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]: rust-lang/rfcs#1184

Author: alexcrichton

src/liballoc/arc.rs

@@ -71,7 +71,8 @@
 
 use boxed::Box;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::atomic;
 use core::atomic::Ordering::{Relaxed, Release, Acquire, SeqCst};

src/liballoc/boxed.rs

@@ -53,7 +53,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use heap;
 use raw_vec::RawVec;

src/liballoc/lib.rs

@@ -75,7 +75,6 @@
 #![feature(coerce_unsized)]
 #![feature(core)]
 #![feature(core_intrinsics)]
-#![feature(core_prelude)]
 #![feature(core_slice_ext)]
 #![feature(custom_attribute)]
 #![feature(fundamental)]
@@ -93,17 +92,17 @@
 #![feature(unsize)]
 #![feature(core_slice_ext)]
 #![feature(core_str_ext)]
+#![cfg_attr(stage0, feature(core, core_prelude))]
 
 #![cfg_attr(test, feature(test, alloc, rustc_private, box_raw))]
 #![cfg_attr(all(not(feature = "external_funcs"), not(feature = "external_crate")),
             feature(libc))]
 
-#[macro_use]
-extern crate core;
-
 #[cfg(all(not(feature = "external_funcs"), not(feature = "external_crate")))]
 extern crate libc;
 
+#[cfg(stage0)] #[macro_use] extern crate core;
+
 // Allow testing this library
 
 #[cfg(test)] #[macro_use] extern crate std;

src/liballoc/rc.rs

@@ -150,7 +150,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 #[cfg(not(test))]
 use boxed::Box;

src/libcollections/binary_heap.rs

@@ -151,7 +151,8 @@
 #![allow(missing_docs)]
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::iter::{FromIterator};
 use core::mem::swap;

src/libcollections/bit.rs

@@ -86,7 +86,8 @@
 //! println!("There are {} primes below {}", num_primes, max_prime);
 //! ```
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cmp::Ordering;
 use core::cmp;

src/libcollections/btree/map.rs

@@ -17,7 +17,8 @@
 
 use self::Entry::*;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cmp::Ordering;
 use core::fmt::Debug;
@@ -530,7 +531,8 @@ enum Continuation<A, B> {
 /// to nodes. By using this module much better safety guarantees can be made, and more search
 /// boilerplate gets cut out.
 mod stack {
-    use core::prelude::*;
+    #[cfg(stage0)]
+    use core::prelude::v1::*;
     use core::marker;
     use core::mem;
     use core::ops::{Deref, DerefMut};

src/libcollections/btree/node.rs

@@ -16,7 +16,8 @@ pub use self::SearchResult::*;
 pub use self::ForceResult::*;
 pub use self::TraversalItem::*;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cmp::Ordering::{Greater, Less, Equal};
 use core::intrinsics::arith_offset;

src/libcollections/btree/set.rs

@@ -11,7 +11,8 @@
 // This is pretty much entirely stolen from TreeSet, since BTreeMap has an identical interface
 // to TreeMap
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cmp::Ordering::{self, Less, Greater, Equal};
 use core::fmt::Debug;

src/libcollections/enum_set.rs

@@ -17,7 +17,9 @@
             reason = "matches collection reform specification, \
                       waiting for dust to settle")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
+
 use core::marker;
 use core::fmt;
 use core::iter::{FromIterator};