Auto merge of #27393 - alexcrichton:no-std-changes, r=brson

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

Closes #27394

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};

src/libcollections/lib.rs

@@ -33,9 +33,7 @@
 #![feature(alloc)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(core)]
 #![feature(core_intrinsics)]
-#![feature(core_prelude)]
 #![feature(core_slice_ext)]
 #![feature(core_str_ext)]
 #![feature(heap_api)]
@@ -62,12 +60,12 @@
 #![feature(utf8_error)]
 #![cfg_attr(test, feature(rand, test))]
 #![cfg_attr(not(test), feature(str_words))]
+#![cfg_attr(stage0, feature(core, core_prelude))]
 
 #![feature(no_std)]
 #![no_std]
 
-#[macro_use]
-extern crate core;
+#[cfg(stage0)] #[macro_use] extern crate core;
 
 extern crate rustc_unicode;
 extern crate alloc;

src/libcollections/linked_list.rs

@@ -21,7 +21,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use alloc::boxed::Box;
 use core::cmp::Ordering;

src/libcollections/string.rs

@@ -12,7 +12,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::fmt;
 use core::hash;

src/libcollections/vec.rs

@@ -58,7 +58,9 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
+
 use alloc::raw_vec::RawVec;
 use alloc::boxed::Box;
 use alloc::heap::EMPTY;

src/libcollections/vec_deque.rs

@@ -18,7 +18,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cmp::Ordering;
 use core::fmt;

src/libcollections/vec_map.rs

@@ -20,7 +20,8 @@
 
 use self::Entry::*;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cmp::{max, Ordering};
 use core::fmt;

src/libcore/fmt/builders.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use prelude::*;
+use prelude::v1::*;
 use fmt::{self, Write, FlagV1};
 
 struct PadAdapter<'a, 'b: 'a> {

src/libcore/fmt/mod.rs

@@ -12,7 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use prelude::*;
+use prelude::v1::*;
 
 use cell::{Cell, RefCell, Ref, RefMut, BorrowState};
 use marker::PhantomData;

src/libcore/fmt/num.rs

@@ -12,7 +12,7 @@
 
 // FIXME: #6220 Implement floating point formatting
 
-use prelude::*;
+use prelude::v1::*;
 
 use fmt;
 use num::Zero;

src/libcore/hash/mod.rs

@@ -62,7 +62,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use prelude::*;
+use prelude::v1::*;
 
 use mem;
 
@@ -183,7 +183,7 @@ pub fn hash<T: Hash, H: Hasher + Default>(value: &T) -> u64 {
 //////////////////////////////////////////////////////////////////////////////
 
 mod impls {
-    use prelude::*;
+    use prelude::v1::*;
 
     use slice;
     use super::*;

src/libcore/hash/sip.rs

@@ -10,8 +10,9 @@
 
 //! An implementation of SipHash 2-4.
 
+use prelude::v1::*;
+
 use ptr;
-use prelude::*;
 use super::Hasher;
 
 /// An implementation of SipHash 2-4.

src/libcore/lib.rs

@@ -60,8 +60,10 @@
        html_playground_url = "http://play.rust-lang.org/")]
 #![doc(test(no_crate_inject))]
 
-#![feature(no_std)]
-#![no_std]
+#![cfg_attr(stage0, feature(no_std))]
+#![cfg_attr(stage0, no_std)]
+#![cfg_attr(not(stage0), feature(no_core))]
+#![cfg_attr(not(stage0), no_core)]
 #![allow(raw_pointer_derive)]
 #![deny(missing_docs)]
 
@@ -168,6 +170,7 @@ mod tuple;
 // compiling the core library when it's compiling this library, so it expands
 // all references to `::core::$foo`
 #[doc(hidden)]
+#[cfg(stage0)]
 mod core {
     pub use intrinsics;     // derive(PartialOrd)
     pub use fmt;            // format_args!

src/libcore/num/f32.rs

@@ -15,7 +15,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use prelude::*;
+use prelude::v1::*;
 
 use intrinsics;
 use mem;

src/libcore/num/f64.rs

@@ -15,7 +15,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use prelude::*;
+use prelude::v1::*;
 
 use intrinsics;
 use mem;

src/libcore/num/flt2dec/bignum.rs

@@ -21,7 +21,8 @@
 
 #![macro_use]
 
-use prelude::*;
+use prelude::v1::*;
+
 use mem;
 use intrinsics;
 
@@ -351,7 +352,7 @@ define_bignum!(Big32x36: type=Digit32, n=36);
 // this one is used for testing only.
 #[doc(hidden)]
 pub mod tests {
-    use prelude::*;
+    use prelude::v1::*;
     define_bignum!(Big8x3: type=u8, n=3);
 }
 

src/libcore/num/flt2dec/decoder.rs

@@ -10,7 +10,7 @@
 
 //! Decodes a floating-point value into individual parts and error ranges.
 
-use prelude::*;
+use prelude::v1::*;
 
 use {f32, f64};
 use num::{Float, FpCategory};

src/libcore/num/flt2dec/mod.rs

@@ -129,7 +129,7 @@ functions.
 #![unstable(feature = "flt2dec",
             reason = "internal routines only exposed for testing")]
 
-use prelude::*;
+use prelude::v1::*;
 use i16;
 use num::Float;
 use slice::bytes;

src/libcore/num/flt2dec/strategy/dragon.rs

@@ -15,7 +15,8 @@ Almost direct (but slightly optimized) Rust translation of Figure 3 of [1].
     quickly and accurately. SIGPLAN Not. 31, 5 (May. 1996), 108-116.
 */
 
-use prelude::*;
+use prelude::v1::*;
+
 use num::Float;
 use cmp::Ordering;
 

src/libcore/num/flt2dec/strategy/grisu.rs

@@ -16,7 +16,8 @@ Rust adaptation of Grisu3 algorithm described in [1]. It uses about
     accurately with integers. SIGPLAN Not. 45, 6 (June 2010), 233-243.
 */
 
-use prelude::*;
+use prelude::v1::*;
+
 use num::Float;
 
 use num::flt2dec::{Decoded, MAX_SIG_DIGITS, round_up};

src/libcore/prelude/mod.rs

@@ -0,0 +1,13 @@
+// Copyright 2015 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.
+
+//! The libcore prelude
+
+pub mod v1;

src/libcore/prelude.rs → src/libcore/prelude/v1.rs

@@ -11,18 +11,8 @@
 //! The core prelude
 //!
 //! This module is intended for users of libcore which do not link to libstd as
-//! well. This module is not imported by default, but using the entire contents
-//! of this module will provide all of the useful traits and types in libcore
-//! that one would expect from the standard library as well.
-//!
-//! There is no method to automatically inject this prelude, and this prelude is
-//! a subset of the standard library's prelude.
-//!
-//! # Example
-//!
-//! ```ignore
-//! use core::prelude::*;
-//! ```
+//! well. This module is imported by default when `#![no_std]` is used in the
+//! same manner as the standard library's prelude.
 
 #![unstable(feature = "core_prelude",
             reason = "the libcore prelude has not been scrutinized and \