syntax: Implement #![no_core]

This commit is an implementation of [RFC 1184][rfc] which tweaks the behavior of
the `#![no_std]` attribute and adds a new `#![no_core]` attribute. The
`#![no_std]` attribute now injects `extern crate core` at the top of the crate
as well as the libcore prelude into all modules (in the same manner as the
standard library's prelude). The `#![no_core]` attribute disables both std and
core injection.

[rfc]: https://github.com/rust-lang/rfcs/pull/1184

2 files changed, 4 insertions, 4 deletions

diff --git a/src/librustc_unicode/lib.rs b/src/librustc_unicode/lib.rs
index b420444d1f5..3a69430d078 100644
--- a/src/librustc_unicode/lib.rs
+++ b/src/librustc_unicode/lib.rs
@@ -33,17 +33,16 @@
        test(no_crate_inject))]
 #![no_std]
 
-#![feature(core)]
 #![feature(core_char_ext)]
-#![feature(core_prelude)]
 #![feature(core_slice_ext)]
 #![feature(core_str_ext)]
 #![feature(iter_arith)]
 #![feature(lang_items)]
 #![feature(no_std)]
 #![feature(staged_api)]
+#![cfg_attr(stage0, feature(core, core_prelude))]
 
-extern crate core;
+#[cfg(stage0)] extern crate core;
 
 mod normalize;
 mod tables;
diff --git a/src/librustc_unicode/u_str.rs b/src/librustc_unicode/u_str.rs
index e329785d271..95214fe2db3 100644
--- a/src/librustc_unicode/u_str.rs
+++ b/src/librustc_unicode/u_str.rs
@@ -14,7 +14,8 @@
 //! unicode parts of the CharExt trait.
 
 use self::GraphemeState::*;
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::char;
 use core::cmp;