Avoiding grouping comprehension targets separately from conditions (#7429)

## Summary

Black seems to treat comprehension targets and conditions as if they're
in a single group -- so if the comprehension expands, all conditions are
rendered on their own line, etc.

Closes https://github.com/astral-sh/ruff/issues/7421.

## Test Plan

`cargo test`

No change in any of the similarity metrics.

Before:

| project | similarity index | total files | changed files |

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1632 |
| django | 0.99982 | 2760 | 37 |
| transformers | 0.99957 | 2587 | 399 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99983 | 3496 | 18 |
| warehouse | 0.99923 | 648 | 18 |
| zulip | 0.99962 | 1437 | 22 |

After:

| project | similarity index | total files | changed files |

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1632 |
| django | 0.99982 | 2760 | 37 |
| transformers | 0.99957 | 2587 | 399 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99983 | 3496 | 18 |
| warehouse | 0.99923 | 648 | 18 |
| zulip | 0.99962 | 1437 | 22 |

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

@@ -73,3 +73,25 @@ a = [
 aaaaaaaaaaaaaaaaaaaaa = [
     o for o in self.registry.values if o.__class__ is not ModelAdmin
 ]
+
+[
+    task
+    for head_name in head_nodes
+    if (task := self.get_task_by_name(head_name))
+    if not None
+]
+
+[
+    f(x, y,)
+    for head_name in head_nodes if head_name
+]
+
+[
+    f(x, y)
+    for head_name in f(x, y,) if head_name
+]
+
+[
+    x
+    for (x, y,) in z if head_name
+]

crates/ruff_python_formatter/src/other/comprehension.rs

@@ -56,16 +56,14 @@ impl FormatNodeRule<Comprehension> for FormatComprehension {
             [
                 token("for"),
                 trailing_comments(before_target_comments),
-                group(&format_args!(
+                Spacer(target),
-                    Spacer(target),
+                ExprTupleWithoutParentheses(target),
-                    ExprTupleWithoutParentheses(target),
+                in_spacer,
-                    in_spacer,
+                leading_comments(before_in_comments),
-                    leading_comments(before_in_comments),
+                token("in"),
-                    token("in"),
+                trailing_comments(trailing_in_comments),
-                    trailing_comments(trailing_in_comments),
+                Spacer(iter),
-                    Spacer(iter),
+                iter.format(),
-                    iter.format(),
-                )),
             ]
         )?;
         if !ifs.is_empty() {
@@ -79,18 +77,18 @@ impl FormatNodeRule<Comprehension> for FormatComprehension {
                             dangling_if_comments
                                 .partition_point(|comment| comment.line_position().is_own_line()),
                         );
-                    joiner.entry(&group(&format_args!(
+                    joiner.entry(&format_args!(
                         leading_comments(own_line_if_comments),
                         token("if"),
                         trailing_comments(end_of_line_if_comments),
                         Spacer(if_case),
                         if_case.format(),
-                    )));
+                    ));
                 }
                 joiner.finish()
             });
 
-            write!(f, [soft_line_break_or_space(), group(&joined)])?;
+            write!(f, [soft_line_break_or_space(), joined])?;
         }
         Ok(())
     }

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

@@ -79,6 +79,28 @@ a = [
 aaaaaaaaaaaaaaaaaaaaa = [
     o for o in self.registry.values if o.__class__ is not ModelAdmin
 ]
+
+[
+    task
+    for head_name in head_nodes
+    if (task := self.get_task_by_name(head_name))
+    if not None
+]
+
+[
+    f(x, y,)
+    for head_name in head_nodes if head_name
+]
+
+[
+    f(x, y)
+    for head_name in f(x, y,) if head_name
+]
+
+[
+    x
+    for (x, y,) in z if head_name
+]
 ```
 
 ## Output
@@ -178,6 +200,40 @@ a = [
 aaaaaaaaaaaaaaaaaaaaa = [
     o for o in self.registry.values if o.__class__ is not ModelAdmin
 ]
+
+[
+    task
+    for head_name in head_nodes
+    if (task := self.get_task_by_name(head_name))
+    if not None
+]
+
+[
+    f(
+        x,
+        y,
+    )
+    for head_name in head_nodes
+    if head_name
+]
+
+[
+    f(x, y)
+    for head_name in f(
+        x,
+        y,
+    )
+    if head_name
+]
+
+[
+    x
+    for (
+        x,
+        y,
+    ) in z
+    if head_name
+]
 ```