Use space separator before parenthesiszed expressions in comprehensions with leading comments.

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

@@ -105,3 +105,66 @@
 # Parenthesized targets and iterators.
 [x for (x) in y]
 [x for x in (y)]
+
+
+# Leading expression comments:
+y = [
+    a
+    for (
+        # comment
+        a
+    ) in (
+        # comment
+        x
+    )
+    if (
+        # asdasd
+        "askldaklsdnmklasmdlkasmdlkasmdlkasmdasd"
+        != "as,mdnaskldmlkasdmlaksdmlkasdlkasdm"
+        and "zxcm,.nzxclm,zxnckmnzxckmnzxczxc" != "zxcasdasdlmnasdlknaslkdnmlaskdm"
+    )
+    if (
+        # comment
+        x
+    )
+]
+
+# Tuple target:
+y = [
+    a
+    for
+        # comment
+        a, b
+     in x
+    if  True
+]
+
+
+y = [
+    a
+    for (
+        # comment
+        a, b
+    )
+    in x
+    if  True
+]
+
+
+y = [
+    a
+    for
+        # comment
+        a
+    in
+        # comment
+        x
+    if
+        # asdasd
+        "askldaklsdnmklasmdlkasmdlkasmdlkasmdasd"
+        != "as,mdnaskldmlkasdmlaksdmlkasdlkasdm"
+        and "zxcm,.nzxclm,zxnckmnzxckmnzxczxc" != "zxcasdasdlmnasdlknaslkdnmlaskdm"
+    if
+        # comment
+        x
+]

crates/ruff_python_formatter/src/other/comprehension.rs

@@ -5,18 +5,47 @@ use ruff_text_size::{Ranged, TextRange};
 
 use crate::comments::{leading_comments, trailing_comments};
 use crate::expression::expr_tuple::TupleParentheses;
+use crate::expression::parentheses::is_expression_parenthesized;
 use crate::prelude::*;
+use crate::preview::is_comprehension_leading_expression_comments_same_line_enabled;
 
 #[derive(Default)]
 pub struct FormatComprehension;
 
 impl FormatNodeRule<Comprehension> for FormatComprehension {
     fn fmt_fields(&self, item: &Comprehension, f: &mut PyFormatter) -> FormatResult<()> {
-        struct Spacer<'a>(&'a Expr);
+        struct Spacer<'a> {
+            expression: &'a Expr,
+            preserve_parentheses: bool,
+        }
 
         impl Format<PyFormatContext<'_>> for Spacer<'_> {
             fn fmt(&self, f: &mut PyFormatter) -> FormatResult<()> {
-                if f.context().comments().has_leading(self.0) {
+                let has_leading_comments = f.context().comments().has_leading(self.expression);
+
+                // Don't add a soft line break for parenthesized expressions with a leading comment.
+                // The comments are rendered **inside** the parentheses and adding a softline break
+                // unnecessarily forces the parentheses to be on their own line.
+                // ```python
+                // y = [
+                //    ...
+                //    if
+                //    (
+                //          # See how the `(` gets forced on its own line? We don't want that.
+                //         ...
+                //     )
+                // ]
+                // ```
+                let will_be_parenthesized =
+                    is_comprehension_leading_expression_comments_same_line_enabled(f.context())
+                        && self.preserve_parentheses
+                        && is_expression_parenthesized(
+                            self.expression.into(),
+                            f.context().comments().ranges(),
+                            f.context().source(),
+                        );
+
+                if has_leading_comments && !will_be_parenthesized {
                     soft_line_break_or_space().fmt(f)
                 } else {
                     space().fmt(f)
@@ -68,13 +97,19 @@ impl FormatNodeRule<Comprehension> for FormatComprehension {
             [
                 token("for"),
                 trailing_comments(before_target_comments),
-                Spacer(target),
+                Spacer {
+                    expression: target,
+                    preserve_parentheses: !target.is_tuple_expr()
+                },
                 ExprTupleWithoutParentheses(target),
                 in_spacer,
                 leading_comments(before_in_comments),
                 token("in"),
                 trailing_comments(trailing_in_comments),
-                Spacer(iter),
+                Spacer {
+                    expression: iter,
+                    preserve_parentheses: true
+                },
                 iter.format(),
             ]
         )?;
@@ -99,7 +134,10 @@ impl FormatNodeRule<Comprehension> for FormatComprehension {
                         leading_comments(own_line_if_comments),
                         token("if"),
                         trailing_comments(end_of_line_if_comments),
-                        Spacer(if_case),
+                        Spacer {
+                            expression: if_case,
+                            preserve_parentheses: true
+                        },
                         if_case.format(),
                     ));
 

crates/ruff_python_formatter/src/preview.rs

@@ -22,3 +22,10 @@ pub(crate) fn is_f_string_formatting_enabled(context: &PyFormatContext) -> bool
 pub(crate) fn is_with_single_item_pre_39_enabled(context: &PyFormatContext) -> bool {
     context.is_preview()
 }
+
+/// See [#12282](https://github.com/astral-sh/ruff/pull/12282).
+pub(crate) fn is_comprehension_leading_expression_comments_same_line_enabled(
+    context: &PyFormatContext,
+) -> bool {
+    context.is_preview()
+}

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

@@ -111,6 +111,69 @@ aaaaaaaaaaaaaaaaaaaaa = [
 # Parenthesized targets and iterators.
 [x for (x) in y]
 [x for x in (y)]
+
+
+# Leading expression comments:
+y = [
+    a
+    for (
+        # comment
+        a
+    ) in (
+        # comment
+        x
+    )
+    if (
+        # asdasd
+        "askldaklsdnmklasmdlkasmdlkasmdlkasmdasd"
+        != "as,mdnaskldmlkasdmlaksdmlkasdlkasdm"
+        and "zxcm,.nzxclm,zxnckmnzxckmnzxczxc" != "zxcasdasdlmnasdlknaslkdnmlaskdm"
+    )
+    if (
+        # comment
+        x
+    )
+]
+
+# Tuple target:
+y = [
+    a
+    for
+        # comment
+        a, b
+     in x
+    if  True
+]
+
+
+y = [
+    a
+    for (
+        # comment
+        a, b
+    )
+    in x
+    if  True
+]
+
+
+y = [
+    a
+    for
+        # comment
+        a
+    in
+        # comment
+        x
+    if
+        # asdasd
+        "askldaklsdnmklasmdlkasmdlkasmdlkasmdasd"
+        != "as,mdnaskldmlkasdmlaksdmlkasdlkasdm"
+        and "zxcm,.nzxclm,zxnckmnzxckmnzxczxc" != "zxcasdasdlmnasdlknaslkdnmlaskdm"
+    if
+        # comment
+        x
+]
 ```
 
 ## Output
@@ -254,7 +317,104 @@ aaaaaaaaaaaaaaaaaaaaa = [
 # Parenthesized targets and iterators.
 [x for (x) in y]
 [x for x in (y)]
-```
 
 
+# Leading expression comments:
+y = [
+    a
+    for
+    (
+        # comment
+        a
+    ) in
+    (
+        # comment
+        x
+    )
+    if
+    (
+        # asdasd
+        "askldaklsdnmklasmdlkasmdlkasmdlkasmdasd"
+        != "as,mdnaskldmlkasdmlaksdmlkasdlkasdm"
+        and "zxcm,.nzxclm,zxnckmnzxckmnzxczxc" != "zxcasdasdlmnasdlknaslkdnmlaskdm"
+    )
+    if
+    (
+        # comment
+        x
+    )
+]
+
+# Tuple target:
+y = [
+    a
+    for
+    # comment
+    a, b in x
+    if True
+]
+
+
+y = [
+    a
+    for (
+        # comment
+        a,
+        b,
+    ) in x
+    if True
+]
 
+
+y = [
+    a
+    for
+    # comment
+    a in
+    # comment
+    x
+    if
+    # asdasd
+    "askldaklsdnmklasmdlkasmdlkasmdlkasmdasd" != "as,mdnaskldmlkasdmlaksdmlkasdlkasdm"
+    and "zxcm,.nzxclm,zxnckmnzxckmnzxczxc" != "zxcasdasdlmnasdlknaslkdnmlaskdm"
+    if
+    # comment
+    x
+]
+```
+
+
+## Preview changes
+```diff
+--- Stable
++++ Preview
+@@ -142,24 +142,20 @@
+ # Leading expression comments:
+ y = [
+     a
+-    for
+-    (
++    for (
+         # comment
+         a
+-    ) in
+-    (
++    ) in (
+         # comment
+         x
+     )
+-    if
+-    (
++    if (
+         # asdasd
+         "askldaklsdnmklasmdlkasmdlkasmdlkasmdasd"
+         != "as,mdnaskldmlkasdmlaksdmlkasdlkasdm"
+         and "zxcm,.nzxclm,zxnckmnzxckmnzxczxc" != "zxcasdasdlmnasdlknaslkdnmlaskdm"
+     )
+-    if
+-    (
++    if (
+         # comment
+         x
+     )
+```