Bump version to 0.0.100

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
   - repo: https://github.com/charliermarsh/ruff-pre-commit
-    rev: v0.0.99
+    rev: v0.0.100
     hooks:
       - id: ruff
 

Cargo.lock

@@ -920,7 +920,7 @@ checksum = "0ce7134b9999ecaf8bcd65542e436736ef32ddca1b3e06094cb6ec5755203b80"
 
 [[package]]
 name = "flake8-to-ruff"
-version = "0.0.99-dev.0"
+version = "0.0.100-dev.0"
 dependencies = [
  "anyhow",
  "clap 4.0.15",
@@ -2209,9 +2209,19 @@ dependencies = [
  "winapi 0.3.9",
 ]
 
+[[package]]
+name = "ropey"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbd22239fafefc42138ca5da064f3c17726a80d2379d817a3521240e78dd0064"
+dependencies = [
+ "smallvec",
+ "str_indices",
+]
+
 [[package]]
 name = "ruff"
-version = "0.0.99"
+version = "0.0.100"
 dependencies = [
  "anyhow",
  "assert_cmd",
@@ -2239,6 +2249,7 @@ dependencies = [
  "path-absolutize",
  "rayon",
  "regex",
+ "ropey",
  "rustpython-ast",
  "rustpython-common",
  "rustpython-parser",
@@ -2559,6 +2570,12 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
 
+[[package]]
+name = "str_indices"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d9199fa80c817e074620be84374a520062ebac833f358d74b37060ce4a0f2c0"
+
 [[package]]
 name = "string_cache"
 version = "0.8.4"

Cargo.toml

@@ -1,11 +1,11 @@
 [workspace]
 members = [
-    "flake8_to_ruff",
+  "flake8_to_ruff",
 ]
 
 [package]
 name = "ruff"
-version = "0.0.99"
+version = "0.0.100"
 edition = "2021"
 
 [lib]
@@ -31,6 +31,7 @@ once_cell = { version = "1.13.1" }
 path-absolutize = { version = "3.0.14", features = ["once_cell_cache", "use_unix_paths_on_wasm"] }
 rayon = { version = "1.5.3" }
 regex = { version = "1.6.0" }
+ropey = { version = "1.5.0" }
 rustpython-ast = { features = ["unparse"], git = "https://github.com/RustPython/RustPython.git", rev = "77b821a1941019fe34f73ce17cea013ae1b98fd0" }
 rustpython-common = { git = "https://github.com/RustPython/RustPython.git", rev = "77b821a1941019fe34f73ce17cea013ae1b98fd0" }
 rustpython-parser = { features = ["lalrpop"], git = "https://github.com/RustPython/RustPython.git", rev = "77b821a1941019fe34f73ce17cea013ae1b98fd0" }

README.md

@@ -49,7 +49,8 @@ Read the [launch blog post](https://notes.crmarsh.com/python-tooling-could-be-mu
    9. [flake8-builtins](#flake8-builtins)
    10. [flake8-print](#flake8-print)
    11. [flake8-quotes](#flake8-quotes)
-   12. [Meta rules](#meta-rules)
+   12. [Ruff-specific rules](#ruff-specific-rules)
+   13. [Meta rules](#meta-rules)
 5. [Editor Integrations](#editor-integrations)
 6. [FAQ](#faq)
 7. [Development](#development)
@@ -89,7 +90,7 @@ Ruff also works with [pre-commit](https://pre-commit.com):
 ```yaml
 repos:
   - repo: https://github.com/charliermarsh/ruff-pre-commit
-    rev: v0.0.99
+    rev: v0.0.100
     hooks:
       - id: ruff
 ```
@@ -325,7 +326,7 @@ The 🛠 emoji indicates that a rule is automatically fixable by the `--fix` com
 | F823 | UndefinedLocal | Local variable `...` referenced before assignment |  |
 | F831 | DuplicateArgumentName | Duplicate argument name in function definition |  |
 | F841 | UnusedVariable | Local variable `...` is assigned to but never used |  |
-| F901 | RaiseNotImplemented | `raise NotImplemented` should be `raise NotImplementedError` |  |
+| F901 | RaiseNotImplemented | `raise NotImplemented` should be `raise NotImplementedError` | 🛠 |
 
 ### pycodestyle (error)
 
@@ -467,6 +468,7 @@ The 🛠 emoji indicates that a rule is automatically fixable by the `--fix` com
 | B013 | RedundantTupleInExceptionHandler | A length-one tuple literal is redundant. Write `except ValueError:` instead of `except (ValueError,):`. |  |
 | B014 | DuplicateHandlerException | Exception handler with duplicate exception: `ValueError` | 🛠 |
 | B017 | NoAssertRaisesException | `assertRaises(Exception):` should be considered evil. |  |
+| B018 | UselessExpression | Found useless expression. Either assign it to a variable or remove it. |  |
 | B025 | DuplicateTryBlockException | try-except block with duplicate exception `Exception` |  |
 
 ### flake8-builtins
@@ -493,6 +495,12 @@ The 🛠 emoji indicates that a rule is automatically fixable by the `--fix` com
 | Q002 | BadQuotesDocstring | Single quote docstring found but double quotes preferred |  |
 | Q003 | AvoidQuoteEscape | Change outer quotes to avoid escaping inner quotes |  |
 
+### Ruff-specific rules
+
+| Code | Name | Message | Fix |
+| ---- | ---- | ------- | --- |
+| X001 | AmbiguousUnicodeCharacter | Use of ambiguous unicode character '𝐁' (did you mean 'B'?) | 🛠 |
+
 ### Meta rules
 
 | Code | Name | Message | Fix |
@@ -684,7 +692,7 @@ extend-ignore = [
 
 ## Development
 
-Ruff is written in Rust (1.64.0). You'll need to install the [Rust toolchain](https://www.rust-lang.org/tools/install)
+Ruff is written in Rust (1.65.0). You'll need to install the [Rust toolchain](https://www.rust-lang.org/tools/install)
 for development.
 
 Assuming you have `cargo` installed, you can run:

benches/source_code_locator.rs

@@ -1,13 +1,16 @@
 use std::path::Path;
 
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use ropey::Rope;
 use ruff::fs;
-use ruff::source_code_locator::compute_offsets;
 
 fn criterion_benchmark(c: &mut Criterion) {
     let contents = fs::read_file(Path::new("resources/test/fixtures/D.py")).unwrap();
-    c.bench_function("compute_offsets", |b| {
-        b.iter(|| compute_offsets(black_box(&contents)))
+    c.bench_function("rope", |b| {
+        b.iter(|| {
+            let rope = Rope::from_str(black_box(&contents));
+            rope.line_to_char(black_box(4));
+        })
     });
 }
 

examples/generate_check_code_prefix.rs

@@ -31,6 +31,8 @@ fn main() {
         .derive("Debug")
         .derive("PartialEq")
         .derive("Eq")
+        .derive("PartialOrd")
+        .derive("Ord")
         .derive("Clone")
         .derive("Serialize")
         .derive("Deserialize");

flake8_to_ruff/Cargo.lock

@@ -771,7 +771,7 @@ checksum = "0ce7134b9999ecaf8bcd65542e436736ef32ddca1b3e06094cb6ec5755203b80"
 
 [[package]]
 name = "flake8_to_ruff"
-version = "0.0.99"
+version = "0.0.100"
 dependencies = [
  "anyhow",
  "clap",
@@ -1975,7 +1975,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.0.99"
+version = "0.0.100"
 dependencies = [
  "anyhow",
  "bincode",

flake8_to_ruff/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "flake8-to-ruff"
-version = "0.0.99-dev.0"
+version = "0.0.100-dev.0"
 edition = "2021"
 
 [lib]

flake8_to_ruff/README.md

@@ -17,7 +17,7 @@ pip install flake8-to-ruff
 
 ### Usage
 
-To run Ruff, try any of the following:
+To run `flake8-to-ruff`:
 
 ```shell
 flake8-to-ruff path/to/setup.cfg
@@ -25,6 +25,60 @@ flake8-to-ruff path/to/tox.ini
 flake8-to-ruff path/to/.flake8
 ```
 
+`flake8-to-ruff` will print the relevant `pyproject.toml` sections to standard output, like so:
+
+```toml
+[tool.ruff]
+exclude = [
+    '.svn',
+    'CVS',
+    '.bzr',
+    '.hg',
+    '.git',
+    '__pycache__',
+    '.tox',
+    '.idea',
+    '.mypy_cache',
+    '.venv',
+    'node_modules',
+    '_state_machine.py',
+    'test_fstring.py',
+    'bad_coding2.py',
+    'badsyntax_*.py',
+]
+select = [
+    'A',
+    'E',
+    'F',
+    'Q',
+]
+ignore = []
+
+[tool.ruff.flake8-quotes]
+inline-quotes = 'single'
+
+[tool.ruff.pep8-naming]
+ignore-names = [
+    'foo',
+    'bar',
+]
+```
+
+### Plugins
+
+`flake8-to-ruff` will attempt to infer any activated plugins based on the settings provided in your
+configuration file.
+
+For example, if your `.flake8` file includes a `docstring-convention` property, `flake8-to-ruff`
+will enable the appropriate [`flake8-docstrings`](https://pypi.org/project/flake8-docstrings/)
+checks.
+
+Alternatively, you can manually specify plugins on the command-line:
+
+```shell
+flake8-to-ruff path/to/.flake8 --plugin flake8-builtins --plugin flake8-quotes
+```
+
 ## Limitations
 
 1. Ruff only supports a subset of the Flake configuration options. `flake8-to-ruff` will warn on and
@@ -33,9 +87,6 @@ flake8-to-ruff path/to/.flake8
 2. Ruff will omit any error codes that are unimplemented or unsupported by Ruff, including error
    codes from unsupported plugins. (See the [Ruff README](https://github.com/charliermarsh/ruff#user-content-how-does-ruff-compare-to-flake8)
    for the complete list of supported plugins.)
-3. `flake8-to-ruff` does not auto-detect your Flake8 plugins, so any reliance on Flake8 plugins that
-   implicitly enable third-party checks will be ignored. Instead, add those error codes to your
-   `select` or `extend-select` fields, so that `flake8-to-ruff` can pick them up.
 
 ## License
 

flake8_to_ruff/examples/poetry.ini

@@ -0,0 +1,36 @@
+[flake8]
+min_python_version = 3.7.0
+max-line-length = 88
+ban-relative-imports = true
+# flake8-use-fstring: https://github.com/MichaelKim0407/flake8-use-fstring#--percent-greedy-and---format-greedy
+format-greedy = 1
+inline-quotes = double
+enable-extensions = TC, TC1
+type-checking-strict = true
+eradicate-whitelist-extend = ^-.*;
+extend-ignore =
+    # E203: Whitespace before ':' (pycqa/pycodestyle#373)
+    E203,
+    # SIM106: Handle error-cases first
+    SIM106,
+    # ANN101: Missing type annotation for self in method
+    ANN101,
+    # ANN102: Missing type annotation for cls in classmethod
+    ANN102,
+    # PIE781: assign-and-return
+    PIE781,
+    # PIE798 no-unnecessary-class: Consider using a module for namespacing instead
+    PIE798,
+per-file-ignores =
+    # TC002: Move third-party import '...' into a type-checking block
+    __init__.py:TC002,
+    # ANN201: Missing return type annotation for public function
+    tests/test_*:ANN201
+    tests/**/test_*:ANN201
+extend-exclude =
+    # Frozen and not subject to change in this repo:
+    get-poetry.py,
+    install-poetry.py,
+    # External to the project's coding standards:
+    tests/fixtures/*,
+    tests/**/fixtures/*,

flake8_to_ruff/examples/python-discord.ini

@@ -0,0 +1,19 @@
+[flake8]
+max-line-length=120
+docstring-convention=all
+import-order-style=pycharm
+application_import_names=bot,tests
+exclude=.cache,.venv,.git,constants.py
+extend-ignore=
+    B311,W503,E226,S311,T000,E731
+    # Missing Docstrings
+    D100,D104,D105,D107,
+    # Docstring Whitespace
+    D203,D212,D214,D215,
+    # Docstring Quotes
+    D301,D302,
+    # Docstring Content
+    D400,D401,D402,D404,D405,D406,D407,D408,D409,D410,D411,D412,D413,D414,D416,D417
+    # Type Annotations
+    ANN002,ANN003,ANN101,ANN102,ANN204,ANN206,ANN401
+per-file-ignores=tests/*:D,ANN

flake8_to_ruff/examples/requests.ini

@@ -0,0 +1,6 @@
+[flake8]
+ignore = E203, E501, W503
+per-file-ignores =
+    requests/__init__.py:E402, F401
+    requests/compat.py:E402, F401
+    tests/compat.py:F401

flake8_to_ruff/src/converter.rs

@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{BTreeSet, HashMap};
 
 use anyhow::Result;
 use ruff::flake8_quotes::settings::Quote;
@@ -6,13 +6,36 @@ use ruff::settings::options::Options;
 use ruff::settings::pyproject::Pyproject;
 use ruff::{flake8_quotes, pep8_naming};
 
-use crate::parser;
+use crate::plugin::Plugin;
+use crate::{parser, plugin};
 
-pub fn convert(config: HashMap<String, HashMap<String, Option<String>>>) -> Result<Pyproject> {
-    // Extract the Flake8 section.
-    let flake8 = config
-        .get("flake8")
-        .expect("Unable to find flake8 section in INI file.");
+pub fn convert(
+    flake8: &HashMap<String, Option<String>>,
+    plugins: Option<Vec<Plugin>>,
+) -> Result<Pyproject> {
+    // Check if the user has specified a `select`. If not, we'll add our own
+    // default `select`, and populate it based on user plugins.
+    let mut select = flake8
+        .get("select")
+        .and_then(|value| {
+            value
+                .as_ref()
+                .map(|value| BTreeSet::from_iter(parser::parse_prefix_codes(value)))
+        })
+        .unwrap_or_else(|| {
+            plugin::resolve_select(
+                flake8,
+                &plugins.unwrap_or_else(|| plugin::infer_plugins(flake8)),
+            )
+        });
+    let mut ignore = flake8
+        .get("ignore")
+        .and_then(|value| {
+            value
+                .as_ref()
+                .map(|value| BTreeSet::from_iter(parser::parse_prefix_codes(value)))
+        })
+        .unwrap_or_default();
 
     // Parse each supported option.
     let mut options: Options = Default::default();
@@ -27,16 +50,18 @@ pub fn convert(config: HashMap<String, HashMap<String, Option<String>>>) -> Resu
                     Err(e) => eprintln!("Unable to parse '{key}' property: {e}"),
                 },
                 "select" => {
-                    options.select = Some(parser::parse_prefix_codes(value.as_ref()));
-                }
-                "extend-select" | "extend_select" => {
-                    options.extend_select = Some(parser::parse_prefix_codes(value.as_ref()));
+                    // No-op (handled above).
                 }
                 "ignore" => {
-                    options.ignore = Some(parser::parse_prefix_codes(value.as_ref()));
+                    // No-op (handled above).
+                }
+                "extend-select" | "extend_select" => {
+                    // Unlike Flake8, use a single explicit `select`.
+                    select.extend(parser::parse_prefix_codes(value.as_ref()));
                 }
                 "extend-ignore" | "extend_ignore" => {
-                    options.extend_ignore = Some(parser::parse_prefix_codes(value.as_ref()));
+                    // Unlike Flake8, use a single explicit `ignore`.
+                    ignore.extend(parser::parse_prefix_codes(value.as_ref()));
                 }
                 "exclude" => {
                     options.exclude = Some(parser::parse_strings(value.as_ref()));
@@ -86,12 +111,19 @@ pub fn convert(config: HashMap<String, HashMap<String, Option<String>>>) -> Resu
                     pep8_naming.staticmethod_decorators =
                         Some(parser::parse_strings(value.as_ref()));
                 }
+                // flake8-docstrings
+                "docstring-convention" => {
+                    // No-op (handled above).
+                }
                 // Unknown
                 _ => eprintln!("Skipping unsupported property: {key}"),
             }
         }
     }
 
+    // Deduplicate and sort.
+    options.select = Some(Vec::from_iter(select));
+    options.ignore = Some(Vec::from_iter(ignore));
     if flake8_quotes != Default::default() {
         options.flake8_quotes = Some(flake8_quotes);
     }
@@ -108,22 +140,28 @@ mod tests {
     use std::collections::HashMap;
 
     use anyhow::Result;
+    use ruff::checks_gen::CheckCodePrefix;
     use ruff::flake8_quotes;
     use ruff::settings::options::Options;
     use ruff::settings::pyproject::Pyproject;
 
     use crate::converter::convert;
+    use crate::plugin::Plugin;
 
     #[test]
     fn it_converts_empty() -> Result<()> {
-        let actual = convert(HashMap::from([("flake8".to_string(), HashMap::from([]))]))?;
+        let actual = convert(&HashMap::from([]), None)?;
         let expected = Pyproject::new(Options {
             line_length: None,
             exclude: None,
             extend_exclude: None,
-            select: None,
+            select: Some(vec![
+                CheckCodePrefix::E,
+                CheckCodePrefix::F,
+                CheckCodePrefix::W,
+            ]),
             extend_select: None,
-            ignore: None,
+            ignore: Some(vec![]),
             extend_ignore: None,
             per_file_ignores: None,
             dummy_variable_rgx: None,
@@ -138,17 +176,21 @@ mod tests {
 
     #[test]
     fn it_converts_dashes() -> Result<()> {
-        let actual = convert(HashMap::from([(
-            "flake8".to_string(),
-            HashMap::from([("max-line-length".to_string(), Some("100".to_string()))]),
-        )]))?;
+        let actual = convert(
+            &HashMap::from([("max-line-length".to_string(), Some("100".to_string()))]),
+            Some(vec![]),
+        )?;
         let expected = Pyproject::new(Options {
             line_length: Some(100),
             exclude: None,
             extend_exclude: None,
-            select: None,
+            select: Some(vec![
+                CheckCodePrefix::E,
+                CheckCodePrefix::F,
+                CheckCodePrefix::W,
+            ]),
             extend_select: None,
-            ignore: None,
+            ignore: Some(vec![]),
             extend_ignore: None,
             per_file_ignores: None,
             dummy_variable_rgx: None,
@@ -163,17 +205,21 @@ mod tests {
 
     #[test]
     fn it_converts_underscores() -> Result<()> {
-        let actual = convert(HashMap::from([(
-            "flake8".to_string(),
-            HashMap::from([("max_line_length".to_string(), Some("100".to_string()))]),
-        )]))?;
+        let actual = convert(
+            &HashMap::from([("max_line_length".to_string(), Some("100".to_string()))]),
+            Some(vec![]),
+        )?;
         let expected = Pyproject::new(Options {
             line_length: Some(100),
             exclude: None,
             extend_exclude: None,
-            select: None,
+            select: Some(vec![
+                CheckCodePrefix::E,
+                CheckCodePrefix::F,
+                CheckCodePrefix::W,
+            ]),
             extend_select: None,
-            ignore: None,
+            ignore: Some(vec![]),
             extend_ignore: None,
             per_file_ignores: None,
             dummy_variable_rgx: None,
@@ -188,17 +234,21 @@ mod tests {
 
     #[test]
     fn it_ignores_parse_errors() -> Result<()> {
-        let actual = convert(HashMap::from([(
-            "flake8".to_string(),
-            HashMap::from([("max_line_length".to_string(), Some("abc".to_string()))]),
-        )]))?;
+        let actual = convert(
+            &HashMap::from([("max_line_length".to_string(), Some("abc".to_string()))]),
+            Some(vec![]),
+        )?;
         let expected = Pyproject::new(Options {
             line_length: None,
             exclude: None,
             extend_exclude: None,
-            select: None,
+            select: Some(vec![
+                CheckCodePrefix::E,
+                CheckCodePrefix::F,
+                CheckCodePrefix::W,
+            ]),
             extend_select: None,
-            ignore: None,
+            ignore: Some(vec![]),
             extend_ignore: None,
             per_file_ignores: None,
             dummy_variable_rgx: None,
@@ -212,18 +262,124 @@ mod tests {
     }
 
     #[test]
-    fn it_converts_extensions() -> Result<()> {
-        let actual = convert(HashMap::from([(
-            "flake8".to_string(),
-            HashMap::from([("inline-quotes".to_string(), Some("single".to_string()))]),
-        )]))?;
+    fn it_converts_plugin_options() -> Result<()> {
+        let actual = convert(
+            &HashMap::from([("inline-quotes".to_string(), Some("single".to_string()))]),
+            Some(vec![]),
+        )?;
         let expected = Pyproject::new(Options {
             line_length: None,
             exclude: None,
             extend_exclude: None,
-            select: None,
+            select: Some(vec![
+                CheckCodePrefix::E,
+                CheckCodePrefix::F,
+                CheckCodePrefix::W,
+            ]),
             extend_select: None,
-            ignore: None,
+            ignore: Some(vec![]),
+            extend_ignore: None,
+            per_file_ignores: None,
+            dummy_variable_rgx: None,
+            target_version: None,
+            flake8_quotes: Some(flake8_quotes::settings::Options {
+                inline_quotes: Some(flake8_quotes::settings::Quote::Single),
+                multiline_quotes: None,
+                docstring_quotes: None,
+                avoid_escape: None,
+            }),
+            pep8_naming: None,
+        });
+        assert_eq!(actual, expected);
+
+        Ok(())
+    }
+
+    #[test]
+    fn it_converts_docstring_conventions() -> Result<()> {
+        let actual = convert(
+            &HashMap::from([(
+                "docstring-convention".to_string(),
+                Some("numpy".to_string()),
+            )]),
+            Some(vec![Plugin::Flake8Docstrings]),
+        )?;
+        let expected = Pyproject::new(Options {
+            line_length: None,
+            exclude: None,
+            extend_exclude: None,
+            select: Some(vec![
+                CheckCodePrefix::D100,
+                CheckCodePrefix::D101,
+                CheckCodePrefix::D102,
+                CheckCodePrefix::D103,
+                CheckCodePrefix::D104,
+                CheckCodePrefix::D105,
+                CheckCodePrefix::D106,
+                CheckCodePrefix::D200,
+                CheckCodePrefix::D201,
+                CheckCodePrefix::D202,
+                CheckCodePrefix::D204,
+                CheckCodePrefix::D205,
+                CheckCodePrefix::D206,
+                CheckCodePrefix::D207,
+                CheckCodePrefix::D208,
+                CheckCodePrefix::D209,
+                CheckCodePrefix::D210,
+                CheckCodePrefix::D211,
+                CheckCodePrefix::D214,
+                CheckCodePrefix::D215,
+                CheckCodePrefix::D300,
+                CheckCodePrefix::D400,
+                CheckCodePrefix::D403,
+                CheckCodePrefix::D404,
+                CheckCodePrefix::D405,
+                CheckCodePrefix::D406,
+                CheckCodePrefix::D407,
+                CheckCodePrefix::D408,
+                CheckCodePrefix::D409,
+                CheckCodePrefix::D410,
+                CheckCodePrefix::D411,
+                CheckCodePrefix::D412,
+                CheckCodePrefix::D414,
+                CheckCodePrefix::D418,
+                CheckCodePrefix::D419,
+                CheckCodePrefix::E,
+                CheckCodePrefix::F,
+                CheckCodePrefix::W,
+            ]),
+            extend_select: None,
+            ignore: Some(vec![]),
+            extend_ignore: None,
+            per_file_ignores: None,
+            dummy_variable_rgx: None,
+            target_version: None,
+            flake8_quotes: None,
+            pep8_naming: None,
+        });
+        assert_eq!(actual, expected);
+
+        Ok(())
+    }
+
+    #[test]
+    fn it_infers_plugins_if_omitted() -> Result<()> {
+        let actual = convert(
+            &HashMap::from([("inline-quotes".to_string(), Some("single".to_string()))]),
+            None,
+        )?;
+        let expected = Pyproject::new(Options {
+            line_length: None,
+            exclude: None,
+            extend_exclude: None,
+            select: Some(vec![
+                CheckCodePrefix::E,
+                CheckCodePrefix::F,
+                CheckCodePrefix::Q,
+                CheckCodePrefix::W,
+            ]),
+            extend_select: None,
+            ignore: Some(vec![]),
             extend_ignore: None,
             per_file_ignores: None,
             dummy_variable_rgx: None,

flake8_to_ruff/src/lib.rs

@@ -2,3 +2,4 @@
 
 pub mod converter;
 mod parser;
+pub mod plugin;

flake8_to_ruff/src/main.rs

@@ -6,6 +6,7 @@ use anyhow::Result;
 use clap::Parser;
 use configparser::ini::Ini;
 use flake8_to_ruff::converter;
+use flake8_to_ruff::plugin::Plugin;
 
 #[derive(Parser)]
 #[command(
@@ -17,6 +18,9 @@ struct Cli {
     /// '.flake8').
     #[arg(required = true)]
     file: PathBuf,
+    /// List of plugins to enable.
+    #[arg(long, value_delimiter = ',')]
+    plugin: Option<Vec<Plugin>>,
 }
 
 fn main() -> Result<()> {
@@ -27,8 +31,13 @@ fn main() -> Result<()> {
     ini.set_multiline(true);
     let config = ini.load(cli.file).map_err(|msg| anyhow::anyhow!(msg))?;
 
+    // Extract the Flake8 section.
+    let flake8 = config
+        .get("flake8")
+        .expect("Unable to find flake8 section in INI file.");
+
     // Create the pyproject.toml.
-    let pyproject = converter::convert(config)?;
+    let pyproject = converter::convert(flake8, cli.plugin)?;
     println!("{}", toml::to_string_pretty(&pyproject)?);
 
     Ok(())

flake8_to_ruff/src/plugin.rs

@@ -0,0 +1,321 @@
+use std::collections::{BTreeSet, HashMap};
+use std::str::FromStr;
+
+use anyhow::anyhow;
+use ruff::checks_gen::CheckCodePrefix;
+
+#[derive(Debug, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub enum Plugin {
+    Flake8Bugbear,
+    Flake8Builtins,
+    Flake8Comprehensions,
+    Flake8Docstrings,
+    Flake8Print,
+    Flake8Quotes,
+    PEP8Naming,
+    Pyupgrade,
+}
+
+impl FromStr for Plugin {
+    type Err = anyhow::Error;
+
+    fn from_str(string: &str) -> Result<Self, Self::Err> {
+        match string {
+            "flake8-bugbear" => Ok(Plugin::Flake8Bugbear),
+            "flake8-builtins" => Ok(Plugin::Flake8Builtins),
+            "flake8-comprehensions" => Ok(Plugin::Flake8Comprehensions),
+            "flake8-docstrings" => Ok(Plugin::Flake8Docstrings),
+            "flake8-print" => Ok(Plugin::Flake8Print),
+            "flake8-quotes" => Ok(Plugin::Flake8Quotes),
+            "pep8-naming" => Ok(Plugin::PEP8Naming),
+            "pyupgrade" => Ok(Plugin::Pyupgrade),
+            _ => Err(anyhow!("Unknown plugin: {}", string)),
+        }
+    }
+}
+
+impl Plugin {
+    pub fn select(&self, flake8: &HashMap<String, Option<String>>) -> Vec<CheckCodePrefix> {
+        match self {
+            Plugin::Flake8Bugbear => vec![CheckCodePrefix::B],
+            Plugin::Flake8Builtins => vec![CheckCodePrefix::A],
+            Plugin::Flake8Comprehensions => vec![CheckCodePrefix::C],
+            Plugin::Flake8Docstrings => {
+                // Use the user-provided docstring.
+                for key in ["docstring-convention", "docstring_convention"] {
+                    if let Some(Some(value)) = flake8.get(key) {
+                        match DocstringConvention::from_str(value) {
+                            Ok(convention) => return convention.select(),
+                            Err(e) => {
+                                eprintln!("Unexpected '{key}' value: {value} ({e}");
+                                return vec![];
+                            }
+                        }
+                    }
+                }
+                // Default to PEP8.
+                DocstringConvention::PEP8.select()
+            }
+            Plugin::Flake8Print => vec![CheckCodePrefix::T],
+            Plugin::Flake8Quotes => vec![CheckCodePrefix::Q],
+            Plugin::PEP8Naming => vec![CheckCodePrefix::N],
+            Plugin::Pyupgrade => vec![CheckCodePrefix::U],
+        }
+    }
+}
+
+pub enum DocstringConvention {
+    All,
+    PEP8,
+    NumPy,
+    Google,
+}
+
+impl FromStr for DocstringConvention {
+    type Err = anyhow::Error;
+
+    fn from_str(string: &str) -> Result<Self, Self::Err> {
+        match string {
+            "all" => Ok(DocstringConvention::All),
+            "pep8" => Ok(DocstringConvention::PEP8),
+            "numpy" => Ok(DocstringConvention::NumPy),
+            "google" => Ok(DocstringConvention::Google),
+            _ => Err(anyhow!("Unknown docstring convention: {}", string)),
+        }
+    }
+}
+
+impl DocstringConvention {
+    fn select(&self) -> Vec<CheckCodePrefix> {
+        match self {
+            DocstringConvention::All => vec![CheckCodePrefix::D],
+            DocstringConvention::PEP8 => vec![
+                // All errors except D203, D212, D213, D214, D215, D404, D405, D406, D407, D408,
+                // D409, D410, D411, D413, D415, D416 and D417.
+                CheckCodePrefix::D100,
+                CheckCodePrefix::D101,
+                CheckCodePrefix::D102,
+                CheckCodePrefix::D103,
+                CheckCodePrefix::D104,
+                CheckCodePrefix::D105,
+                CheckCodePrefix::D106,
+                CheckCodePrefix::D107,
+                CheckCodePrefix::D200,
+                CheckCodePrefix::D201,
+                CheckCodePrefix::D202,
+                // CheckCodePrefix::D203,
+                CheckCodePrefix::D204,
+                CheckCodePrefix::D205,
+                CheckCodePrefix::D206,
+                CheckCodePrefix::D207,
+                CheckCodePrefix::D208,
+                CheckCodePrefix::D209,
+                CheckCodePrefix::D210,
+                CheckCodePrefix::D211,
+                // CheckCodePrefix::D212,
+                // CheckCodePrefix::D213,
+                // CheckCodePrefix::D214,
+                // CheckCodePrefix::D215,
+                CheckCodePrefix::D300,
+                CheckCodePrefix::D400,
+                CheckCodePrefix::D402,
+                CheckCodePrefix::D403,
+                // CheckCodePrefix::D404,
+                // CheckCodePrefix::D405,
+                // CheckCodePrefix::D406,
+                // CheckCodePrefix::D407,
+                // CheckCodePrefix::D408,
+                // CheckCodePrefix::D409,
+                // CheckCodePrefix::D410,
+                // CheckCodePrefix::D411,
+                CheckCodePrefix::D412,
+                // CheckCodePrefix::D413,
+                CheckCodePrefix::D414,
+                // CheckCodePrefix::D415,
+                // CheckCodePrefix::D416,
+                // CheckCodePrefix::D417,
+                CheckCodePrefix::D418,
+                CheckCodePrefix::D419,
+            ],
+            DocstringConvention::NumPy => vec![
+                // All errors except D107, D203, D212, D213, D402, D413, D415, D416, and D417.
+                CheckCodePrefix::D100,
+                CheckCodePrefix::D101,
+                CheckCodePrefix::D102,
+                CheckCodePrefix::D103,
+                CheckCodePrefix::D104,
+                CheckCodePrefix::D105,
+                CheckCodePrefix::D106,
+                // CheckCodePrefix::D107,
+                CheckCodePrefix::D200,
+                CheckCodePrefix::D201,
+                CheckCodePrefix::D202,
+                // CheckCodePrefix::D203,
+                CheckCodePrefix::D204,
+                CheckCodePrefix::D205,
+                CheckCodePrefix::D206,
+                CheckCodePrefix::D207,
+                CheckCodePrefix::D208,
+                CheckCodePrefix::D209,
+                CheckCodePrefix::D210,
+                CheckCodePrefix::D211,
+                // CheckCodePrefix::D212,
+                // CheckCodePrefix::D213,
+                CheckCodePrefix::D214,
+                CheckCodePrefix::D215,
+                CheckCodePrefix::D300,
+                CheckCodePrefix::D400,
+                // CheckCodePrefix::D402,
+                CheckCodePrefix::D403,
+                CheckCodePrefix::D404,
+                CheckCodePrefix::D405,
+                CheckCodePrefix::D406,
+                CheckCodePrefix::D407,
+                CheckCodePrefix::D408,
+                CheckCodePrefix::D409,
+                CheckCodePrefix::D410,
+                CheckCodePrefix::D411,
+                CheckCodePrefix::D412,
+                // CheckCodePrefix::D413,
+                CheckCodePrefix::D414,
+                // CheckCodePrefix::D415,
+                // CheckCodePrefix::D416,
+                // CheckCodePrefix::D417,
+                CheckCodePrefix::D418,
+                CheckCodePrefix::D419,
+            ],
+            DocstringConvention::Google => vec![
+                // All errors except D203, D204, D213, D215, D400, D401, D404, D406, D407, D408,
+                // D409 and D413.
+                CheckCodePrefix::D100,
+                CheckCodePrefix::D101,
+                CheckCodePrefix::D102,
+                CheckCodePrefix::D103,
+                CheckCodePrefix::D104,
+                CheckCodePrefix::D105,
+                CheckCodePrefix::D106,
+                CheckCodePrefix::D107,
+                CheckCodePrefix::D200,
+                CheckCodePrefix::D201,
+                CheckCodePrefix::D202,
+                // CheckCodePrefix::D203,
+                // CheckCodePrefix::D204,
+                CheckCodePrefix::D205,
+                CheckCodePrefix::D206,
+                CheckCodePrefix::D207,
+                CheckCodePrefix::D208,
+                CheckCodePrefix::D209,
+                CheckCodePrefix::D210,
+                CheckCodePrefix::D211,
+                CheckCodePrefix::D212,
+                // CheckCodePrefix::D213,
+                CheckCodePrefix::D214,
+                // CheckCodePrefix::D215,
+                CheckCodePrefix::D300,
+                // CheckCodePrefix::D400,
+                CheckCodePrefix::D402,
+                CheckCodePrefix::D403,
+                // CheckCodePrefix::D404,
+                CheckCodePrefix::D405,
+                // CheckCodePrefix::D406,
+                // CheckCodePrefix::D407,
+                // CheckCodePrefix::D408,
+                // CheckCodePrefix::D409,
+                CheckCodePrefix::D410,
+                CheckCodePrefix::D411,
+                CheckCodePrefix::D412,
+                // CheckCodePrefix::D413,
+                CheckCodePrefix::D414,
+                CheckCodePrefix::D415,
+                CheckCodePrefix::D416,
+                CheckCodePrefix::D417,
+                CheckCodePrefix::D418,
+                CheckCodePrefix::D419,
+            ],
+        }
+    }
+}
+
+/// Infer the enabled plugins based on user-provided settings.
+pub fn infer_plugins(flake8: &HashMap<String, Option<String>>) -> Vec<Plugin> {
+    let mut plugins = BTreeSet::new();
+    for key in flake8.keys() {
+        match key.as_str() {
+            // flake8-docstrings
+            "docstring-convention" | "docstring_convention" => {
+                plugins.insert(Plugin::Flake8Docstrings);
+            }
+            // flake8-builtins
+            "builtins-ignorelist" | "builtins_ignorelist" => {
+                plugins.insert(Plugin::Flake8Builtins);
+            }
+            // flake8-quotes
+            "quotes" | "inline-quotes" | "inline_quotes" => {
+                plugins.insert(Plugin::Flake8Quotes);
+            }
+            "multiline-quotes" | "multiline_quotes" => {
+                plugins.insert(Plugin::Flake8Quotes);
+            }
+            "docstring-quotes" | "docstring_quotes" => {
+                plugins.insert(Plugin::Flake8Quotes);
+            }
+            "avoid-escape" | "avoid_escape" => {
+                plugins.insert(Plugin::Flake8Quotes);
+            }
+            // pep8-naming
+            "ignore-names" | "ignore_names" => {
+                plugins.insert(Plugin::PEP8Naming);
+            }
+            "classmethod-decorators" | "classmethod_decorators" => {
+                plugins.insert(Plugin::PEP8Naming);
+            }
+            "staticmethod-decorators" | "staticmethod_decorators" => {
+                plugins.insert(Plugin::PEP8Naming);
+            }
+            _ => {}
+        }
+    }
+    Vec::from_iter(plugins)
+}
+
+/// Resolve the set of enabled `CheckCodePrefix` values for the given plugins.
+pub fn resolve_select(
+    flake8: &HashMap<String, Option<String>>,
+    plugins: &[Plugin],
+) -> BTreeSet<CheckCodePrefix> {
+    // Include default Pyflakes and pycodestyle checks.
+    let mut select = BTreeSet::from([CheckCodePrefix::E, CheckCodePrefix::F, CheckCodePrefix::W]);
+
+    // Add prefix codes for every plugin.
+    for plugin in plugins {
+        for prefix in plugin.select(flake8) {
+            select.insert(prefix);
+        }
+    }
+
+    select
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashMap;
+
+    use crate::plugin::{infer_plugins, Plugin};
+
+    #[test]
+    fn it_infers_plugins() {
+        let actual = infer_plugins(&HashMap::from([(
+            "inline-quotes".to_string(),
+            Some("single".to_string()),
+        )]));
+        let expected = vec![Plugin::Flake8Quotes];
+        assert_eq!(actual, expected);
+
+        let actual = infer_plugins(&HashMap::from([(
+            "staticmethod-decorators".to_string(),
+            Some("[]".to_string()),
+        )]));
+        let expected = vec![Plugin::PEP8Naming];
+        assert_eq!(actual, expected);
+    }
+}

resources/test/fixtures/B018.py

@@ -0,0 +1,55 @@
+class Foo1:
+    """abc"""
+
+
+class Foo2:
+    """abc"""
+
+    a = 2
+    "str"  # Str (no raise)
+    f"{int}"  # JoinedStr (no raise)
+    1j  # Number (complex)
+    1  # Number (int)
+    1.0  # Number (float)
+    b"foo"  # Binary
+    True  # NameConstant (True)
+    False  # NameConstant (False)
+    None  # NameConstant (None)
+    [1, 2]  # list
+    {1, 2}  # set
+    {"foo": "bar"}  # dict
+
+
+class Foo3:
+    123
+    a = 2
+    "str"
+    1
+
+
+def foo1():
+    """my docstring"""
+
+
+def foo2():
+    """my docstring"""
+    a = 2
+    "str"  # Str (no raise)
+    f"{int}"  # JoinedStr (no raise)
+    1j  # Number (complex)
+    1  # Number (int)
+    1.0  # Number (float)
+    b"foo"  # Binary
+    True  # NameConstant (True)
+    False  # NameConstant (False)
+    None  # NameConstant (None)
+    [1, 2]  # list
+    {1, 2}  # set
+    {"foo": "bar"}  # dict
+
+
+def foo3():
+    123
+    a = 2
+    "str"
+    3

resources/test/fixtures/F821_3.py

@@ -0,0 +1,14 @@
+"""Test (edge case): accesses of object named `dict`."""
+
+# OK
+dict = {"parameters": {}}
+dict["parameters"]["userId"] = "userId"
+dict["parameters"]["itemId"] = "itemId"
+del dict["parameters"]["itemId"]
+
+# F821 Undefined name `key`
+# F821 Undefined name `value`
+x: dict["key", "value"]
+
+# OK
+x: dict[str, str]

resources/test/fixtures/X001.py

@@ -0,0 +1,6 @@
+x = "𝐁ad string"
+
+
+def f():
+    """Here's a comment with an unusual parenthesis: ）"""
+    ...

rust-toolchain

@@ -1 +1 @@
-1.64.0
+1.65.0

src/autofix/fixer.rs

@@ -1,10 +1,14 @@
+use std::borrow::Cow;
 use std::collections::BTreeSet;
 
 use itertools::Itertools;
+use ropey::RopeBuilder;
 use rustpython_parser::ast::Location;
 
+use crate::ast::types::Range;
 use crate::autofix::{Fix, Patch};
 use crate::checks::Check;
+use crate::source_code_locator::SourceCodeLocator;
 
 // TODO(charlie): The model here is awkward because `Apply` is only relevant at
 // higher levels in the execution flow.
@@ -36,24 +40,28 @@ impl From<bool> for Mode {
 }
 
 /// Auto-fix errors in a file, and write the fixed source code to disk.
-pub fn fix_file(checks: &mut [Check], contents: &str) -> Option<String> {
+pub fn fix_file<'a>(
+    checks: &'a mut [Check],
+    locator: &'a SourceCodeLocator<'a>,
+) -> Option<Cow<'a, str>> {
     if checks.iter().all(|check| check.fix.is_none()) {
         return None;
     }
 
     Some(apply_fixes(
         checks.iter_mut().filter_map(|check| check.fix.as_mut()),
-        contents,
+        locator,
     ))
 }
 
 /// Apply a series of fixes.
-fn apply_fixes<'a>(fixes: impl Iterator<Item = &'a mut Fix>, contents: &str) -> String {
-    let lines: Vec<&str> = contents.lines().collect();
-
-    let mut output: String = Default::default();
-    let mut last_pos: Location = Default::default();
-    let mut applied: BTreeSet<&Patch> = Default::default();
+fn apply_fixes<'a>(
+    fixes: impl Iterator<Item = &'a mut Fix>,
+    locator: &'a SourceCodeLocator<'a>,
+) -> Cow<'a, str> {
+    let mut output = RopeBuilder::new();
+    let mut last_pos: Location = Location::new(1, 0);
+    let mut applied: BTreeSet<&Patch> = BTreeSet::new();
 
     for fix in fixes.sorted_by_key(|fix| fix.patch.location) {
         // If we already applied an identical fix as part of another correction, skip
@@ -69,44 +77,27 @@ fn apply_fixes<'a>(fixes: impl Iterator<Item = &'a mut Fix>, contents: &str) ->
             continue;
         }
 
-        if fix.patch.location.row() > last_pos.row() {
-            if last_pos.row() > 0 || last_pos.column() > 0 {
-                output.push_str(&lines[last_pos.row() - 1][last_pos.column()..]);
-                output.push('\n');
-            }
-            for line in &lines[last_pos.row()..fix.patch.location.row() - 1] {
-                output.push_str(line);
-                output.push('\n');
-            }
-            output.push_str(&lines[fix.patch.location.row() - 1][..fix.patch.location.column()]);
-            output.push_str(&fix.patch.content);
-        } else {
-            output.push_str(
-                &lines[last_pos.row() - 1][last_pos.column()..fix.patch.location.column()],
-            );
-            output.push_str(&fix.patch.content);
-        }
-        last_pos = fix.patch.end_location;
+        // Add all contents from `last_pos` to `fix.patch.location`.
+        let slice = locator.slice_source_code_range(&Range {
+            location: last_pos,
+            end_location: fix.patch.location,
+        });
+        output.append(&slice);
 
+        // Add the patch itself.
+        output.append(&fix.patch.content);
+
+        // Track that the fix was applied.
+        last_pos = fix.patch.end_location;
         applied.insert(&fix.patch);
         fix.applied = true;
     }
 
-    if last_pos.row() > 0
-        && (last_pos.row() - 1) < lines.len()
-        && (last_pos.row() > 0 || last_pos.column() > 0)
-    {
-        output.push_str(&lines[last_pos.row() - 1][last_pos.column()..]);
-        output.push('\n');
-    }
-    if last_pos.row() < lines.len() {
-        for line in &lines[last_pos.row()..] {
-            output.push_str(line);
-            output.push('\n');
-        }
-    }
+    // Add the remaining content.
+    let slice = locator.slice_source_code_at(&last_pos);
+    output.append(&slice);
 
-    output
+    Cow::from(output.finish())
 }
 
 #[cfg(test)]
@@ -116,11 +107,13 @@ mod tests {
 
     use crate::autofix::fixer::apply_fixes;
     use crate::autofix::{Fix, Patch};
+    use crate::SourceCodeLocator;
 
     #[test]
     fn empty_file() -> Result<()> {
         let mut fixes = vec![];
-        let actual = apply_fixes(fixes.iter_mut(), "");
+        let locator = SourceCodeLocator::new("");
+        let actual = apply_fixes(fixes.iter_mut(), &locator);
         let expected = "";
 
         assert_eq!(actual, expected);
@@ -138,12 +131,12 @@ mod tests {
             },
             applied: false,
         }];
-        let actual = apply_fixes(
-            fixes.iter_mut(),
+        let locator = SourceCodeLocator::new(
             "class A(object):
         ...
 ",
         );
+        let actual = apply_fixes(fixes.iter_mut(), &locator);
 
         let expected = "class A(Bar):
         ...
@@ -164,12 +157,12 @@ mod tests {
             },
             applied: false,
         }];
-        let actual = apply_fixes(
-            fixes.iter_mut(),
+        let locator = SourceCodeLocator::new(
             "class A(object):
         ...
 ",
         );
+        let actual = apply_fixes(fixes.iter_mut(), &locator);
 
         let expected = "class A:
         ...
@@ -200,12 +193,12 @@ mod tests {
                 applied: false,
             },
         ];
-        let actual = apply_fixes(
-            fixes.iter_mut(),
+        let locator = SourceCodeLocator::new(
             "class A(object, object):
         ...
 ",
         );
+        let actual = apply_fixes(fixes.iter_mut(), &locator);
 
         let expected = "class A:
         ...
@@ -236,12 +229,12 @@ mod tests {
                 applied: false,
             },
         ];
-        let actual = apply_fixes(
-            fixes.iter_mut(),
+        let locator = SourceCodeLocator::new(
             "class A(object):
     ...
 ",
         );
+        let actual = apply_fixes(fixes.iter_mut(), &locator);
 
         let expected = "class A:
     ...

src/check_ast.rs

@@ -79,6 +79,7 @@ pub struct Checker<'a> {
     in_f_string: Option<Range>,
     in_annotation: bool,
     in_literal: bool,
+    in_subscript: bool,
     seen_import_boundary: bool,
     futures_allowed: bool,
     annotations_future_enabled: bool,
@@ -118,6 +119,7 @@ impl<'a> Checker<'a> {
             in_f_string: Default::default(),
             in_annotation: Default::default(),
             in_literal: Default::default(),
+            in_subscript: Default::default(),
             seen_import_boundary: Default::default(),
             futures_allowed: true,
             annotations_future_enabled: Default::default(),
@@ -238,6 +240,7 @@ where
                 decorator_list,
                 returns,
                 args,
+                body,
                 ..
             }
             | StmtKind::AsyncFunctionDef {
@@ -245,6 +248,7 @@ where
                 decorator_list,
                 returns,
                 args,
+                body,
                 ..
             } => {
                 if self.settings.enabled.contains(&CheckCode::E743) {
@@ -298,6 +302,10 @@ where
                     }
                 }
 
+                if self.settings.enabled.contains(&CheckCode::B018) {
+                    flake8_bugbear::plugins::useless_expression(self, body);
+                }
+
                 self.check_builtin_shadowing(name, Range::from_located(stmt), true);
 
                 // Visit the decorators and arguments, but avoid the body, which will be
@@ -368,6 +376,7 @@ where
                 bases,
                 keywords,
                 decorator_list,
+                body,
                 ..
             } => {
                 if self.settings.enabled.contains(&CheckCode::U004) {
@@ -399,6 +408,10 @@ where
                     }
                 }
 
+                if self.settings.enabled.contains(&CheckCode::B018) {
+                    flake8_bugbear::plugins::useless_expression(self, body);
+                }
+
                 self.check_builtin_shadowing(
                     name,
                     self.locate_check(Range::from_located(stmt)),
@@ -717,9 +730,7 @@ where
             StmtKind::Raise { exc, .. } => {
                 if self.settings.enabled.contains(&CheckCode::F901) {
                     if let Some(expr) = exc {
-                        if let Some(check) = pyflakes::checks::raise_not_implemented(expr) {
-                            self.checks.push(check);
-                        }
+                        pyflakes::plugins::raise_not_implemented(self, expr);
                     }
                 }
             }
@@ -1490,36 +1501,56 @@ where
                 }
             }
             ExprKind::Subscript { value, slice, ctx } => {
-                match typing::match_annotated_subscript(value, &self.from_imports) {
-                    Some(subscript) => match subscript {
-                        // Ex) Optional[int]
-                        SubscriptKind::AnnotatedSubscript => {
-                            self.visit_expr(value);
-                            self.visit_annotation(slice);
-                            self.visit_expr_context(ctx);
-                        }
-                        // Ex) Annotated[int, "Hello, world!"]
-                        SubscriptKind::PEP593AnnotatedSubscript => {
-                            // First argument is a type (including forward references); the rest are
-                            // arbitrary Python objects.
-                            self.visit_expr(value);
-                            if let ExprKind::Tuple { elts, ctx } = &slice.node {
-                                if let Some(expr) = elts.first() {
-                                    self.visit_expr(expr);
-                                    self.in_annotation = false;
-                                    for expr in elts.iter().skip(1) {
-                                        self.visit_expr(expr);
-                                    }
-                                    self.in_annotation = true;
+                // Only allow annotations in `ExprContext::Load`. If we have, e.g.,
+                // `obj["foo"]["bar"]`, we need to avoid treating the `obj["foo"]`
+                // portion as an annotation, despite having `ExprContext::Load`. Thus, we track
+                // the `ExprContext` at the top-level.
+                let prev_in_subscript = self.in_subscript;
+                if self.in_subscript {
+                    visitor::walk_expr(self, expr);
+                } else if matches!(ctx, ExprContext::Store | ExprContext::Del) {
+                    self.in_subscript = true;
+                    visitor::walk_expr(self, expr);
+                } else {
+                    self.in_subscript = true;
+                    match typing::match_annotated_subscript(value, &self.from_imports) {
+                        Some(subscript) => {
+                            match subscript {
+                                // Ex) Optional[int]
+                                SubscriptKind::AnnotatedSubscript => {
+                                    self.visit_expr(value);
+                                    self.visit_annotation(slice);
                                     self.visit_expr_context(ctx);
                                 }
-                            } else {
-                                error!("Found non-ExprKind::Tuple argument to PEP 593 Annotation.")
+                                // Ex) Annotated[int, "Hello, world!"]
+                                SubscriptKind::PEP593AnnotatedSubscript => {
+                                    // First argument is a type (including forward references); the
+                                    // rest are arbitrary Python
+                                    // objects.
+                                    self.visit_expr(value);
+                                    if let ExprKind::Tuple { elts, ctx } = &slice.node {
+                                        if let Some(expr) = elts.first() {
+                                            self.visit_expr(expr);
+                                            self.in_annotation = false;
+                                            for expr in elts.iter().skip(1) {
+                                                self.visit_expr(expr);
+                                            }
+                                            self.in_annotation = true;
+                                            self.visit_expr_context(ctx);
+                                        }
+                                    } else {
+                                        error!(
+                                            "Found non-ExprKind::Tuple argument to PEP 593 \
+                                             Annotation."
+                                        )
+                                    }
+                                }
                             }
                         }
-                    },
-                    None => visitor::walk_expr(self, expr),
+                        None => visitor::walk_expr(self, expr),
+                    }
                 }
+                self.in_subscript = prev_in_subscript;
             }
             _ => visitor::walk_expr(self, expr),
         }

src/check_tokens.rs

@@ -2,17 +2,20 @@
 
 use rustpython_parser::lexer::{LexResult, Tok};
 
+use crate::autofix::fixer;
 use crate::checks::{Check, CheckCode};
 use crate::flake8_quotes::docstring_detection::StateMachine;
 use crate::source_code_locator::SourceCodeLocator;
-use crate::{flake8_quotes, pycodestyle, Settings};
+use crate::{flake8_quotes, pycodestyle, rules, Settings};
 
 pub fn check_tokens(
     checks: &mut Vec<Check>,
     locator: &SourceCodeLocator,
     tokens: &[LexResult],
     settings: &Settings,
+    autofix: &fixer::Mode,
 ) {
+    let enforce_ambiguous_unicode_character = settings.enabled.contains(&CheckCode::X001);
     let enforce_invalid_escape_sequence = settings.enabled.contains(&CheckCode::W605);
     let enforce_quotes = settings.enabled.contains(&CheckCode::Q000)
         | settings.enabled.contains(&CheckCode::Q001)
@@ -21,6 +24,18 @@ pub fn check_tokens(
 
     let mut state_machine: StateMachine = Default::default();
     for (start, tok, end) in tokens.iter().flatten() {
+        // X001
+        if enforce_ambiguous_unicode_character {
+            if matches!(tok, Tok::String { .. }) {
+                checks.extend(rules::checks::ambiguous_unicode_character(
+                    locator,
+                    start,
+                    end,
+                    autofix.patch(),
+                ));
+            }
+        }
+
         // W605
         if enforce_invalid_escape_sequence {
             if matches!(tok, Tok::String { .. }) {

src/checks.rs

@@ -84,6 +84,7 @@ pub enum CheckCode {
     B013,
     B014,
     B017,
+    B018,
     B025,
     // flake8-comprehensions
     C400,
@@ -180,6 +181,8 @@ pub enum CheckCode {
     N816,
     N817,
     N818,
+    // Ruff
+    X001,
     // Meta
     M001,
 }
@@ -197,6 +200,7 @@ pub enum CheckCategory {
     Flake8Builtins,
     Flake8Print,
     Flake8Quotes,
+    Ruff,
     Meta,
 }
 
@@ -214,6 +218,7 @@ impl CheckCategory {
             CheckCategory::Pyupgrade => "pyupgrade",
             CheckCategory::Pydocstyle => "pydocstyle",
             CheckCategory::PEP8Naming => "pep8-naming",
+            CheckCategory::Ruff => "Ruff-specific rules",
             CheckCategory::Meta => "Meta rules",
         }
     }
@@ -294,6 +299,7 @@ pub enum CheckKind {
     RedundantTupleInExceptionHandler(String),
     DuplicateHandlerException(Vec<String>),
     NoAssertRaisesException,
+    UselessExpression,
     DuplicateTryBlockException(String),
     // flake8-comprehensions
     UnnecessaryGeneratorList,
@@ -390,6 +396,8 @@ pub enum CheckKind {
     MixedCaseVariableInGlobalScope(String),
     CamelcaseImportedAsAcronym(String, String),
     ErrorSuffixOnExceptionName(String),
+    // Ruff
+    AmbiguousUnicodeCharacter(char, char),
     // Meta
     UnusedNOQA(Option<Vec<String>>),
 }
@@ -400,11 +408,12 @@ impl CheckCode {
     pub fn lint_source(&self) -> &'static LintSource {
         match self {
             CheckCode::E501 | CheckCode::W292 | CheckCode::M001 => &LintSource::Lines,
-            CheckCode::W605
-            | CheckCode::Q000
+            CheckCode::Q000
             | CheckCode::Q001
             | CheckCode::Q002
-            | CheckCode::Q003 => &LintSource::Tokens,
+            | CheckCode::Q003
+            | CheckCode::W605
+            | CheckCode::X001 => &LintSource::Tokens,
             CheckCode::E902 => &LintSource::FileSystem,
             _ => &LintSource::AST,
         }
@@ -476,6 +485,7 @@ impl CheckCode {
             }
             CheckCode::B014 => CheckKind::DuplicateHandlerException(vec!["ValueError".to_string()]),
             CheckCode::B017 => CheckKind::NoAssertRaisesException,
+            CheckCode::B018 => CheckKind::UselessExpression,
             CheckCode::B025 => CheckKind::DuplicateTryBlockException("Exception".to_string()),
             // flake8-comprehensions
             CheckCode::C400 => CheckKind::UnnecessaryGeneratorList,
@@ -604,6 +614,8 @@ impl CheckCode {
                 CheckKind::CamelcaseImportedAsAcronym("...".to_string(), "...".to_string())
             }
             CheckCode::N818 => CheckKind::ErrorSuffixOnExceptionName("...".to_string()),
+            // Ruff
+            CheckCode::X001 => CheckKind::AmbiguousUnicodeCharacter('𝐁', 'B'),
             // Meta
             CheckCode::M001 => CheckKind::UnusedNOQA(None),
         }
@@ -665,6 +677,7 @@ impl CheckCode {
             CheckCode::B013 => CheckCategory::Flake8Bugbear,
             CheckCode::B014 => CheckCategory::Flake8Bugbear,
             CheckCode::B017 => CheckCategory::Flake8Bugbear,
+            CheckCode::B018 => CheckCategory::Flake8Bugbear,
             CheckCode::B025 => CheckCategory::Flake8Bugbear,
             CheckCode::C400 => CheckCategory::Flake8Comprehensions,
             CheckCode::C401 => CheckCategory::Flake8Comprehensions,
@@ -755,6 +768,7 @@ impl CheckCode {
             CheckCode::N816 => CheckCategory::PEP8Naming,
             CheckCode::N817 => CheckCategory::PEP8Naming,
             CheckCode::N818 => CheckCategory::PEP8Naming,
+            CheckCode::X001 => CheckCategory::Ruff,
             CheckCode::M001 => CheckCategory::Meta,
         }
     }
@@ -822,6 +836,7 @@ impl CheckKind {
             CheckKind::RedundantTupleInExceptionHandler(_) => &CheckCode::B013,
             CheckKind::DuplicateHandlerException(_) => &CheckCode::B014,
             CheckKind::NoAssertRaisesException => &CheckCode::B017,
+            CheckKind::UselessExpression => &CheckCode::B018,
             CheckKind::DuplicateTryBlockException(_) => &CheckCode::B025,
             // flake8-comprehensions
             CheckKind::UnnecessaryGeneratorList => &CheckCode::C400,
@@ -918,6 +933,8 @@ impl CheckKind {
             CheckKind::MixedCaseVariableInGlobalScope(..) => &CheckCode::N816,
             CheckKind::CamelcaseImportedAsAcronym(..) => &CheckCode::N817,
             CheckKind::ErrorSuffixOnExceptionName(..) => &CheckCode::N818,
+            // Ruff
+            CheckKind::AmbiguousUnicodeCharacter(..) => &CheckCode::X001,
             // Meta
             CheckKind::UnusedNOQA(_) => &CheckCode::M001,
         }
@@ -1110,6 +1127,9 @@ impl CheckKind {
                  `assertRaisesRegex`, or use the context manager form of `assertRaises`."
                     .to_string()
             }
+            CheckKind::UselessExpression => {
+                "Found useless expression. Either assign it to a variable or remove it.".to_string()
+            }
             CheckKind::DuplicateTryBlockException(name) => {
                 format!("try-except block with duplicate exception `{name}`")
             }
@@ -1398,6 +1418,13 @@ impl CheckKind {
             CheckKind::ErrorSuffixOnExceptionName(name) => {
                 format!("Exception name `{name}` should be named with an Error suffix")
             }
+            // Ruff
+            CheckKind::AmbiguousUnicodeCharacter(confusable, representant) => {
+                format!(
+                    "Use of ambiguous unicode character '{confusable}' (did you mean \
+                     '{representant}'?)"
+                )
+            }
             // Meta
             CheckKind::UnusedNOQA(codes) => match codes {
                 None => "Unused `noqa` directive".to_string(),
@@ -1439,7 +1466,8 @@ impl CheckKind {
     pub fn fixable(&self) -> bool {
         matches!(
             self,
-            CheckKind::BlankLineAfterLastSection(_)
+            CheckKind::AmbiguousUnicodeCharacter(_, _)
+                | CheckKind::BlankLineAfterLastSection(_)
                 | CheckKind::BlankLineAfterSection(_)
                 | CheckKind::BlankLineAfterSummary
                 | CheckKind::BlankLineBeforeSection(_)
@@ -1461,6 +1489,7 @@ impl CheckKind {
                 | CheckKind::OneBlankLineBeforeClass(_)
                 | CheckKind::PPrintFound
                 | CheckKind::PrintFound
+                | CheckKind::RaiseNotImplemented
                 | CheckKind::SectionNameEndsInColon(_)
                 | CheckKind::SectionNotOverIndented(_)
                 | CheckKind::SectionUnderlineAfterName(_)

src/checks_gen.rs

@@ -1,11 +1,11 @@
 //! File automatically generated by examples/generate_check_code_prefix.rs.
 
 use serde::{Deserialize, Serialize};
-use strum_macros::{AsRefStr, EnumString};
+use strum_macros::EnumString;
 
 use crate::checks::CheckCode;
 
-#[derive(AsRefStr, EnumString, Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
+#[derive(EnumString, Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Serialize, Deserialize)]
 pub enum CheckCodePrefix {
     A,
     A0,
@@ -24,6 +24,7 @@ pub enum CheckCodePrefix {
     B013,
     B014,
     B017,
+    B018,
     B02,
     B025,
     C,
@@ -227,6 +228,10 @@ pub enum CheckCodePrefix {
     W6,
     W60,
     W605,
+    X,
+    X0,
+    X00,
+    X001,
 }
 
 #[derive(PartialEq, Eq, PartialOrd, Ord)]
@@ -254,6 +259,7 @@ impl CheckCodePrefix {
                 CheckCode::B013,
                 CheckCode::B014,
                 CheckCode::B017,
+                CheckCode::B018,
                 CheckCode::B025,
             ],
             CheckCodePrefix::B0 => vec![
@@ -264,24 +270,25 @@ impl CheckCodePrefix {
                 CheckCode::B013,
                 CheckCode::B014,
                 CheckCode::B017,
+                CheckCode::B018,
                 CheckCode::B025,
             ],
             CheckCodePrefix::B00 => vec![CheckCode::B002, CheckCode::B006, CheckCode::B007],
             CheckCodePrefix::B002 => vec![CheckCode::B002],
             CheckCodePrefix::B006 => vec![CheckCode::B006],
             CheckCodePrefix::B007 => vec![CheckCode::B007],
-            CheckCodePrefix::B01 => {
-                vec![
-                    CheckCode::B011,
-                    CheckCode::B013,
-                    CheckCode::B014,
-                    CheckCode::B017,
-                ]
-            }
+            CheckCodePrefix::B01 => vec![
+                CheckCode::B011,
+                CheckCode::B013,
+                CheckCode::B014,
+                CheckCode::B017,
+                CheckCode::B018,
+            ],
             CheckCodePrefix::B011 => vec![CheckCode::B011],
             CheckCodePrefix::B013 => vec![CheckCode::B013],
             CheckCodePrefix::B014 => vec![CheckCode::B014],
             CheckCodePrefix::B017 => vec![CheckCode::B017],
+            CheckCodePrefix::B018 => vec![CheckCode::B018],
             CheckCodePrefix::B02 => vec![CheckCode::B025],
             CheckCodePrefix::B025 => vec![CheckCode::B025],
             CheckCodePrefix::C => vec![
@@ -584,14 +591,12 @@ impl CheckCodePrefix {
                 CheckCode::E742,
                 CheckCode::E743,
             ],
-            CheckCodePrefix::E71 => {
-                vec![
-                    CheckCode::E711,
-                    CheckCode::E712,
-                    CheckCode::E713,
-                    CheckCode::E714,
-                ]
-            }
+            CheckCodePrefix::E71 => vec![
+                CheckCode::E711,
+                CheckCode::E712,
+                CheckCode::E713,
+                CheckCode::E714,
+            ],
             CheckCodePrefix::E711 => vec![CheckCode::E711],
             CheckCodePrefix::E712 => vec![CheckCode::E712],
             CheckCodePrefix::E713 => vec![CheckCode::E713],
@@ -684,14 +689,12 @@ impl CheckCodePrefix {
             CheckCodePrefix::F62 => vec![CheckCode::F621, CheckCode::F622],
             CheckCodePrefix::F621 => vec![CheckCode::F621],
             CheckCodePrefix::F622 => vec![CheckCode::F622],
-            CheckCodePrefix::F63 => {
-                vec![
-                    CheckCode::F631,
-                    CheckCode::F632,
-                    CheckCode::F633,
-                    CheckCode::F634,
-                ]
-            }
+            CheckCodePrefix::F63 => vec![
+                CheckCode::F631,
+                CheckCode::F632,
+                CheckCode::F633,
+                CheckCode::F634,
+            ],
             CheckCodePrefix::F631 => vec![CheckCode::F631],
             CheckCodePrefix::F632 => vec![CheckCode::F632],
             CheckCodePrefix::F633 => vec![CheckCode::F633],
@@ -808,30 +811,24 @@ impl CheckCodePrefix {
             CheckCodePrefix::N816 => vec![CheckCode::N816],
             CheckCodePrefix::N817 => vec![CheckCode::N817],
             CheckCodePrefix::N818 => vec![CheckCode::N818],
-            CheckCodePrefix::Q => {
-                vec![
-                    CheckCode::Q000,
-                    CheckCode::Q001,
-                    CheckCode::Q002,
-                    CheckCode::Q003,
-                ]
-            }
-            CheckCodePrefix::Q0 => {
-                vec![
-                    CheckCode::Q000,
-                    CheckCode::Q001,
-                    CheckCode::Q002,
-                    CheckCode::Q003,
-                ]
-            }
-            CheckCodePrefix::Q00 => {
-                vec![
-                    CheckCode::Q000,
-                    CheckCode::Q001,
-                    CheckCode::Q002,
-                    CheckCode::Q003,
-                ]
-            }
+            CheckCodePrefix::Q => vec![
+                CheckCode::Q000,
+                CheckCode::Q001,
+                CheckCode::Q002,
+                CheckCode::Q003,
+            ],
+            CheckCodePrefix::Q0 => vec![
+                CheckCode::Q000,
+                CheckCode::Q001,
+                CheckCode::Q002,
+                CheckCode::Q003,
+            ],
+            CheckCodePrefix::Q00 => vec![
+                CheckCode::Q000,
+                CheckCode::Q001,
+                CheckCode::Q002,
+                CheckCode::Q003,
+            ],
             CheckCodePrefix::Q000 => vec![CheckCode::Q000],
             CheckCodePrefix::Q001 => vec![CheckCode::Q001],
             CheckCodePrefix::Q002 => vec![CheckCode::Q002],
@@ -886,6 +883,10 @@ impl CheckCodePrefix {
             CheckCodePrefix::W6 => vec![CheckCode::W605],
             CheckCodePrefix::W60 => vec![CheckCode::W605],
             CheckCodePrefix::W605 => vec![CheckCode::W605],
+            CheckCodePrefix::X => vec![CheckCode::X001],
+            CheckCodePrefix::X0 => vec![CheckCode::X001],
+            CheckCodePrefix::X00 => vec![CheckCode::X001],
+            CheckCodePrefix::X001 => vec![CheckCode::X001],
         }
     }
 }
@@ -910,6 +911,7 @@ impl CheckCodePrefix {
             CheckCodePrefix::B013 => PrefixSpecificity::Explicit,
             CheckCodePrefix::B014 => PrefixSpecificity::Explicit,
             CheckCodePrefix::B017 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::B018 => PrefixSpecificity::Explicit,
             CheckCodePrefix::B02 => PrefixSpecificity::Tens,
             CheckCodePrefix::B025 => PrefixSpecificity::Explicit,
             CheckCodePrefix::C => PrefixSpecificity::Category,
@@ -1113,6 +1115,10 @@ impl CheckCodePrefix {
             CheckCodePrefix::W6 => PrefixSpecificity::Hundreds,
             CheckCodePrefix::W60 => PrefixSpecificity::Tens,
             CheckCodePrefix::W605 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::X => PrefixSpecificity::Category,
+            CheckCodePrefix::X0 => PrefixSpecificity::Hundreds,
+            CheckCodePrefix::X00 => PrefixSpecificity::Tens,
+            CheckCodePrefix::X001 => PrefixSpecificity::Explicit,
         }
     }
 }

src/cst/matchers.rs

@@ -1,18 +1,8 @@
 use anyhow::Result;
 use libcst_native::Module;
-use rustpython_ast::Located;
 
-use crate::ast::types::Range;
-use crate::source_code_locator::SourceCodeLocator;
-
-pub fn match_tree<'a, T>(
-    locator: &'a SourceCodeLocator,
-    located: &'a Located<T>,
-) -> Result<Module<'a>> {
-    match libcst_native::parse_module(
-        locator.slice_source_code_range(&Range::from_located(located)),
-        None,
-    ) {
+pub fn match_module(module_text: &str) -> Result<Module> {
+    match libcst_native::parse_module(module_text, None) {
         Ok(module) => Ok(module),
         Err(_) => return Err(anyhow::anyhow!("Failed to extract CST from source.")),
     }

src/docstrings/helpers.rs

@@ -25,12 +25,15 @@ pub fn leading_space(line: &str) -> String {
 }
 
 /// Extract the leading indentation from a docstring.
-pub fn indentation<'a>(checker: &'a Checker, docstring: &Expr) -> &'a str {
+pub fn indentation<'a>(checker: &'a Checker, docstring: &Expr) -> String {
     let range = Range::from_located(docstring);
-    checker.locator.slice_source_code_range(&Range {
-        location: Location::new(range.location.row(), 0),
-        end_location: Location::new(range.location.row(), range.location.column()),
-    })
+    checker
+        .locator
+        .slice_source_code_range(&Range {
+            location: Location::new(range.location.row(), 0),
+            end_location: Location::new(range.location.row(), range.location.column()),
+        })
+        .to_string()
 }
 
 /// Replace any non-whitespace characters from an indentation string.

src/flake8_bugbear/plugins/mod.rs

@@ -5,6 +5,7 @@ pub use mutable_argument_default::mutable_argument_default;
 pub use redundant_tuple_in_exception_handler::redundant_tuple_in_exception_handler;
 pub use unary_prefix_increment::unary_prefix_increment;
 pub use unused_loop_control_variable::unused_loop_control_variable;
+pub use useless_expression::useless_expression;
 
 mod assert_false;
 mod assert_raises_exception;
@@ -13,3 +14,4 @@ mod mutable_argument_default;
 mod redundant_tuple_in_exception_handler;
 mod unary_prefix_increment;
 mod unused_loop_control_variable;
+mod useless_expression;

src/flake8_bugbear/plugins/useless_expression.rs

@@ -0,0 +1,30 @@
+use rustpython_ast::{Constant, ExprKind, Stmt, StmtKind};
+
+use crate::ast::types::{CheckLocator, Range};
+use crate::check_ast::Checker;
+use crate::checks::{Check, CheckKind};
+
+pub fn useless_expression(checker: &mut Checker, body: &[Stmt]) {
+    for stmt in body {
+        if let StmtKind::Expr { value } = &stmt.node {
+            match &value.node {
+                ExprKind::List { .. } | ExprKind::Dict { .. } | ExprKind::Set { .. } => {
+                    checker.add_check(Check::new(
+                        CheckKind::UselessExpression,
+                        checker.locate_check(Range::from_located(value)),
+                    ));
+                }
+                ExprKind::Constant { value: val, .. } => match &val {
+                    Constant::Str { .. } => {}
+                    _ => {
+                        checker.add_check(Check::new(
+                            CheckKind::UselessExpression,
+                            checker.locate_check(Range::from_located(value)),
+                        ));
+                    }
+                },
+                _ => {}
+            }
+        }
+    }
+}

src/flake8_comprehensions/fixes.rs

@@ -6,8 +6,9 @@ use libcst_native::{
     SmallStatement, Statement, Tuple,
 };
 
+use crate::ast::types::Range;
 use crate::autofix::Fix;
-use crate::cst::matchers::match_tree;
+use crate::cst::matchers::match_module;
 use crate::source_code_locator::SourceCodeLocator;
 
 fn match_expr<'a, 'b>(module: &'a mut Module<'b>) -> Result<&'a mut Expr<'b>> {
@@ -44,7 +45,8 @@ pub fn fix_unnecessary_generator_list(
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
     // Expr(Call(GeneratorExp)))) -> Expr(ListComp)))
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -86,7 +88,8 @@ pub fn fix_unnecessary_generator_set(
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
     // Expr(Call(GeneratorExp)))) -> Expr(SetComp)))
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -128,7 +131,8 @@ pub fn fix_unnecessary_generator_dict(
     locator: &SourceCodeLocator,
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -194,7 +198,8 @@ pub fn fix_unnecessary_list_comprehension_set(
 ) -> Result<Fix> {
     // Expr(Call(ListComp)))) ->
     // Expr(SetComp)))
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -234,7 +239,8 @@ pub fn fix_unnecessary_literal_set(
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
     // Expr(Call(List|Tuple)))) -> Expr(Set)))
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let mut call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -281,7 +287,8 @@ pub fn fix_unnecessary_literal_dict(
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
     // Expr(Call(List|Tuple)))) -> Expr(Dict)))
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -351,8 +358,9 @@ pub fn fix_unnecessary_collection_call(
     locator: &SourceCodeLocator,
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
-    // Expr(Call("list" | "tuple" | "dict")))) -> Expr(List|Tuple|Dict)))
-    let mut tree = match_tree(locator, expr)?;
+    // Expr(Call("list" | "tuple" | "dict")))) -> Expr(List|Tuple|Dict)
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let name = if let Expression::Name(name) = &call.func.as_ref() {
@@ -463,7 +471,8 @@ pub fn fix_unnecessary_literal_within_tuple_call(
     locator: &SourceCodeLocator,
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -518,7 +527,8 @@ pub fn fix_unnecessary_literal_within_list_call(
     locator: &SourceCodeLocator,
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -576,7 +586,8 @@ pub fn fix_unnecessary_list_call(
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
     // Expr(Call(List|Tuple)))) -> Expr(List|Tuple)))
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
     let call = match_call(body)?;
     let arg = match_arg(call)?;
@@ -598,7 +609,8 @@ pub fn fix_unnecessary_comprehension(
     locator: &SourceCodeLocator,
     expr: &rustpython_ast::Expr,
 ) -> Result<Fix> {
-    let mut tree = match_tree(locator, expr)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(expr));
+    let mut tree = match_module(&module_text)?;
     let mut body = match_expr(&mut tree)?;
 
     match &body.value {

src/flake8_quotes/checks.rs

@@ -148,13 +148,22 @@ mod tests {
     use crate::checks::{Check, CheckCode};
     use crate::flake8_quotes::settings::Quote;
     use crate::linter::tokenize;
-    use crate::{flake8_quotes, fs, linter, noqa, Settings};
+    use crate::{flake8_quotes, fs, linter, noqa, Settings, SourceCodeLocator};
 
     fn check_path(path: &Path, settings: &Settings, autofix: &fixer::Mode) -> Result<Vec<Check>> {
         let contents = fs::read_file(path)?;
         let tokens: Vec<LexResult> = tokenize(&contents);
+        let locator = SourceCodeLocator::new(&contents);
         let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
-        linter::check_path(path, &contents, tokens, &noqa_line_for, settings, autofix)
+        linter::check_path(
+            path,
+            &contents,
+            tokens,
+            &locator,
+            &noqa_line_for,
+            settings,
+            autofix,
+        )
     }
 
     #[test_case(Path::new("doubles.py"))]

src/lib.rs

@@ -11,6 +11,7 @@ use crate::autofix::fixer::Mode;
 use crate::checks::Check;
 use crate::linter::{check_path, tokenize};
 use crate::settings::configuration::Configuration;
+use crate::source_code_locator::SourceCodeLocator;
 
 mod ast;
 pub mod autofix;
@@ -41,6 +42,7 @@ mod pydocstyle;
 mod pyflakes;
 mod python;
 mod pyupgrade;
+mod rules;
 pub mod settings;
 pub mod source_code_locator;
 pub mod visibility;
@@ -65,6 +67,9 @@ pub fn check(path: &Path, contents: &str, autofix: bool) -> Result<Vec<Check>> {
     // Tokenize once.
     let tokens: Vec<LexResult> = tokenize(contents);
 
+    // Initialize the SourceCodeLocator (which computes offsets lazily).
+    let locator = SourceCodeLocator::new(contents);
+
     // Determine the noqa line for every line in the source.
     let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
 
@@ -73,6 +78,7 @@ pub fn check(path: &Path, contents: &str, autofix: bool) -> Result<Vec<Check>> {
         path,
         contents,
         tokens,
+        &locator,
         &noqa_line_for,
         &settings,
         &if autofix { Mode::Generate } else { Mode::None },

src/linter.rs

@@ -54,6 +54,7 @@ pub(crate) fn check_path(
     path: &Path,
     contents: &str,
     tokens: Vec<LexResult>,
+    locator: &SourceCodeLocator,
     noqa_line_for: &[usize],
     settings: &Settings,
     autofix: &fixer::Mode,
@@ -61,16 +62,13 @@ pub(crate) fn check_path(
     // Aggregate all checks.
     let mut checks: Vec<Check> = vec![];
 
-    // Initialize the SourceCodeLocator (which computes offsets lazily).
-    let locator = SourceCodeLocator::new(contents);
-
     // Run the token-based checks.
     if settings
         .enabled
         .iter()
         .any(|check_code| matches!(check_code.lint_source(), LintSource::Tokens))
     {
-        check_tokens(&mut checks, &locator, &tokens, settings);
+        check_tokens(&mut checks, locator, &tokens, settings, autofix);
     }
 
     // Run the AST-based checks.
@@ -81,7 +79,7 @@ pub(crate) fn check_path(
     {
         match parse_program_tokens(tokens, "<filename>") {
             Ok(python_ast) => {
-                checks.extend(check_ast(&python_ast, &locator, settings, autofix, path))
+                checks.extend(check_ast(&python_ast, locator, settings, autofix, path))
             }
             Err(parse_error) => {
                 if settings.enabled.contains(&CheckCode::E999) {
@@ -123,19 +121,29 @@ pub fn lint_stdin(
     // Tokenize once.
     let tokens: Vec<LexResult> = tokenize(stdin);
 
+    // Initialize the SourceCodeLocator (which computes offsets lazily).
+    let locator = SourceCodeLocator::new(stdin);
+
     // Determine the noqa line for every line in the source.
     let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
 
     // Generate checks.
-    let mut checks = check_path(path, stdin, tokens, &noqa_line_for, settings, autofix)?;
+    let mut checks = check_path(
+        path,
+        stdin,
+        tokens,
+        &locator,
+        &noqa_line_for,
+        settings,
+        autofix,
+    )?;
 
     // Apply autofix, write results to stdout.
     if matches!(autofix, fixer::Mode::Apply) {
-        let output = match fix_file(&mut checks, stdin) {
-            None => stdin.to_string(),
-            Some(content) => content,
-        };
-        io::stdout().write_all(output.as_bytes())?;
+        match fix_file(&mut checks, &locator) {
+            None => io::stdout().write_all(stdin.as_bytes()),
+            Some(contents) => io::stdout().write_all(contents.as_bytes()),
+        }?;
     }
 
     // Convert to messages.
@@ -167,16 +175,27 @@ pub fn lint_path(
     // Tokenize once.
     let tokens: Vec<LexResult> = tokenize(&contents);
 
+    // Initialize the SourceCodeLocator (which computes offsets lazily).
+    let locator = SourceCodeLocator::new(&contents);
+
     // Determine the noqa line for every line in the source.
     let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
 
     // Generate checks.
-    let mut checks = check_path(path, &contents, tokens, &noqa_line_for, settings, autofix)?;
+    let mut checks = check_path(
+        path,
+        &contents,
+        tokens,
+        &locator,
+        &noqa_line_for,
+        settings,
+        autofix,
+    )?;
 
     // Apply autofix.
     if matches!(autofix, fixer::Mode::Apply) {
-        if let Some(fixed_contents) = fix_file(&mut checks, &contents) {
-            write(path, fixed_contents)?;
+        if let Some(fixed_contents) = fix_file(&mut checks, &locator) {
+            write(path, fixed_contents.as_ref())?;
         }
     };
 
@@ -198,6 +217,9 @@ pub fn add_noqa_to_path(path: &Path, settings: &Settings) -> Result<usize> {
     // Tokenize once.
     let tokens: Vec<LexResult> = tokenize(&contents);
 
+    // Initialize the SourceCodeLocator (which computes offsets lazily).
+    let locator = SourceCodeLocator::new(&contents);
+
     // Determine the noqa line for every line in the source.
     let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
 
@@ -206,6 +228,7 @@ pub fn add_noqa_to_path(path: &Path, settings: &Settings) -> Result<usize> {
         path,
         &contents,
         tokens,
+        &locator,
         &noqa_line_for,
         settings,
         &fixer::Mode::None,
@@ -243,13 +266,27 @@ mod tests {
     use crate::autofix::fixer;
     use crate::checks::{Check, CheckCode};
     use crate::linter::tokenize;
-    use crate::{fs, linter, noqa, settings, Settings};
+    use crate::source_code_locator::SourceCodeLocator;
+    use crate::{fs, linter, noqa, settings};
 
-    fn check_path(path: &Path, settings: &Settings, autofix: &fixer::Mode) -> Result<Vec<Check>> {
+    fn check_path(
+        path: &Path,
+        settings: &settings::Settings,
+        autofix: &fixer::Mode,
+    ) -> Result<Vec<Check>> {
         let contents = fs::read_file(path)?;
         let tokens: Vec<LexResult> = tokenize(&contents);
+        let locator = SourceCodeLocator::new(&contents);
         let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
-        linter::check_path(path, &contents, tokens, &noqa_line_for, settings, autofix)
+        linter::check_path(
+            path,
+            &contents,
+            tokens,
+            &locator,
+            &noqa_line_for,
+            settings,
+            autofix,
+        )
     }
 
     #[test_case(CheckCode::A001, Path::new("A001.py"); "A001")]
@@ -262,6 +299,7 @@ mod tests {
     #[test_case(CheckCode::B013, Path::new("B013.py"); "B013")]
     #[test_case(CheckCode::B014, Path::new("B014.py"); "B014")]
     #[test_case(CheckCode::B017, Path::new("B017.py"); "B017")]
+    #[test_case(CheckCode::B018, Path::new("B018.py"); "B018")]
     #[test_case(CheckCode::B025, Path::new("B025.py"); "B025")]
     #[test_case(CheckCode::C400, Path::new("C400.py"); "C400")]
     #[test_case(CheckCode::C401, Path::new("C401.py"); "C401")]
@@ -366,6 +404,7 @@ mod tests {
     #[test_case(CheckCode::F821, Path::new("F821_0.py"); "F821_0")]
     #[test_case(CheckCode::F821, Path::new("F821_1.py"); "F821_1")]
     #[test_case(CheckCode::F821, Path::new("F821_2.py"); "F821_2")]
+    #[test_case(CheckCode::F821, Path::new("F821_3.py"); "F821_3")]
     #[test_case(CheckCode::F822, Path::new("F822.py"); "F822")]
     #[test_case(CheckCode::F823, Path::new("F823.py"); "F823")]
     #[test_case(CheckCode::F831, Path::new("F831.py"); "F831")]
@@ -400,6 +439,7 @@ mod tests {
     #[test_case(CheckCode::W292, Path::new("W292_1.py"); "W292_1")]
     #[test_case(CheckCode::W292, Path::new("W292_2.py"); "W292_2")]
     #[test_case(CheckCode::W605, Path::new("W605.py"); "W605")]
+    #[test_case(CheckCode::X001, Path::new("X001.py"); "X001")]
     fn checks(check_code: CheckCode, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", check_code.as_ref(), path.to_string_lossy());
         let mut checks = check_path(

src/pycodestyle/checks.rs

@@ -271,7 +271,7 @@ pub fn invalid_escape_sequence(
     });
 
     // Determine whether the string is single- or triple-quoted.
-    let quote = extract_quote(text);
+    let quote = extract_quote(&text);
     let quote_pos = text.find(quote).unwrap();
     let prefix = text[..quote_pos].to_lowercase();
     let body = &text[(quote_pos + quote.len())..(text.len() - quote.len())];
@@ -299,9 +299,9 @@ pub fn invalid_escape_sequence(
                             start.column() + prefix.len() + quote.len() + col_offset,
                         )
                     } else {
-                        Location::new(start.row() + row_offset, col_offset + 1)
+                        Location::new(start.row() + row_offset, col_offset)
                     };
-                    let end_location = Location::new(location.row(), location.column() + 1);
+                    let end_location = Location::new(location.row(), location.column() + 2);
                     checks.push(Check::new(
                         CheckKind::InvalidEscapeSequence(next_char),
                         Range {

src/pydocstyle/plugins.rs

@@ -210,7 +210,7 @@ pub fn blank_before_after_function(checker: &mut Checker, definition: &Definitio
                         .count();
 
                     // Avoid D202 violations for blank lines followed by inner functions or classes.
-                    if blank_lines_after == 1 && INNER_FUNCTION_OR_CLASS_REGEX.is_match(after) {
+                    if blank_lines_after == 1 && INNER_FUNCTION_OR_CLASS_REGEX.is_match(&after) {
                         return;
                     }
 
@@ -387,7 +387,7 @@ pub fn indent(checker: &mut Checker, definition: &Definition) {
                 return;
             }
 
-            let docstring_indent = helpers::indentation(checker, docstring).to_string();
+            let docstring_indent = helpers::indentation(checker, docstring);
             let mut has_seen_tab = docstring_indent.contains('\t');
             let mut is_over_indented = true;
             let mut over_indented_lines = vec![];
@@ -537,7 +537,7 @@ pub fn newline_after_last_paragraph(checker: &mut Checker, definition: &Definiti
                                 // Insert a newline just before the end-quote(s).
                                 let content = format!(
                                     "\n{}",
-                                    helpers::clean(helpers::indentation(checker, docstring))
+                                    helpers::clean(&helpers::indentation(checker, docstring))
                                 );
                                 check.amend(Fix::insertion(
                                     content,
@@ -916,7 +916,7 @@ fn blanks_and_section_underline(
                 // Add a dashed line (of the appropriate length) under the section header.
                 let content = format!(
                     "{}{}\n",
-                    helpers::clean(helpers::indentation(checker, docstring)),
+                    helpers::clean(&helpers::indentation(checker, docstring)),
                     "-".repeat(context.section_name.len())
                 );
                 check.amend(Fix::insertion(
@@ -950,7 +950,7 @@ fn blanks_and_section_underline(
                 // Add a dashed line (of the appropriate length) under the section header.
                 let content = format!(
                     "{}{}\n",
-                    helpers::clean(helpers::indentation(checker, docstring)),
+                    helpers::clean(&helpers::indentation(checker, docstring)),
                     "-".repeat(context.section_name.len())
                 );
                 check.amend(Fix::insertion(
@@ -1026,7 +1026,7 @@ fn blanks_and_section_underline(
                     // Replace the existing underline with a line of the appropriate length.
                     let content = format!(
                         "{}{}\n",
-                        helpers::clean(helpers::indentation(checker, docstring)),
+                        helpers::clean(&helpers::indentation(checker, docstring)),
                         "-".repeat(context.section_name.len())
                     );
                     check.amend(Fix::replacement(
@@ -1054,7 +1054,7 @@ fn blanks_and_section_underline(
 
         if checker.settings.enabled.contains(&CheckCode::D215) {
             let leading_space = helpers::leading_space(non_empty_line);
-            let indentation = helpers::indentation(checker, docstring).to_string();
+            let indentation = helpers::indentation(checker, docstring);
             if leading_space.len() > indentation.len() {
                 let mut check = Check::new(
                     CheckKind::SectionUnderlineNotOverIndented(context.section_name.to_string()),
@@ -1195,7 +1195,7 @@ fn common_section(
 
     if checker.settings.enabled.contains(&CheckCode::D214) {
         let leading_space = helpers::leading_space(context.line);
-        let indentation = helpers::indentation(checker, docstring).to_string();
+        let indentation = helpers::indentation(checker, docstring);
         if leading_space.len() > indentation.len() {
             let mut check = Check::new(
                 CheckKind::SectionNotOverIndented(context.section_name.to_string()),

src/pyflakes/checks.rs

@@ -10,16 +10,6 @@ use rustpython_parser::ast::{
 use crate::ast::types::{BindingKind, CheckLocator, FunctionScope, Range, Scope, ScopeKind};
 use crate::checks::{Check, CheckKind};
 
-/// F634
-pub fn if_tuple(test: &Expr, location: Range) -> Option<Check> {
-    if let ExprKind::Tuple { elts, .. } = &test.node {
-        if !elts.is_empty() {
-            return Some(Check::new(CheckKind::IfTuple, location));
-        }
-    }
-    None
-}
-
 /// F631
 pub fn assert_tuple(test: &Expr, location: Range) -> Option<Check> {
     if let ExprKind::Tuple { elts, .. } = &test.node {
@@ -30,6 +20,16 @@ pub fn assert_tuple(test: &Expr, location: Range) -> Option<Check> {
     None
 }
 
+/// F634
+pub fn if_tuple(test: &Expr, location: Range) -> Option<Check> {
+    if let ExprKind::Tuple { elts, .. } = &test.node {
+        if !elts.is_empty() {
+            return Some(Check::new(CheckKind::IfTuple, location));
+        }
+    }
+    None
+}
+
 /// F841
 pub fn unused_variables(
     scope: &Scope,
@@ -78,33 +78,6 @@ pub fn default_except_not_last(handlers: &[Excepthandler]) -> Option<Check> {
     None
 }
 
-/// F901
-pub fn raise_not_implemented(expr: &Expr) -> Option<Check> {
-    match &expr.node {
-        ExprKind::Call { func, .. } => {
-            if let ExprKind::Name { id, .. } = &func.node {
-                if id == "NotImplemented" {
-                    return Some(Check::new(
-                        CheckKind::RaiseNotImplemented,
-                        Range::from_located(expr),
-                    ));
-                }
-            }
-        }
-        ExprKind::Name { id, .. } => {
-            if id == "NotImplemented" {
-                return Some(Check::new(
-                    CheckKind::RaiseNotImplemented,
-                    Range::from_located(expr),
-                ));
-            }
-        }
-        _ => {}
-    }
-
-    None
-}
-
 /// F831
 pub fn duplicate_arguments(arguments: &Arguments) -> Vec<Check> {
     let mut checks: Vec<Check> = vec![];

src/pyflakes/fixes.rs

@@ -2,9 +2,10 @@ use anyhow::Result;
 use libcst_native::{Codegen, ImportNames, NameOrAttribute, SmallStatement, Statement};
 use rustpython_ast::Stmt;
 
+use crate::ast::types::Range;
 use crate::autofix::{helpers, Fix};
 use crate::cst::helpers::compose_module_path;
-use crate::cst::matchers::match_tree;
+use crate::cst::matchers::match_module;
 use crate::source_code_locator::SourceCodeLocator;
 
 /// Generate a Fix to remove any unused imports from an `import` statement.
@@ -15,7 +16,8 @@ pub fn remove_unused_imports(
     parent: Option<&Stmt>,
     deleted: &[&Stmt],
 ) -> Result<Fix> {
-    let mut tree = match_tree(locator, stmt)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(stmt));
+    let mut tree = match_module(&module_text)?;
 
     let body = if let Some(Statement::Simple(body)) = tree.body.first_mut() {
         body
@@ -72,7 +74,8 @@ pub fn remove_unused_import_froms(
     parent: Option<&Stmt>,
     deleted: &[&Stmt],
 ) -> Result<Fix> {
-    let mut tree = match_tree(locator, stmt)?;
+    let module_text = locator.slice_source_code_range(&Range::from_located(stmt));
+    let mut tree = match_module(&module_text)?;
 
     let body = if let Some(Statement::Simple(body)) = tree.body.first_mut() {
         body

src/pyflakes/plugins/assert_tuple.rs

@@ -4,6 +4,7 @@ use crate::ast::types::{CheckLocator, Range};
 use crate::check_ast::Checker;
 use crate::pyflakes::checks;
 
+/// F631
 pub fn assert_tuple(checker: &mut Checker, stmt: &Stmt, test: &Expr) {
     if let Some(check) = checks::assert_tuple(test, checker.locate_check(Range::from_located(stmt)))
     {

src/pyflakes/plugins/if_tuple.rs

@@ -4,6 +4,7 @@ use crate::ast::types::{CheckLocator, Range};
 use crate::check_ast::Checker;
 use crate::pyflakes::checks;
 
+/// F634
 pub fn if_tuple(checker: &mut Checker, stmt: &Stmt, test: &Expr) {
     if let Some(check) = checks::if_tuple(test, checker.locate_check(Range::from_located(stmt))) {
         checker.add_check(check);

src/pyflakes/plugins/invalid_print_syntax.rs

@@ -4,6 +4,7 @@ use crate::ast::types::{Binding, BindingKind, Range};
 use crate::check_ast::Checker;
 use crate::checks::{Check, CheckKind};
 
+/// F633
 pub fn invalid_print_syntax(checker: &mut Checker, left: &Expr) {
     if let ExprKind::Name { id, .. } = &left.node {
         if id == "print" {

src/pyflakes/plugins/mod.rs

@@ -1,7 +1,9 @@
 pub use assert_tuple::assert_tuple;
 pub use if_tuple::if_tuple;
 pub use invalid_print_syntax::invalid_print_syntax;
+pub use raise_not_implemented::raise_not_implemented;
 
 mod assert_tuple;
 mod if_tuple;
 mod invalid_print_syntax;
+mod raise_not_implemented;

src/pyflakes/plugins/raise_not_implemented.rs

@@ -0,0 +1,43 @@
+use rustpython_ast::{Expr, ExprKind};
+
+use crate::ast::types::{CheckLocator, Range};
+use crate::autofix::Fix;
+use crate::check_ast::Checker;
+use crate::checks::{Check, CheckKind};
+
+fn match_not_implemented(expr: &Expr) -> Option<&Expr> {
+    match &expr.node {
+        ExprKind::Call { func, .. } => {
+            if let ExprKind::Name { id, .. } = &func.node {
+                if id == "NotImplemented" {
+                    return Some(func);
+                }
+            }
+        }
+        ExprKind::Name { id, .. } => {
+            if id == "NotImplemented" {
+                return Some(expr);
+            }
+        }
+        _ => {}
+    }
+    None
+}
+
+/// F901
+pub fn raise_not_implemented(checker: &mut Checker, expr: &Expr) {
+    if let Some(expr) = match_not_implemented(expr) {
+        let mut check = Check::new(
+            CheckKind::RaiseNotImplemented,
+            checker.locate_check(Range::from_located(expr)),
+        );
+        if checker.patch() {
+            check.amend(Fix::replacement(
+                "NotImplementedError".to_string(),
+                expr.location,
+                expr.end_location.unwrap(),
+            ))
+        }
+        checker.add_check(check);
+    }
+}

src/pyupgrade/fixes.rs

@@ -16,14 +16,14 @@ pub fn remove_class_def_base(
     bases: &[Expr],
     keywords: &[Keyword],
 ) -> Option<Fix> {
-    let content = locator.slice_source_code_at(stmt_at);
+    let contents = locator.slice_source_code_at(stmt_at);
 
     // Case 1: `object` is the only base.
     if bases.len() == 1 && keywords.is_empty() {
         let mut fix_start = None;
         let mut fix_end = None;
         let mut count: usize = 0;
-        for (start, tok, end) in lexer::make_tokenizer(content).flatten() {
+        for (start, tok, end) in lexer::make_tokenizer(&contents).flatten() {
             if matches!(tok, Tok::Lpar) {
                 if count == 0 {
                     fix_start = Some(helpers::to_absolute(&start, stmt_at));
@@ -56,7 +56,7 @@ pub fn remove_class_def_base(
         let mut fix_start: Option<Location> = None;
         let mut fix_end: Option<Location> = None;
         let mut seen_comma = false;
-        for (start, tok, end) in lexer::make_tokenizer(content).flatten() {
+        for (start, tok, end) in lexer::make_tokenizer(&contents).flatten() {
             let start = helpers::to_absolute(&start, stmt_at);
             if seen_comma {
                 if matches!(tok, Tok::Newline) {
@@ -83,7 +83,7 @@ pub fn remove_class_def_base(
         // isn't a comma.
         let mut fix_start: Option<Location> = None;
         let mut fix_end: Option<Location> = None;
-        for (start, tok, end) in lexer::make_tokenizer(content).flatten() {
+        for (start, tok, end) in lexer::make_tokenizer(&contents).flatten() {
             let start = helpers::to_absolute(&start, stmt_at);
             let end = helpers::to_absolute(&end, stmt_at);
             if start == expr_at {
@@ -106,7 +106,7 @@ pub fn remove_super_arguments(locator: &SourceCodeLocator, expr: &Expr) -> Optio
     let range = Range::from_located(expr);
     let contents = locator.slice_source_code_range(&range);
 
-    let mut tree = match libcst_native::parse_module(contents, None) {
+    let mut tree = match libcst_native::parse_module(&contents, None) {
         Ok(m) => m,
         Err(_) => return None,
     };

src/rules/mod.rs

@@ -0,0 +1,3 @@
+//! Module for Ruff-specific rules.
+
+pub mod checks;

src/snapshots/ruff__linter__tests__B018_B018.py.snap

@@ -0,0 +1,197 @@
+---
+source: src/linter.rs
+expression: checks
+---
+- kind: UselessExpression
+  location:
+    row: 11
+    column: 4
+  end_location:
+    row: 11
+    column: 6
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 12
+    column: 4
+  end_location:
+    row: 12
+    column: 5
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 13
+    column: 4
+  end_location:
+    row: 13
+    column: 7
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 14
+    column: 4
+  end_location:
+    row: 14
+    column: 10
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 15
+    column: 4
+  end_location:
+    row: 15
+    column: 8
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 16
+    column: 4
+  end_location:
+    row: 16
+    column: 9
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 17
+    column: 4
+  end_location:
+    row: 17
+    column: 8
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 18
+    column: 4
+  end_location:
+    row: 18
+    column: 10
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 19
+    column: 4
+  end_location:
+    row: 19
+    column: 10
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 20
+    column: 4
+  end_location:
+    row: 20
+    column: 18
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 24
+    column: 4
+  end_location:
+    row: 24
+    column: 7
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 27
+    column: 4
+  end_location:
+    row: 27
+    column: 5
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 39
+    column: 4
+  end_location:
+    row: 39
+    column: 6
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 40
+    column: 4
+  end_location:
+    row: 40
+    column: 5
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 41
+    column: 4
+  end_location:
+    row: 41
+    column: 7
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 42
+    column: 4
+  end_location:
+    row: 42
+    column: 10
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 43
+    column: 4
+  end_location:
+    row: 43
+    column: 8
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 44
+    column: 4
+  end_location:
+    row: 44
+    column: 9
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 45
+    column: 4
+  end_location:
+    row: 45
+    column: 8
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 46
+    column: 4
+  end_location:
+    row: 46
+    column: 10
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 47
+    column: 4
+  end_location:
+    row: 47
+    column: 10
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 48
+    column: 4
+  end_location:
+    row: 48
+    column: 18
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 52
+    column: 4
+  end_location:
+    row: 52
+    column: 7
+  fix: ~
+- kind: UselessExpression
+  location:
+    row: 55
+    column: 4
+  end_location:
+    row: 55
+    column: 5
+  fix: ~
+

src/snapshots/ruff__linter__tests__F821_F821_3.py.snap

@@ -0,0 +1,23 @@
+---
+source: src/linter.rs
+expression: checks
+---
+- kind:
+    UndefinedName: key
+  location:
+    row: 11
+    column: 8
+  end_location:
+    row: 11
+    column: 13
+  fix: ~
+- kind:
+    UndefinedName: value
+  location:
+    row: 11
+    column: 15
+  end_location:
+    row: 11
+    column: 22
+  fix: ~
+

src/snapshots/ruff__linter__tests__F901_F901.py.snap

@@ -8,8 +8,17 @@ expression: checks
     column: 10
   end_location:
     row: 2
-    column: 26
-  fix: ~
+    column: 24
+  fix:
+    patch:
+      content: NotImplementedError
+      location:
+        row: 2
+        column: 10
+      end_location:
+        row: 2
+        column: 24
+    applied: false
 - kind: RaiseNotImplemented
   location:
     row: 6
@@ -17,5 +26,14 @@ expression: checks
   end_location:
     row: 6
     column: 24
-  fix: ~
+  fix:
+    patch:
+      content: NotImplementedError
+      location:
+        row: 6
+        column: 10
+      end_location:
+        row: 6
+        column: 24
+    applied: false
 

src/snapshots/ruff__linter__tests__W605_W605.py.snap

@@ -9,13 +9,13 @@ expression: checks
     column: 9
   end_location:
     row: 2
-    column: 10
+    column: 11
   fix: ~
 - kind:
     InvalidEscapeSequence: "."
   location:
     row: 6
-    column: 1
+    column: 0
   end_location:
     row: 6
     column: 2
@@ -27,13 +27,13 @@ expression: checks
     column: 5
   end_location:
     row: 11
-    column: 6
+    column: 7
   fix: ~
 - kind:
     InvalidEscapeSequence: _
   location:
     row: 18
-    column: 6
+    column: 5
   end_location:
     row: 18
     column: 7

src/snapshots/ruff__linter__tests__X001_X001.py.snap

@@ -0,0 +1,45 @@
+---
+source: src/linter.rs
+expression: checks
+---
+- kind:
+    AmbiguousUnicodeCharacter:
+      - 𝐁
+      - B
+  location:
+    row: 1
+    column: 5
+  end_location:
+    row: 1
+    column: 6
+  fix:
+    patch:
+      content: B
+      location:
+        row: 1
+        column: 5
+      end_location:
+        row: 1
+        column: 6
+    applied: false
+- kind:
+    AmbiguousUnicodeCharacter:
+      - ）
+      - )
+  location:
+    row: 5
+    column: 53
+  end_location:
+    row: 5
+    column: 54
+  fix:
+    patch:
+      content: )
+      location:
+        row: 5
+        column: 53
+      end_location:
+        row: 5
+        column: 54
+    applied: false
+

src/source_code_locator.rs

@@ -1,115 +1,59 @@
 //! Struct used to efficiently slice source code at (row, column) Locations.
 
+use std::borrow::Cow;
+
 use once_cell::unsync::OnceCell;
+use ropey::Rope;
 use rustpython_ast::Location;
 
 use crate::ast::types::Range;
 
 pub struct SourceCodeLocator<'a> {
     contents: &'a str,
-    offsets: OnceCell<Vec<Vec<usize>>>,
-}
-
-pub fn compute_offsets(contents: &str) -> Vec<Vec<usize>> {
-    let mut offsets = vec![vec![]];
-    let mut line_index = 0;
-    let mut char_index = 0;
-    let mut newline = false;
-    for (i, char) in contents.char_indices() {
-        offsets[line_index].push(i);
-
-        newline = char == '\n';
-        if newline {
-            line_index += 1;
-            offsets.push(vec![]);
-            char_index = i + char.len_utf8();
-        }
-    }
-    // If we end in a newline, add an extra character to indicate the start of that
-    // line.
-    if newline {
-        offsets[line_index].push(char_index);
-    }
-    offsets
+    rope: OnceCell<Rope>,
 }
 
 impl<'a> SourceCodeLocator<'a> {
     pub fn new(contents: &'a str) -> Self {
         SourceCodeLocator {
             contents,
-            offsets: OnceCell::new(),
+            rope: OnceCell::new(),
         }
     }
 
-    fn get_or_init_offsets(&self) -> &Vec<Vec<usize>> {
-        self.offsets.get_or_init(|| compute_offsets(self.contents))
+    fn get_or_init_rope(&self) -> &Rope {
+        self.rope.get_or_init(|| Rope::from_str(self.contents))
     }
 
-    pub fn slice_source_code_at(&self, location: &Location) -> &'a str {
-        let offsets = self.get_or_init_offsets();
-        let offset = offsets[location.row() - 1][location.column()];
-        &self.contents[offset..]
+    pub fn slice_source_code_at(&self, location: &Location) -> Cow<'_, str> {
+        let rope = self.get_or_init_rope();
+        let offset = rope.line_to_char(location.row() - 1) + location.column();
+        Cow::from(rope.slice(offset..))
     }
 
-    pub fn slice_source_code_range(&self, range: &Range) -> &'a str {
-        let offsets = self.get_or_init_offsets();
-        let start = offsets[range.location.row() - 1][range.location.column()];
-        let end = offsets[range.end_location.row() - 1][range.end_location.column()];
-        &self.contents[start..end]
+    pub fn slice_source_code_range(&self, range: &Range) -> Cow<'_, str> {
+        let rope = self.get_or_init_rope();
+        let start = rope.line_to_char(range.location.row() - 1) + range.location.column();
+        let end = rope.line_to_char(range.end_location.row() - 1) + range.end_location.column();
+        Cow::from(rope.slice(start..end))
     }
 
     pub fn partition_source_code_at(
         &self,
         outer: &Range,
         inner: &Range,
-    ) -> (&'a str, &'a str, &'a str) {
-        let offsets = self.get_or_init_offsets();
-        let outer_start = offsets[outer.location.row() - 1][outer.location.column()];
-        let outer_end = offsets[outer.end_location.row() - 1][outer.end_location.column()];
-        let inner_start = offsets[inner.location.row() - 1][inner.location.column()];
-        let inner_end = offsets[inner.end_location.row() - 1][inner.end_location.column()];
+    ) -> (Cow<'_, str>, Cow<'_, str>, Cow<'_, str>) {
+        let rope = self.get_or_init_rope();
+        let outer_start = rope.line_to_char(outer.location.row() - 1) + outer.location.column();
+        let outer_end =
+            rope.line_to_char(outer.end_location.row() - 1) + outer.end_location.column();
+        let inner_start = rope.line_to_char(inner.location.row() - 1) + inner.location.column();
+        let inner_end =
+            rope.line_to_char(inner.end_location.row() - 1) + inner.end_location.column();
         (
-            &self.contents[outer_start..inner_start],
-            &self.contents[inner_start..inner_end],
-            &self.contents[inner_end..outer_end],
+            Cow::from(rope.slice(outer_start..inner_start)),
+            Cow::from(rope.slice(inner_start..inner_end)),
+            Cow::from(rope.slice(inner_end..outer_end)),
         )
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use crate::source_code_locator::SourceCodeLocator;
-
-    #[test]
-    fn source_code_locator_init() {
-        let content = "x = 1";
-        let locator = SourceCodeLocator::new(content);
-        let offsets = locator.get_or_init_offsets();
-        assert_eq!(offsets.len(), 1);
-        assert_eq!(offsets[0], [0, 1, 2, 3, 4]);
-
-        let content = "x = 1\n";
-        let locator = SourceCodeLocator::new(content);
-        let offsets = locator.get_or_init_offsets();
-        assert_eq!(offsets.len(), 2);
-        assert_eq!(offsets[0], [0, 1, 2, 3, 4, 5]);
-        assert_eq!(offsets[1], [6]);
-
-        let content = "x = 1\ny = 2\nz = x + y\n";
-        let locator = SourceCodeLocator::new(content);
-        let offsets = locator.get_or_init_offsets();
-        assert_eq!(offsets.len(), 4);
-        assert_eq!(offsets[0], [0, 1, 2, 3, 4, 5]);
-        assert_eq!(offsets[1], [6, 7, 8, 9, 10, 11]);
-        assert_eq!(offsets[2], [12, 13, 14, 15, 16, 17, 18, 19, 20, 21]);
-        assert_eq!(offsets[3], [22]);
-
-        let content = "# \u{4e9c}\nclass Foo:\n    \"\"\".\"\"\"";
-        let locator = SourceCodeLocator::new(content);
-        let offsets = locator.get_or_init_offsets();
-        assert_eq!(offsets.len(), 3);
-        assert_eq!(offsets[0], [0, 1, 2, 5]);
-        assert_eq!(offsets[1], [6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]);
-        assert_eq!(offsets[2], [17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27]);
-    }
-}