Only omit optinal parens if the expression ends or starts with a pare…

…nthesized expression

crates/ruff_python_formatter/src/expression/mod.rs

@@ -198,37 +198,30 @@ impl<'ast> IntoFormat<PyFormatContext<'ast>> for Expr {
 ///
 /// This mimics Black's [`_maybe_split_omitting_optional_parens`](https://github.com/psf/black/blob/d1248ca9beaf0ba526d265f4108836d89cf551b7/src/black/linegen.py#L746-L820)
 fn can_omit_optional_parentheses(expr: &Expr, context: &PyFormatContext) -> bool {
-    let mut visitor = MaxOperatorPriorityVisitor::new(context.source());
-
+    let mut visitor = CanOmitOptionalParenthesesVisitor::new(context.source());
     visitor.visit_subexpression(expr);
-
-    let (max_operator_priority, operation_count, any_parenthesized_expression) = visitor.finish();
-
-    if operation_count > 1 {
-        false
-    } else if max_operator_priority == OperatorPriority::Attribute {
-        true
-    } else {
-        // Only use the more complex IR when there is any expression that we can possibly split by
-        any_parenthesized_expression
-    }
+    visitor.can_omit()
 }
 
 #[derive(Clone, Debug)]
-struct MaxOperatorPriorityVisitor<'input> {
+struct CanOmitOptionalParenthesesVisitor<'input> {
     max_priority: OperatorPriority,
     max_priority_count: u32,
     any_parenthesized_expressions: bool,
+    last: Option<&'input Expr>,
+    first: Option<&'input Expr>,
     source: &'input str,
 }
 
-impl<'input> MaxOperatorPriorityVisitor<'input> {
+impl<'input> CanOmitOptionalParenthesesVisitor<'input> {
     fn new(source: &'input str) -> Self {
         Self {
             source,
             max_priority: OperatorPriority::None,
             max_priority_count: 0,
             any_parenthesized_expressions: false,
+            last: None,
+            first: None,
         }
     }
 
@@ -305,6 +298,7 @@ impl<'input> MaxOperatorPriorityVisitor<'input> {
                 self.any_parenthesized_expressions = true;
                 // Only walk the function, the arguments are always parenthesized
                 self.visit_expr(func);
+                self.last = Some(expr);
                 return;
             }
             Expr::Subscript(_) => {
@@ -351,23 +345,41 @@ impl<'input> MaxOperatorPriorityVisitor<'input> {
         walk_expr(self, expr);
     }
 
-    fn finish(self) -> (OperatorPriority, u32, bool) {
-        (
-            self.max_priority,
-            self.max_priority_count,
-            self.any_parenthesized_expressions,
-        )
+    fn can_omit(self) -> bool {
+        if self.max_priority_count > 1 {
+            false
+        } else if self.max_priority == OperatorPriority::Attribute {
+            true
+        } else if !self.any_parenthesized_expressions {
+            // Only use the more complex IR when there is any expression that we can possibly split by
+            false
+        } else {
+            // Only use the layout if the first or last expression has parentheses of some sort.
+            let first_parenthesized = self
+                .first
+                .map_or(false, |first| has_parentheses(first, self.source));
+            let last_parenthesized = self
+                .last
+                .map_or(false, |last| has_parentheses(last, self.source));
+            first_parenthesized || last_parenthesized
+        }
     }
 }
 
-impl<'input> PreorderVisitor<'input> for MaxOperatorPriorityVisitor<'input> {
+impl<'input> PreorderVisitor<'input> for CanOmitOptionalParenthesesVisitor<'input> {
     fn visit_expr(&mut self, expr: &'input Expr) {
+        self.last = Some(expr);
+
         // Rule only applies for non-parenthesized expressions.
         if is_expression_parenthesized(AnyNodeRef::from(expr), self.source) {
             self.any_parenthesized_expressions = true;
         } else {
             self.visit_subexpression(expr);
         }
+
+        if self.first.is_none() {
+            self.first = Some(expr);
+        }
     }
 }
 

crates/ruff_python_formatter/src/lib.rs

@@ -280,8 +280,15 @@ if True:
     #[test]
     fn quick_test() {
         let src = r#"
-def foo() -> tuple[int, int, int,]:
-    return 2
+if a * [
+    bbbbbbbbbbbbbbbbbbbbbb,
+    cccccccccccccccccccccccccccccdddddddddddddddddddddddddd,
+] + a * e * [
+    ffff,
+    gggg,
+    hhhhhhhhhhhhhh,
+] * c:
+    pass
 
 "#;
         // Tokenize once