From 05951dd3387055a3ab0b5a01666eaa01ae5576a3 Mon Sep 17 00:00:00 2001
From: qdegraaf <34540841+qdegraaf@users.noreply.github.com>
Date: Fri, 8 Sep 2023 11:40:58 +0200
Subject: [PATCH] Fix inconsistent `expr_lambda` formatting (#6318)

---
 .../test/fixtures/ruff/expression/lambda.py   | 35 +++++++++
 .../src/expression/expr_lambda.rs             |  5 ++
 .../format@expression__lambda.py.snap         | 73 ++++++++++++++++++-
 3 files changed, 109 insertions(+), 4 deletions(-)

diff --git a/crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/lambda.py b/crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/lambda.py
index 32a57bed4a..12e167d413 100644
--- a/crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/lambda.py
+++ b/crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/lambda.py
@@ -118,3 +118,38 @@ lambda a, /, c: a
     # 4
     None # 5
 )
+
+(
+    lambda
+    # comment
+    *x: x
+)
+
+(
+    lambda
+    # comment 1
+    *
+    # comment 2
+    x:
+    # comment 3
+    x
+)
+
+(
+    lambda # comment 1
+    * # comment 2
+    x: # comment 3
+    x
+)
+
+lambda *x\
+    :x
+
+(
+    lambda
+    # comment
+    *\
+        x: x
+)
+
+
diff --git a/crates/ruff_python_formatter/src/expression/expr_lambda.rs b/crates/ruff_python_formatter/src/expression/expr_lambda.rs
index 54cd619b13..d2244596e0 100644
--- a/crates/ruff_python_formatter/src/expression/expr_lambda.rs
+++ b/crates/ruff_python_formatter/src/expression/expr_lambda.rs
@@ -43,6 +43,11 @@ impl FormatNodeRule<ExprLambda> for FormatExprLambda {
             write!(f, [dangling_comments(dangling)])?;
         }
 
+        // Insert hard line break if body has leading comment to ensure consistent formatting
+        if comments.has_leading(body.as_ref()) {
+            write!(f, [hard_line_break()])?;
+        }
+
         write!(f, [body.format()])
     }
 
diff --git a/crates/ruff_python_formatter/tests/snapshots/format@expression__lambda.py.snap b/crates/ruff_python_formatter/tests/snapshots/format@expression__lambda.py.snap
index 73e3bcc04d..7585e7f371 100644
--- a/crates/ruff_python_formatter/tests/snapshots/format@expression__lambda.py.snap
+++ b/crates/ruff_python_formatter/tests/snapshots/format@expression__lambda.py.snap
@@ -124,6 +124,41 @@ lambda a, /, c: a
     # 4
     None # 5
 )
+
+(
+    lambda
+    # comment
+    *x: x
+)
+
+(
+    lambda
+    # comment 1
+    *
+    # comment 2
+    x:
+    # comment 3
+    x
+)
+
+(
+    lambda # comment 1
+    * # comment 2
+    x: # comment 3
+    x
+)
+
+lambda *x\
+    :x
+
+(
+    lambda
+    # comment
+    *\
+        x: x
+)
+
+
 ```
 
 ## Output
@@ -185,7 +220,8 @@ lambda x: lambda y: lambda z: (
 # Trailing
 
 a = (
-    lambda: # Dangling
+    lambda: 
+    # Dangling
     1
 )
 
@@ -232,22 +268,51 @@ lambda a, /, c: a
 
 # Dangling comments without parameters.
 (
-    lambda: # 3
+    lambda: 
+    # 3
     None
 )
 
 (
-    lambda: # 3
+    lambda: 
+    # 3
     None
 )
 
 (
-    lambda: # 1
+    lambda: 
+    # 1
     # 2
     # 3
     # 4
     None  # 5
 )
+
+(
+    lambda # comment
+    *x: x
+)
+
+(
+    lambda # comment 1
+    # comment 2
+    *x: 
+    # comment 3
+    x
+)
+
+(
+    lambda # comment 1
+    # comment 2
+    *x: x  # comment 3
+)
+
+lambda *x: x
+
+(
+    lambda # comment
+    *x: x
+)
 ```