Hug closing } when f-string expression has a format specifier

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

@@ -242,18 +242,22 @@
 }"  # comment 19
 # comment 20
 
-# Single-quoted f-strings with a format specificer can be multiline
-f"aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
-    variable:.3f} ddddddddddddddd eeeeeeee"
+# The specifier of an f-string must hug the closing `}` because a multiline format specifier is invalid syntax in a single
+# quoted f-string.
+f"aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {variable
+:.3f} ddddddddddddddd eeeeeeee"
+
+# The same applies for triple quoted f-strings, except that we need to preserve the newline before the closing `}`.
+# or we risk altering the meaning of the f-string.
+f"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {variable
+    :.3f} ddddddddddddddd eeeeeeee"""
+f"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {variable:.3f
+} ddddddddddddddd eeeeeeee"""
 
-# But, if it's triple-quoted then we can't or the format specificer will have a
-# trailing newline
-f"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
-    variable:.3f} ddddddddddddddd eeeeeeee"""
-
-# But, we can break the ones which don't have a format specifier
-f"""fooooooooooooooooooo barrrrrrrrrrrrrrrrrrr {
-        xxxxxxxxxxxxxxx:.3f} aaaaaaaaaaaaaaaaa { xxxxxxxxxxxxxxxxxxxx } bbbbbbbbbbbb"""
+aaaaaaaaaaa = f"""asaaaaaaaaaaaaaaaa {
+   aaaaaaaaaaaa + bbbbbbbbbbbb + ccccccccccccccc + dddddddd
+   # comment
+   :.3f} cccccccccc"""
 
 # Throw in a random comment in it but surprise, this is not a comment but just a text
 # which is part of the format specifier
@@ -289,6 +293,13 @@
          # comment 21
          }"
 
+x = f"{
+    x!s:>{
+        0
+        # comment 21-2
+    }}"
+
+
 x = f"""
 {              # comment 22
  x =   :.0{y # comment 23
@@ -313,6 +324,21 @@
     # comment 28
 } woah {x}"
 
+
+f"""{foo
+      :a{
+      a # comment 29
+      # comment 30
+      }
+}"""
+
+# Regression test for https://github.com/astral-sh/ruff/issues/18672
+f"{
+    # comment 31
+    foo
+   :>
+}"
+
 # Assignment statement
 
 # Even though this f-string has multiline expression, thus allowing us to break it at the

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

@@ -240,18 +240,20 @@
 }"  # comment 19
 # comment 20
 
-# Single-quoted t-strings with a format specificer can be multiline
+# The specifier of a t-string must hug the closing `}` because a multiline format specifier is invalid syntax in a single
+# quoted f-string.
 t"aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
-    variable:.3f} ddddddddddddddd eeeeeeee"
+    variable
+    :.3f} ddddddddddddddd eeeeeeee"
 
-# But, if it's triple-quoted then we can't or the format specificer will have a
-# trailing newline
-t"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
-    variable:.3f} ddddddddddddddd eeeeeeee"""
+# The same applies for triple quoted t-strings, except that we need to preserve the newline before the closing `}`.
+# or we risk altering the meaning of the f-string.
+t"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {variable
+    :.3f} ddddddddddddddd eeeeeeee"""
+t"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {variable
+    :.3f
+} ddddddddddddddd eeeeeeee"""
 
-# But, we can break the ones which don't have a format specifier
-t"""fooooooooooooooooooo barrrrrrrrrrrrrrrrrrr {
-        xxxxxxxxxxxxxxx:.3f} aaaaaaaaaaaaaaaaa { xxxxxxxxxxxxxxxxxxxx } bbbbbbbbbbbb"""
 
 # Throw in a random comment in it but surprise, this is not a comment but just a text
 # which is part of the format specifier
@@ -287,6 +289,12 @@
          # comment 21
          }"
 
+x = f"{
+    x!s:>{
+        0
+        # comment 21-2
+    }}"
+
 x = t"""
 {              # comment 22
  x =   :.0{y # comment 23

crates/ruff_python_formatter/src/comments/placement.rs

@@ -321,28 +321,33 @@ fn handle_enclosed_comment<'a>(
         },
         AnyNodeRef::FString(fstring) => CommentPlacement::dangling(fstring, comment),
         AnyNodeRef::TString(tstring) => CommentPlacement::dangling(tstring, comment),
-        AnyNodeRef::InterpolatedElement(_) => {
-            // Handle comments after the format specifier (should be rare):
-            //
-            // ```python
-            // f"literal {
-            //     expr:.3f
-            //     # comment
-            // }"
-            // ```
-            //
-            // This is a valid comment placement.
-            if matches!(
-                comment.preceding_node(),
-                Some(
-                    AnyNodeRef::InterpolatedElement(_)
-                        | AnyNodeRef::InterpolatedStringLiteralElement(_)
-                )
-            ) {
-                CommentPlacement::trailing(comment.enclosing_node(), comment)
-            } else {
-                handle_bracketed_end_of_line_comment(comment, source)
+        AnyNodeRef::InterpolatedElement(element) => {
+            if let Some(preceding) = comment.preceding_node() {
+                if comment.line_position().is_own_line() && element.format_spec.is_some() {
+                    return if comment.following_node().is_some() {
+                        // Own line comment before format specifier
+                        // ```py
+                        // aaaaaaaaaaa = f"""asaaaaaaaaaaaaaaaa {
+                        //    aaaaaaaaaaaa + bbbbbbbbbbbb + ccccccccccccccc + dddddddd
+                        //    # comment
+                        //    :.3f} cccccccccc"""
+                        // ```
+                        CommentPlacement::trailing(preceding, comment)
+                    } else {
+                        // TODO: This can be removed once format specifiers with a newline are a syntax error.
+                        // This is to handle cases like:
+                        // ```py
+                        // x = f"{x  !s
+                        //          :>0
+                        //          # comment 21
+                        // }"
+                        // ```
+                        CommentPlacement::trailing(element, comment)
+                    };
+                }
             }
+
+            handle_bracketed_end_of_line_comment(comment, source)
         }
 
         AnyNodeRef::ExprList(_)

crates/ruff_python_formatter/src/context.rs

@@ -7,7 +7,7 @@ use ruff_python_parser::Tokens;
 
 use crate::PyFormatOptions;
 use crate::comments::Comments;
-use crate::other::interpolated_string_element::InterpolatedElementContext;
+use crate::other::interpolated_string::InterpolatedStringContext;
 
 pub struct PyFormatContext<'a> {
     options: PyFormatOptions,
@@ -143,7 +143,7 @@ pub(crate) enum InterpolatedStringState {
     /// curly brace in `f"foo {x}"`.
     ///
     /// The containing `FStringContext` is the surrounding f-string context.
-    InsideInterpolatedElement(InterpolatedElementContext),
+    InsideInterpolatedElement(InterpolatedStringContext),
     /// The formatter is outside an f-string.
     #[default]
     Outside,
@@ -153,7 +153,7 @@ impl InterpolatedStringState {
     pub(crate) fn can_contain_line_breaks(self) -> Option<bool> {
         match self {
             InterpolatedStringState::InsideInterpolatedElement(context) => {
-                Some(context.can_contain_line_breaks())
+                Some(context.is_multiline())
             }
             InterpolatedStringState::Outside => None,
         }

crates/ruff_python_formatter/src/other/interpolated_string.rs

@@ -21,8 +21,8 @@ impl InterpolatedStringContext {
         self.enclosing_flags
     }
 
-    pub(crate) const fn layout(self) -> InterpolatedStringLayout {
-        self.layout
+    pub(crate) const fn is_multiline(self) -> bool {
+        matches!(self.layout, InterpolatedStringLayout::Multiline)
     }
 }