Add option to provide a reason to --add-noqa (#21294)

Co-authored-by: Claude <noreply@anthropic.com>

crates/ruff/src/args.rs

@@ -415,8 +415,13 @@ pub struct CheckCommand {
     )]
     pub statistics: bool,
     /// Enable automatic additions of `noqa` directives to failing lines.
+    /// Optionally provide a reason to append after the codes.
     #[arg(
         long,
+        value_name = "REASON",
+        default_missing_value = "",
+        num_args = 0..=1,
+        require_equals = true,
         // conflicts_with = "add_noqa",
         conflicts_with = "show_files",
         conflicts_with = "show_settings",
@@ -428,7 +433,7 @@ pub struct CheckCommand {
         conflicts_with = "fix",
         conflicts_with = "diff",
     )]
-    pub add_noqa: bool,
+    pub add_noqa: Option<String>,
     /// See the files Ruff will be run against with the current settings.
     #[arg(
         long,
@@ -1057,7 +1062,7 @@ Possible choices:
 /// etc.).
 #[expect(clippy::struct_excessive_bools)]
 pub struct CheckArguments {
-    pub add_noqa: bool,
+    pub add_noqa: Option<String>,
     pub diff: bool,
     pub exit_non_zero_on_fix: bool,
     pub exit_zero: bool,

crates/ruff/src/commands/add_noqa.rs

@@ -21,6 +21,7 @@ pub(crate) fn add_noqa(
     files: &[PathBuf],
     pyproject_config: &PyprojectConfig,
     config_arguments: &ConfigArguments,
+    reason: Option<&str>,
 ) -> Result<usize> {
     // Collect all the files to check.
     let start = Instant::now();
@@ -76,7 +77,14 @@ pub(crate) fn add_noqa(
                     return None;
                 }
             };
-            match add_noqa_to_path(path, package, &source_kind, source_type, &settings.linter) {
+            match add_noqa_to_path(
+                path,
+                package,
+                &source_kind,
+                source_type,
+                &settings.linter,
+                reason,
+            ) {
                 Ok(count) => Some(count),
                 Err(e) => {
                     error!("Failed to add noqa to {}: {e}", path.display());

crates/ruff/src/lib.rs

@@ -319,12 +319,20 @@ pub fn check(args: CheckCommand, global_options: GlobalConfigArgs) -> Result<Exi
         warn_user!("Detected debug build without --no-cache.");
     }
 
-    if cli.add_noqa {
+    if let Some(reason) = &cli.add_noqa {
         if !fix_mode.is_generate() {
             warn_user!("--fix is incompatible with --add-noqa.");
         }
+        if reason.contains(['\n', '\r']) {
+            return Err(anyhow::anyhow!(
+                "--add-noqa <reason> cannot contain newline characters"
+            ));
+        }
+
+        let reason_opt = (!reason.is_empty()).then_some(reason.as_str());
+
         let modifications =
-            commands::add_noqa::add_noqa(&files, &pyproject_config, &config_arguments)?;
+            commands::add_noqa::add_noqa(&files, &pyproject_config, &config_arguments, reason_opt)?;
         if modifications > 0 && config_arguments.log_level >= LogLevel::Default {
             let s = if modifications == 1 { "" } else { "s" };
             #[expect(clippy::print_stderr)]

crates/ruff/tests/cli/lint.rs

@@ -1760,6 +1760,64 @@ from foo import (  # noqa: F401
     Ok(())
 }
 
+#[test]
+fn add_noqa_with_reason() -> Result<()> {
+    let fixture = CliTest::new()?;
+    fixture.write_file(
+        "test.py",
+        r#"import os
+
+def foo():
+    x = 1
+"#,
+    )?;
+
+    assert_cmd_snapshot!(fixture
+        .check_command()
+        .arg("--add-noqa=TODO: fix")
+        .arg("--select=F401,F841")
+        .arg("test.py"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Added 2 noqa directives.
+    ");
+
+    let content = fs::read_to_string(fixture.root().join("test.py"))?;
+    insta::assert_snapshot!(content, @r"
+import os  # noqa: F401 TODO: fix
+
+def foo():
+    x = 1  # noqa: F841 TODO: fix
+");
+
+    Ok(())
+}
+
+#[test]
+fn add_noqa_with_newline_in_reason() -> Result<()> {
+    let fixture = CliTest::new()?;
+    fixture.write_file("test.py", "import os\n")?;
+
+    assert_cmd_snapshot!(fixture
+        .check_command()
+        .arg("--add-noqa=line1\nline2")
+        .arg("--select=F401")
+        .arg("test.py"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    ruff failed
+      Cause: --add-noqa <reason> cannot contain newline characters
+    "###);
+
+    Ok(())
+}
+
 /// Infer `3.11` from `requires-python` in `pyproject.toml`.
 #[test]
 fn requires_python() -> Result<()> {

crates/ruff_linter/src/linter.rs

@@ -377,6 +377,7 @@ pub fn add_noqa_to_path(
     source_kind: &SourceKind,
     source_type: PySourceType,
     settings: &LinterSettings,
+    reason: Option<&str>,
 ) -> Result<usize> {
     // Parse once.
     let target_version = settings.resolve_target_version(path);
@@ -425,6 +426,7 @@ pub fn add_noqa_to_path(
         &settings.external,
         &directives.noqa_line_for,
         stylist.line_ending(),
+        reason,
     )
 }
 

crates/ruff_linter/src/noqa.rs

@@ -39,7 +39,7 @@ pub fn generate_noqa_edits(
     let exemption = FileExemption::from(&file_directives);
     let directives = NoqaDirectives::from_commented_ranges(comment_ranges, external, path, locator);
     let comments = find_noqa_comments(diagnostics, locator, &exemption, &directives, noqa_line_for);
-    build_noqa_edits_by_diagnostic(comments, locator, line_ending)
+    build_noqa_edits_by_diagnostic(comments, locator, line_ending, None)
 }
 
 /// A directive to ignore a set of rules either for a given line of Python source code or an entire file (e.g.,
@@ -715,6 +715,7 @@ impl Display for LexicalError {
 impl Error for LexicalError {}
 
 /// Adds noqa comments to suppress all messages of a file.
+#[expect(clippy::too_many_arguments)]
 pub(crate) fn add_noqa(
     path: &Path,
     diagnostics: &[Diagnostic],
@@ -723,6 +724,7 @@ pub(crate) fn add_noqa(
     external: &[String],
     noqa_line_for: &NoqaMapping,
     line_ending: LineEnding,
+    reason: Option<&str>,
 ) -> Result<usize> {
     let (count, output) = add_noqa_inner(
         path,
@@ -732,12 +734,14 @@ pub(crate) fn add_noqa(
         external,
         noqa_line_for,
         line_ending,
+        reason,
     );
 
     fs::write(path, output)?;
     Ok(count)
 }
 
+#[expect(clippy::too_many_arguments)]
 fn add_noqa_inner(
     path: &Path,
     diagnostics: &[Diagnostic],
@@ -746,6 +750,7 @@ fn add_noqa_inner(
     external: &[String],
     noqa_line_for: &NoqaMapping,
     line_ending: LineEnding,
+    reason: Option<&str>,
 ) -> (usize, String) {
     let mut count = 0;
 
@@ -757,7 +762,7 @@ fn add_noqa_inner(
 
     let comments = find_noqa_comments(diagnostics, locator, &exemption, &directives, noqa_line_for);
 
-    let edits = build_noqa_edits_by_line(comments, locator, line_ending);
+    let edits = build_noqa_edits_by_line(comments, locator, line_ending, reason);
 
     let contents = locator.contents();
 
@@ -783,6 +788,7 @@ fn build_noqa_edits_by_diagnostic(
     comments: Vec<Option<NoqaComment>>,
     locator: &Locator,
     line_ending: LineEnding,
+    reason: Option<&str>,
 ) -> Vec<Option<Edit>> {
     let mut edits = Vec::default();
     for comment in comments {
@@ -794,6 +800,7 @@ fn build_noqa_edits_by_diagnostic(
                     FxHashSet::from_iter([comment.code]),
                     locator,
                     line_ending,
+                    reason,
                 ) {
                     edits.push(Some(noqa_edit.into_edit()));
                 }
@@ -808,6 +815,7 @@ fn build_noqa_edits_by_line<'a>(
     comments: Vec<Option<NoqaComment<'a>>>,
     locator: &Locator,
     line_ending: LineEnding,
+    reason: Option<&'a str>,
 ) -> BTreeMap<TextSize, NoqaEdit<'a>> {
     let mut comments_by_line = BTreeMap::default();
     for comment in comments.into_iter().flatten() {
@@ -831,6 +839,7 @@ fn build_noqa_edits_by_line<'a>(
                 .collect(),
             locator,
             line_ending,
+            reason,
         ) {
             edits.insert(offset, edit);
         }
@@ -927,6 +936,7 @@ struct NoqaEdit<'a> {
     noqa_codes: FxHashSet<&'a SecondaryCode>,
     codes: Option<&'a Codes<'a>>,
     line_ending: LineEnding,
+    reason: Option<&'a str>,
 }
 
 impl NoqaEdit<'_> {
@@ -954,6 +964,9 @@ impl NoqaEdit<'_> {
                 push_codes(writer, self.noqa_codes.iter().sorted_unstable());
             }
         }
+        if let Some(reason) = self.reason {
+            write!(writer, " {reason}").unwrap();
+        }
         write!(writer, "{}", self.line_ending.as_str()).unwrap();
     }
 }
@@ -970,6 +983,7 @@ fn generate_noqa_edit<'a>(
     noqa_codes: FxHashSet<&'a SecondaryCode>,
     locator: &Locator,
     line_ending: LineEnding,
+    reason: Option<&'a str>,
 ) -> Option<NoqaEdit<'a>> {
     let line_range = locator.full_line_range(offset);
 
@@ -999,6 +1013,7 @@ fn generate_noqa_edit<'a>(
         noqa_codes,
         codes,
         line_ending,
+        reason,
     })
 }
 
@@ -2832,6 +2847,7 @@ mod tests {
             &[],
             &noqa_line_for,
             LineEnding::Lf,
+            None,
         );
         assert_eq!(count, 0);
         assert_eq!(output, format!("{contents}"));
@@ -2855,6 +2871,7 @@ mod tests {
             &[],
             &noqa_line_for,
             LineEnding::Lf,
+            None,
         );
         assert_eq!(count, 1);
         assert_eq!(output, "x = 1  # noqa: F841\n");
@@ -2885,6 +2902,7 @@ mod tests {
             &[],
             &noqa_line_for,
             LineEnding::Lf,
+            None,
         );
         assert_eq!(count, 1);
         assert_eq!(output, "x = 1  # noqa: E741, F841\n");
@@ -2915,6 +2933,7 @@ mod tests {
             &[],
             &noqa_line_for,
             LineEnding::Lf,
+            None,
         );
         assert_eq!(count, 0);
         assert_eq!(output, "x = 1  # noqa");