avoid extra parentheses for nested collections

crates/ruff_python_formatter/src/other/comprehension.rs

@@ -1,5 +1,5 @@
 use ruff_formatter::{Buffer, FormatResult, format_args, write};
-use ruff_python_ast::{Comprehension, Expr};
+use ruff_python_ast::{self as ast, Comprehension, Expr};
 use ruff_python_trivia::{SimpleTokenKind, find_only_token_in_range};
 use ruff_text_size::{Ranged, TextRange};
 
@@ -117,7 +117,11 @@ impl FormatNodeRule<Comprehension> for FormatComprehension {
                     maybe_parenthesize_expression(
                         iter,
                         item,
-                        Parenthesize::IfBreaksParenthesizedNested
+                        if needs_nested_parentheses(iter) {
+                            Parenthesize::IfBreaksParenthesizedNested
+                        } else {
+                            Parenthesize::IfBreaks
+                        }
                     )
                 ]
             )?;
@@ -188,3 +192,68 @@ impl Format<PyFormatContext<'_>> for ExprTupleWithoutParentheses<'_> {
         }
     }
 }
+
+/// Returns `true` if the expression needs additional parentheses when used as the `in` clause of a
+/// comprehension.
+///
+/// For example, we need to parenthesize a long attribute expression:
+///
+/// ```python
+/// [
+///     a
+///     for graph_path_expression in (
+///         refined_constraint.condition_as_predicate.variables
+///     )
+/// ]
+/// ```
+///
+/// but avoid adding additional parentheses to a set or other collection:
+///
+/// ```python
+/// [
+///     x
+///     for x in {  # _not_ `({`
+///         x
+///         for x in "long line long line long line long line long line long line long line"
+///     }
+/// ]
+/// ```
+fn needs_nested_parentheses(expr: &Expr) -> bool {
+    match expr {
+        Expr::Tuple(_)
+        | Expr::List(_)
+        | Expr::Set(_)
+        | Expr::Dict(_)
+        | Expr::ListComp(_)
+        | Expr::SetComp(_)
+        | Expr::DictComp(_) => false,
+
+        Expr::Starred(ast::ExprStarred { value, .. }) => needs_nested_parentheses(value),
+
+        Expr::BoolOp(_)
+        | Expr::Named(_)
+        | Expr::BinOp(_)
+        | Expr::UnaryOp(_)
+        | Expr::Lambda(_)
+        | Expr::If(_)
+        | Expr::Generator(_)
+        | Expr::Await(_)
+        | Expr::Yield(_)
+        | Expr::YieldFrom(_)
+        | Expr::Compare(_)
+        | Expr::Call(_)
+        | Expr::Attribute(_)
+        | Expr::Subscript(_)
+        | Expr::Name(_)
+        | Expr::Slice(_)
+        | Expr::IpyEscapeCommand(_)
+        | Expr::NumberLiteral(_)
+        | Expr::BooleanLiteral(_)
+        | Expr::NoneLiteral(_)
+        | Expr::StringLiteral(_)
+        | Expr::BytesLiteral(_)
+        | Expr::FString(_)
+        | Expr::TString(_)
+        | Expr::EllipsisLiteral(_) => true,
+    }
+}