From 39867f3c9fea0e01b5b199d8c2b6b0889284cc85 Mon Sep 17 00:00:00 2001
From: aticu <15schnic@gmail.com>
Date: Wed, 14 Oct 2020 01:13:48 +0200
Subject: [PATCH] Fixed false positive for `unused_parens` lint

---
 compiler/rustc_lint/src/unused.rs               | 11 +++++++++--
 src/test/ui/lint/lint-unnecessary-parens.fixed  |  2 ++
 src/test/ui/lint/lint-unnecessary-parens.rs     |  2 ++
 src/test/ui/lint/lint-unnecessary-parens.stderr |  8 ++++----
 4 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 3abd9a6325d6e..51ec599493399 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -751,13 +751,20 @@ impl UnusedDelimLint for UnusedParens {
                 if !Self::is_expr_delims_necessary(inner, followed_by_block)
                     && value.attrs.is_empty()
                     && !value.span.from_expansion()
+                    && (ctx != UnusedDelimsCtx::LetScrutineeExpr
+                        || match inner.kind {
+                            ast::ExprKind::Binary(
+                                rustc_span::source_map::Spanned { node, .. },
+                                _,
+                                _,
+                            ) if node.lazy() => false,
+                            _ => true,
+                        })
                 {
                     self.emit_unused_delims_expr(cx, value, ctx, left_pos, right_pos)
                 }
             }
             ast::ExprKind::Let(_, ref expr) => {
-                // FIXME(#60336): Properly handle `let true = (false && true)`
-                // actually needing the parenthesis.
                 self.check_unused_delims_expr(
                     cx,
                     expr,
diff --git a/src/test/ui/lint/lint-unnecessary-parens.fixed b/src/test/ui/lint/lint-unnecessary-parens.fixed
index c9dec395580f1..9c144324f2f7e 100644
--- a/src/test/ui/lint/lint-unnecessary-parens.fixed
+++ b/src/test/ui/lint/lint-unnecessary-parens.fixed
@@ -60,6 +60,8 @@ fn main() {
     if (v == X { y: true }) {}
     if (X { y: true } == v) {}
     if (X { y: false }.y) {}
+    // this shouldn't warn, because the parens are necessary to disambiguate let chains
+    if let true = (true && false) {}
 
     while (X { y: false }.foo(true)) {}
     while (true | X { y: false }.y) {}
diff --git a/src/test/ui/lint/lint-unnecessary-parens.rs b/src/test/ui/lint/lint-unnecessary-parens.rs
index 884bb4d2e99b6..4fd9cabb3b0b2 100644
--- a/src/test/ui/lint/lint-unnecessary-parens.rs
+++ b/src/test/ui/lint/lint-unnecessary-parens.rs
@@ -60,6 +60,8 @@ fn main() {
     if (v == X { y: true }) {}
     if (X { y: true } == v) {}
     if (X { y: false }.y) {}
+    // this shouldn't warn, because the parens are necessary to disambiguate let chains
+    if let true = (true && false) {}
 
     while (X { y: false }.foo(true)) {}
     while (true | X { y: false }.y) {}
diff --git a/src/test/ui/lint/lint-unnecessary-parens.stderr b/src/test/ui/lint/lint-unnecessary-parens.stderr
index 1abf47c8af521..9eae7da90047e 100644
--- a/src/test/ui/lint/lint-unnecessary-parens.stderr
+++ b/src/test/ui/lint/lint-unnecessary-parens.stderr
@@ -83,25 +83,25 @@ LL |     while let 1 = (2) {}
    |                   ^^^ help: remove these parentheses
 
 error: unnecessary parentheses around method argument
-  --> $DIR/lint-unnecessary-parens.rs:71:24
+  --> $DIR/lint-unnecessary-parens.rs:73:24
    |
 LL |     X { y: false }.foo((true));
    |                        ^^^^^^ help: remove these parentheses
 
 error: unnecessary parentheses around assigned value
-  --> $DIR/lint-unnecessary-parens.rs:73:18
+  --> $DIR/lint-unnecessary-parens.rs:75:18
    |
 LL |     let mut _a = (0);
    |                  ^^^ help: remove these parentheses
 
 error: unnecessary parentheses around assigned value
-  --> $DIR/lint-unnecessary-parens.rs:74:10
+  --> $DIR/lint-unnecessary-parens.rs:76:10
    |
 LL |     _a = (0);
    |          ^^^ help: remove these parentheses
 
 error: unnecessary parentheses around assigned value
-  --> $DIR/lint-unnecessary-parens.rs:75:11
+  --> $DIR/lint-unnecessary-parens.rs:77:11
    |
 LL |     _a += (1);
    |           ^^^ help: remove these parentheses