fix assignment instability without parameters too

crates/ruff_python_formatter/src/expression/expr_lambda.rs

@@ -121,14 +121,16 @@ impl FormatNodeRule<ExprLambda> for FormatExprLambda {
                 write!(f, [space()])?;
             }
             // In preview, always parenthesize the body if there are dangling comments.
-            else if is_parenthesize_lambda_bodies_enabled(f.context()) {
+            else if preview {
                 let (dangling_end_of_line, dangling_own_line) = dangling.split_at(
                     dangling
                         .iter()
                         .position(|comment| comment.line_position().is_own_line())
                         .unwrap_or(dangling.len()),
                 );
-                return write!(
+
+                let fmt_body = format_with(|f: &mut PyFormatter| {
+                    write!(
                         f,
                         [
                             space(),
@@ -140,13 +142,19 @@ impl FormatNodeRule<ExprLambda> for FormatExprLambda {
                             )),
                             token(")")
                         ]
-                );
+                    )
+                });
+
+                return match self.layout {
+                    ExprLambdaLayout::Assignment => fits_expanded(&fmt_body).fmt(f),
+                    ExprLambdaLayout::Default => fmt_body.fmt(f),
+                };
             } else {
                 write!(f, [dangling_comments(dangling)])?;
             }
         }
 
-        if is_parenthesize_lambda_bodies_enabled(f.context()) {
+        if preview {
             let body_comments = comments.leading_dangling_trailing(&**body);
             let fmt_body = format_with(|f: &mut PyFormatter| {
                 // If the body has comments, we always want to preserve the parentheses. This also

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

@@ -1461,7 +1461,7 @@ transform = (
 ```diff
 --- Stable
 +++ Preview
-@@ -27,30 +27,10 @@
+@@ -27,35 +27,14 @@
  # Trailing
  
  # Leading
@@ -1496,7 +1496,13 @@ transform = (
  )  # Trailing
  # Trailing
  
-@@ -74,7 +54,9 @@
+-a = (
+-    lambda:  # Dangling
++a = lambda: (  # Dangling
+     1
+ )
+ 
+@@ -74,7 +53,9 @@
  
  # lambda arguments don't have parentheses, so we never add a magic trailing comma ...
  def f(
@@ -1507,7 +1513,43 @@ transform = (
  ):
      pass
  
-@@ -136,16 +118,18 @@
+@@ -102,22 +83,25 @@
+ 
+ # Dangling comments without parameters.
+ (
+-    lambda:  # 3
+-    None
++    lambda: (  # 3
++        None
++    )
+ )
+ 
+ (
+-    lambda:
+-    # 3
+-    None
++    lambda: (
++        # 3
++        None
++    )
+ )
+ 
+ (
+-    lambda:  # 1
+-    # 2
+-    # 3
+-    # 4
+-    None  # 5
++    lambda: (  # 1
++        # 2
++        # 3
++        # 4
++        None
++    )  # 5
+ )
+ 
+ (
+@@ -136,16 +120,18 @@
      lambda
      # comment 1
      # comment 2
@@ -1531,7 +1573,54 @@ transform = (
  )
  
  lambda *x: x
-@@ -192,11 +176,12 @@
+@@ -161,30 +147,34 @@
+ )
+ 
+ (
+-    lambda:  # comment
+-    x
++    lambda: (  # comment
++        x
++    )
+ )
+ 
+ (
+-    lambda:
+-    # comment
+-    x
++    lambda: (
++        # comment
++        x
++    )
+ )
+ 
+ (
+-    lambda:  # comment
+-    x
++    lambda: (  # comment
++        x
++    )
+ )
+ 
+ (
+-    lambda:
+-    # comment
+-    x
++    lambda: (
++        # comment
++        x
++    )
+ )
+ 
+ (
+-    lambda:  # comment
+-    (  # comment
++    lambda: (  # comment
++        # comment
+         x
+     )
+ )
+@@ -192,11 +182,12 @@
  (
      lambda  # 1
      # 2
@@ -1549,7 +1638,7 @@ transform = (
  )
  
  (
-@@ -204,9 +189,10 @@
+@@ -204,9 +195,10 @@
      # 2
      x,  # 3
      # 4
@@ -1563,7 +1652,7 @@ transform = (
  )
  
  (
-@@ -218,71 +204,79 @@
+@@ -218,71 +210,79 @@
  
  # Leading
  lambda x: (
@@ -1702,7 +1791,7 @@ transform = (
  
  
  # Regression tests for https://github.com/astral-sh/ruff/issues/8179
-@@ -291,9 +285,9 @@
+@@ -291,9 +291,9 @@
          c,
          d,
          e,
@@ -1715,7 +1804,7 @@ transform = (
      )
  
  
-@@ -302,15 +296,9 @@
+@@ -302,15 +302,9 @@
          c,
          d,
          e,
@@ -1734,7 +1823,7 @@ transform = (
          g=10,
      )
  
-@@ -320,9 +308,9 @@
+@@ -320,9 +314,9 @@
          c,
          d,
          e,
@@ -1747,7 +1836,7 @@ transform = (
      )
  
  
-@@ -338,9 +326,9 @@
+@@ -338,9 +332,9 @@
  
  class C:
      function_dict: Dict[Text, Callable[[CRFToken], Any]] = {
@@ -1760,7 +1849,7 @@ transform = (
      }
  
  
-@@ -352,42 +340,40 @@
+@@ -352,42 +346,40 @@
  def foo():
      if True:
          if True:
@@ -1819,7 +1908,7 @@ transform = (
          CREATE TABLE {table} AS
          SELECT ROW_NUMBER() OVER () AS id, {var}
          FROM (
-@@ -402,18 +388,19 @@
+@@ -402,18 +394,19 @@
  long_assignment_target.with_attribute.and_a_slice[with_an_index] = (
      # 1
      # 2
@@ -1846,7 +1935,7 @@ transform = (
  )
  
  very_long_variable_name_x, very_long_variable_name_y = (
-@@ -421,8 +408,8 @@
+@@ -421,8 +414,8 @@
      lambda b: b * another_very_long_expression_here,
  )
  
@@ -1857,7 +1946,7 @@ transform = (
          x, more_args, additional_parameters
      )
  )
-@@ -458,12 +445,12 @@
+@@ -458,12 +451,12 @@
      [
          # Not fluent
          param(
@@ -1872,7 +1961,7 @@ transform = (
          ),
          param(
              lambda left, right: (
-@@ -472,9 +459,9 @@
+@@ -472,9 +465,9 @@
          ),
          param(lambda left, right: ibis.timestamp("2017-04-01").cast(dt.date)),
          param(
@@ -1885,7 +1974,7 @@ transform = (
          ),
          # This is too long on one line in the lambda body and gets wrapped
          # inside the body.
-@@ -508,16 +495,18 @@
+@@ -508,16 +501,18 @@
  ]
  
  # adds parentheses around the body
@@ -1907,7 +1996,7 @@ transform = (
  
  lambda x, y, z: (
      x + y + z
-@@ -528,7 +517,7 @@
+@@ -528,7 +523,7 @@
      x + y + z  # trailing eol body
  )
  
@@ -1916,7 +2005,7 @@ transform = (
  
  lambda x, y, z: (
      # leading body
-@@ -540,21 +529,23 @@
+@@ -540,21 +535,23 @@
  )
  
  (
@@ -1950,7 +2039,7 @@ transform = (
      # dangling header comment
      source_bucket
      if name == source_bucket_name
-@@ -562,8 +553,7 @@
+@@ -562,8 +559,7 @@
  )
  
  (
@@ -1960,7 +2049,7 @@ transform = (
          source_bucket
          if name == source_bucket_name
          else storage.Bucket(mock_service, destination_bucket_name)
-@@ -571,61 +561,70 @@
+@@ -571,61 +567,70 @@
  )
  
  (
@@ -2063,7 +2152,7 @@ transform = (
  )
  
  (
-@@ -638,27 +637,31 @@
+@@ -638,27 +643,31 @@
  (
      lambda
      # comment
@@ -2103,7 +2192,7 @@ transform = (
  )
  
  (
-@@ -666,19 +669,20 @@
+@@ -666,19 +675,20 @@
      # 2
      left,  # 3
      # 4
@@ -2134,7 +2223,7 @@ transform = (
          )
      )
  )
-@@ -696,18 +700,17 @@
+@@ -696,46 +706,50 @@
  foo(
      lambda from_ts,  # but still wrap the body if it gets too long
      to_ts,
@@ -2161,4 +2250,52 @@ transform = (
  )  # trailing comment
  
  (
+-    lambda:  # comment
+-    1
++    lambda: (  # comment
++        1
++    )
+ )
+ 
+ (
+-    lambda:  # comment
+-    1
++    lambda: (  # comment
++        1
++    )
+ )
+ 
+ (
+-    lambda:
+-    # comment
+-    1
++    lambda: (
++        # comment
++        1
++    )
+ )
+ 
+ (
+-    lambda:  # comment 1
+-    # comment 2
+-    1
++    lambda: (  # comment 1
++        # comment 2
++        1
++    )
+ )
+ 
+ (
+-    lambda:  # comment 1
+-    # comment 2
+-    # comment 3
+-    # comment 4
+-    1
++    lambda: (  # comment 1
++        # comment 2
++        # comment 3
++        # comment 4
++        1
++    )
+ )
 ```