Indent lambda parameters if parameters wrap

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/lambda.options.json

@@ -0,0 +1,8 @@
+[
+  {
+    "preview": "disabled"
+  },
+  {
+    "preview": "enabled"
+  }
+]

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

@@ -204,6 +204,71 @@ def f(
     z
 )
 
+
+# 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
+
+
+# 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,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    y,
+    z
+] # Trailing
+# Trailing
+
 lambda self, araa, kkkwargs=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs), e=1, f=2, g=2: d
 
 # Regression tests for https://github.com/astral-sh/ruff/issues/8179

crates/ruff_python_formatter/src/comments/placement.rs

@@ -1805,18 +1805,6 @@ fn handle_lambda_comment<'a>(
     locator: &Locator,
 ) -> CommentPlacement<'a> {
     if let Some(parameters) = lambda.parameters.as_deref() {
-        // Comments between the `lambda` and the parameters are dangling on the lambda:
-        // ```python
-        // (
-        //     lambda  # comment
-        //     x:
-        //     y
-        // )
-        // ```
-        if comment.start() < parameters.start() {
-            return CommentPlacement::dangling(comment.enclosing_node(), comment);
-        }
-
         // Comments between the parameters and the body are dangling on the lambda:
         // ```python
         // (

crates/ruff_python_formatter/src/context.rs

@@ -43,6 +43,14 @@ impl<'a> PyFormatContext<'a> {
     pub(crate) fn comments(&self) -> &Comments<'a> {
         &self.comments
     }
+
+    pub(crate) const fn is_preview(&self) -> bool {
+        self.options.preview().is_enabled()
+    }
+
+    pub(crate) const fn is_stable(&self) -> bool {
+        !self.is_preview()
+    }
 }
 
 impl FormatContext for PyFormatContext<'_> {

crates/ruff_python_formatter/src/expression/expr_lambda.rs

@@ -4,7 +4,8 @@ use ruff_python_ast::ExprLambda;
 use ruff_text_size::Ranged;
 
 use crate::comments::{dangling_comments, SourceComment};
-use crate::expression::parentheses::{NeedsParentheses, OptionalParentheses};
+use crate::expression::parentheses::{NeedsParentheses, OptionalParentheses, Parenthesize};
+use crate::expression::{has_own_parentheses, maybe_parenthesize_expression};
 use crate::other::parameters::ParametersParentheses;
 use crate::prelude::*;
 
@@ -25,7 +26,7 @@ impl FormatNodeRule<ExprLambda> for FormatExprLambda {
         write!(f, [token("lambda")])?;
 
         if let Some(parameters) = parameters {
-            // In this context, a dangling comment can either be a comment between the `lambda` the
+            // In this context, a dangling comment can either be a comment between the `lambda` and the
             // parameters, or a comment between the parameters and the body.
             let (dangling_before_parameters, dangling_after_parameters) = dangling
                 .split_at(dangling.partition_point(|comment| comment.end() < parameters.start()));
@@ -36,20 +37,30 @@ impl FormatNodeRule<ExprLambda> for FormatExprLambda {
                 write!(f, [dangling_comments(dangling_before_parameters)])?;
             }
 
-            write!(
-                f,
-                [parameters
-                    .format()
-                    .with_options(ParametersParentheses::Never)]
-            )?;
+            group(&format_with(|f: &mut PyFormatter| {
+                if f.context().node_level().is_parenthesized() {
+                    soft_block_indent(
+                        &parameters
+                            .format()
+                            .with_options(ParametersParentheses::Never),
+                    )
+                    .fmt(f)
+                } else {
+                    parameters
+                        .format()
+                        .with_options(ParametersParentheses::Never)
+                        .fmt(f)
+                }?;
 
-            write!(f, [token(":")])?;
+                token(":").fmt(f)?;
 
-            if dangling_after_parameters.is_empty() {
-                write!(f, [space()])?;
-            } else {
-                write!(f, [dangling_comments(dangling_after_parameters)])?;
-            }
+                if dangling_after_parameters.is_empty() {
+                    space().fmt(f)
+                } else {
+                    dangling_comments(dangling_after_parameters).fmt(f)
+                }
+            }))
+            .fmt(f)?;
         } else {
             write!(f, [token(":")])?;
 
@@ -61,7 +72,12 @@ impl FormatNodeRule<ExprLambda> for FormatExprLambda {
             }
         }
 
-        write!(f, [body.format()])
+        // Avoid parenthesizing lists, dictionaries, etc.
+        if f.context().is_stable() || has_own_parentheses(body, f.context()).is_some() {
+            body.format().fmt(f)
+        } else {
+            maybe_parenthesize_expression(body, item, Parenthesize::IfBreaksOrIfRequired).fmt(f)
+        }
     }
 
     fn fmt_dangling_comments(

crates/ruff_python_formatter/src/expression/expr_named_expr.rs

@@ -69,6 +69,7 @@ impl NeedsParentheses for ExprNamedExpr {
             || parent.is_stmt_delete()
             || parent.is_stmt_for()
             || parent.is_stmt_function_def()
+            || parent.is_expr_lambda()
         {
             OptionalParentheses::Always
         } else {

crates/ruff_python_formatter/src/lib.rs

@@ -206,14 +206,7 @@ if True:
     #[test]
     fn quick_test() {
         let source = r#"
-def main() -> None:
-    if True:
-        some_very_long_variable_name_abcdefghijk = Foo()
-        some_very_long_variable_name_abcdefghijk = some_very_long_variable_name_abcdefghijk[
-            some_very_long_variable_name_abcdefghijk.some_very_long_attribute_name
-            == "This is a very long string abcdefghijk"
-        ]
-
+lambda self, araa, kkkwargs=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs), e=1, f=2, g=2: d
 "#;
         let source_type = PySourceType::Python;
         let (tokens, comment_ranges) = tokens_and_ranges(source, source_type).unwrap();

crates/ruff_python_formatter/src/options.rs

@@ -108,7 +108,7 @@ impl PyFormatOptions {
         self.line_ending
     }
 
-    pub fn preview(&self) -> PreviewMode {
+    pub const fn preview(&self) -> PreviewMode {
         self.preview
     }
 

crates/ruff_python_formatter/src/other/parameters.rs

@@ -247,7 +247,7 @@ impl FormatNodeRule<Parameters> for FormatParameters {
             + usize::from(kwarg.is_some());
 
         if self.parentheses == ParametersParentheses::Never {
-            write!(f, [group(&format_inner), dangling_comments(dangling)])
+            write!(f, [format_inner, dangling_comments(dangling)])
         } else if num_parameters == 0 {
             let mut f = WithNodeLevel::new(NodeLevel::ParenthesizedExpression, f);
             // No parameters, format any dangling comments between `()`