Format lambda expression (#5806)

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

@@ -0,0 +1,63 @@
+# Leading
+lambda x: x  # Trailing
+# Trailing
+
+# Leading
+lambda x, y: x  # Trailing
+# Trailing
+
+# Leading
+lambda x, y: x, y  # Trailing
+# Trailing
+
+# Leading
+lambda x, /, y: x  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: x  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (x, y, z)  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (
+    x,
+    y,
+z)  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (
+    x,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+z)  # Trailing
+# Trailing
+
+
+a = (
+    lambda  # Dangling
+           : 1
+)

crates/ruff_python_formatter/src/expression/expr_lambda.rs

@@ -1,22 +1,62 @@
+use crate::comments::dangling_comments;
 use crate::context::PyFormatContext;
 use crate::expression::parentheses::{NeedsParentheses, OptionalParentheses};
-use crate::{not_yet_implemented_custom_text, FormatNodeRule, PyFormatter};
+use crate::other::arguments::ArgumentsParentheses;
+use crate::AsFormat;
+use crate::{FormatNodeRule, PyFormatter};
+use ruff_formatter::prelude::{space, text};
 use ruff_formatter::{write, Buffer, FormatResult};
-use ruff_python_ast::node::AnyNodeRef;
+use ruff_python_ast::node::{AnyNodeRef, AstNode};
 use rustpython_parser::ast::ExprLambda;
 
 #[derive(Default)]
 pub struct FormatExprLambda;
 
 impl FormatNodeRule<ExprLambda> for FormatExprLambda {
-    fn fmt_fields(&self, _item: &ExprLambda, f: &mut PyFormatter) -> FormatResult<()> {
+    fn fmt_fields(&self, item: &ExprLambda, f: &mut PyFormatter) -> FormatResult<()> {
+        let ExprLambda {
+            range: _,
+            args,
+            body,
+        } = item;
+
+        // It's possible for some `Arguments` of `lambda`s to be assigned dangling comments.
+        //
+        // a = (
+        //     lambda  # Dangling
+        //     : 1
+        // )
+        let comments = f.context().comments().clone();
+        let dangling = comments.dangling_comments(args.as_any_node_ref());
+
+        write!(f, [text("lambda")])?;
+
+        if !args.args.is_empty() {
             write!(
                 f,
-            [not_yet_implemented_custom_text(
+                [
-                "lambda NOT_YET_IMPLEMENTED_lambda: True"
+                    space(),
-            )]
+                    args.format()
+                        .with_options(ArgumentsParentheses::SkipInsideLambda),
+                ]
+            )?;
+        }
+
+        write!(
+            f,
+            [
+                text(":"),
+                space(),
+                body.format(),
+                dangling_comments(dangling)
+            ]
         )
     }
+
+    fn fmt_dangling_comments(&self, _node: &ExprLambda, _f: &mut PyFormatter) -> FormatResult<()> {
+        // Override. Dangling comments are handled in `fmt_fields`.
+        Ok(())
+    }
 }
 
 impl NeedsParentheses for ExprLambda {

crates/ruff_python_formatter/src/other/arguments.rs

@@ -3,7 +3,7 @@ use std::usize;
 use ruff_text_size::{TextRange, TextSize};
 use rustpython_parser::ast::{Arguments, Ranged};
 
-use ruff_formatter::{format_args, write};
+use ruff_formatter::{format_args, write, FormatRuleWithOptions};
 use ruff_python_ast::node::{AnyNodeRef, AstNode};
 use ruff_python_whitespace::{first_non_trivia_token, SimpleTokenizer, Token, TokenKind};
 
@@ -16,8 +16,28 @@ use crate::expression::parentheses::parenthesized;
 use crate::prelude::*;
 use crate::FormatNodeRule;
 
+#[derive(Eq, PartialEq, Debug, Default)]
+pub enum ArgumentsParentheses {
+    #[default]
+    Default,
+
+    /// Arguments should never be inside parentheses for lambda expressions.
+    SkipInsideLambda,
+}
+
 #[derive(Default)]
-pub struct FormatArguments;
+pub struct FormatArguments {
+    parentheses: ArgumentsParentheses,
+}
+
+impl FormatRuleWithOptions<Arguments, PyFormatContext<'_>> for FormatArguments {
+    type Options = ArgumentsParentheses;
+
+    fn with_options(mut self, options: Self::Options) -> Self {
+        self.parentheses = options;
+        self
+    }
+}
 
 impl FormatNodeRule<Arguments> for FormatArguments {
     fn fmt_fields(&self, item: &Arguments, f: &mut PyFormatter) -> FormatResult<()> {
@@ -170,7 +190,9 @@ impl FormatNodeRule<Arguments> for FormatArguments {
             + kwonlyargs.len()
             + usize::from(kwarg.is_some());
 
-        if num_arguments == 0 {
+        if self.parentheses == ArgumentsParentheses::SkipInsideLambda {
+            group(&format_inner).fmt(f)?;
+        } else if num_arguments == 0 {
             // No arguments, format any dangling comments between `()`
             write!(
                 f,

crates/ruff_python_formatter/tests/snapshots/black_compatibility@py_38__pep_570.py.snap

@@ -56,21 +56,15 @@ lambda a, b=1, /, c=2, d=3, *, e=4, f=5: 1
 ```diff
 --- Black
 +++ Ruff
-@@ -35,10 +35,10 @@
+@@ -35,7 +35,7 @@
      pass
  
  
 -lambda a, /: a
-+lambda NOT_YET_IMPLEMENTED_lambda: True
++lambda: a
  
--lambda a, b, /, c, d, *, e, f: a
+ lambda a, b, /, c, d, *, e, f: a
-+lambda NOT_YET_IMPLEMENTED_lambda: True
  
--lambda a, b, /, c, d, *args, e, f, **kwargs: args
-+lambda NOT_YET_IMPLEMENTED_lambda: True
- 
--lambda a, b=1, /, c=2, d=3, *, e=4, f=5: 1
-+lambda NOT_YET_IMPLEMENTED_lambda: True
 ```
 
 ## Ruff Output
@@ -113,13 +107,13 @@ def long_one_with_long_parameter_names(
     pass
 
 
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda: a
 
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda a, b, /, c, d, *, e, f: a
 
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda a, b, /, c, d, *args, e, f, **kwargs: args
 
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda a, b=1, /, c=2, d=3, *, e=4, f=5: 1
 ```
 
 ## Black Output

crates/ruff_python_formatter/tests/snapshots/black_compatibility@py_38__pep_572.py.snap

@@ -68,21 +68,6 @@ while x := f(x):
      pass
  [y := f(x), y**2, y**3]
  filtered_data = [y for x in data if (y := f(x)) is None]
-@@ -19,10 +19,10 @@
-     pass
- 
- 
--lambda: (x := 1)
--(x := lambda: 1)
--(x := lambda: (y := 1))
--lambda line: (m := re.match(pattern, line)) and m.group(1)
-+lambda NOT_YET_IMPLEMENTED_lambda: True
-+(x := lambda NOT_YET_IMPLEMENTED_lambda: True)
-+(x := lambda NOT_YET_IMPLEMENTED_lambda: True)
-+lambda NOT_YET_IMPLEMENTED_lambda: True
- x = (y := 0)
- (z := (y := (x := 0)))
- (info := (name, phone, *rest))
 @@ -33,7 +33,7 @@
  foo(cat=(category := "vector"))
  if any(len(longline := l) >= 100 for l in lines):
@@ -128,10 +113,10 @@ def foo(answer: (p := 42) = 5):
     pass
 
 
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda: (x := 1)
-(x := lambda NOT_YET_IMPLEMENTED_lambda: True)
+(x := lambda: 1)
-(x := lambda NOT_YET_IMPLEMENTED_lambda: True)
+(x := lambda: (y := 1))
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda line: (m := re.match(pattern, line)) and m.group(1)
 x = (y := 0)
 (z := (y := (x := 0)))
 (info := (name, phone, *rest))

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__bracketmatch.py.snap

@@ -1,48 +0,0 @@
----
-source: crates/ruff_python_formatter/tests/fixtures.rs
-input_file: crates/ruff_python_formatter/resources/test/fixtures/black/simple_cases/bracketmatch.py
----
-## Input
-
-```py
-for ((x in {}) or {})['a'] in x:
-    pass
-pem_spam = lambda l, spam = {
-    "x": 3
-}: not spam.get(l.strip())
-lambda x=lambda y={1: 3}: y['x':lambda y: {1: 2}]: x
-```
-
-## Black Differences
-
-```diff
---- Black
-+++ Ruff
-@@ -1,4 +1,4 @@
- for ((x in {}) or {})["a"] in x:
-     pass
--pem_spam = lambda l, spam={"x": 3}: not spam.get(l.strip())
--lambda x=lambda y={1: 3}: y["x" : lambda y: {1: 2}]: x
-+pem_spam = lambda NOT_YET_IMPLEMENTED_lambda: True
-+lambda NOT_YET_IMPLEMENTED_lambda: True
-```
-
-## Ruff Output
-
-```py
-for ((x in {}) or {})["a"] in x:
-    pass
-pem_spam = lambda NOT_YET_IMPLEMENTED_lambda: True
-lambda NOT_YET_IMPLEMENTED_lambda: True
-```
-
-## Black Output
-
-```py
-for ((x in {}) or {})["a"] in x:
-    pass
-pem_spam = lambda l, spam={"x": 3}: not spam.get(l.strip())
-lambda x=lambda y={1: 3}: y["x" : lambda y: {1: 2}]: x
-```
-
-

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__expression.py.snap

@@ -274,34 +274,32 @@ last_call()
  Name
  None
  True
-@@ -31,18 +31,15 @@
+@@ -31,7 +31,7 @@
  -1
  ~int and not v1 ^ 123 + v2 | True
  (~int) and (not ((v1 ^ (123 + v2)) | True))
 -+(really ** -(confusing ** ~(operator**-precedence)))
 ++really ** -confusing ** ~operator**-precedence
  flags & ~select.EPOLLIN and waiters.write_task is not None
--lambda arg: None
+ lambda arg: None
--lambda a=True: a
+ lambda a=True: a
--lambda a, b, c=True: a
+@@ -39,10 +39,11 @@
--lambda a, b, c=True, *, d=(1 << v2), e="str": a
+ lambda a, b, c=True, *, d=(1 << v2), e="str": a
--lambda a, b, c=True, *vararg, d=(v1 << 2), e="str", **kwargs: a + b
+ lambda a, b, c=True, *vararg, d=(v1 << 2), e="str", **kwargs: a + b
--manylambdas = lambda x=lambda y=lambda z=1: z: y(): x()
+ manylambdas = lambda x=lambda y=lambda z=1: z: y(): x()
 -foo = lambda port_id, ignore_missing: {
 -    "port1": port1_resource,
 -    "port2": port2_resource,
 -}[port_id]
-+lambda NOT_YET_IMPLEMENTED_lambda: True
++foo = (
-+lambda NOT_YET_IMPLEMENTED_lambda: True
++    lambda port_id, ignore_missing: {"port1": port1_resource, "port2": port2_resource}[
-+lambda NOT_YET_IMPLEMENTED_lambda: True
++        port_id
-+lambda NOT_YET_IMPLEMENTED_lambda: True
++    ]
-+lambda NOT_YET_IMPLEMENTED_lambda: True
++)
-+manylambdas = lambda NOT_YET_IMPLEMENTED_lambda: True
-+foo = lambda NOT_YET_IMPLEMENTED_lambda: True
  1 if True else 2
  str or None if True else str or bytes or None
  (str or None) if True else (str or bytes or None)
-@@ -57,7 +54,13 @@
+@@ -57,7 +58,13 @@
  {"2.7": dead, "3.7": (long_live or die_hard), **{"3.6": verygood}}
  {**a, **b, **c}
  {"2.7", "3.6", "3.7", "3.8", "3.9", ("4.0" if gilectomy else "3.10")}
@@ -316,7 +314,7 @@ last_call()
  ()
  (1,)
  (1, 2)
-@@ -101,7 +104,10 @@
+@@ -101,7 +108,10 @@
  {a: b * -2 for a, b in dictionary.items()}
  {
      k: v
@@ -328,7 +326,7 @@ last_call()
  }
  Python3 > Python2 > COBOL
  Life is Life
-@@ -115,7 +121,7 @@
+@@ -115,7 +125,7 @@
      arg,
      another,
      kwarg="hey",
@@ -337,7 +335,7 @@ last_call()
  )  # note: no trailing comma pre-3.6
  call(*gidgets[:2])
  call(a, *gidgets[:2])
-@@ -152,13 +158,13 @@
+@@ -152,13 +162,13 @@
  slice[0:1]
  slice[0:1:2]
  slice[:]
@@ -354,7 +352,7 @@ last_call()
  numpy[0, :]
  numpy[:, i]
  numpy[0, :2]
-@@ -172,7 +178,7 @@
+@@ -172,7 +182,7 @@
  numpy[1 : c + 1, c]
  numpy[-(c + 1) :, d]
  numpy[:, l[-2]]
@@ -363,7 +361,7 @@ last_call()
  numpy[np.newaxis, :]
  (str or None) if (sys.version_info[0] > (3,)) else (str or bytes or None)
  {"2.7": dead, "3.7": long_live or die_hard}
-@@ -208,24 +214,14 @@
+@@ -208,24 +218,14 @@
  what_is_up_with_those_new_coord_names = (coord_names | set(vars_to_create)) - set(
      vars_to_remove
  )
@@ -396,7 +394,7 @@ last_call()
  Ø = set()
  authors.łukasz.say_thanks()
  mapping = {
-@@ -237,10 +233,10 @@
+@@ -237,10 +237,10 @@
  
  
  def gen():
@@ -411,16 +409,7 @@ last_call()
  
  
  async def f():
-@@ -249,7 +245,7 @@
+@@ -328,13 +328,18 @@
- 
- print(*[] or [1])
- print(**{1: 3} if False else {x: x for x in range(3)})
--print(*lambda x: x)
-+print(*lambda NOT_YET_IMPLEMENTED_lambda: True)
- assert not Test, "Short message"
- assert this is ComplexTest and not requirements.fit_in_a_single_line(
-     force=False
-@@ -328,13 +324,18 @@
  ):
      return True
  if (
@@ -442,7 +431,7 @@ last_call()
      ^ aaaaaaaa.i << aaaaaaaa.k >> aaaaaaaa.l**aaaaaaaa.m // aaaaaaaa.n
  ):
      return True
-@@ -342,7 +343,8 @@
+@@ -342,7 +347,8 @@
      ~aaaaaaaaaaaaaaaa.a
      + aaaaaaaaaaaaaaaa.b
      - aaaaaaaaaaaaaaaa.c * aaaaaaaaaaaaaaaa.d @ aaaaaaaaaaaaaaaa.e
@@ -492,13 +481,17 @@ not great
 (~int) and (not ((v1 ^ (123 + v2)) | True))
 +really ** -confusing ** ~operator**-precedence
 flags & ~select.EPOLLIN and waiters.write_task is not None
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda arg: None
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda a=True: a
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda a, b, c=True: a
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda a, b, c=True, *, d=(1 << v2), e="str": a
-lambda NOT_YET_IMPLEMENTED_lambda: True
+lambda a, b, c=True, *vararg, d=(v1 << 2), e="str", **kwargs: a + b
-manylambdas = lambda NOT_YET_IMPLEMENTED_lambda: True
+manylambdas = lambda x=lambda y=lambda z=1: z: y(): x()
-foo = lambda NOT_YET_IMPLEMENTED_lambda: True
+foo = (
+    lambda port_id, ignore_missing: {"port1": port1_resource, "port2": port2_resource}[
+        port_id
+    ]
+)
 1 if True else 2
 str or None if True else str or bytes or None
 (str or None) if True else (str or bytes or None)
@@ -704,7 +697,7 @@ async def f():
 
 print(*[] or [1])
 print(**{1: 3} if False else {x: x for x in range(3)})
-print(*lambda NOT_YET_IMPLEMENTED_lambda: True)
+print(*lambda x: x)
 assert not Test, "Short message"
 assert this is ComplexTest and not requirements.fit_in_a_single_line(
     force=False

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__fmtonoff.py.snap

@@ -269,9 +269,8 @@ d={'a':1,
 +
  # fmt: on
  def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
--    offset = attr.ib(default=attr.Factory(lambda: _r.uniform(1, 2)))
+     offset = attr.ib(default=attr.Factory(lambda: _r.uniform(1, 2)))
 -    assert task._cancel_stack[: len(old_stack)] == old_stack
-+    offset = attr.ib(default=attr.Factory(lambda NOT_YET_IMPLEMENTED_lambda: True))
 +    assert task._cancel_stack[ : len(old_stack)] == old_stack
  
  
@@ -451,7 +450,7 @@ def function_signature_stress_test(
 
 # fmt: on
 def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
-    offset = attr.ib(default=attr.Factory(lambda NOT_YET_IMPLEMENTED_lambda: True))
+    offset = attr.ib(default=attr.Factory(lambda: _r.uniform(1, 2)))
     assert task._cancel_stack[ : len(old_stack)] == old_stack
 
 

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__function.py.snap

@@ -126,9 +126,8 @@ def __await__(): return (yield)
  
  
  def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
--    offset = attr.ib(default=attr.Factory(lambda: _r.uniform(10000, 200000)))
+     offset = attr.ib(default=attr.Factory(lambda: _r.uniform(10000, 200000)))
 -    assert task._cancel_stack[: len(old_stack)] == old_stack
-+    offset = attr.ib(default=attr.Factory(lambda NOT_YET_IMPLEMENTED_lambda: True))
 +    assert task._cancel_stack[ : len(old_stack)] == old_stack
  
  
@@ -225,7 +224,7 @@ def function_signature_stress_test(
 
 
 def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
-    offset = attr.ib(default=attr.Factory(lambda NOT_YET_IMPLEMENTED_lambda: True))
+    offset = attr.ib(default=attr.Factory(lambda: _r.uniform(10000, 200000)))
     assert task._cancel_stack[ : len(old_stack)] == old_stack
 
 

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__power_op_spacing.py.snap

@@ -80,7 +80,7 @@ return np.divide(
  c = -(5**2)
  d = 5 ** f["hi"]
 -e = lazy(lambda **kwargs: 5)
-+e = lazy(lambda NOT_YET_IMPLEMENTED_lambda: True)
++e = lazy(lambda: 5)
  f = f() ** 5
  g = a.b**c.d
  h = 5 ** funcs.f()
@@ -89,7 +89,7 @@ return np.divide(
  c = -(5.0**2.0)
  d = 5.0 ** f["hi"]
 -e = lazy(lambda **kwargs: 5)
-+e = lazy(lambda NOT_YET_IMPLEMENTED_lambda: True)
++e = lazy(lambda: 5)
  f = f() ** 5.0
  g = a.b**c.d
  h = 5.0 ** funcs.f()
@@ -115,7 +115,7 @@ a = 5**~4
 b = 5 ** f()
 c = -(5**2)
 d = 5 ** f["hi"]
-e = lazy(lambda NOT_YET_IMPLEMENTED_lambda: True)
+e = lazy(lambda: 5)
 f = f() ** 5
 g = a.b**c.d
 h = 5 ** funcs.f()
@@ -134,7 +134,7 @@ a = 5.0**~4.0
 b = 5.0 ** f()
 c = -(5.0**2.0)
 d = 5.0 ** f["hi"]
-e = lazy(lambda NOT_YET_IMPLEMENTED_lambda: True)
+e = lazy(lambda: 5)
 f = f() ** 5.0
 g = a.b**c.d
 h = 5.0 ** funcs.f()

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__remove_for_brackets.py.snap

@@ -31,15 +31,6 @@ for (((((k, v))))) in d.items():
 ```diff
 --- Black
 +++ Ruff
-@@ -5,7 +5,7 @@
- # Don't touch tuple brackets after `in`
- for module in (core, _unicodefun):
-     if hasattr(module, "_verify_python3_env"):
--        module._verify_python3_env = lambda: None
-+        module._verify_python3_env = lambda NOT_YET_IMPLEMENTED_lambda: True
- 
- # Brackets remain for long for loop lines
- for (
 @@ -17,9 +17,7 @@
  for (
      k,
@@ -63,7 +54,7 @@ for k, v in d.items():
 # Don't touch tuple brackets after `in`
 for module in (core, _unicodefun):
     if hasattr(module, "_verify_python3_env"):
-        module._verify_python3_env = lambda NOT_YET_IMPLEMENTED_lambda: True
+        module._verify_python3_env = lambda: None
 
 # Brackets remain for long for loop lines
 for (

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__slices.py.snap

@@ -56,11 +56,9 @@ ham[lower + offset : upper + offset]
  slice[ham[c::d] :: 1]
  slice[ham[cheese**2 : -1] : 1 : 1, ham[1:2]]
 -slice[:-1:]
--slice[lambda: None : lambda: None]
--slice[lambda x, y, *args, really=2, **kwargs: None :, None::]
 +slice[ : -1 :]
-+slice[lambda NOT_YET_IMPLEMENTED_lambda: True : lambda NOT_YET_IMPLEMENTED_lambda: True]
+ slice[lambda: None : lambda: None]
-+slice[lambda NOT_YET_IMPLEMENTED_lambda: True :, None::]
+ slice[lambda x, y, *args, really=2, **kwargs: None :, None::]
  slice[1 or 2 : True and False]
  slice[not so_simple : 1 < val <= 10]
  slice[(1 for i in range(42)) : x]
@@ -94,8 +92,8 @@ slice[c, c + 1, d::]
 slice[ham[c::d] :: 1]
 slice[ham[cheese**2 : -1] : 1 : 1, ham[1:2]]
 slice[ : -1 :]
-slice[lambda NOT_YET_IMPLEMENTED_lambda: True : lambda NOT_YET_IMPLEMENTED_lambda: True]
+slice[lambda: None : lambda: None]
-slice[lambda NOT_YET_IMPLEMENTED_lambda: True :, None::]
+slice[lambda x, y, *args, really=2, **kwargs: None :, None::]
 slice[1 or 2 : True and False]
 slice[not so_simple : 1 < val <= 10]
 slice[(1 for i in range(42)) : x]

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

@@ -0,0 +1,136 @@
+---
+source: crates/ruff_python_formatter/tests/fixtures.rs
+input_file: crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/lambda.py
+---
+## Input
+```py
+# Leading
+lambda x: x  # Trailing
+# Trailing
+
+# Leading
+lambda x, y: x  # Trailing
+# Trailing
+
+# Leading
+lambda x, y: x, y  # Trailing
+# Trailing
+
+# Leading
+lambda x, /, y: x  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: x  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (x, y, z)  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (
+    x,
+    y,
+z)  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (
+    x,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+z)  # Trailing
+# Trailing
+
+
+a = (
+    lambda  # Dangling
+           : 1
+)```
+
+## Output
+```py
+# Leading
+lambda x: x  # Trailing
+# Trailing
+
+# Leading
+lambda x, y: x  # Trailing
+# Trailing
+
+# Leading
+lambda x, y: x, y  # Trailing
+# Trailing
+
+# Leading
+lambda x, /, y: x  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: x  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (x, y, z)  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (x, y, z)  # Trailing
+# Trailing
+
+# Leading
+lambda x: lambda y: lambda z: (
+    x,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    z,
+)  # Trailing
+# Trailing
+
+
+a = (
+    lambda: 1  # Dangling
+)
+```
+
+
+