[`pydocstyle`] Implement autofix for `D403` (#3731)

crates/ruff/resources/test/fixtures/pydocstyle/D403.py

@@ -0,0 +1,15 @@
+def bad_function():
+    """this docstring is not capitalized"""
+
+def good_function():
+    """This docstring is capitalized."""
+
+def other_function():
+    """
+    This docstring is capitalized."""
+
+def another_function():
+    """ This docstring is capitalized."""
+
+def utf8_function():
+    """éste docstring is capitalized."""

crates/ruff/src/rules/pydocstyle/mod.rs

@@ -30,7 +30,8 @@ mod tests {
     #[test_case(Rule::EndsInPeriod, Path::new("D.py"); "D400_0")]
     #[test_case(Rule::EndsInPeriod, Path::new("D400.py"); "D400_1")]
     #[test_case(Rule::EndsInPunctuation, Path::new("D.py"); "D415")]
-    #[test_case(Rule::FirstLineCapitalized, Path::new("D.py"); "D403")]
+    #[test_case(Rule::FirstLineCapitalized, Path::new("D.py"); "D403_0")]
+    #[test_case(Rule::FirstLineCapitalized, Path::new("D403.py"); "D403_1")]
     #[test_case(Rule::FitsOnOneLine, Path::new("D.py"); "D200")]
     #[test_case(Rule::IndentWithSpaces, Path::new("D.py"); "D206")]
     #[test_case(Rule::UndocumentedMagicMethod, Path::new("D.py"); "D105")]

crates/ruff/src/rules/pydocstyle/rules/capitalized.rs

@@ -1,17 +1,33 @@
-use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_diagnostics::{AlwaysAutofixableViolation, Diagnostic, Edit};
 use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::str::leading_quote;
 use ruff_python_ast::types::Range;
+use unicode_width::UnicodeWidthStr;
 
 use crate::checkers::ast::Checker;
 use crate::docstrings::definition::{DefinitionKind, Docstring};
+use crate::registry::AsRule;
 
 #[violation]
-pub struct FirstLineCapitalized;
+pub struct FirstLineCapitalized {
+    pub first_word: String,
+    pub capitalized_word: String,
+}
 
-impl Violation for FirstLineCapitalized {
+impl AlwaysAutofixableViolation for FirstLineCapitalized {
     #[derive_message_formats]
     fn message(&self) -> String {
-        format!("First word of the first line should be properly capitalized")
+        format!(
+            "First word of the first line should be capitalized: `{}` -> `{}`",
+            self.first_word, self.capitalized_word
+        )
+    }
+
+    fn autofix_title(&self) -> String {
+        format!(
+            "Capitalize `{}` to `{}`",
+            self.first_word, self.capitalized_word
+        )
     }
 }
 
@@ -37,14 +53,36 @@ pub fn capitalized(checker: &mut Checker, docstring: &Docstring) {
             return;
         }
     }
-    let Some(first_char) = first_word.chars().next() else {
+    let mut first_word_chars = first_word.chars();
+    let Some(first_char) = first_word_chars.next() else {
         return;
     };
     if first_char.is_uppercase() {
         return;
     };
-    checker.diagnostics.push(Diagnostic::new(
-        FirstLineCapitalized,
+
+    let capitalized_word = first_char.to_uppercase().to_string() + first_word_chars.as_str();
+
+    let mut diagnostic = Diagnostic::new(
+        FirstLineCapitalized {
+            first_word: first_word.to_string(),
+            capitalized_word: capitalized_word.to_string(),
+        },
         Range::from(docstring.expr),
-    ));
+    );
+
+    if checker.patch(diagnostic.kind.rule()) {
+        if let Some(pattern) = leading_quote(docstring.contents) {
+            diagnostic.amend(Edit::replacement(
+                capitalized_word,
+                docstring.expr.location.with_col_offset(pattern.width()),
+                docstring
+                    .expr
+                    .location
+                    .with_col_offset(pattern.width() + first_word.width()),
+            ));
+        }
+    }
+
+    checker.diagnostics.push(diagnostic);
 }

crates/ruff/src/rules/pydocstyle/snapshots/ruff__rules__pydocstyle__tests__D403_D403.py.snap

@@ -0,0 +1,25 @@
+---
+source: crates/ruff/src/rules/pydocstyle/mod.rs
+expression: diagnostics
+---
+- kind:
+    name: FirstLineCapitalized
+    body: "First word of the first line should be capitalized: `this` -> `This`"
+    suggestion: "Capitalize `this` to `This`"
+    fixable: true
+  location:
+    row: 2
+    column: 4
+  end_location:
+    row: 2
+    column: 43
+  fix:
+    content: This
+    location:
+      row: 2
+      column: 7
+    end_location:
+      row: 2
+      column: 11
+  parent: ~
+