Remove utf-8 encoding declaration (#618)

README.md

@@ -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.
 

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')

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 +1593,7 @@ 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/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/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
+---
+[]
+