Fix bracket spacing for single-element tuples in f-string expressions (#15537)

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

@@ -718,3 +718,11 @@ print(f"{ {1: 2}.keys() }")
 print(f"{({1, 2, 3}) - ({2})}")
 print(f"{1, 2, {3} }")
 print(f"{(1, 2, {3})}")
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/15535
+print(f"{ {}, }")  # A single item tuple gets parenthesized
+print(f"{ {}.values(), }")
+print(f"{ {}, 1 }")  # A tuple with multiple elements doesn't get parenthesized
+print(f"{  # Tuple with multiple elements that doesn't fit on a single line gets parenthesized
+    {}, 1,
+}")

crates/ruff_python_formatter/src/other/f_string_element.rs

@@ -204,18 +204,13 @@ impl Format<PyFormatContext<'_>> for FormatFStringExpressionElement<'_> {
             // before the closing curly brace is not strictly necessary, but it's
             // added to maintain consistency.
             let bracket_spacing =
-                match left_most(expression, comments.ranges(), f.context().source()) {
+                needs_bracket_spacing(expression, f.context()).then_some(format_with(|f| {
-                    Expr::Dict(_) | Expr::DictComp(_) | Expr::Set(_) | Expr::SetComp(_) => {
+                    if self.context.can_contain_line_breaks() {
-                        Some(format_with(|f| {
+                        soft_line_break_or_space().fmt(f)
-                            if self.context.can_contain_line_breaks() {
+                    } else {
-                                soft_line_break_or_space().fmt(f)
+                        space().fmt(f)
-                            } else {
-                                space().fmt(f)
-                            }
-                        }))
                     }
-                    _ => None,
+                }));
-                };
 
             let item = format_with(|f: &mut PyFormatter| {
                 // Update the context to be inside the f-string expression element.
@@ -290,3 +285,19 @@ impl Format<PyFormatContext<'_>> for FormatFStringExpressionElement<'_> {
         }
     }
 }
+
+fn needs_bracket_spacing(expr: &Expr, context: &PyFormatContext) -> bool {
+    // Ruff parenthesizes single element tuples, that's why we shouldn't insert
+    // a space around the curly braces for those.
+    if expr
+        .as_tuple_expr()
+        .is_some_and(|tuple| !tuple.parenthesized && tuple.elts.len() == 1)
+    {
+        return false;
+    }
+
+    matches!(
+        left_most(expr, context.comments().ranges(), context.source()),
+        Expr::Dict(_) | Expr::DictComp(_) | Expr::Set(_) | Expr::SetComp(_)
+    )
+}

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

@@ -724,6 +724,14 @@ print(f"{ {1: 2}.keys() }")
 print(f"{({1, 2, 3}) - ({2})}")
 print(f"{1, 2, {3} }")
 print(f"{(1, 2, {3})}")
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/15535
+print(f"{ {}, }")  # A single item tuple gets parenthesized
+print(f"{ {}.values(), }")
+print(f"{ {}, 1 }")  # A tuple with multiple elements doesn't get parenthesized
+print(f"{  # Tuple with multiple elements that doesn't fit on a single line gets parenthesized
+    {}, 1,
+}")
 ```
 
 ## Outputs
@@ -1506,6 +1514,19 @@ print(f"{ {1: 2}.keys() }")
 print(f"{({1, 2, 3}) - ({2})}")
 print(f"{1, 2, {3}}")
 print(f"{(1, 2, {3})}")
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/15535
+print(f"{({},)}")  # A single item tuple gets parenthesized
+print(f"{({}.values(),)}")
+print(f"{ {}, 1 }")  # A tuple with multiple elements doesn't get parenthesized
+print(
+    f"{  # Tuple with multiple elements that doesn't fit on a single line gets parenthesized
+        (
+            {},
+            1,
+        )
+    }"
+)
 ```
 
 
@@ -2288,4 +2309,17 @@ print(f"{ {1: 2}.keys() }")
 print(f"{({1, 2, 3}) - ({2})}")
 print(f"{1, 2, {3}}")
 print(f"{(1, 2, {3})}")
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/15535
+print(f"{({},)}")  # A single item tuple gets parenthesized
+print(f"{({}.values(),)}")
+print(f"{ {}, 1 }")  # A tuple with multiple elements doesn't get parenthesized
+print(
+    f"{  # Tuple with multiple elements that doesn't fit on a single line gets parenthesized
+        (
+            {},
+            1,
+        )
+    }"
+)
 ```