Allow leading :: in use items

Author: Keegan McAllister

src/libsyntax/parse/parser.rs

@@ -5973,6 +5973,10 @@ impl<'a> Parser<'a> {
     fn parse_view_path(&mut self) -> P<ViewPath> {
         let lo = self.span.lo;
 
+        // Allow a leading :: because the paths are absolute either way.
+        // This occurs with "use $crate::..." in macros.
+        self.eat(&token::ModSep);
+
         if self.check(&token::OpenDelim(token::Brace)) {
             // use {foo,bar}
             let idents = self.parse_unspanned_seq(

src/test/run-pass/crate-leading-sep.rs

@@ -0,0 +1,14 @@
+// Copyright 2014 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() {
+    use ::std::mem;
+    mem::drop(2u);
+}

src/test/run-pass/macro-crate-use.rs

@@ -0,0 +1,27 @@
+// Copyright 2014 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.
+
+#![feature(macro_rules)]
+
+pub fn increment(x: uint) -> uint {
+    x + 1
+}
+
+#[macro_export]
+macro_rules! increment {
+    ($x:expr) => ({
+        use $crate::increment;
+        increment($x)
+    })
+}
+
+fn main() {
+    assert_eq!(increment!(3), 4);
+}