler {
+    fn document_url(params: &SignatureHelpParams) -> Cow<Url> {
+        Cow::Borrowed(&params.text_document_position_params.text_document.uri)
+    }
+
+    fn run_with_snapshot(
+        db: &ProjectDatabase,
+        snapshot: DocumentSnapshot,
+        _client: &Client,
+        params: SignatureHelpParams,
+    ) -> crate::server::Result<Option<SignatureHelp>> {
+        if snapshot.client_settings().is_language_services_disabled() {
+            return Ok(None);
+        }
+
+        let Some(file) = snapshot.file(db) else {
+            tracing::debug!("Failed to resolve file for {:?}", params);
+            return Ok(None);
+        };
+
+        let source = source_text(db, file);
+        let line_index = line_index(db, file);
+        let offset = params.text_document_position_params.position.to_text_size(
+            &source,
+            &line_index,
+            snapshot.encoding(),
+        );
+
+        // Extract signature help capabilities from the client
+        let resolved_capabilities = snapshot.resolved_client_capabilities();
+
+        let Some(signature_help_info) = signature_help(db, file, offset) else {
+            return Ok(None);
+        };
+
+        // Compute active parameter from the active signature
+        let active_parameter = signature_help_info
+            .active_signature
+            .and_then(|s| signature_help_info.signatures.get(s))
+            .and_then(|sig| sig.active_parameter)
+            .and_then(|p| u32::try_from(p).ok());
+
+        // Convert from IDE types to LSP types
+        let signatures = signature_help_info
+            .signatures
+            .into_iter()
+            .map(|sig| {
+                let parameters = sig
+                    .parameters
+                    .into_iter()
+                    .map(|param| {
+                        let label = if resolved_capabilities.signature_label_offset_support {
+                            // Find the parameter's offset in the signature label
+                            if let Some(start) = sig.label.find(&param.label) {
+                                let encoding = snapshot.encoding();
+
+                                // Convert byte offsets to character offsets based on negotiated encoding
+                                let start_char_offset = match encoding {
+                                    PositionEncoding::UTF8 => start,
+                                    PositionEncoding::UTF16 => {
+                                        sig.label[..start].encode_utf16().count()
+                                    }
+                                    PositionEncoding::UTF32 => sig.label[..start].chars().count(),
+                                };
+
+                                let end_char_offset = match encoding {
+                                    PositionEncoding::UTF8 => start + param.label.len(),
+                                    PositionEncoding::UTF16 => sig.label
+                                        [..start + param.label.len()]
+                                        .encode_utf16()
+                                        .count(),
+                                    PositionEncoding::UTF32 => {
+                                        sig.label[..start + param.label.len()].chars().count()
+                                    }
+                                };
+
+                                let start_u32 =
+                                    u32::try_from(start_char_offset).unwrap_or(u32::MAX);
+                                let end_u32 = u32::try_from(end_char_offset).unwrap_or(u32::MAX);
+                                ParameterLabel::LabelOffsets([start_u32, end_u32])
+                            } else {
+                                ParameterLabel::Simple(param.label)
+                            }
+                        } else {
+                            ParameterLabel::Simple(param.label)
+                        };
+
+                        ParameterInformation {
+                            label,
+                            documentation: param.documentation.map(Documentation::String),
+                        }
+                    })
+                    .collect();
+
+                let active_parameter = if resolved_capabilities.signature_active_parameter_support {
+                    sig.active_parameter.and_then(|p| u32::try_from(p).ok())
+                } else {
+                    None
+                };
+
+                SignatureInformation {
+                    label: sig.label,
+                    documentation: sig.documentation.map(Documentation::String),
+                    parameters: Some(parameters),
+                    active_parameter,
+                }
+            })
+            .collect();
+
+        let signature_help = SignatureHelp {
+            signatures,
+            active_signature: signature_help_info
+                .active_signature
+                .and_then(|s| u32::try_from(s).ok()),
+            active_parameter,
+        };
+
+        Ok(Some(signature_help))
+    }
+}
+
+impl RetriableRequestHandler for SignatureHelpRequestHandler {}

crates/ty_server/src/session.rs

@@ -16,7 +16,7 @@ use ty_project::{ProjectDatabase, ProjectMetadata};
 
 pub(crate) use self::capabilities::ResolvedClientCapabilities;
 pub use self::index::DocumentQuery;
-pub(crate) use self::options::{AllOptions, ClientOptions};
+pub(crate) use self::options::{AllOptions, ClientOptions, DiagnosticMode};
 pub(crate) use self::settings::ClientSettings;
 use crate::document::{DocumentKey, DocumentVersion, NotebookDocument};
 use crate::session::request_queue::RequestQueue;

crates/ty_server/src/session/capabilities.rs

@@ -22,6 +22,12 @@ pub(crate) struct ResolvedClientCapabilities {
 
     /// Whether the client supports multiline semantic tokens
     pub(crate) semantic_tokens_multiline_support: bool,
+
+    /// Whether the client supports signature label offsets in signature help
+    pub(crate) signature_label_offset_support: bool,
+
+    /// Whether the client supports per-signature active parameter in signature help
+    pub(crate) signature_active_parameter_support: bool,
 }
 
 impl ResolvedClientCapabilities {
@@ -95,6 +101,34 @@ impl ResolvedClientCapabilities {
             .and_then(|semantic_tokens| semantic_tokens.multiline_token_support)
             .unwrap_or(false);
 
+        let signature_label_offset_support = client_capabilities
+            .text_document
+            .as_ref()
+            .and_then(|text_document| {
+                text_document
+                    .signature_help
+                    .as_ref()?
+                    .signature_information
+                    .as_ref()?
+                    .parameter_information
+                    .as_ref()?
+                    .label_offset_support
+            })
+            .unwrap_or_default();
+
+        let signature_active_parameter_support = client_capabilities
+            .text_document
+            .as_ref()
+            .and_then(|text_document| {
+                text_document
+                    .signature_help
+                    .as_ref()?
+                    .signature_information
+                    .as_ref()?
+                    .active_parameter_support
+            })
+            .unwrap_or_default();
+
         Self {
             code_action_deferred_edit_resolution: code_action_data_support
                 && code_action_edit_resolution,
@@ -106,6 +140,8 @@ impl ResolvedClientCapabilities {
             type_definition_link_support: declaration_link_support,
             hover_prefer_markdown,
             semantic_tokens_multiline_support,
+            signature_label_offset_support,
+            signature_active_parameter_support,
         }
     }
 }

crates/ty_server/src/session/options.rs

@@ -25,6 +25,10 @@ impl GlobalOptions {
     pub(crate) fn into_settings(self) -> ClientSettings {
         self.client.into_settings()
     }
+
+    pub(crate) fn diagnostic_mode(&self) -> DiagnosticMode {
+        self.client.diagnostic_mode.unwrap_or_default()
+    }
 }
 
 /// This is a direct representation of the workspace settings schema, which inherits the schema of

crates/ty_test/src/lib.rs

@@ -340,7 +340,7 @@ fn run_test(
                 Err(failures) => return Some(failures),
             };
 
-            diagnostics.extend(type_diagnostics.into_iter().cloned());
+            diagnostics.extend(type_diagnostics);
             diagnostics.sort_by(|left, right| {
                 left.rendering_sort_key(db)
                     .cmp(&right.rendering_sort_key(db))

crates/ty_wasm/src/lib.rs

@@ -14,6 +14,7 @@ use ruff_notebook::Notebook;
 use ruff_python_formatter::formatted_file;
 use ruff_source_file::{LineIndex, OneIndexed, SourceLocation};
 use ruff_text_size::{Ranged, TextSize};
+use ty_ide::signature_help;
 use ty_ide::{MarkupKind, goto_type_definition, hover, inlay_hints};
 use ty_project::ProjectMetadata;
 use ty_project::metadata::options::Options;
@@ -385,6 +386,51 @@ impl Workspace {
 
         Ok(result)
     }
+
+    #[wasm_bindgen(js_name = "signatureHelp")]
+    pub fn signature_help(
+        &self,
+        file_id: &FileHandle,
+        position: Position,
+    ) -> Result<Option<SignatureHelp>, Error> {
+        let source = source_text(&self.db, file_id.file);
+        let index = line_index(&self.db, file_id.file);
+
+        let offset = position.to_text_size(&source, &index, self.position_encoding)?;
+
+        let Some(signature_help_info) = signature_help(&self.db, file_id.file, offset) else {
+            return Ok(None);
+        };
+
+        let signatures = signature_help_info
+            .signatures
+            .into_iter()
+            .map(|sig| {
+                let parameters = sig
+                    .parameters
+                    .into_iter()
+                    .map(|param| ParameterInformation {
+                        label: param.label,
+                        documentation: param.documentation,
+                    })
+                    .collect();
+
+                SignatureInformation {
+                    label: sig.label,
+                    documentation: sig.documentation,
+                    parameters,
+                    active_parameter: sig.active_parameter.and_then(|p| u32::try_from(p).ok()),
+                }
+            })
+            .collect();
+
+        Ok(Some(SignatureHelp {
+            signatures,
+            active_signature: signature_help_info
+                .active_signature
+                .and_then(|s| u32::try_from(s).ok()),
+        }))
+    }
 }
 
 pub(crate) fn into_error<E: std::fmt::Display>(err: E) -> Error {
@@ -749,6 +795,35 @@ pub struct SemanticToken {
     pub range: Range,
 }
 
+#[wasm_bindgen]
+#[derive(Clone)]
+pub struct SignatureHelp {
+    #[wasm_bindgen(getter_with_clone)]
+    pub signatures: Vec<SignatureInformation>,
+    pub active_signature: Option<u32>,
+}
+
+#[wasm_bindgen]
+#[derive(Clone)]
+pub struct SignatureInformation {
+    #[wasm_bindgen(getter_with_clone)]
+    pub label: String,
+    #[wasm_bindgen(getter_with_clone)]
+    pub documentation: Option<String>,
+    #[wasm_bindgen(getter_with_clone)]
+    pub parameters: Vec<ParameterInformation>,
+    pub active_parameter: Option<u32>,
+}
+
+#[wasm_bindgen]
+#[derive(Clone)]
+pub struct ParameterInformation {
+    #[wasm_bindgen(getter_with_clone)]
+    pub label: String,
+    #[wasm_bindgen(getter_with_clone)]
+    pub documentation: Option<String>,
+}
+
 #[wasm_bindgen]
 impl SemanticToken {
     pub fn kinds() -> Vec<String> {

docs/integrations.md

@@ -80,7 +80,7 @@ You can add the following configuration to `.gitlab-ci.yml` to run a `ruff forma
   stage: build
   interruptible: true
   image:
-    name: ghcr.io/astral-sh/ruff:0.12.2-alpine
+    name: ghcr.io/astral-sh/ruff:0.12.3-alpine
   before_script:
     - cd $CI_PROJECT_DIR
     - ruff --version
@@ -106,7 +106,7 @@ Ruff can be used as a [pre-commit](https://pre-commit.com) hook via [`ruff-pre-c
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.12.2
+  rev: v0.12.3
   hooks:
     # Run the linter.
     - id: ruff
@@ -119,7 +119,7 @@ To enable lint fixes, add the `--fix` argument to the lint hook:
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.12.2
+  rev: v0.12.3
   hooks:
     # Run the linter.
     - id: ruff
@@ -133,7 +133,7 @@ To avoid running on Jupyter Notebooks, remove `jupyter` from the list of allowed
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.12.2
+  rev: v0.12.3
   hooks:
     # Run the linter.
     - id: ruff

docs/tutorial.md

@@ -369,7 +369,7 @@ This tutorial has focused on Ruff's command-line interface, but Ruff can also be
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.12.2
+  rev: v0.12.3
   hooks:
     # Run the linter.
     - id: ruff

playground/ty/src/Editor/Editor.tsx

@@ -152,7 +152,8 @@ class PlaygroundServer
     languages.DocumentFormattingEditProvider,
     languages.CompletionItemProvider,
     languages.DocumentSemanticTokensProvider,
-    languages.DocumentRangeSemanticTokensProvider
+    languages.DocumentRangeSemanticTokensProvider,
+    languages.SignatureHelpProvider
 {
   private typeDefinitionProviderDisposable: IDisposable;
   private editorOpenerDisposable: IDisposable;
@@ -162,6 +163,7 @@ class PlaygroundServer
   private completionDisposable: IDisposable;
   private semanticTokensDisposable: IDisposable;
   private rangeSemanticTokensDisposable: IDisposable;
+  private signatureHelpDisposable: IDisposable;
 
   constructor(
     private monaco: Monaco,
@@ -191,9 +193,13 @@ class PlaygroundServer
     this.editorOpenerDisposable = monaco.editor.registerEditorOpener(this);
     this.formatDisposable =
       monaco.languages.registerDocumentFormattingEditProvider("python", this);
+    this.signatureHelpDisposable =
+      monaco.languages.registerSignatureHelpProvider("python", this);
   }
 
   triggerCharacters: string[] = ["."];
+  signatureHelpTriggerCharacters: string[] = ["(", ","];
+  signatureHelpRetriggerCharacters: string[] = [")"];
 
   getLegend(): languages.SemanticTokensLegend {
     return {
@@ -292,6 +298,61 @@ class PlaygroundServer
 
   resolveCompletionItem: undefined;
 
+  provideSignatureHelp(
+    model: editor.ITextModel,
+    position: Position,
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    _token: CancellationToken,
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    _context: languages.SignatureHelpContext,
+  ): languages.ProviderResult<languages.SignatureHelpResult> {
+    const selectedFile = this.props.files.selected;
+
+    if (selectedFile == null) {
+      return;
+    }
+
+    const selectedHandle = this.props.files.handles[selectedFile];
+
+    if (selectedHandle == null) {
+      return;
+    }
+
+    const signatureHelp = this.props.workspace.signatureHelp(
+      selectedHandle,
+      new TyPosition(position.lineNumber, position.column),
+    );
+
+    if (signatureHelp == null) {
+      return undefined;
+    }
+
+    return {
+      dispose() {},
+      value: {
+        signatures: signatureHelp.signatures.map((sig) => ({
+          label: sig.label,
+          documentation: sig.documentation
+            ? { value: sig.documentation }
+            : undefined,
+          parameters: sig.parameters.map((param) => ({
+            label: param.label,
+            documentation: param.documentation
+              ? { value: param.documentation }
+              : undefined,
+          })),
+          activeParameter: sig.active_parameter,
+        })),
+        activeSignature: signatureHelp.active_signature ?? 0,
+        activeParameter:
+          signatureHelp.active_signature != null
+            ? (signatureHelp.signatures[signatureHelp.active_signature]
+                ?.active_parameter ?? 0)
+            : 0,
+      },
+    };
+  }
+
   provideInlayHints(
     _model: editor.ITextModel,
     range: Range,
@@ -569,6 +630,7 @@ class PlaygroundServer
     this.rangeSemanticTokensDisposable.dispose();
     this.semanticTokensDisposable.dispose();
     this.completionDisposable.dispose();
+    this.signatureHelpDisposable.dispose();
   }
 }
 

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "ruff"
-version = "0.12.2"
+version = "0.12.3"
 description = "An extremely fast Python linter and code formatter, written in Rust."
 authors = [{ name = "Astral Software Inc.", email = "hey@astral.sh" }]
 readme = "README.md"

scripts/benchmarks/pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "scripts"
-version = "0.12.2"
+version = "0.12.3"
 description = ""
 authors = ["Charles Marsh <charlie.r.marsh@gmail.com>"]