fix(rustc_lint): better detect when parens are necessary

compiler/rustc_lint/src/unused.rs

@@ -476,8 +476,11 @@ trait UnusedDelimLint {
 
         lhs_needs_parens
             || (followed_by_block
-                && match inner.kind {
+                && match &inner.kind {
                     ExprKind::Ret(_) | ExprKind::Break(..) | ExprKind::Yield(..) => true,
+                    ExprKind::Range(_lhs, Some(rhs), _limits) => {
+                        matches!(rhs.kind, ExprKind::Block(..))
+                    }
                     _ => parser::contains_exterior_struct_lit(&inner),
                 })
     }

src/test/ui/lint/unused/issue-90807-unused-paren-error.rs

@@ -0,0 +1,9 @@
+// Make sure unused parens lint emit is emitted for loop and match.
+// See https://github.com/rust-lang/rust/issues/90807
+// and https://github.com/rust-lang/rust/pull/91956#discussion_r771647953
+#![deny(unused_parens)]
+
+fn main() {
+    for _ in (1..loop { break 2 }) {} //~ERROR
+    for _ in (1..match () { () => 2 }) {} //~ERROR
+}

src/test/ui/lint/unused/issue-90807-unused-paren-error.stderr

@@ -0,0 +1,31 @@
+error: unnecessary parentheses around `for` iterator expression
+  --> $DIR/issue-90807-unused-paren-error.rs:7:14
+   |
+LL |     for _ in (1..loop { break 2 }) {}
+   |              ^                   ^
+   |
+note: the lint level is defined here
+  --> $DIR/issue-90807-unused-paren-error.rs:4:9
+   |
+LL | #![deny(unused_parens)]
+   |         ^^^^^^^^^^^^^
+help: remove these parentheses
+   |
+LL -     for _ in (1..loop { break 2 }) {}
+LL +     for _ in 1..loop { break 2 } {}
+   | 
+
+error: unnecessary parentheses around `for` iterator expression
+  --> $DIR/issue-90807-unused-paren-error.rs:8:14
+   |
+LL |     for _ in (1..match () { () => 2 }) {}
+   |              ^                       ^
+   |
+help: remove these parentheses
+   |
+LL -     for _ in (1..match () { () => 2 }) {}
+LL +     for _ in 1..match () { () => 2 } {}
+   | 
+
+error: aborting due to 2 previous errors
+

src/test/ui/lint/unused/issue-90807-unused-paren.rs

@@ -0,0 +1,8 @@
+// check-pass
+// Make sure unused parens lint doesn't emit a false positive.
+// See https://github.com/rust-lang/rust/issues/90807
+#![deny(unused_parens)]
+
+fn main() {
+    for _ in (1..{ 2 }) {}
+}