From 0b2c9f03efc248680a8e7eeedb6e5f8da5947774 Mon Sep 17 00:00:00 2001
From: Owen Sanchez <pengowen816@gmail.com>
Date: Fri, 11 Aug 2017 13:43:33 -0700
Subject: [PATCH 1/2] Fix unused_result lint triggering when a function returns
 `()` or `!`

Add a test for this case
---
 src/librustc_lint/unused.rs |  2 ++
 src/test/ui/issue-43806.rs  | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 src/test/ui/issue-43806.rs

diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index ba17df4cdca4b..e5b818cd5fb5a 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -146,6 +146,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
 
         let t = cx.tables.expr_ty(&expr);
         let ty_warned = match t.sty {
+            ty::TyTuple(ref tys, _) if tys.is_empty() => return,
+            ty::TyNever => return,
             ty::TyAdt(def, _) => check_must_use(cx, def.did, s.span, ""),
             _ => false,
         };
diff --git a/src/test/ui/issue-43806.rs b/src/test/ui/issue-43806.rs
new file mode 100644
index 0000000000000..df7f756127c4d
--- /dev/null
+++ b/src/test/ui/issue-43806.rs
@@ -0,0 +1,26 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// run-pass
+
+#![deny(unused_results)]
+
+fn foo() {}
+
+fn bar() -> ! {
+    loop {}
+}
+
+fn qux() {
+    foo();
+    bar();
+}
+
+fn main() {}

From eeb748aa12a3bb7f6bbd1205385fa0a0adbef90c Mon Sep 17 00:00:00 2001
From: Owen Sanchez <pengowen816@gmail.com>
Date: Fri, 11 Aug 2017 21:52:16 -0700
Subject: [PATCH 2/2] Don't trigger unused_result on functions returning empty
 enums

---
 src/librustc_lint/unused.rs | 8 +++++++-
 src/test/ui/issue-43806.rs  | 7 +++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index e5b818cd5fb5a..7773891b5d066 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -148,7 +148,13 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
         let ty_warned = match t.sty {
             ty::TyTuple(ref tys, _) if tys.is_empty() => return,
             ty::TyNever => return,
-            ty::TyAdt(def, _) => check_must_use(cx, def.did, s.span, ""),
+            ty::TyAdt(def, _) => {
+                if def.variants.is_empty() {
+                    return;
+                } else {
+                    check_must_use(cx, def.did, s.span, "")
+                }
+            },
             _ => false,
         };
 
diff --git a/src/test/ui/issue-43806.rs b/src/test/ui/issue-43806.rs
index df7f756127c4d..7757a503c7e87 100644
--- a/src/test/ui/issue-43806.rs
+++ b/src/test/ui/issue-43806.rs
@@ -12,15 +12,22 @@
 
 #![deny(unused_results)]
 
+enum Void {}
+
 fn foo() {}
 
 fn bar() -> ! {
     loop {}
 }
 
+fn baz() -> Void {
+    loop {}
+}
+
 fn qux() {
     foo();
     bar();
+    baz();
 }
 
 fn main() {}