E501/W505/formatter: Exclude nested pragma comments from line width calculation (#24071)

Closes #18470

## Summary

Exclude nested pragma comments like the `# noqa` in `test # comment 1 # noqa` from `E501`, `W505` and the formatter's line width calculation. 


## Test Plan

- Added linter test fixture `E501_5.py` with preview test cases for
nested pragmas (`# comment #noqa`, `## noqa`, `# comment # type:
ignore`)
- Added formatter test fixture `trailing_pragma_nested.py` demonstrating
stable vs preview reserved width behavior
- Doctests for `find_trailing_pragma_offset` in `pragmas.rs`

---------

Co-authored-by: Micha Reiser <micha@reiser.io>

Author: seroperson

crates/ruff_linter/resources/test/fixtures/pycodestyle/E501_5.py

@@ -0,0 +1,14 @@
+# OK - trailing noqa after another comment (88 characters before noqa pragma)
+"shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:aaa"  # comment  # noqa: F401
+
+# Error - trailing noqa after another comment (89 characters before noqa pragma)
+"shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:aaaa"  # comment  # noqa: F401
+
+# OK - double hash before noqa (80 characters before noqa pragma)
+"shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:aaa"  ## noqa: F401
+
+# OK - trailing type: ignore after another comment (88 characters before pragma)
+"shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:aaa"  # comment  # type: ignore
+
+# Error - trailing type: ignore after another comment (89 characters before pragma)
+"shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:aaaa"  # comment  # type: ignore

crates/ruff_linter/src/preview.rs

@@ -324,3 +324,9 @@ pub(crate) const fn is_up006_future_annotations_fix_enabled(settings: &LinterSet
 pub const fn is_warning_severity_enabled(preview: PreviewMode) -> bool {
     preview.is_enabled()
 }
+
+/// <https://github.com/astral-sh/ruff/pull/24071>
+/// Make sure to stabilize the corresponding formatter preview behavior when stabilizing this preview style.
+pub(crate) const fn is_trailing_pragma_in_line_length_enabled(preview: PreviewMode) -> bool {
+    preview.is_enabled()
+}

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

@@ -75,6 +75,7 @@ mod tests {
         Ok(())
     }
 
+    #[test_case(Rule::LineTooLong, Path::new("E501_5.py"))]
     #[test_case(Rule::RedundantBackslash, Path::new("E502.py"))]
     #[test_case(Rule::TooManyNewlinesAtEndOfFile, Path::new("W391_0.py"))]
     #[test_case(Rule::TooManyNewlinesAtEndOfFile, Path::new("W391_1.py"))]

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

@@ -1,10 +1,12 @@
 use std::ops::Deref;
 
-use ruff_python_trivia::{CommentRanges, is_pragma_comment};
+use ruff_python_trivia::{CommentRanges, find_trailing_pragma_offset, is_pragma_comment};
 use ruff_source_file::Line;
 use ruff_text_size::{TextLen, TextRange};
 
 use crate::line_width::{IndentWidth, LineLength, LineWidthBuilder};
+use crate::preview::is_trailing_pragma_in_line_length_enabled;
+use crate::settings::types::PreviewMode;
 
 #[derive(Debug)]
 pub(super) struct Overlong {
@@ -21,6 +23,7 @@ impl Overlong {
         limit: LineLength,
         task_tags: &[String],
         tab_size: IndentWidth,
+        preview: PreviewMode,
     ) -> Option<Self> {
         // The maximum width of the line is the number of bytes multiplied by the tab size (the
         // worst-case scenario is that the line is all tabs). If the maximum width is less than the
@@ -37,7 +40,7 @@ impl Overlong {
         }
 
         // Strip trailing comments and re-measure the line, if needed.
-        let line = StrippedLine::from_line(line, comment_ranges, task_tags);
+        let line = StrippedLine::from_line(line, comment_ranges, task_tags, preview);
         let width = match &line {
             StrippedLine::WithoutPragma(line) => {
                 let width = measure(line.as_str(), tab_size);
@@ -116,7 +119,12 @@ enum StrippedLine<'a> {
 impl<'a> StrippedLine<'a> {
     /// Strip trailing comments from a [`Line`], if the line ends with a pragma comment (like
     /// `# type: ignore`) or, if necessary, a task comment (like `# TODO`).
-    fn from_line(line: &'a Line<'a>, comment_ranges: &CommentRanges, task_tags: &[String]) -> Self {
+    fn from_line(
+        line: &'a Line<'a>,
+        comment_ranges: &CommentRanges,
+        task_tags: &[String],
+        preview: PreviewMode,
+    ) -> Self {
         let [comment_range] = comment_ranges.comments_in_range(line.range()) else {
             return Self::Unchanged(line);
         };
@@ -125,9 +133,18 @@ impl<'a> StrippedLine<'a> {
         let comment_range = comment_range - line.start();
         let comment = &line.as_str()[comment_range];
 
-        // Ex) `# type: ignore`
-        if is_pragma_comment(comment) {
-            // Remove the pragma from the line.
+        // Ex) `# type: ignore` or (in preview) `# some comment # noqa: F401`
+        if is_trailing_pragma_in_line_length_enabled(preview) {
+            if let Some(offset) = find_trailing_pragma_offset(comment) {
+                // Strip only the pragma suffix from the comment, preserving any
+                // preceding non-pragma comment text.
+                let pragma_start = usize::from(comment_range.start()) + offset;
+                let prefix = line[..pragma_start].trim_end();
+                return Self::WithoutPragma(Line::new(prefix, line.start()));
+            }
+        }
+        // Stable behavior: only strip when the entire comment is a pragma.
+        else if is_pragma_comment(comment) {
             let prefix = &line.as_str()[..usize::from(comment_range.start())].trim_end();
             return Self::WithoutPragma(Line::new(prefix, line.start()));
         }

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

@@ -104,6 +104,7 @@ pub(crate) fn doc_line_too_long(
             &[]
         },
         settings.tab_size,
+        settings.preview,
     ) {
         context.report_diagnostic(
             DocLineTooLong(overlong.width(), limit.value() as usize),

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

@@ -100,6 +100,7 @@ pub(crate) fn line_too_long(
             &[]
         },
         settings.tab_size,
+        settings.preview,
     ) {
         context.report_diagnostic(
             LineTooLong(overlong.width(), limit.value() as usize),

crates/ruff_linter/src/rules/pycodestyle/snapshots/ruff_linter__rules__pycodestyle__tests__preview__E501_E501_5.py.snap

@@ -0,0 +1,20 @@
+---
+source: crates/ruff_linter/src/rules/pycodestyle/mod.rs
+---
+E501 Line too long (89 > 88)
+ --> E501_5.py:5:89
+  |
+4 | # Error - trailing noqa after another comment (89 characters before noqa pragma)
+5 | "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:aaaa"  # comment  # noqa: F401
+  |                                                                                         ^
+6 |
+7 | # OK - double hash before noqa (80 characters before noqa pragma)
+  |
+
+E501 Line too long (89 > 88)
+  --> E501_5.py:14:89
+   |
+13 | # Error - trailing type: ignore after another comment (89 characters before pragma)
+14 | "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:" + "shape:aaaa"  # comment  # type: ignore
+   |                                                                                         ^
+   |

crates/ruff_python_formatter/resources/test/fixtures/ruff/trailing_pragma_nested.py

@@ -0,0 +1,17 @@
+# Trailing pragma after another comment - the pragma portion should not count
+# toward reserved width in preview mode.
+
+# The expression is long enough that the formatter would break it if the full
+# comment width were reserved, but short enough to fit if only the non-pragma
+# prefix is reserved.
+i = ("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)  # comment  # noqa: F401
+i = ("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)  # comment  # type: ignore
+i = ("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)  # comment  # pyright: ignore
+i = ("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)  ## noqa: F401
+
+# Plain pragma (no nested comment) - should behave the same in stable and preview
+i = ("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)  # noqa: F401
+i = ("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)  # type: ignore
+
+# Not a pragma - should reserve full width in both modes
+i = ("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)  # comment  # not a pragma

crates/ruff_python_formatter/src/comments/format.rs

@@ -3,13 +3,15 @@ use std::borrow::Cow;
 use ruff_formatter::{FormatError, FormatOptions, SourceCode, format_args, write};
 use ruff_python_ast::{AnyNodeRef, NodeKind, PySourceType};
 use ruff_python_trivia::{
-    CommentLinePosition, is_pragma_comment, lines_after, lines_after_ignoring_trivia, lines_before,
+    CommentLinePosition, find_trailing_pragma_offset, is_pragma_comment, lines_after,
+    lines_after_ignoring_trivia, lines_before,
 };
 use ruff_text_size::{Ranged, TextLen, TextRange};
 
 use crate::comments::SourceComment;
 use crate::context::NodeLevel;
 use crate::prelude::*;
+use crate::preview::is_trailing_pragma_in_comment_width_enabled;
 use crate::statement::suite::should_insert_blank_line_after_class_in_stub_file;
 
 /// Formats the leading comments of a node.
@@ -376,14 +378,26 @@ impl Format<PyFormatContext<'_>> for FormatTrailingEndOfLineComment<'_> {
 
         let normalized_comment = normalize_comment(self.comment, source)?;
 
-        // Don't reserve width for excluded pragma comments.
-        let reserved_width = if is_pragma_comment(&normalized_comment) {
+        // Don't reserve width for pragma comments. In preview, comments
+        // containing a trailing pragma (e.g., `# comment # noqa: F401`) only
+        // reserve width for the non-pragma prefix.
+        let non_pragma_comment_part = if is_trailing_pragma_in_comment_width_enabled(f.context()) {
+            match find_trailing_pragma_offset(&normalized_comment) {
+                Some(offset) => normalized_comment[..offset].trim_end(),
+                None => &normalized_comment,
+            }
+        } else if is_pragma_comment(&normalized_comment) {
+            ""
+        } else {
+            &normalized_comment
+        };
+
+        let reserved_width = if non_pragma_comment_part.is_empty() {
             0
         } else {
             // Start with 2 because of the two leading spaces.
-
             2u32.saturating_add(
-                TextWidth::from_text(&normalized_comment, f.options().indent_width())
+                TextWidth::from_text(non_pragma_comment_part, f.options().indent_width())
                     .width()
                     .expect("Expected comment not to contain any newlines")
                     .value(),

crates/ruff_python_formatter/src/preview.rs

@@ -20,3 +20,13 @@ pub(crate) const fn is_hug_parens_with_braces_and_square_brackets_enabled(
 pub(crate) const fn is_fluent_layout_split_first_call_enabled(context: &PyFormatContext) -> bool {
     context.is_preview()
 }
+
+/// Returns `true` if the
+/// [trailing pragma width handling in comments](https://github.com/astral-sh/ruff/pull/24071)
+/// is enabled.
+/// When enabled, comments like `# text # noqa: F401` only reserve width for
+/// the non-pragma prefix (`# text`), not the trailing pragma.
+/// Make sure to stabilize the corresponding linter preview behavior when stabilizing this preview style.
+pub(crate) const fn is_trailing_pragma_in_comment_width_enabled(context: &PyFormatContext) -> bool {
+    context.is_preview()
+}