Suppress unused_parens for labeled break

Author: chenyukang

compiler/rustc_lint/src/unused.rs

@@ -914,7 +914,16 @@ trait UnusedDelimLint {
                 (value, UnusedDelimsCtx::ReturnValue, false, Some(left), None, true)
             }
 
-            Break(_, Some(ref value)) => {
+            Break(label, Some(ref value)) => {
+                // Don't lint on `break 'label ({...})` - the parens are necessary
+                // to disambiguate from `break 'label {...}` which would be a syntax error.
+                // This avoids conflicts with the `break_with_label_and_loop` lint.
+                if label.is_some()
+                    && matches!(value.kind, ast::ExprKind::Paren(ref inner)
+                        if matches!(inner.kind, ast::ExprKind::Block(..)))
+                {
+                    return;
+                }
                 (value, UnusedDelimsCtx::BreakValue, false, None, None, true)
             }
 

tests/ui/lint/unused/break-label-with-parens-147542.rs

@@ -0,0 +1,22 @@
+//@ check-pass
+
+// Regression test for #147542
+// Ensures that we don't suggest removing parens in a break with label and loop
+// when the parens are necessary for correct parsing.
+
+#![warn(unused_parens)]
+#![warn(break_with_label_and_loop)]
+
+fn xyz() -> usize {
+    'foo: {
+        // parens bellow are necessary break of break with label and loop
+        break 'foo ({
+            println!("Hello!");
+            123
+        });
+    }
+}
+
+fn main() {
+    xyz();
+}