Add an AST sanity checking pass and use it to catch some illegal lifetime/label names

src/test/compile-fail/label-static.rs

@@ -0,0 +1,15 @@
+// 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.
+
+fn main() {
+    'static: loop { //~ ERROR invalid label name `'static`
+        break 'static //~ ERROR invalid label name `'static`
+    }
+}

src/test/compile-fail/lifetime-underscore.rs

@@ -0,0 +1,27 @@
+// 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.
+
+#![deny(lifetime_underscore)]
+
+fn _f<'_>() //~ ERROR invalid lifetime name `'_`
+//~^ WARN this was previously accepted
+    -> &'_ u8 //~ ERROR invalid lifetime name `'_`
+    //~^ WARN this was previously accepted
+{
+    panic!();
+}
+
+fn main() {
+    '_: loop { //~ ERROR invalid label name `'_`
+    //~^ WARN this was previously accepted
+        break '_ //~ ERROR invalid label name `'_`
+        //~^ WARN this was previously accepted
+    }
+}