Bump version to 0.0.104

.cargo/config.toml

@@ -0,0 +1,2 @@
+[alias]
+dev = "run --package ruff_dev --bin ruff_dev"

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
   - repo: https://github.com/charliermarsh/ruff-pre-commit
-    rev: v0.0.103
+    rev: v0.0.104
     hooks:
       - id: ruff
 

CONTRIBUTING.md

@@ -1,17 +1,17 @@
-# Contributing to ruff
+# Contributing to Ruff
 
-Welcome! We're happy to have you here. Thank you in advance for your contribution to ruff.
+Welcome! We're happy to have you here. Thank you in advance for your contribution to Ruff.
 
 ## The basics
 
-ruff welcomes contributions in the form of Pull Requests. For small changes (e.g., bug fixes), feel
+Ruff welcomes contributions in the form of Pull Requests. For small changes (e.g., bug fixes), feel
 free to submit a PR. For larger changes (e.g., new lint rules, new functionality, new configuration
 options), consider submitting an [Issue](https://github.com/charliermarsh/ruff/issues) outlining
 your proposed change.
 
 ### Prerequisites
 
-ruff is written in Rust. You'll need to install the
+Ruff is written in Rust. You'll need to install the
 [Rust toolchain](https://www.rust-lang.org/tools/install) for development.
 
 You'll also need [Insta](https://insta.rs/docs/) to update snapshot tests:
@@ -22,7 +22,7 @@ cargo install cargo-insta
 
 ### Development
 
-After cloning the repository, run ruff locally with:
+After cloning the repository, run Ruff locally with:
 
 ```shell
 cargo run resources/test/fixtures --no-cache
@@ -32,9 +32,9 @@ Prior to opening a pull request, ensure that your code has been auto-formatted,
 both the lint and test validation checks:
 
 ```shell
-cargo fmt     # Auto-formatting...
-cargo clippy  # Linting...
-cargo test    # Testing...
+cargo +nightly fmt --all     # Auto-formatting...
+cargo +nightly clippy --all  # Linting...
+cargo +nightly test --all    # Testing...
 ```
 
 These checks will run on GitHub Actions when you open your Pull Request, but running them locally
@@ -45,12 +45,13 @@ prior to merging.
 
 ### Example: Adding a new lint rule
 
-There are three phases to adding a new lint rule:
+There are four phases to adding a new lint rule:
 
 1. Define the rule in `src/checks.rs`.
-2. Define the _logic_ for triggering the rule in `src/check_ast.rs` (for AST-based checks)
-   or `src/check_lines.rs` (for text-based checks).
+2. Define the _logic_ for triggering the rule in `src/check_ast.rs` (for AST-based checks),
+   `src/check_tokens.rs` (for token-based checks), or `src/check_lines.rs` (for text-based checks).
 3. Add a test fixture.
+4. Update the generated files (documentation and generated code).
 
 To define the rule, open up `src/checks.rs`. You'll need to define both a `CheckCode` and
 `CheckKind`. As an example, you can grep for `E402` and `ModuleImportNotAtTopOfFile`, and follow the
@@ -58,37 +59,33 @@ pattern implemented therein.
 
 To trigger the rule, you'll likely want to augment the logic in `src/check_ast.rs`, which defines
 the Python AST visitor, responsible for iterating over the abstract syntax tree and collecting
-lint-rule violations as it goes. Grep for the `Check::new` invocations to understand how other,
-similar rules are implemented.
+lint-rule violations as it goes. If you need to inspect the AST, you can run `cargo dev print-ast`
+with a Python file. Grep for the `Check::new` invocations to understand how other, similar rules
+are implemented.
 
 To add a test fixture, create a file under `resources/test/fixtures`, named to match the `CheckCode`
 you defined earlier (e.g., `E402.py`). This file should contain a variety of violations and
-non-violations designed to evaluate and demonstrate the behavior of your lint rule. Run ruff locally
-with (e.g.) `cargo run resources/test/fixtures/E402.py`. Once you're satisfied with the output,
-codify the behavior as a snapshot test by adding a new function to the `mod tests` section of
-`src/linter.rs`, like so:
+non-violations designed to evaluate and demonstrate the behavior of your lint rule. Run Ruff locally
+with (e.g.) `cargo run resources/test/fixtures/E402.py --no-cache`. Once you're satisfied with the
+output, codify the behavior as a snapshot test by adding a new `testcase` macro to the `mod tests`
+section of `src/linter.rs`, like so:
 
 ```rust
-#[test]
-fn e402() -> Result<()> {
-    let mut checks = check_path(
-        Path::new("./resources/test/fixtures/E402.py"),
-        &settings::Settings::for_rule(CheckCode::E402),
-        &fixer::Mode::Generate,
-    )?;
-    checks.sort_by_key(|check| check.location);
-    insta::assert_yaml_snapshot!(checks);
-    Ok(())
-}
+#[test_case(CheckCode::A001, Path::new("A001.py"); "A001")]
+...
 ```
 
 Then, run `cargo test`. Your test will fail, but you'll be prompted to follow-up with
 `cargo insta review`. Accept the generated snapshot, then commit the snapshot file alongside the
 rest of your changes.
 
+Finally, to update the documentation, run `cargo dev generate-rules-table` from the repo root. To
+update the generated prefix map, run `cargo dev generate-check-code-prefix`. Both of these commands
+should be run whenever a new check is added to the codebase.
+
 ### Example: Adding a new configuration option
 
-ruff's user-facing settings live in two places: first, the command-line options defined with
+Ruff's user-facing settings live in two places: first, the command-line options defined with
 [clap](https://docs.rs/clap/latest/clap/) via the `Cli` struct in `src/main.rs`; and second, the
 `Config` struct defined `src/pyproject.rs`, which is responsible for extracting user-defined
 settings from a `pyproject.toml` file.
@@ -103,9 +100,9 @@ acceptable unused variables (e.g., `_`).
 
 ## Release process
 
-As of now, ruff has an ad hoc release process: releases are cut with high frequency via GitHub
+As of now, Ruff has an ad hoc release process: releases are cut with high frequency via GitHub
 Actions, which automatically generates the appropriate wheels across architectures and publishes
 them to [PyPI](https://pypi.org/project/ruff/).
 
-ruff follows the [semver](https://semver.org/) versioning standard. However, as pre-1.0 software,
+Ruff follows the [semver](https://semver.org/) versioning standard. However, as pre-1.0 software,
 even patch releases may contain [non-backwards-compatible changes](https://semver.org/#spec-item-4).

Cargo.lock

@@ -920,7 +920,7 @@ checksum = "0ce7134b9999ecaf8bcd65542e436736ef32ddca1b3e06094cb6ec5755203b80"
 
 [[package]]
 name = "flake8-to-ruff"
-version = "0.0.103-dev.0"
+version = "0.0.104-dev.0"
 dependencies = [
  "anyhow",
  "clap 4.0.15",
@@ -2221,7 +2221,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.0.103"
+version = "0.0.104"
 dependencies = [
  "anyhow",
  "assert_cmd",
@@ -2266,7 +2266,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_dev"
-version = "0.0.103"
+version = "0.0.104"
 dependencies = [
  "anyhow",
  "clap 4.0.15",

Cargo.toml

@@ -6,7 +6,7 @@ members = [
 
 [package]
 name = "ruff"
-version = "0.0.103"
+version = "0.0.104"
 edition = "2021"
 
 [lib]

README.md

@@ -93,7 +93,7 @@ Ruff also works with [pre-commit](https://pre-commit.com):
 ```yaml
 repos:
   - repo: https://github.com/charliermarsh/ruff-pre-commit
-    rev: v0.0.103
+    rev: v0.0.104
     hooks:
       - id: ruff
 ```
@@ -300,7 +300,7 @@ By default, Ruff enables all `E` and `F` error codes, which correspond to those
 
 The 🛠 emoji indicates that a rule is automatically fixable by the `--fix` command-line option.
 
-<!-- Sections automatically generated by examples/generate_rules_table.rs. -->
+<!-- Sections automatically generated by `cargo dev generate-rules-table`. -->
 <!-- Begin auto-generated sections. -->
 
 ### Pyflakes
@@ -322,7 +322,7 @@ For more, see [Pyflakes](https://pypi.org/project/pyflakes/2.5.0/) on PyPI.
 | F621 | ExpressionsInStarAssignment | Too many expressions in star-unpacking assignment |  |
 | F622 | TwoStarredExpressions | Two starred expressions in assignment |  |
 | F631 | AssertTuple | Assert test is a non-empty tuple, which is always `True` |  |
-| F632 | IsLiteral | Use `==` and `!=` to compare constant literals |  |
+| F632 | IsLiteral | Use `==` and `!=` to compare constant literals | 🛠 |
 | F633 | InvalidPrintSyntax | Use of `>>` is invalid with `print` function |  |
 | F634 | IfTuple | If test is a tuple, which is always `True` |  |
 | F701 | BreakOutsideLoop | `break` outside loop |  |
@@ -426,6 +426,7 @@ For more, see [pyupgrade](https://pypi.org/project/pyupgrade/3.2.0/) on PyPI.
 | U006 | UsePEP585Annotation | Use `list` instead of `List` for type annotations | 🛠 |
 | U007 | UsePEP604Annotation | Use `X \| Y` for type annotations | 🛠 |
 | U008 | SuperCallWithParameters | Use `super()` instead of `super(__class__, self)` | 🛠 |
+| U009 | PEP3120UnnecessaryCodingComment | utf-8 encoding declaration is unnecessary | 🛠 |
 
 ### pep8-naming
 
@@ -606,7 +607,7 @@ including:
 - [`flake8-quotes`](https://pypi.org/project/flake8-quotes/)
 - [`flake8-comprehensions`](https://pypi.org/project/flake8-comprehensions/)
 - [`flake8-bugbear`](https://pypi.org/project/flake8-bugbear/) (15/32)
-- [`pyupgrade`](https://pypi.org/project/pyupgrade/) (10/34)
+- [`pyupgrade`](https://pypi.org/project/pyupgrade/) (11/34)
 - [`autoflake`](https://pypi.org/project/autoflake/) (1/7)
 
 Beyond rule-set parity, Ruff suffers from the following limitations vis-à-vis Flake8:
@@ -630,7 +631,7 @@ Today, Ruff can be used to replace Flake8 when used with any of the following pl
 - [`flake8-bugbear`](https://pypi.org/project/flake8-bugbear/) (15/32)
 
 Ruff also implements the functionality that you get from [`yesqa`](https://github.com/asottile/yesqa),
-and a subset of the rules implemented in [`pyupgrade`](https://pypi.org/project/pyupgrade/) (10/34).
+and a subset of the rules implemented in [`pyupgrade`](https://pypi.org/project/pyupgrade/) (11/34).
 
 If you're looking to use Ruff, but rely on an unsupported Flake8 plugin, free to file an Issue.
 

flake8_to_ruff/Cargo.lock

@@ -771,7 +771,7 @@ checksum = "0ce7134b9999ecaf8bcd65542e436736ef32ddca1b3e06094cb6ec5755203b80"
 
 [[package]]
 name = "flake8_to_ruff"
-version = "0.0.103"
+version = "0.0.104"
 dependencies = [
  "anyhow",
  "clap",
@@ -1975,7 +1975,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.0.103"
+version = "0.0.104"
 dependencies = [
  "anyhow",
  "bincode",

flake8_to_ruff/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "flake8-to-ruff"
-version = "0.0.103-dev.0"
+version = "0.0.104-dev.0"
 edition = "2021"
 
 [lib]

resources/test/fixtures/B015.py

@@ -22,3 +22,6 @@ data = [x for x in [1, 2, 3] if x in (1, 2)]
 
 class TestClass:
     1 == 1
+
+
+print(1 == 1)

resources/test/fixtures/F632.py

@@ -3,3 +3,6 @@ if x is "abc":
 
 if 123 is not y:
     pass
+
+if "123" is x < 3:
+    pass

resources/test/fixtures/N803.py

@@ -1,7 +1,7 @@
-def func(a, A):
-    return a, A
+def func(_, a, A):
+    return _, a, A
 
 
 class Class:
-    def method(self, a, A):
-        return a, A
+    def method(self, _, a, A):
+        return _, a, A

resources/test/fixtures/N804.py

@@ -1,19 +1,43 @@
+from abc import ABCMeta
+
+
 class Class:
-    @classmethod
-    def bad_class_method(this):
+    def bad_method(this):
+        pass
+
+    if False:
+
+        def extra_bad_method(this):
+            pass
+
+    def good_method(self):
         pass
 
     @classmethod
-    def good_class_method(cls):
-        pass
-
-    def method(self):
+    def class_method(cls):
         pass
 
     @staticmethod
     def static_method(x):
         return x
 
+    def __init__(self):
+        ...
+
+    def __new__(cls, *args, **kwargs):
+        ...
+
+    def __init_subclass__(self, default_name, **kwargs):
+        ...
+
+
+class MetaClass(ABCMeta):
+    def bad_method(self):
+        pass
+
+    def good_method(cls):
+        pass
+
 
 def func(x):
     return x

resources/test/fixtures/N805.py

@@ -1,11 +1,11 @@
-import random
+from abc import ABCMeta
 
 
 class Class:
     def bad_method(this):
         pass
 
-    if random.random(0, 2) == 0:
+    if False:
 
         def extra_bad_method(this):
             pass
@@ -21,6 +21,23 @@ class Class:
     def static_method(x):
         return x
 
+    def __init__(self):
+        ...
+
+    def __new__(cls, *args, **kwargs):
+        ...
+
+    def __init_subclass__(self, default_name, **kwargs):
+        ...
+
+
+class MetaClass(ABCMeta):
+    def bad_method(self):
+        pass
+
+    def good_method(cls):
+        pass
+
 
 def func(x):
     return x

resources/test/fixtures/U009_0.py

@@ -0,0 +1,3 @@
+# coding=utf8
+
+print('Hello world')

resources/test/fixtures/U009_1.py

@@ -0,0 +1,4 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+print('Hello world')

resources/test/fixtures/U009_2.py

@@ -0,0 +1,5 @@
+#!/usr/bin/python
+# A coding comment is only valid in the first two lines, so this one is not checked.
+# -*- coding: utf-8 -*-
+
+print('Hello world')

resources/test/fixtures/U009_3.py

@@ -0,0 +1,4 @@
+#!/usr/bin/python
+# -*- coding: something-else -*-
+
+print('Hello world')

ruff_dev/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff_dev"
-version = "0.0.103"
+version = "0.0.104"
 edition = "2021"
 
 [dependencies]

ruff_dev/src/generate_check_code_prefix.rs

@@ -11,7 +11,7 @@ use itertools::Itertools;
 use ruff::checks::CheckCode;
 use strum::IntoEnumIterator;
 
-const FILE: &str = "../src/checks_gen.rs";
+const FILE: &str = "src/checks_gen.rs";
 
 #[derive(Parser)]
 #[command(author, version, about, long_about = None)]

ruff_dev/src/generate_rules_table.rs

@@ -3,13 +3,13 @@
 use std::fs;
 use std::fs::OpenOptions;
 use std::io::Write;
+use std::path::PathBuf;
 
 use anyhow::Result;
 use clap::Args;
 use ruff::checks::{CheckCategory, CheckCode};
 use strum::IntoEnumIterator;
 
-const FILE: &str = "../README.md";
 const BEGIN_PRAGMA: &str = "<!-- Begin auto-generated sections. -->";
 const END_PRAGMA: &str = "<!-- End auto-generated sections. -->";
 
@@ -64,7 +64,11 @@ pub fn main(cli: &Cli) -> Result<()> {
         print!("{}", output);
     } else {
         // Read the existing file.
-        let existing = fs::read_to_string(FILE)?;
+        let file = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+            .parent()
+            .expect("Failed to find root directory")
+            .join("README.md");
+        let existing = fs::read_to_string(&file)?;
 
         // Extract the prefix.
         let index = existing
@@ -79,7 +83,7 @@ pub fn main(cli: &Cli) -> Result<()> {
         let suffix = &existing[index..];
 
         // Write the prefix, new contents, and suffix.
-        let mut f = OpenOptions::new().write(true).truncate(true).open(FILE)?;
+        let mut f = OpenOptions::new().write(true).truncate(true).open(&file)?;
         write!(f, "{}\n\n", prefix)?;
         write!(f, "{}", output)?;
         write!(f, "{}", suffix)?;

src/ast/types.rs

@@ -1,6 +1,7 @@
 use std::collections::BTreeMap;
 use std::sync::atomic::{AtomicUsize, Ordering};
 
+use rustpython_ast::{Expr, Keyword};
 use rustpython_parser::ast::{Located, Location};
 
 fn id() -> usize {
@@ -30,9 +31,17 @@ pub struct FunctionScope {
     pub uses_locals: bool,
 }
 
+#[derive(Clone, Debug, Default)]
+pub struct ClassScope<'a> {
+    pub name: &'a str,
+    pub bases: &'a [Expr],
+    pub keywords: &'a [Keyword],
+    pub decorator_list: &'a [Expr],
+}
+
 #[derive(Clone, Debug)]
-pub enum ScopeKind {
-    Class,
+pub enum ScopeKind<'a> {
+    Class(ClassScope<'a>),
     Function(FunctionScope),
     Generator,
     Module,
@@ -40,15 +49,15 @@ pub enum ScopeKind {
 }
 
 #[derive(Clone, Debug)]
-pub struct Scope {
+pub struct Scope<'a> {
     pub id: usize,
-    pub kind: ScopeKind,
+    pub kind: ScopeKind<'a>,
     pub import_starred: bool,
     pub values: BTreeMap<String, Binding>,
 }
 
-impl Scope {
-    pub fn new(kind: ScopeKind) -> Self {
+impl<'a> Scope<'a> {
+    pub fn new(kind: ScopeKind<'a>) -> Self {
         Scope {
             id: id(),
             kind,

src/check_ast.rs

@@ -15,8 +15,8 @@ use crate::ast::helpers::{extract_handler_names, match_name_or_attr_from_module}
 use crate::ast::operations::extract_all_names;
 use crate::ast::relocate::relocate_expr;
 use crate::ast::types::{
-    Binding, BindingContext, BindingKind, CheckLocator, FunctionScope, ImportKind, Range, Scope,
-    ScopeKind,
+    Binding, BindingContext, BindingKind, CheckLocator, ClassScope, FunctionScope, ImportKind,
+    Range, Scope, ScopeKind,
 };
 use crate::ast::visitor::{walk_excepthandler, Visitor};
 use crate::ast::{helpers, operations, visitor};
@@ -66,7 +66,7 @@ pub struct Checker<'a> {
     // at various points in time.
     pub(crate) parents: Vec<&'a Stmt>,
     pub(crate) parent_stack: Vec<usize>,
-    scopes: Vec<Scope>,
+    scopes: Vec<Scope<'a>>,
     scope_stack: Vec<usize>,
     dead_scopes: Vec<usize>,
     deferred_string_annotations: Vec<(Range, &'a str)>,
@@ -274,6 +274,7 @@ where
                     if let Some(check) =
                         pep8_naming::checks::invalid_first_argument_name_for_class_method(
                             self.current_scope(),
+                            name,
                             decorator_list,
                             args,
                             &self.settings.pep8_naming,
@@ -286,6 +287,7 @@ where
                 if self.settings.enabled.contains(&CheckCode::N805) {
                     if let Some(check) = pep8_naming::checks::invalid_first_argument_name_for_method(
                         self.current_scope(),
+                        name,
                         decorator_list,
                         args,
                         &self.settings.pep8_naming,
@@ -296,7 +298,7 @@ where
 
                 if self.settings.enabled.contains(&CheckCode::N807) {
                     if let Some(check) =
-                        pep8_naming::checks::dunder_function_name(stmt, self.current_scope(), name)
+                        pep8_naming::checks::dunder_function_name(self.current_scope(), stmt, name)
                     {
                         self.checks.push(check);
                     }
@@ -360,7 +362,7 @@ where
                 if self.settings.enabled.contains(&CheckCode::F706) {
                     if let Some(scope_index) = self.scope_stack.last().cloned() {
                         match self.scopes[scope_index].kind {
-                            ScopeKind::Class | ScopeKind::Module => {
+                            ScopeKind::Class(_) | ScopeKind::Module => {
                                 self.checks.push(Check::new(
                                     CheckKind::ReturnOutsideFunction,
                                     self.locate_check(Range::from_located(stmt)),
@@ -377,7 +379,6 @@ where
                 keywords,
                 decorator_list,
                 body,
-                ..
             } => {
                 if self.settings.enabled.contains(&CheckCode::U004) {
                     pyupgrade::plugins::useless_object_inheritance(
@@ -427,7 +428,12 @@ where
                 for expr in decorator_list {
                     self.visit_expr(expr)
                 }
-                self.push_scope(Scope::new(ScopeKind::Class))
+                self.push_scope(Scope::new(ScopeKind::Class(ClassScope {
+                    name,
+                    bases,
+                    keywords,
+                    decorator_list,
+                })))
             }
             StmtKind::Import { names } => {
                 if self.settings.enabled.contains(&CheckCode::E402) {
@@ -809,6 +815,11 @@ where
                 }
             }
             StmtKind::Delete { .. } => {}
+            StmtKind::Expr { value, .. } => {
+                if self.settings.enabled.contains(&CheckCode::B015) {
+                    flake8_bugbear::plugins::useless_comparison(self, value)
+                }
+            }
             _ => {}
         }
 
@@ -1251,7 +1262,7 @@ where
             ExprKind::Yield { .. } | ExprKind::YieldFrom { .. } | ExprKind::Await { .. } => {
                 let scope = self.current_scope();
                 if self.settings.enabled.contains(&CheckCode::F704) {
-                    if matches!(scope.kind, ScopeKind::Class | ScopeKind::Module) {
+                    if matches!(scope.kind, ScopeKind::Class(_) | ScopeKind::Module) {
                         self.checks.push(Check::new(
                             CheckKind::YieldOutsideFunction,
                             self.locate_check(Range::from_located(expr)),
@@ -1319,12 +1330,13 @@ where
                 }
 
                 if self.settings.enabled.contains(&CheckCode::F632) {
-                    self.checks.extend(pyflakes::checks::is_literal(
+                    pyflakes::plugins::invalid_literal_comparison(
+                        self,
                         left,
                         ops,
                         comparators,
                         self.locate_check(Range::from_located(expr)),
-                    ));
+                    );
                 }
 
                 if self.settings.enabled.contains(&CheckCode::E721) {
@@ -1334,12 +1346,6 @@ where
                         self.locate_check(Range::from_located(expr)),
                     ));
                 }
-
-                if self.settings.enabled.contains(&CheckCode::B015) {
-                    if let Some(parent) = self.parents.last() {
-                        flake8_bugbear::plugins::useless_comparison(self, left, parent);
-                    }
-                }
             }
             ExprKind::Constant {
                 value: Constant::Str(value),
@@ -1717,7 +1723,7 @@ where
 
         if self.settings.enabled.contains(&CheckCode::N803) {
             if let Some(check) =
-                pep8_naming::checks::invalid_argument_name(Range::from_located(arg), &arg.node.arg)
+                pep8_naming::checks::invalid_argument_name(&arg.node.arg, Range::from_located(arg))
             {
                 self.checks.push(check);
             }
@@ -1791,7 +1797,7 @@ impl<'a> Checker<'a> {
             .expect("Attempted to pop without scope.");
     }
 
-    fn push_scope(&mut self, scope: Scope) {
+    fn push_scope(&mut self, scope: Scope<'a>) {
         self.scope_stack.push(self.scopes.len());
         self.scopes.push(scope);
     }
@@ -1896,7 +1902,7 @@ impl<'a> Checker<'a> {
             let mut import_starred = false;
             for scope_index in self.scope_stack.iter().rev() {
                 let scope = &mut self.scopes[*scope_index];
-                if matches!(scope.kind, ScopeKind::Class) {
+                if matches!(scope.kind, ScopeKind::Class(_)) {
                     if id == "__class__" {
                         return;
                     } else if !first_iter && !in_generator {
@@ -2433,7 +2439,7 @@ impl<'a> Checker<'a> {
     }
 
     fn check_builtin_shadowing(&mut self, name: &str, location: Range, is_attribute: bool) {
-        if is_attribute && matches!(self.current_scope().kind, ScopeKind::Class) {
+        if is_attribute && matches!(self.current_scope().kind, ScopeKind::Class(_)) {
             if self.settings.enabled.contains(&CheckCode::A003) {
                 if let Some(check) = flake8_builtins::checks::builtin_shadowing(
                     name,

src/check_lines.rs

@@ -2,6 +2,8 @@
 
 use std::collections::BTreeMap;
 
+use once_cell::sync::Lazy;
+use regex::Regex;
 use rustpython_parser::ast::Location;
 
 use crate::ast::types::Range;
@@ -11,6 +13,10 @@ use crate::noqa;
 use crate::noqa::Directive;
 use crate::settings::Settings;
 
+// Regex from PEP263
+static CODING_COMMENT_REGEX: Lazy<Regex> =
+    Lazy::new(|| Regex::new(r"^[ \t\f]*#.*?coding[:=][ \t]*utf-?8").expect("Invalid regex"));
+
 /// Whether the given line is too long and should be reported.
 fn should_enforce_line_length(line: &str, length: usize, limit: usize) -> bool {
     if length > limit {
@@ -52,6 +58,27 @@ pub fn check_lines(
             .map(|lineno| lineno - 1)
             .unwrap_or(lineno);
 
+        if lineno < 2 {
+            // PEP3120 makes utf-8 the default encoding.
+            if CODING_COMMENT_REGEX.is_match(line) {
+                let line_length = line.len();
+                let mut check = Check::new(
+                    CheckKind::PEP3120UnnecessaryCodingComment,
+                    Range {
+                        location: Location::new(lineno + 1, 0),
+                        end_location: Location::new(lineno + 1, line_length + 1),
+                    },
+                );
+                if autofix.patch() {
+                    check.amend(Fix::deletion(
+                        Location::new(lineno + 1, 0),
+                        Location::new(lineno + 1, line_length + 1),
+                    ));
+                }
+                line_checks.push(check);
+            }
+        }
+
         if enforce_noqa {
             noqa_directives
                 .entry(noqa_lineno)

src/checks.rs

@@ -124,6 +124,7 @@ pub enum CheckCode {
     U006,
     U007,
     U008,
+    U009,
     // pydocstyle
     D100,
     D101,
@@ -365,6 +366,7 @@ pub enum CheckKind {
     UsePEP585Annotation(String),
     UsePEP604Annotation,
     SuperCallWithParameters,
+    PEP3120UnnecessaryCodingComment,
     // pydocstyle
     BlankLineAfterLastSection(String),
     BlankLineAfterSection(String),
@@ -438,7 +440,9 @@ impl CheckCode {
     /// physical lines).
     pub fn lint_source(&self) -> &'static LintSource {
         match self {
-            CheckCode::E501 | CheckCode::W292 | CheckCode::M001 => &LintSource::Lines,
+            CheckCode::E501 | CheckCode::W292 | CheckCode::M001 | CheckCode::U009 => {
+                &LintSource::Lines
+            }
             CheckCode::Q000
             | CheckCode::Q001
             | CheckCode::Q002
@@ -573,6 +577,7 @@ impl CheckCode {
             CheckCode::U006 => CheckKind::UsePEP585Annotation("List".to_string()),
             CheckCode::U007 => CheckKind::UsePEP604Annotation,
             CheckCode::U008 => CheckKind::SuperCallWithParameters,
+            CheckCode::U009 => CheckKind::PEP3120UnnecessaryCodingComment,
             // pydocstyle
             CheckCode::D100 => CheckKind::PublicModule,
             CheckCode::D101 => CheckKind::PublicClass,
@@ -750,6 +755,7 @@ impl CheckCode {
             CheckCode::U006 => CheckCategory::Pyupgrade,
             CheckCode::U007 => CheckCategory::Pyupgrade,
             CheckCode::U008 => CheckCategory::Pyupgrade,
+            CheckCode::U009 => CheckCategory::Pyupgrade,
             CheckCode::D100 => CheckCategory::Pydocstyle,
             CheckCode::D101 => CheckCategory::Pydocstyle,
             CheckCode::D102 => CheckCategory::Pydocstyle,
@@ -918,6 +924,7 @@ impl CheckKind {
             CheckKind::UsePEP604Annotation => &CheckCode::U007,
             CheckKind::UselessObjectInheritance(_) => &CheckCode::U004,
             CheckKind::SuperCallWithParameters => &CheckCode::U008,
+            CheckKind::PEP3120UnnecessaryCodingComment => &CheckCode::U009,
             // pydocstyle
             CheckKind::BlankLineAfterLastSection(_) => &CheckCode::D413,
             CheckKind::BlankLineAfterSection(_) => &CheckCode::D410,
@@ -1478,6 +1485,9 @@ impl CheckKind {
             CheckKind::ErrorSuffixOnExceptionName(name) => {
                 format!("Exception name `{name}` should be named with an Error suffix")
             }
+            CheckKind::PEP3120UnnecessaryCodingComment => {
+                "utf-8 encoding declaration is unnecessary".to_string()
+            }
             // Ruff
             CheckKind::AmbiguousUnicodeCharacterString(confusable, representant) => {
                 format!(
@@ -1583,6 +1593,8 @@ impl CheckKind {
                 | CheckKind::UsePEP604Annotation
                 | CheckKind::UselessMetaclassType
                 | CheckKind::UselessObjectInheritance(_)
+                | CheckKind::PEP3120UnnecessaryCodingComment
+                | CheckKind::IsLiteral
         )
     }
 }

src/checks_gen.rs

@@ -230,6 +230,7 @@ pub enum CheckCodePrefix {
     U006,
     U007,
     U008,
+    U009,
     W,
     W2,
     W29,
@@ -877,6 +878,7 @@ impl CheckCodePrefix {
                 CheckCode::U006,
                 CheckCode::U007,
                 CheckCode::U008,
+                CheckCode::U009,
             ],
             CheckCodePrefix::U0 => vec![
                 CheckCode::U001,
@@ -887,6 +889,7 @@ impl CheckCodePrefix {
                 CheckCode::U006,
                 CheckCode::U007,
                 CheckCode::U008,
+                CheckCode::U009,
             ],
             CheckCodePrefix::U00 => vec![
                 CheckCode::U001,
@@ -897,6 +900,7 @@ impl CheckCodePrefix {
                 CheckCode::U006,
                 CheckCode::U007,
                 CheckCode::U008,
+                CheckCode::U009,
             ],
             CheckCodePrefix::U001 => vec![CheckCode::U001],
             CheckCodePrefix::U002 => vec![CheckCode::U002],
@@ -906,6 +910,7 @@ impl CheckCodePrefix {
             CheckCodePrefix::U006 => vec![CheckCode::U006],
             CheckCodePrefix::U007 => vec![CheckCode::U007],
             CheckCodePrefix::U008 => vec![CheckCode::U008],
+            CheckCodePrefix::U009 => vec![CheckCode::U009],
             CheckCodePrefix::W => vec![CheckCode::W292, CheckCode::W605],
             CheckCodePrefix::W2 => vec![CheckCode::W292],
             CheckCodePrefix::W29 => vec![CheckCode::W292],
@@ -1143,6 +1148,7 @@ impl CheckCodePrefix {
             CheckCodePrefix::U006 => PrefixSpecificity::Explicit,
             CheckCodePrefix::U007 => PrefixSpecificity::Explicit,
             CheckCodePrefix::U008 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::U009 => PrefixSpecificity::Explicit,
             CheckCodePrefix::W => PrefixSpecificity::Category,
             CheckCodePrefix::W2 => PrefixSpecificity::Hundreds,
             CheckCodePrefix::W29 => PrefixSpecificity::Tens,

src/cst/matchers.rs

@@ -1,5 +1,5 @@
 use anyhow::Result;
-use libcst_native::Module;
+use libcst_native::{Expr, Module, SmallStatement, Statement};
 
 pub fn match_module(module_text: &str) -> Result<Module> {
     match libcst_native::parse_module(module_text, None) {
@@ -7,3 +7,15 @@ pub fn match_module(module_text: &str) -> Result<Module> {
         Err(_) => Err(anyhow::anyhow!("Failed to extract CST from source.")),
     }
 }
+
+pub fn match_expr<'a, 'b>(module: &'a mut Module<'b>) -> Result<&'a mut Expr<'b>> {
+    if let Some(Statement::Simple(expr)) = module.body.first_mut() {
+        if let Some(SmallStatement::Expr(expr)) = expr.body.first_mut() {
+            Ok(expr)
+        } else {
+            Err(anyhow::anyhow!("Expected node to be: SmallStatement::Expr"))
+        }
+    } else {
+        Err(anyhow::anyhow!("Expected node to be: Statement::Simple"))
+    }
+}

src/flake8_bugbear/plugins/useless_comparison.rs

@@ -1,14 +1,14 @@
-use rustpython_ast::{Expr, Stmt, StmtKind};
+use rustpython_ast::{Expr, ExprKind};
 
 use crate::ast::types::{CheckLocator, Range};
 use crate::check_ast::Checker;
 use crate::checks::{Check, CheckKind};
 
-pub fn useless_comparison(checker: &mut Checker, expr: &Expr, parent: &Stmt) {
-    if let StmtKind::Expr { .. } = &parent.node {
+pub fn useless_comparison(checker: &mut Checker, expr: &Expr) {
+    if let ExprKind::Compare { left, .. } = &expr.node {
         checker.add_check(Check::new(
             CheckKind::UselessComparison,
-            checker.locate_check(Range::from_located(expr)),
+            checker.locate_check(Range::from_located(left)),
         ));
     }
 }

src/flake8_comprehensions/fixes.rs

@@ -1,28 +1,15 @@
 use anyhow::Result;
 use libcst_native::{
     Arg, Call, Codegen, Dict, DictComp, DictElement, Element, Expr, Expression, LeftCurlyBrace,
-    LeftParen, LeftSquareBracket, List, ListComp, Module, Name, ParenthesizableWhitespace,
-    RightCurlyBrace, RightParen, RightSquareBracket, Set, SetComp, SimpleString, SimpleWhitespace,
-    SmallStatement, Statement, Tuple,
+    LeftParen, LeftSquareBracket, List, ListComp, Name, ParenthesizableWhitespace, RightCurlyBrace,
+    RightParen, RightSquareBracket, Set, SetComp, SimpleString, SimpleWhitespace, Tuple,
 };
 
 use crate::ast::types::Range;
 use crate::autofix::Fix;
-use crate::cst::matchers::match_module;
+use crate::cst::matchers::{match_expr, match_module};
 use crate::source_code_locator::SourceCodeLocator;
 
-fn match_expr<'a, 'b>(module: &'a mut Module<'b>) -> Result<&'a mut Expr<'b>> {
-    if let Some(Statement::Simple(expr)) = module.body.first_mut() {
-        if let Some(SmallStatement::Expr(expr)) = expr.body.first_mut() {
-            Ok(expr)
-        } else {
-            Err(anyhow::anyhow!("Expected node to be: SmallStatement::Expr"))
-        }
-    } else {
-        Err(anyhow::anyhow!("Expected node to be: Statement::Simple"))
-    }
-}
-
 fn match_call<'a, 'b>(expr: &'a mut Expr<'b>) -> Result<&'a mut Call<'b>> {
     if let Expression::Call(call) = &mut expr.value {
         Ok(call)

src/linter.rs

@@ -439,6 +439,10 @@ mod tests {
     #[test_case(CheckCode::U006, Path::new("U006.py"); "U006")]
     #[test_case(CheckCode::U007, Path::new("U007.py"); "U007")]
     #[test_case(CheckCode::U008, Path::new("U008.py"); "U008")]
+    #[test_case(CheckCode::U009, Path::new("U009_0.py"); "U009_0")]
+    #[test_case(CheckCode::U009, Path::new("U009_1.py"); "U009_1")]
+    #[test_case(CheckCode::U009, Path::new("U009_2.py"); "U009_2")]
+    #[test_case(CheckCode::U009, Path::new("U009_3.py"); "U009_3")]
     #[test_case(CheckCode::W292, Path::new("W292_0.py"); "W292_0")]
     #[test_case(CheckCode::W292, Path::new("W292_1.py"); "W292_1")]
     #[test_case(CheckCode::W292, Path::new("W292_2.py"); "W292_2")]

src/pep8_naming/checks.rs

@@ -1,8 +1,9 @@
-use itertools::Itertools;
 use rustpython_ast::{Arguments, Expr, ExprKind, Stmt};
 
 use crate::ast::types::{FunctionScope, Range, Scope, ScopeKind};
 use crate::checks::{Check, CheckKind};
+use crate::pep8_naming::helpers;
+use crate::pep8_naming::helpers::FunctionType;
 use crate::pep8_naming::settings::Settings;
 
 /// N801
@@ -25,7 +26,7 @@ pub fn invalid_class_name(class_def: &Stmt, name: &str) -> Option<Check> {
 
 /// N802
 pub fn invalid_function_name(func_def: &Stmt, name: &str, settings: &Settings) -> Option<Check> {
-    if !is_lower(name)
+    if name.to_lowercase() != name
         && !settings
             .ignore_names
             .iter()
@@ -40,8 +41,8 @@ pub fn invalid_function_name(func_def: &Stmt, name: &str, settings: &Settings) -
 }
 
 /// N803
-pub fn invalid_argument_name(location: Range, name: &str) -> Option<Check> {
-    if !is_lower(name) {
+pub fn invalid_argument_name(name: &str, location: Range) -> Option<Check> {
+    if name.to_lowercase() != name {
         return Some(Check::new(
             CheckKind::InvalidArgumentName(name.to_string()),
             location,
@@ -53,21 +54,15 @@ pub fn invalid_argument_name(location: Range, name: &str) -> Option<Check> {
 /// N804
 pub fn invalid_first_argument_name_for_class_method(
     scope: &Scope,
+    name: &str,
     decorator_list: &[Expr],
     args: &Arguments,
     settings: &Settings,
 ) -> Option<Check> {
-    if !matches!(scope.kind, ScopeKind::Class) {
-        return None;
-    }
-
-    if decorator_list.iter().any(|decorator| {
-        if let ExprKind::Name { id, .. } = &decorator.node {
-            settings.classmethod_decorators.contains(id)
-        } else {
-            false
-        }
-    }) {
+    if matches!(
+        helpers::function_type(scope, name, decorator_list, settings),
+        FunctionType::ClassMethod
+    ) {
         if let Some(arg) = args.args.first() {
             if arg.node.arg != "cls" {
                 return Some(Check::new(
@@ -83,31 +78,22 @@ pub fn invalid_first_argument_name_for_class_method(
 /// N805
 pub fn invalid_first_argument_name_for_method(
     scope: &Scope,
+    name: &str,
     decorator_list: &[Expr],
     args: &Arguments,
     settings: &Settings,
 ) -> Option<Check> {
-    if !matches!(scope.kind, ScopeKind::Class) {
-        return None;
-    }
-
-    if decorator_list.iter().any(|decorator| {
-        if let ExprKind::Name { id, .. } = &decorator.node {
-            settings.classmethod_decorators.contains(id)
-                || settings.staticmethod_decorators.contains(id)
-        } else {
-            false
-        }
-    }) {
-        return None;
-    }
-
-    if let Some(arg) = args.args.first() {
-        if arg.node.arg != "self" {
-            return Some(Check::new(
-                CheckKind::InvalidFirstArgumentNameForMethod,
-                Range::from_located(arg),
-            ));
+    if matches!(
+        helpers::function_type(scope, name, decorator_list, settings),
+        FunctionType::Method
+    ) {
+        if let Some(arg) = args.args.first() {
+            if arg.node.arg != "self" {
+                return Some(Check::new(
+                    CheckKind::InvalidFirstArgumentNameForMethod,
+                    Range::from_located(arg),
+                ));
+            }
         }
     }
     None
@@ -128,18 +114,16 @@ pub fn non_lowercase_variable_in_function(scope: &Scope, expr: &Expr, name: &str
 }
 
 /// N807
-pub fn dunder_function_name(func_def: &Stmt, scope: &Scope, name: &str) -> Option<Check> {
-    if matches!(scope.kind, ScopeKind::Class) {
+pub fn dunder_function_name(scope: &Scope, stmt: &Stmt, name: &str) -> Option<Check> {
+    if matches!(scope.kind, ScopeKind::Class(_)) {
         return None;
     }
-
     if name.starts_with("__") && name.ends_with("__") {
         return Some(Check::new(
             CheckKind::DunderFunctionName,
-            Range::from_located(func_def),
+            Range::from_located(stmt),
         ));
     }
-
     None
 }
 
@@ -149,7 +133,7 @@ pub fn constant_imported_as_non_constant(
     name: &str,
     asname: &str,
 ) -> Option<Check> {
-    if is_upper(name) && !is_upper(asname) {
+    if helpers::is_upper(name) && !helpers::is_upper(asname) {
         return Some(Check::new(
             CheckKind::ConstantImportedAsNonConstant(name.to_string(), asname.to_string()),
             Range::from_located(import_from),
@@ -164,7 +148,7 @@ pub fn lowercase_imported_as_non_lowercase(
     name: &str,
     asname: &str,
 ) -> Option<Check> {
-    if is_lower(name) && asname.to_lowercase() != asname {
+    if !helpers::is_upper(name) && helpers::is_lower(name) && asname.to_lowercase() != asname {
         return Some(Check::new(
             CheckKind::LowercaseImportedAsNonLowercase(name.to_string(), asname.to_string()),
             Range::from_located(import_from),
@@ -179,7 +163,7 @@ pub fn camelcase_imported_as_lowercase(
     name: &str,
     asname: &str,
 ) -> Option<Check> {
-    if is_camelcase(name) && is_lower(asname) {
+    if helpers::is_camelcase(name) && helpers::is_lower(asname) {
         return Some(Check::new(
             CheckKind::CamelcaseImportedAsLowercase(name.to_string(), asname.to_string()),
             Range::from_located(import_from),
@@ -194,7 +178,11 @@ pub fn camelcase_imported_as_constant(
     name: &str,
     asname: &str,
 ) -> Option<Check> {
-    if is_camelcase(name) && is_upper(asname) && !is_acronym(name, asname) {
+    if helpers::is_camelcase(name)
+        && !helpers::is_lower(asname)
+        && helpers::is_upper(asname)
+        && !helpers::is_acronym(name, asname)
+    {
         return Some(Check::new(
             CheckKind::CamelcaseImportedAsConstant(name.to_string(), asname.to_string()),
             Range::from_located(import_from),
@@ -205,10 +193,10 @@ pub fn camelcase_imported_as_constant(
 
 /// N815
 pub fn mixed_case_variable_in_class_scope(scope: &Scope, expr: &Expr, name: &str) -> Option<Check> {
-    if !matches!(scope.kind, ScopeKind::Class) {
+    if !matches!(scope.kind, ScopeKind::Class(_)) {
         return None;
     }
-    if is_mixed_case(name) {
+    if helpers::is_mixed_case(name) {
         return Some(Check::new(
             CheckKind::MixedCaseVariableInClassScope(name.to_string()),
             Range::from_located(expr),
@@ -226,7 +214,7 @@ pub fn mixed_case_variable_in_global_scope(
     if !matches!(scope.kind, ScopeKind::Module) {
         return None;
     }
-    if is_mixed_case(name) {
+    if helpers::is_mixed_case(name) {
         return Some(Check::new(
             CheckKind::MixedCaseVariableInGlobalScope(name.to_string()),
             Range::from_located(expr),
@@ -241,7 +229,11 @@ pub fn camelcase_imported_as_acronym(
     name: &str,
     asname: &str,
 ) -> Option<Check> {
-    if is_camelcase(name) && is_upper(asname) && is_acronym(name, asname) {
+    if helpers::is_camelcase(name)
+        && !helpers::is_lower(asname)
+        && helpers::is_upper(asname)
+        && helpers::is_acronym(name, asname)
+    {
         return Some(Check::new(
             CheckKind::CamelcaseImportedAsAcronym(name.to_string(), asname.to_string()),
             Range::from_located(import_from),
@@ -272,101 +264,3 @@ pub fn error_suffix_on_exception_name(
     }
     None
 }
-
-fn is_lower(s: &str) -> bool {
-    let mut cased = false;
-    for c in s.chars() {
-        if c.is_uppercase() {
-            return false;
-        } else if !cased && c.is_lowercase() {
-            cased = true;
-        }
-    }
-    cased
-}
-
-fn is_upper(s: &str) -> bool {
-    let mut cased = false;
-    for c in s.chars() {
-        if c.is_lowercase() {
-            return false;
-        } else if (!cased) && c.is_uppercase() {
-            cased = true;
-        }
-    }
-    cased
-}
-
-fn is_camelcase(name: &str) -> bool {
-    !is_lower(name) && !is_upper(name) && !name.contains('_')
-}
-
-fn is_mixed_case(name: &str) -> bool {
-    !is_lower(name)
-        && name
-            .strip_prefix('_')
-            .unwrap_or(name)
-            .chars()
-            .next()
-            .map_or_else(|| false, |c| c.is_lowercase())
-}
-
-fn is_acronym(name: &str, asname: &str) -> bool {
-    name.chars().filter(|c| c.is_uppercase()).join("") == asname
-}
-
-#[cfg(test)]
-mod tests {
-    use super::{is_acronym, is_camelcase, is_lower, is_mixed_case, is_upper};
-
-    #[test]
-    fn test_is_lower() -> () {
-        assert!(is_lower("abc"));
-        assert!(is_lower("a_b_c"));
-        assert!(is_lower("a2c"));
-        assert!(!is_lower("aBc"));
-        assert!(!is_lower("ABC"));
-        assert!(!is_lower(""));
-        assert!(!is_lower("_"));
-    }
-
-    #[test]
-    fn test_is_upper() -> () {
-        assert!(is_upper("ABC"));
-        assert!(is_upper("A_B_C"));
-        assert!(is_upper("A2C"));
-        assert!(!is_upper("aBc"));
-        assert!(!is_upper("abc"));
-        assert!(!is_upper(""));
-        assert!(!is_upper("_"));
-    }
-
-    #[test]
-    fn test_is_camelcase() -> () {
-        assert!(is_camelcase("Camel"));
-        assert!(is_camelcase("CamelCase"));
-        assert!(!is_camelcase("camel"));
-        assert!(!is_camelcase("camel_case"));
-        assert!(!is_camelcase("CAMEL"));
-        assert!(!is_camelcase("CAMEL_CASE"));
-    }
-
-    #[test]
-    fn test_is_mixed_case() -> () {
-        assert!(is_mixed_case("mixedCase"));
-        assert!(is_mixed_case("mixed_Case"));
-        assert!(is_mixed_case("_mixed_Case"));
-        assert!(!is_mixed_case("mixed_case"));
-        assert!(!is_mixed_case("MIXED_CASE"));
-        assert!(!is_mixed_case(""));
-        assert!(!is_mixed_case("_"));
-    }
-
-    #[test]
-    fn test_is_acronym() -> () {
-        assert!(is_acronym("AB", "AB"));
-        assert!(is_acronym("AbcDef", "AD"));
-        assert!(!is_acronym("AbcDef", "Ad"));
-        assert!(!is_acronym("AbcDef", "AB"));
-    }
-}

src/pep8_naming/helpers.rs

@@ -0,0 +1,160 @@
+use itertools::Itertools;
+use rustpython_ast::{Expr, ExprKind};
+
+use crate::ast::helpers::match_name_or_attr;
+use crate::ast::types::{Scope, ScopeKind};
+use crate::pep8_naming::settings::Settings;
+
+const CLASS_METHODS: [&str; 3] = ["__new__", "__init_subclass__", "__class_getitem__"];
+const METACLASS_BASES: [&str; 2] = ["type", "ABCMeta"];
+
+pub enum FunctionType {
+    Function,
+    Method,
+    ClassMethod,
+    StaticMethod,
+}
+
+/// Classify a function based on its scope, name, and decorators.
+pub fn function_type(
+    scope: &Scope,
+    name: &str,
+    decorator_list: &[Expr],
+    settings: &Settings,
+) -> FunctionType {
+    if let ScopeKind::Class(scope) = &scope.kind {
+        // Special-case class method, like `__new__`.
+        if CLASS_METHODS.contains(&name)
+            // The class itself extends a known metaclass, so all methods are class methods.
+            || scope.bases.iter().any(|expr| {
+                METACLASS_BASES
+                    .iter()
+                    .any(|target| match_name_or_attr(expr, target))
+            })
+            // The method is decorated with a class method decorator (like `@classmethod`).
+            || decorator_list.iter().any(|expr| {
+            if let ExprKind::Name { id, .. } = &expr.node {
+                settings.classmethod_decorators.contains(id)
+            } else {
+                false
+            }
+        }) {
+            FunctionType::ClassMethod
+        } else if decorator_list.iter().any(|expr| {
+            if let ExprKind::Name { id, .. } = &expr.node {
+                settings.staticmethod_decorators.contains(id)
+            } else {
+                false
+            }
+        }) {
+            // The method is decorated with a static method decorator (like
+            // `@staticmethod`).
+            FunctionType::StaticMethod
+        } else {
+            // It's an instance method.
+            FunctionType::Method
+        }
+    } else {
+        FunctionType::Function
+    }
+}
+
+pub fn is_lower(s: &str) -> bool {
+    let mut cased = false;
+    for c in s.chars() {
+        if c.is_uppercase() {
+            return false;
+        } else if !cased && c.is_lowercase() {
+            cased = true;
+        }
+    }
+    cased
+}
+
+pub fn is_upper(s: &str) -> bool {
+    let mut cased = false;
+    for c in s.chars() {
+        if c.is_lowercase() {
+            return false;
+        } else if !cased && c.is_uppercase() {
+            cased = true;
+        }
+    }
+    cased
+}
+
+pub fn is_camelcase(name: &str) -> bool {
+    !is_lower(name) && !is_upper(name) && !name.contains('_')
+}
+
+pub fn is_mixed_case(name: &str) -> bool {
+    !is_lower(name)
+        && name
+            .strip_prefix('_')
+            .unwrap_or(name)
+            .chars()
+            .next()
+            .map_or_else(|| false, |c| c.is_lowercase())
+}
+
+pub fn is_acronym(name: &str, asname: &str) -> bool {
+    name.chars().filter(|c| c.is_uppercase()).join("") == asname
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::pep8_naming::helpers::{
+        is_acronym, is_camelcase, is_lower, is_mixed_case, is_upper,
+    };
+
+    #[test]
+    fn test_is_lower() -> () {
+        assert!(is_lower("abc"));
+        assert!(is_lower("a_b_c"));
+        assert!(is_lower("a2c"));
+        assert!(!is_lower("aBc"));
+        assert!(!is_lower("ABC"));
+        assert!(!is_lower(""));
+        assert!(!is_lower("_"));
+    }
+
+    #[test]
+    fn test_is_upper() -> () {
+        assert!(is_upper("ABC"));
+        assert!(is_upper("A_B_C"));
+        assert!(is_upper("A2C"));
+        assert!(!is_upper("aBc"));
+        assert!(!is_upper("abc"));
+        assert!(!is_upper(""));
+        assert!(!is_upper("_"));
+    }
+
+    #[test]
+    fn test_is_camelcase() -> () {
+        assert!(is_camelcase("Camel"));
+        assert!(is_camelcase("CamelCase"));
+        assert!(!is_camelcase("camel"));
+        assert!(!is_camelcase("camel_case"));
+        assert!(!is_camelcase("CAMEL"));
+        assert!(!is_camelcase("CAMEL_CASE"));
+    }
+
+    #[test]
+    fn test_is_mixed_case() -> () {
+        assert!(is_mixed_case("mixedCase"));
+        assert!(is_mixed_case("mixed_Case"));
+        assert!(is_mixed_case("_mixed_Case"));
+        assert!(!is_mixed_case("mixed_case"));
+        assert!(!is_mixed_case("MIXED_CASE"));
+        assert!(!is_mixed_case(""));
+        assert!(!is_mixed_case("_"));
+    }
+
+    #[test]
+    fn test_is_acronym() -> () {
+        assert!(is_acronym("AB", "AB"));
+        assert!(is_acronym("AbcDef", "AD"));
+        assert!(!is_acronym("AbcDef", "Ad"));
+        assert!(!is_acronym("AbcDef", "AB"));
+    }
+}

src/pep8_naming/mod.rs

@@ -1,2 +1,3 @@
 pub mod checks;
+mod helpers;
 pub mod settings;

src/pyflakes/checks.rs

@@ -1,10 +1,8 @@
 use std::collections::BTreeSet;
 
-use itertools::izip;
 use regex::Regex;
 use rustpython_parser::ast::{
-    Arg, Arguments, Cmpop, Constant, Excepthandler, ExcepthandlerKind, Expr, ExprKind, Stmt,
-    StmtKind,
+    Arg, Arguments, Constant, Excepthandler, ExcepthandlerKind, Expr, ExprKind, Stmt, StmtKind,
 };
 
 use crate::ast::types::{BindingKind, CheckLocator, FunctionScope, Range, Scope, ScopeKind};
@@ -166,45 +164,6 @@ pub fn repeated_keys(
     checks
 }
 
-fn is_constant(expr: &Expr) -> bool {
-    match &expr.node {
-        ExprKind::Constant { .. } => true,
-        ExprKind::Tuple { elts, .. } => elts.iter().all(is_constant),
-        _ => false,
-    }
-}
-
-fn is_singleton(expr: &Expr) -> bool {
-    matches!(
-        expr.node,
-        ExprKind::Constant {
-            value: Constant::None | Constant::Bool(_) | Constant::Ellipsis,
-            ..
-        }
-    )
-}
-
-fn is_constant_non_singleton(expr: &Expr) -> bool {
-    is_constant(expr) && !is_singleton(expr)
-}
-
-/// F632
-pub fn is_literal(left: &Expr, ops: &[Cmpop], comparators: &[Expr], location: Range) -> Vec<Check> {
-    let mut checks: Vec<Check> = vec![];
-
-    let mut left = left;
-    for (op, right) in izip!(ops, comparators) {
-        if matches!(op, Cmpop::Is | Cmpop::IsNot)
-            && (is_constant_non_singleton(left) || is_constant_non_singleton(right))
-        {
-            checks.push(Check::new(CheckKind::IsLiteral, location));
-        }
-        left = right;
-    }
-
-    checks
-}
-
 /// F621, F622
 pub fn starred_expressions(
     elts: &[Expr],

src/pyflakes/fixes.rs

@@ -1,11 +1,14 @@
 use anyhow::Result;
-use libcst_native::{Codegen, ImportNames, NameOrAttribute, SmallStatement, Statement};
+use libcst_native::{
+    Codegen, CompOp, Comparison, ComparisonTarget, Expr, Expression, 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_module;
+use crate::cst::matchers::{match_expr, match_module};
 use crate::source_code_locator::SourceCodeLocator;
 
 /// Generate a Fix to remove any unused imports from an `import` statement.
@@ -138,3 +141,66 @@ pub fn remove_unused_import_froms(
         ))
     }
 }
+
+fn match_comparison<'a, 'b>(expr: &'a mut Expr<'b>) -> Result<&'a mut Comparison<'b>> {
+    if let Expression::Comparison(comparison) = &mut expr.value {
+        Ok(comparison)
+    } else {
+        Err(anyhow::anyhow!(
+            "Expected node to be: Expression::Comparison"
+        ))
+    }
+}
+
+/// Generate a Fix to replace invalid is/is not comparisons with equal/not equal
+pub fn fix_invalid_literal_comparison(locator: &SourceCodeLocator, location: Range) -> Result<Fix> {
+    let module_text = locator.slice_source_code_range(&location);
+    let mut tree = match_module(&module_text)?;
+    let mut expr = match_expr(&mut tree)?;
+    let cmp = match_comparison(expr)?;
+    let target = cmp
+        .comparisons
+        .get(0)
+        .ok_or_else(|| anyhow::anyhow!("Expected one ComparisonTarget"))?;
+
+    let new_operator = match &target.operator {
+        CompOp::Is {
+            whitespace_before: b,
+            whitespace_after: a,
+        } => Ok(CompOp::Equal {
+            whitespace_before: b.clone(),
+            whitespace_after: a.clone(),
+        }),
+        CompOp::IsNot {
+            whitespace_before: b,
+            whitespace_after: a,
+            whitespace_between: _,
+        } => Ok(CompOp::NotEqual {
+            whitespace_before: b.clone(),
+            whitespace_after: a.clone(),
+        }),
+        op => Err(anyhow::anyhow!(
+            "Unexpected operator: {:?}. Expected Is or IsNot.",
+            op
+        )),
+    }?;
+
+    expr.value = Expression::Comparison(Box::new(Comparison {
+        left: cmp.left.clone(),
+        comparisons: vec![ComparisonTarget {
+            operator: new_operator,
+            comparator: target.comparator.clone(),
+        }],
+        lpar: cmp.lpar.clone(),
+        rpar: cmp.rpar.clone(),
+    }));
+
+    let mut state = Default::default();
+    tree.codegen(&mut state);
+
+    Ok(Fix::replacement(
+        state.to_string(),
+        location.location,
+        location.end_location,
+    ))
+}

src/pyflakes/plugins/invalid_literal_comparisons.rs

@@ -0,0 +1,62 @@
+use itertools::izip;
+use log::error;
+use rustpython_ast::{Cmpop, Constant, Expr, ExprKind};
+
+use crate::ast::types::Range;
+use crate::check_ast::Checker;
+use crate::checks::{Check, CheckKind};
+use crate::pyflakes::fixes::fix_invalid_literal_comparison;
+
+fn is_singleton(expr: &Expr) -> bool {
+    matches!(
+        expr.node,
+        ExprKind::Constant {
+            value: Constant::None | Constant::Bool(_) | Constant::Ellipsis,
+            ..
+        }
+    )
+}
+
+fn is_constant(expr: &Expr) -> bool {
+    match &expr.node {
+        ExprKind::Constant { .. } => true,
+        ExprKind::Tuple { elts, .. } => elts.iter().all(is_constant),
+        _ => false,
+    }
+}
+
+fn is_constant_non_singleton(expr: &Expr) -> bool {
+    is_constant(expr) && !is_singleton(expr)
+}
+
+/// F632
+pub fn invalid_literal_comparison(
+    checker: &mut Checker,
+    left: &Expr,
+    ops: &[Cmpop],
+    comparators: &[Expr],
+    location: Range,
+) {
+    let mut left = left;
+    for (op, right) in izip!(ops, comparators) {
+        if matches!(op, Cmpop::Is | Cmpop::IsNot)
+            && (is_constant_non_singleton(left) || is_constant_non_singleton(right))
+        {
+            let mut check = Check::new(CheckKind::IsLiteral, location);
+            if checker.patch() {
+                match fix_invalid_literal_comparison(
+                    checker.locator,
+                    Range {
+                        location: left.location,
+                        end_location: right.end_location.unwrap(),
+                    },
+                ) {
+                    Ok(fix) => check.amend(fix),
+                    Err(e) => error!("Failed to fix invalid comparison: {}", e),
+                }
+            }
+            checker.add_check(check);
+        }
+        left = right;
+    }
+}

src/pyflakes/plugins/mod.rs

@@ -1,9 +1,11 @@
 pub use assert_tuple::assert_tuple;
 pub use if_tuple::if_tuple;
+pub use invalid_literal_comparisons::invalid_literal_comparison;
 pub use invalid_print_syntax::invalid_print_syntax;
 pub use raise_not_implemented::raise_not_implemented;
 
 mod assert_tuple;
 mod if_tuple;
+mod invalid_literal_comparisons;
 mod invalid_print_syntax;
 mod raise_not_implemented;

src/rules/checks.rs

@@ -9,7 +9,7 @@ use crate::checks::CheckKind;
 use crate::source_code_locator::SourceCodeLocator;
 use crate::Check;
 
-/// See: https://github.com/microsoft/vscode/blob/095ddabc52b82498ee7f718a34f9dd11d59099a8/src/vs/base/common/strings.ts#L1195
+/// See: https://github.com/microsoft/vscode/blob/095ddabc52b82498ee7f718a34f9dd11d59099a8/src/vs/base/common/strings.ts#L1094
 static CONFUSABLES: Lazy<BTreeMap<u32, u32>> = Lazy::new(|| {
     BTreeMap::from([
         (8232, 32),

src/snapshots/ruff__linter__tests__F632_F632.py.snap

@@ -9,7 +9,16 @@ expression: checks
   end_location:
     row: 1
     column: 13
-  fix: ~
+  fix:
+    patch:
+      content: "x == \"abc\""
+      location:
+        row: 1
+        column: 3
+      end_location:
+        row: 1
+        column: 13
+    applied: false
 - kind: IsLiteral
   location:
     row: 4
@@ -17,5 +26,31 @@ expression: checks
   end_location:
     row: 4
     column: 15
-  fix: ~
+  fix:
+    patch:
+      content: 123 != y
+      location:
+        row: 4
+        column: 3
+      end_location:
+        row: 4
+        column: 15
+    applied: false
+- kind: IsLiteral
+  location:
+    row: 7
+    column: 9
+  end_location:
+    row: 7
+    column: 17
+  fix:
+    patch:
+      content: "\"123\" == x"
+      location:
+        row: 7
+        column: 3
+      end_location:
+        row: 7
+        column: 13
+    applied: false
 

src/snapshots/ruff__linter__tests__N803_N803.py.snap

@@ -6,18 +6,18 @@ expression: checks
     InvalidArgumentName: A
   location:
     row: 1
-    column: 12
+    column: 15
   end_location:
     row: 1
-    column: 13
+    column: 16
   fix: ~
 - kind:
     InvalidArgumentName: A
   location:
     row: 6
-    column: 24
+    column: 27
   end_location:
     row: 6
-    column: 25
+    column: 28
   fix: ~
 

src/snapshots/ruff__linter__tests__N804_N804.py.snap

@@ -4,10 +4,18 @@ expression: checks
 ---
 - kind: InvalidFirstArgumentNameForClassMethod
   location:
-    row: 3
-    column: 25
+    row: 30
+    column: 26
   end_location:
-    row: 3
-    column: 29
+    row: 30
+    column: 30
+  fix: ~
+- kind: InvalidFirstArgumentNameForClassMethod
+  location:
+    row: 35
+    column: 19
+  end_location:
+    row: 35
+    column: 23
   fix: ~
 

src/snapshots/ruff__linter__tests__U009_U009_0.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/linter.rs
+expression: checks
+---
+- kind: PEP3120UnnecessaryCodingComment
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 1
+    column: 14
+  fix:
+    patch:
+      content: ""
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 1
+        column: 14
+    applied: false
+

src/snapshots/ruff__linter__tests__U009_U009_1.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/linter.rs
+expression: checks
+---
+- kind: PEP3120UnnecessaryCodingComment
+  location:
+    row: 2
+    column: 0
+  end_location:
+    row: 2
+    column: 24
+  fix:
+    patch:
+      content: ""
+      location:
+        row: 2
+        column: 0
+      end_location:
+        row: 2
+        column: 24
+    applied: false
+

src/snapshots/ruff__linter__tests__U009_U009_2.py.snap

@@ -0,0 +1,6 @@
+---
+source: src/linter.rs
+expression: checks
+---
+[]
+

src/snapshots/ruff__linter__tests__U009_U009_3.py.snap

@@ -0,0 +1,6 @@
+---
+source: src/linter.rs
+expression: checks
+---
+[]
+