From 6b7fcf720a714b07ab8dc5d21aac03ade62bbdcc Mon Sep 17 00:00:00 2001
From: Michael Howell <michael@notriddle.com>
Date: Tue, 14 Dec 2021 22:44:27 -0700
Subject: [PATCH 1/2] fix(rustc_lint): better detect when parens are necessary

Fixes #90807
---
 compiler/rustc_lint/src/unused.rs                   | 5 ++++-
 src/test/ui/lint/unused/issue-90807-unused-paren.rs | 8 ++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/lint/unused/issue-90807-unused-paren.rs

diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index da1edcf6fe3b4..23a5407950e12 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/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) => {
+                        !classify::expr_requires_semi_to_be_stmt(&rhs)
+                    }
                     _ => parser::contains_exterior_struct_lit(&inner),
                 })
     }
diff --git a/src/test/ui/lint/unused/issue-90807-unused-paren.rs b/src/test/ui/lint/unused/issue-90807-unused-paren.rs
new file mode 100644
index 0000000000000..4c0930f967d89
--- /dev/null
+++ b/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 }) {}
+}

From f4a0321c03884d2f7e71e9850c7524cabdb73c7c Mon Sep 17 00:00:00 2001
From: Michael Howell <michael@notriddle.com>
Date: Fri, 17 Dec 2021 14:12:31 -0700
Subject: [PATCH 2/2] fix(rustc_lint): mark the parens around `(1..loop {})` as
 unused

---
 compiler/rustc_lint/src/unused.rs             |  2 +-
 .../unused/issue-90807-unused-paren-error.rs  |  9 ++++++
 .../issue-90807-unused-paren-error.stderr     | 31 +++++++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/lint/unused/issue-90807-unused-paren-error.rs
 create mode 100644 src/test/ui/lint/unused/issue-90807-unused-paren-error.stderr

diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 23a5407950e12..f0ec930345ad5 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -479,7 +479,7 @@ trait UnusedDelimLint {
                 && match &inner.kind {
                     ExprKind::Ret(_) | ExprKind::Break(..) | ExprKind::Yield(..) => true,
                     ExprKind::Range(_lhs, Some(rhs), _limits) => {
-                        !classify::expr_requires_semi_to_be_stmt(&rhs)
+                        matches!(rhs.kind, ExprKind::Block(..))
                     }
                     _ => parser::contains_exterior_struct_lit(&inner),
                 })
diff --git a/src/test/ui/lint/unused/issue-90807-unused-paren-error.rs b/src/test/ui/lint/unused/issue-90807-unused-paren-error.rs
new file mode 100644
index 0000000000000..2fca2e262657e
--- /dev/null
+++ b/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
+}
diff --git a/src/test/ui/lint/unused/issue-90807-unused-paren-error.stderr b/src/test/ui/lint/unused/issue-90807-unused-paren-error.stderr
new file mode 100644
index 0000000000000..4e158e126ac1f
--- /dev/null
+++ b/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
+