Skip unused_parens report for Paren(Path(..)) in macro.

fixes rust-lang#120642

Author: surechen

compiler/rustc_lint/src/unused.rs

@@ -1232,6 +1232,7 @@ impl EarlyLintPass for UnusedParens {
                     ast::TyKind::BareFn(b)
                         if self.with_self_ty_parens && b.generic_params.len() > 0 => {}
                     ast::TyKind::ImplTrait(_, bounds) if bounds.len() > 1 => {}
+                    ast::TyKind::Path(_, _) if ty.span.from_expansion() => {}
                     _ => {
                         let spans = r
                             .span

tests/ui/lint/unused/unused_parens/unused-parens-in-macro-issue-120642.rs

@@ -0,0 +1,29 @@
+//@ check-pass
+#![warn(unused_parens)]
+#![deny(warnings)]
+
+trait Foo {
+    fn bar();
+}
+
+macro_rules! problem {
+    ($ty:ident) => {
+        impl<$ty: Foo> Foo for ($ty,) {
+            fn bar() { <$ty>::bar() }
+        }
+    };
+    ($ty:ident $(, $rest:ident)*) => {
+        impl<$ty: Foo, $($rest: Foo),*> Foo for ($ty, $($rest),*) {
+            fn bar() {
+                <$ty>::bar();
+                <($($rest),*)>::bar()
+            }
+        }
+
+        problem!($($rest),*);
+    }
+}
+
+fn main() {
+    problem!(T1, T2, T3);
+}