Allow up to two newlines before trailing clause body comments (#7575)

## Summary

This is the peer to https://github.com/astral-sh/ruff/pull/7557, but for
"leading" clause comments, like:

```python
if True:
    pass


# comment
else:
    pass
```

In this case, we again want to allow up to two newlines at the top
level.

## Test Plan

`cargo test`

No changes.

Before:

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

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1631 |
| django | 0.99983 | 2760 | 36 |
| transformers | 0.99963 | 2587 | 323 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99979 | 3496 | 22 |
| warehouse | 0.99967 | 648 | 15 |
| zulip | 0.99972 | 1437 | 21 |

After:

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

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1631 |
| django | 0.99983 | 2760 | 36 |
| transformers | 0.99963 | 2587 | 323 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99979 | 3496 | 22 |
| warehouse | 0.99967 | 648 | 15 |
| zulip | 0.99972 | 1437 | 21 |

crates/ruff_python_formatter/resources/test/fixtures/ruff/statement/if.py

@@ -186,6 +186,28 @@ if True:
 else:
     pass
 
+if True:
+    pass
+# comment
+else:
+    pass
+
+if True:
+    pass
+
+# comment
+else:
+    pass
+
+if True:
+    pass
+
+
+# comment
+else:
+    pass
+
+
 # Regression test for https://github.com/astral-sh/ruff/issues/5337
 if parent_body:
     if current_body:

crates/ruff_python_formatter/src/comments/format.rs

@@ -86,9 +86,13 @@ impl Format<PyFormatContext<'_>> for FormatLeadingAlternateBranchComments<'_> {
         if let Some(first_leading) = self.comments.first() {
             // Leading comments only preserves the lines after the comment but not before.
             // Insert the necessary lines.
-            if lines_before(first_leading.start(), f.context().source()) > 1 {
-                write!(f, [empty_line()])?;
-            }
+            write!(
+                f,
+                [empty_lines(lines_before(
+                    first_leading.start(),
+                    f.context().source()
+                ))]
+            )?;
 
             write!(f, [leading_comments(self.comments)])?;
         } else if let Some(last_preceding) = self.last_node {

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

@@ -192,6 +192,28 @@ if True:
 else:
     pass
 
+if True:
+    pass
+# comment
+else:
+    pass
+
+if True:
+    pass
+
+# comment
+else:
+    pass
+
+if True:
+    pass
+
+
+# comment
+else:
+    pass
+
+
 # Regression test for https://github.com/astral-sh/ruff/issues/5337
 if parent_body:
     if current_body:
@@ -400,6 +422,28 @@ if True:
 else:
     pass
 
+if True:
+    pass
+# comment
+else:
+    pass
+
+if True:
+    pass
+
+# comment
+else:
+    pass
+
+if True:
+    pass
+
+
+# comment
+else:
+    pass
+
+
 # Regression test for https://github.com/astral-sh/ruff/issues/5337
 if parent_body:
     if current_body: