Preserve dangling f-string comments

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/fstring.py

@@ -0,0 +1,26 @@
+(
+    f'{one}'
+    f'{two}'
+)
+
+
+rf"Not-so-tricky \"quote"
+
+# Regression test for fstrings dropping comments
+result_f = (
+    'Traceback (most recent call last):\n'
+    f'  File "{__file__}", line {lineno_f+5}, in _check_recursive_traceback_display\n'
+    '    f()\n'
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    '    f()\n'
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    '    f()\n'
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    '    f()\n'
+    # XXX: The following line changes depending on whether the tests
+    # are run through the interactive interpreter or with -m
+    # It also varies depending on the platform (stack size)
+    # Fortunately, we don't care about exactness here, so we use regex
+    r'  \[Previous line repeated (\d+) more times\]' '\n'
+    'RecursionError: maximum recursion depth exceeded\n'
+)

crates/ruff_python_formatter/src/comments/placement.rs

@@ -73,6 +73,13 @@ pub(super) fn place_comment<'a>(
             handle_leading_class_with_decorators_comment(comment, class_def)
         }
         AnyNodeRef::StmtImportFrom(import_from) => handle_import_from_comment(comment, import_from),
+        AnyNodeRef::ExprConstant(_) => {
+            if let Some(AnyNodeRef::ExprFString(fstring)) = comment.enclosing_parent() {
+                CommentPlacement::dangling(fstring, comment)
+            } else {
+                CommentPlacement::Default(comment)
+            }
+        }
         AnyNodeRef::ExprList(_)
         | AnyNodeRef::ExprSet(_)
         | AnyNodeRef::ExprGeneratorExp(_)

crates/ruff_python_formatter/src/comments/visitor.rs

@@ -77,6 +77,7 @@ impl<'ast> PreorderVisitor<'ast> for CommentsVisitor<'ast> {
                 enclosing: enclosing_node,
                 preceding: self.preceding_node,
                 following: Some(node),
+                parent: self.parents.iter().rev().nth(1).copied(),
                 line_position: text_position(*comment_range, self.source_code),
                 slice: self.source_code.slice(*comment_range),
             };
@@ -117,6 +118,7 @@ impl<'ast> PreorderVisitor<'ast> for CommentsVisitor<'ast> {
 
             let comment = DecoratedComment {
                 enclosing: node,
+                parent: self.parents.last().copied(),
                 preceding: self.preceding_node,
                 following: None,
                 line_position: text_position(*comment_range, self.source_code),
@@ -179,6 +181,7 @@ pub(super) struct DecoratedComment<'a> {
     enclosing: AnyNodeRef<'a>,
     preceding: Option<AnyNodeRef<'a>>,
     following: Option<AnyNodeRef<'a>>,
+    parent: Option<AnyNodeRef<'a>>,
     line_position: CommentLinePosition,
     slice: SourceCodeSlice,
 }
@@ -204,6 +207,11 @@ impl<'a> DecoratedComment<'a> {
         self.enclosing
     }
 
+    /// Returns the parent of the enclosing node, if any
+    pub(super) fn enclosing_parent(&self) -> Option<AnyNodeRef<'a>> {
+        self.parent
+    }
+
     /// Returns the slice into the source code.
     pub(super) fn slice(&self) -> &SourceCodeSlice {
         &self.slice

crates/ruff_python_formatter/tests/snapshots/format@expression__fstring.py.snap

@@ -0,0 +1,64 @@
+---
+source: crates/ruff_python_formatter/tests/fixtures.rs
+input_file: crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/fstring.py
+---
+## Input
+```py
+(
+    f'{one}'
+    f'{two}'
+)
+
+
+rf"Not-so-tricky \"quote"
+
+# Regression test for fstrings dropping comments
+result_f = (
+    'Traceback (most recent call last):\n'
+    f'  File "{__file__}", line {lineno_f+5}, in _check_recursive_traceback_display\n'
+    '    f()\n'
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    '    f()\n'
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    '    f()\n'
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    '    f()\n'
+    # XXX: The following line changes depending on whether the tests
+    # are run through the interactive interpreter or with -m
+    # It also varies depending on the platform (stack size)
+    # Fortunately, we don't care about exactness here, so we use regex
+    r'  \[Previous line repeated (\d+) more times\]' '\n'
+    'RecursionError: maximum recursion depth exceeded\n'
+)
+```
+
+## Output
+```py
+(f"{one}" f"{two}")
+
+
+rf'Not-so-tricky "quote'
+
+# Regression test for fstrings dropping comments
+result_f = (
+    "Traceback (most recent call last):\n"
+    f'  File "{__file__}", line {lineno_f+5}, in _check_recursive_traceback_display\n'
+    "    f()\n"
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    "    f()\n"
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    "    f()\n"
+    f'  File "{__file__}", line {lineno_f+1}, in f\n'
+    "    f()\n"
+    # XXX: The following line changes depending on whether the tests
+    # are run through the interactive interpreter or with -m
+    # It also varies depending on the platform (stack size)
+    # Fortunately, we don't care about exactness here, so we use regex
+    r"  \[Previous line repeated (\d+) more times\]"
+    "\n"
+    "RecursionError: maximum recursion depth exceeded\n"
+)
+```
+
+
+