add warnings for unused lifetime parameters

src/test/ui/single-use-lifetime/zero-uses-in-fn.rs

@@ -0,0 +1,19 @@
+// Copyright 2016 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.
+
+// Test that we DO warn when lifetime name is not used at all.
+
+#![deny(unused_lifetime)]
+#![allow(dead_code)]
+#![allow(unused_variables)]
+
+fn d<'a>() { } //~ ERROR `'a` never used
+
+fn main() { }

src/test/ui/single-use-lifetime/zero-uses-in-fn.stderr

@@ -0,0 +1,14 @@
+error: lifetime parameter `'a` never used
+  --> $DIR/zero-uses-in-fn.rs:17:6
+   |
+LL | fn d<'a>() { } //~ ERROR `'a` never used
+   |      ^^
+   |
+note: lint level defined here
+  --> $DIR/zero-uses-in-fn.rs:13:9
+   |
+LL | #![deny(unused_lifetime)]
+   |         ^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/single-use-lifetime/zero-uses-in-impl.rs

@@ -0,0 +1,21 @@
+// Copyright 2016 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.
+
+// Test that we DO warn when lifetime name is not used at all.
+
+#![deny(unused_lifetime)]
+#![allow(dead_code)]
+#![allow(unused_variables)]
+
+struct Foo { }
+
+impl<'a> Foo { } //~ ERROR `'a` never used
+
+fn main() { }

src/test/ui/single-use-lifetime/zero-uses-in-impl.stderr

@@ -0,0 +1,14 @@
+error: lifetime parameter `'a` never used
+  --> $DIR/zero-uses-in-impl.rs:19:6
+   |
+LL | impl<'a> Foo { } //~ ERROR `'a` never used
+   |      ^^
+   |
+note: lint level defined here
+  --> $DIR/zero-uses-in-impl.rs:13:9
+   |
+LL | #![deny(unused_lifetime)]
+   |         ^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+