[pycodestyle] Whitespace after decorator (E204)

crates/ruff_linter/resources/test/fixtures/pycodestyle/E204.py

@@ -0,0 +1,27 @@
+def foo(fun):
+    def wrapper():
+        print('before')
+        fun()
+        print('after')
+    return wrapper
+
+# No error
+@foo
+def bar():
+    print('bar')
+
+# E204
+@ foo
+def baz():
+    print('baz')
+
+class Test:
+    # No error
+    @foo
+    def bar(self):
+        print('bar')
+
+    # E204
+    @ foo
+    def baz(self):
+        print('baz')

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

@@ -368,6 +368,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::UnusedAsync) {
                 ruff::rules::unused_async(checker, function_def);
             }
+            if checker.enabled(Rule::WhitespaceAfterDecorator) {
+                pycodestyle::rules::whitespace_after_decorator(checker, decorator_list);
+            }
         }
         Stmt::Return(_) => {
             if checker.enabled(Rule::ReturnOutsideFunction) {
@@ -531,6 +534,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::MetaClassABCMeta) {
                 refurb::rules::metaclass_abcmeta(checker, class_def);
             }
+            if checker.enabled(Rule::WhitespaceAfterDecorator) {
+                pycodestyle::rules::whitespace_after_decorator(checker, decorator_list);
+            }
         }
         Stmt::Import(ast::StmtImport { names, range: _ }) => {
             if checker.enabled(Rule::MultipleImportsOnOneLine) {

crates/ruff_linter/src/codes.rs

@@ -91,6 +91,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pycodestyle, "E202") => (RuleGroup::Nursery, rules::pycodestyle::rules::logical_lines::WhitespaceBeforeCloseBracket),
         #[allow(deprecated)]
         (Pycodestyle, "E203") => (RuleGroup::Nursery, rules::pycodestyle::rules::logical_lines::WhitespaceBeforePunctuation),
+        (Pycodestyle, "E204") => (RuleGroup::Preview, rules::pycodestyle::rules::WhitespaceAfterDecorator),
         #[allow(deprecated)]
         (Pycodestyle, "E211") => (RuleGroup::Nursery, rules::pycodestyle::rules::logical_lines::WhitespaceBeforeParameters),
         #[allow(deprecated)]

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

@@ -20,6 +20,7 @@ pub(crate) use tab_indentation::*;
 pub(crate) use too_many_newlines_at_end_of_file::*;
 pub(crate) use trailing_whitespace::*;
 pub(crate) use type_comparison::*;
+pub(crate) use whitespace_after_decorator::*;
 
 mod ambiguous_class_name;
 mod ambiguous_function_name;
@@ -43,3 +44,4 @@ mod tab_indentation;
 mod too_many_newlines_at_end_of_file;
 mod trailing_whitespace;
 mod type_comparison;
+mod whitespace_after_decorator;

crates/ruff_linter/src/rules/pycodestyle/rules/whitespace_after_decorator.rs

@@ -0,0 +1,64 @@
+use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::Decorator;
+use ruff_python_trivia::is_python_whitespace;
+use ruff_text_size::{TextLen, TextRange};
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for whitespace after a decorator.
+///
+/// ## Why is this bad?
+/// Whitespace after a decorator is not PEP8 compliant.
+///
+/// ## Example
+///
+/// ```python
+/// @ decorator
+/// def foo():
+///    pass
+/// ```
+/// Use instead:
+/// ``` python
+/// @decorator
+/// def foo():
+///   pass
+/// ```
+
+#[violation]
+pub struct WhitespaceAfterDecorator;
+
+impl AlwaysFixableViolation for WhitespaceAfterDecorator {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("Whitespace after decorator")
+    }
+
+    fn fix_title(&self) -> String {
+        "Remove whitespace after decorator".to_string()
+    }
+}
+
+/// E204
+pub(crate) fn whitespace_after_decorator(checker: &mut Checker, decorator_list: &[Decorator]) {
+    // Get the locator from the checker
+    let locator = checker.locator();
+
+    // Iterate over the list of decorators
+    for decorator in decorator_list {
+        // Obtain the text of the decorator using lactor.slice(decorator)
+        let decorator_text = locator.slice(decorator);
+
+        // Get the text after the @ symbol
+        let after_at = &decorator_text[1..];
+
+        // Check if there is a whitespace after the @ symbol by using is_python_whitespace
+        if is_python_whitespace(after_at.chars().next().unwrap()) {
+            let range = TextRange::empty(locator.contents().text_len());
+            checker
+                .diagnostics
+                .push(Diagnostic::new(WhitespaceAfterDecorator, range));
+        }
+    }
+}