Resolve absolute paths as extern under a feature flag

src/test/ui/feature-gate-extern_absolute_paths.rs

@@ -0,0 +1,15 @@
+// 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.
+
+use core::default; //~ ERROR unresolved import `core`
+
+fn main() {
+    let _: u8 = ::core::default::Default(); //~ ERROR failed to resolve
+}

src/test/ui/feature-gate-extern_absolute_paths.stderr

@@ -0,0 +1,14 @@
+error[E0432]: unresolved import `core`
+  --> $DIR/feature-gate-extern_absolute_paths.rs:11:5
+   |
+11 | use core::default; //~ ERROR unresolved import `core`
+   |     ^^^^ Maybe a missing `extern crate core;`?
+
+error[E0433]: failed to resolve. Maybe a missing `extern crate core;`?
+  --> $DIR/feature-gate-extern_absolute_paths.rs:14:19
+   |
+14 |     let _: u8 = ::core::default::Default(); //~ ERROR failed to resolve
+   |                   ^^^^ Maybe a missing `extern crate core;`?
+
+error: aborting due to 2 previous errors
+