From 3471bc8306e206ed7d5cc86b1eeadc9a8bb8bc76 Mon Sep 17 00:00:00 2001
From: mibac138 <5672750+mibac138@users.noreply.github.com>
Date: Tue, 5 May 2020 01:55:03 +0200
Subject: [PATCH 1/3] Fix unused_parens false positive when using binary
 operations

---
 src/librustc_lint/unused.rs                     | 16 ++++++++++++----
 .../ui/lint/issue-71290-unused-paren-binop.rs   | 17 +++++++++++++++++
 2 files changed, 29 insertions(+), 4 deletions(-)
 create mode 100644 src/test/ui/lint/issue-71290-unused-paren-binop.rs

diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index ddd252cb290e4..4f7a1f9c31091 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -380,11 +380,19 @@ trait UnusedDelimLint {
     );
 
     fn is_expr_delims_necessary(inner: &ast::Expr, followed_by_block: bool) -> bool {
-        followed_by_block
-            && match inner.kind {
-                ExprKind::Ret(_) | ExprKind::Break(..) => true,
-                _ => parser::contains_exterior_struct_lit(&inner),
+        // Prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`
+        let lhs_needs_parens = match &inner.kind {
+            ExprKind::Binary(_, lhs, _rhs) => {
+                !rustc_ast::util::classify::expr_requires_semi_to_be_stmt(&*lhs)
             }
+            _ => false,
+        };
+        lhs_needs_parens
+            || (followed_by_block
+                && match inner.kind {
+                    ExprKind::Ret(_) | ExprKind::Break(..) => true,
+                    _ => parser::contains_exterior_struct_lit(&inner),
+                })
     }
 
     fn emit_unused_delims_expr(
diff --git a/src/test/ui/lint/issue-71290-unused-paren-binop.rs b/src/test/ui/lint/issue-71290-unused-paren-binop.rs
new file mode 100644
index 0000000000000..619be02566f56
--- /dev/null
+++ b/src/test/ui/lint/issue-71290-unused-paren-binop.rs
@@ -0,0 +1,17 @@
+// check-pass
+// Make sure unused parens lint doesn't emit a false positive.
+// See https://github.com/rust-lang/rust/issues/71290 for details.
+
+fn x() -> u8 {
+    ({ 0 }) + 1
+}
+
+fn y() -> u8 {
+    ({ 0 } + 1)
+}
+
+pub fn foo(a: bool, b: bool) -> u8 {
+    (if a { 1 } else { 0 } + if b { 1 } else { 0 })
+}
+
+fn main() {}

From 717a7a8486a448d7c746db213d1d987593088692 Mon Sep 17 00:00:00 2001
From: Michael <5672750+mibac138@users.noreply.github.com>
Date: Tue, 5 May 2020 16:58:13 +0200
Subject: [PATCH 2/3] Update src/test/ui/lint/issue-71290-unused-paren-binop.rs

Co-authored-by: Bastian Kauschke <bastian_kauschke@hotmail.de>
---
 src/test/ui/lint/issue-71290-unused-paren-binop.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/test/ui/lint/issue-71290-unused-paren-binop.rs b/src/test/ui/lint/issue-71290-unused-paren-binop.rs
index 619be02566f56..f11d2d377378c 100644
--- a/src/test/ui/lint/issue-71290-unused-paren-binop.rs
+++ b/src/test/ui/lint/issue-71290-unused-paren-binop.rs
@@ -1,6 +1,7 @@
 // check-pass
 // Make sure unused parens lint doesn't emit a false positive.
 // See https://github.com/rust-lang/rust/issues/71290 for details.
+#![deny(unused_parens)]
 
 fn x() -> u8 {
     ({ 0 }) + 1

From 4b7a92838c98929a9f4c7a64583b5ea49ebb3a35 Mon Sep 17 00:00:00 2001
From: mibac138 <5672750+mibac138@users.noreply.github.com>
Date: Wed, 6 May 2020 01:50:55 +0200
Subject: [PATCH 3/3] Fix unused_parens nested binary op false positive

---
 src/librustc_lint/unused.rs                      | 16 ++++++++++++----
 .../ui/lint/issue-71290-unused-paren-binop.rs    |  5 +++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index 4f7a1f9c31091..c24079a6e4be2 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -381,12 +381,20 @@ trait UnusedDelimLint {
 
     fn is_expr_delims_necessary(inner: &ast::Expr, followed_by_block: bool) -> bool {
         // Prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`
-        let lhs_needs_parens = match &inner.kind {
-            ExprKind::Binary(_, lhs, _rhs) => {
-                !rustc_ast::util::classify::expr_requires_semi_to_be_stmt(&*lhs)
+        let lhs_needs_parens = {
+            let mut innermost = inner;
+            loop {
+                if let ExprKind::Binary(_, lhs, _rhs) = &innermost.kind {
+                    innermost = lhs;
+                    if !rustc_ast::util::classify::expr_requires_semi_to_be_stmt(innermost) {
+                        break true;
+                    }
+                } else {
+                    break false;
+                }
             }
-            _ => false,
         };
+
         lhs_needs_parens
             || (followed_by_block
                 && match inner.kind {
diff --git a/src/test/ui/lint/issue-71290-unused-paren-binop.rs b/src/test/ui/lint/issue-71290-unused-paren-binop.rs
index f11d2d377378c..24d77e36d94f5 100644
--- a/src/test/ui/lint/issue-71290-unused-paren-binop.rs
+++ b/src/test/ui/lint/issue-71290-unused-paren-binop.rs
@@ -15,4 +15,9 @@ pub fn foo(a: bool, b: bool) -> u8 {
     (if a { 1 } else { 0 } + if b { 1 } else { 0 })
 }
 
+pub fn bar() -> u8 {
+    // Make sure nested expressions are handled correctly as well
+    ({ 0 } + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9)
+}
+
 fn main() {}