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]: https://github.com/rust-lang/rfcs/pull/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/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 \

src/libcore/str/pattern.rs

@@ -16,7 +16,8 @@
 #![unstable(feature = "pattern",
             reason = "API not fully fleshed out and ready to be stabilized")]
 
-use prelude::*;
+use prelude::v1::*;
+
 use cmp;
 use usize;
 

src/liblibc/lib.rs

@@ -14,7 +14,8 @@
 #![crate_type = "rlib"]
 #![cfg_attr(not(feature = "cargo-build"), unstable(feature = "libc",
                                                    reason = "use `libc` from crates.io"))]
-#![cfg_attr(not(feature = "cargo-build"), feature(staged_api, core, no_std))]
+#![cfg_attr(not(feature = "cargo-build"), feature(staged_api, no_std))]
+#![cfg_attr(all(not(feature = "cargo-build"), stage0), feature(core))]
 #![cfg_attr(not(feature = "cargo-build"), staged_api)]
 #![cfg_attr(not(feature = "cargo-build"), no_std)]
 #![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -78,7 +79,7 @@
 #![allow(bad_style, raw_pointer_derive)]
 #![cfg_attr(target_os = "nacl", allow(unused_imports))]
 #[cfg(feature = "cargo-build")] extern crate std as core;
-#[cfg(not(feature = "cargo-build"))] extern crate core;
+#[cfg(all(stage0, not(feature = "cargo-build")))] extern crate core;
 
 #[cfg(test)] extern crate std;
 #[cfg(test)] extern crate test;

src/librand/chacha.rs

@@ -10,7 +10,9 @@
 
 //! The ChaCha random number generator.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
+
 use {Rng, SeedableRng, Rand};
 
 const KEY_WORDS    : usize =  8; // 8 words for the 256-bit key

src/librand/distributions/mod.rs

@@ -17,7 +17,9 @@
 //! internally. The `IndependentSample` trait is for generating values
 //! that do not need to record state.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
+
 use core::num::Float;
 use core::marker::PhantomData;
 

src/librand/distributions/range.rs

@@ -12,7 +12,8 @@
 
 // this is surprisingly complicated to be both generic & correct
 
-use core::prelude::PartialOrd;
+#[cfg(stage0)]
+use core::prelude::v1::PartialOrd;
 
 use Rng;
 use distributions::{Sample, IndependentSample};

src/librand/isaac.rs

@@ -12,7 +12,9 @@
 
 #![allow(non_camel_case_types)]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
+
 use core::slice;
 use core::iter::repeat;
 use core::num::Wrapping as w;

src/librand/lib.rs

@@ -28,26 +28,26 @@
 #![staged_api]
 #![unstable(feature = "rand",
             reason = "use `rand` from crates.io")]
-#![feature(core)]
 #![feature(core_float)]
-#![feature(core_prelude)]
 #![feature(core_slice_ext)]
 #![feature(no_std)]
 #![feature(num_bits_bytes)]
 #![feature(staged_api)]
 #![feature(step_by)]
+#![cfg_attr(stage0, feature(core, core_prelude))]
 
 #![cfg_attr(test, feature(test, rand, rustc_private, iter_order))]
 
 #![allow(deprecated)]
 
-#[macro_use]
-extern crate core;
+#[cfg(stage0)] #[macro_use] extern crate core;
 
 #[cfg(test)] #[macro_use] extern crate std;
 #[cfg(test)] #[macro_use] extern crate log;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
+
 use core::marker::PhantomData;
 
 pub use isaac::{IsaacRng, Isaac64Rng};

src/librand/rand_impls.rs

@@ -10,7 +10,9 @@
 
 //! The implementations of `Rand` for the built-in types.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
+
 use core::char;
 use core::isize;
 use core::usize;

src/librand/reseeding.rs

@@ -11,7 +11,8 @@
 //! A wrapper around another RNG that reseeds it after it
 //! generates a certain number of random bytes.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use {Rng, SeedableRng};
 

src/librustc_bitflags/lib.rs

@@ -290,13 +290,6 @@ macro_rules! bitflags {
     };
 }
 
-// This is a no_std crate. So the test code's invocation of #[derive] etc, via
-// bitflags!, will use names from the underlying crates.
-#[cfg(test)]
-mod core {
-    pub use std::{fmt, hash, clone, cmp, marker, option};
-}
-
 #[cfg(test)]
 #[allow(non_upper_case_globals)]
 mod tests {

src/librustc_driver/test.rs

@@ -46,7 +46,7 @@ struct RH<'a> {
     sub: &'a [RH<'a>]
 }
 
-const EMPTY_SOURCE_STR: &'static str = "#![feature(no_std)] #![no_std]";
+const EMPTY_SOURCE_STR: &'static str = "#![feature(no_core)] #![no_core]";
 
 struct ExpectErrorEmitter {
     messages: Vec<String>

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;

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;

src/libstd/ffi/os_str.rs

@@ -32,7 +32,8 @@
 #![unstable(feature = "os_str",
             reason = "recently added as part of path/io reform")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use borrow::{Borrow, Cow, ToOwned};
 use ffi::CString;

src/libstd/fs.rs

@@ -17,7 +17,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use fmt;
 use ffi::OsString;

src/libstd/io/cursor.rs

@@ -292,7 +292,8 @@ impl Write for Cursor<Vec<u8>> {
 
 #[cfg(test)]
 mod tests {
-    use core::prelude::*;
+    #[cfg(stage0)]
+    use core::prelude::v1::*;
 
     use io::prelude::*;
     use io::{Cursor, SeekFrom};

src/libstd/io/impls.rs

@@ -8,7 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use boxed::Box;
 use cmp;

src/libstd/io/util.rs

@@ -10,6 +10,7 @@
 
 #![allow(missing_copy_implementations)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use io::{self, Read, Write, ErrorKind, BufRead};

src/libstd/lib.rs

@@ -213,7 +213,6 @@
 #![feature(core)]
 #![feature(core_float)]
 #![feature(core_intrinsics)]
-#![feature(core_prelude)]
 #![feature(core_simd)]
 #![feature(drain)]
 #![feature(fnbox)]
@@ -250,6 +249,7 @@
 #![cfg_attr(test, feature(float_from_str_radix, range_inclusive, float_extras, hash_default))]
 #![cfg_attr(test, feature(test, rustc_private, float_consts))]
 #![cfg_attr(target_env = "msvc", feature(link_args))]
+#![cfg_attr(stage0, feature(core, core_prelude))]
 
 // Don't link to std. We are std.
 #![no_std]
@@ -257,13 +257,17 @@
 #![allow(trivial_casts)]
 #![deny(missing_docs)]
 
+#[cfg(stage0)] #[macro_use] extern crate core;
+
 #[cfg(test)] extern crate test;
 #[cfg(test)] #[macro_use] extern crate log;
 
-#[macro_use]
+// We want to reexport a few macros from core but libcore has already been
+// imported by the compiler (via our #[no_std] attribute) In this case we just
+// add a new crate name so we can attach the reexports to it.
 #[macro_reexport(assert, assert_eq, debug_assert, debug_assert_eq,
     unreachable, unimplemented, write, writeln)]
-extern crate core;
+extern crate core as __core;
 
 #[macro_use]
 #[macro_reexport(vec, format)]
@@ -410,11 +414,3 @@ pub mod __rand {
 // the rustdoc documentation for primitive types. Using `include!`
 // because rustdoc only looks for these modules at the crate level.
 include!("primitive_docs.rs");
-
-// The expansion of --test has a few references to `::std::$foo` so this module
-// is necessary to get things to compile.
-#[cfg(test)]
-mod std {
-    pub use option;
-    pub use realstd::env;
-}

src/libstd/net/udp.rs

@@ -11,6 +11,7 @@
 #![unstable(feature = "udp", reason = "remaining functions have not been \
                                        scrutinized enough to be stabilized")]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use fmt;

src/libstd/num/f32.rs

@@ -15,6 +15,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 #![allow(missing_docs)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use core::num;

src/libstd/num/f64.rs

@@ -15,6 +15,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 #![allow(missing_docs)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use core::num;

src/libstd/num/mod.rs

@@ -43,7 +43,8 @@ pub fn test_num<T>(ten: T, two: T) where
 
 #[cfg(test)]
 mod tests {
-    use core::prelude::*;
+    #[cfg(stage0)]
+    use core::prelude::v1::*;
     use super::*;
     use i8;
     use i16;

src/libstd/path.rs

@@ -98,7 +98,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use ascii::*;
 use borrow::{Borrow, IntoCow, ToOwned, Cow};
@@ -134,7 +135,8 @@ use self::platform::{is_sep_byte, is_verbatim_sep, MAIN_SEP_STR, parse_prefix};
 #[cfg(unix)]
 mod platform {
     use super::Prefix;
-    use core::prelude::*;
+    #[cfg(stage0)]
+    use core::prelude::v1::*;
     use ffi::OsStr;
 
     #[inline]
@@ -157,7 +159,8 @@ mod platform {
 
 #[cfg(windows)]
 mod platform {
-    use core::prelude::*;
+    #[cfg(stage0)]
+    use core::prelude::v1::*;
     use ascii::*;
 
     use super::{os_str_as_u8_slice, u8_slice_as_os_str, Prefix};
@@ -1747,7 +1750,8 @@ impl AsRef<Path> for PathBuf {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use core::prelude::*;
+    #[cfg(stage0)]
+    use core::prelude::v1::*;
     use string::{ToString, String};
     use vec::Vec;
 

src/libstd/process.rs

@@ -815,7 +815,7 @@ mod tests {
     #[cfg(target_os="android")]
     #[test]
     fn test_inherit_env() {
-        use std::env;
+        use env;
 
         let mut result = env_cmd().output().unwrap();
         let output = String::from_utf8(result.stdout).unwrap();

src/libstd/rand/mod.rs

@@ -57,6 +57,7 @@
 
 #![unstable(feature = "rand")]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use cell::RefCell;

src/libstd/rand/os.rs

@@ -15,7 +15,7 @@ pub use self::imp::OsRng;
 
 #[cfg(all(unix, not(target_os = "ios")))]
 mod imp {
-    use prelude::v1::*;
+    #[cfg(stage0)] use prelude::v1::*;
     use self::OsRngInner::*;
 
     use fs::File;
@@ -251,6 +251,7 @@ mod imp {
 
 #[cfg(windows)]
 mod imp {
+    #[cfg(stage0)]
     use prelude::v1::*;
 
     use io;

src/libstd/rand/reader.rs

@@ -12,7 +12,7 @@
 
 #![allow(dead_code)]
 
-use prelude::v1::*;
+#[cfg(stage0)] use prelude::v1::*;
 use io::prelude::*;
 use rand::Rng;
 

src/libstd/rt/args.rs

@@ -19,7 +19,8 @@
 //!
 //! FIXME #7756: Would be nice for this to not exist.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 use vec::Vec;
 
 /// One-time global initialization.
@@ -140,7 +141,8 @@ mod imp {
           target_os = "ios",
           target_os = "windows"))]
 mod imp {
-    use core::prelude::*;
+    #[cfg(stage0)]
+    use core::prelude::v1::*;
     use vec::Vec;
 
     pub unsafe fn init(_argc: isize, _argv: *const *const u8) {

src/libstd/rt/backtrace.rs

@@ -12,6 +12,7 @@
 
 #![allow(non_camel_case_types)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use env;

src/libstd/sync/future.rs

@@ -39,7 +39,8 @@
                         outside in crates.io first")]
 #![allow(deprecated)]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 use core::mem::replace;
 
 use boxed::Box;

src/libstd/sync/mpsc/mod.rs

@@ -265,6 +265,7 @@
 // And now that you've seen all the races that I found and attempted to fix,
 // here's the code for you to find some more!
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use sync::Arc;

src/libstd/sync/mpsc/mpsc_queue.rs

@@ -40,7 +40,8 @@
 
 pub use self::PopResult::*;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use alloc::boxed::Box;
 use core::ptr;

src/libstd/sync/mpsc/oneshot.rs

@@ -37,7 +37,8 @@ pub use self::UpgradeResult::*;
 pub use self::SelectionResult::*;
 use self::MyUpgrade::*;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use sync::mpsc::Receiver;
 use sync::mpsc::blocking::{self, SignalToken};

src/libstd/sync/mpsc/select.rs

@@ -57,7 +57,8 @@
                       but no guarantees beyond this are being made")]
 
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cell::{Cell, UnsafeCell};
 use core::marker;

src/libstd/sync/mpsc/shared.rs

@@ -20,7 +20,8 @@
 
 pub use self::Failure::*;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cmp;
 use core::isize;

src/libstd/sync/mpsc/spsc_queue.rs

@@ -33,7 +33,8 @@
 //! concurrently between two threads. This data structure is safe to use and
 //! enforces the semantics that there is one pusher and one popper.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use alloc::boxed::Box;
 use core::ptr;

src/libstd/sync/mpsc/stream.rs

@@ -22,7 +22,8 @@ pub use self::UpgradeResult::*;
 pub use self::SelectionResult::*;
 use self::Message::*;
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::cmp;
 use core::isize;

src/libstd/sync/mpsc/sync.rs

@@ -33,7 +33,8 @@
 /// of a synchronous channel. There are a few branches for the unbuffered case,
 /// but they're mostly just relevant to blocking senders.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 pub use self::Failure::*;
 use self::Blocker::*;

src/libstd/sync/once.rs

@@ -13,6 +13,7 @@
 //! This primitive is meant to be used to run one-time initialization. An
 //! example use case would be for initializing an FFI library.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use isize;

src/libstd/sys/common/backtrace.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 use io::prelude::*;
 

src/libstd/sys/common/mod.rs

@@ -10,6 +10,7 @@
 
 #![allow(missing_docs)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 pub mod backtrace;

src/libstd/sys/common/poison.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use cell::Cell;

src/libstd/sys/common/thread_info.rs

@@ -10,7 +10,8 @@
 
 #![allow(dead_code)] // stack_guard isn't used right now on all platforms
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use cell::RefCell;
 use string::String;

src/libstd/sys/common/thread_local.rs

@@ -58,6 +58,7 @@
 #![unstable(feature = "thread_local_internals")]
 #![allow(dead_code)] // sys isn't exported yet
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use sync::atomic::{self, AtomicUsize, Ordering};

src/libstd/sys/common/wtf8.rs

@@ -25,7 +25,8 @@
 // unix (it's mostly used on windows), so don't worry about dead code here.
 #![allow(dead_code)]
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use core::char::{encode_utf8_raw, encode_utf16_raw};
 use core::str::next_code_point;

src/libstd/sys/unix/backtrace.rs

@@ -83,6 +83,7 @@
 /// to symbols. This is a bit of a hokey implementation as-is, but it works for
 /// all unix platforms we support right now, so it at least gets the job done.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 use io::prelude::*;
 

src/libstd/sys/unix/condvar.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use cell::UnsafeCell;

src/libstd/sys/unix/ext/fs.rs

@@ -12,6 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use fs::{self, Permissions, OpenOptions};

src/libstd/sys/unix/ext/process.rs

@@ -14,6 +14,7 @@
 
 use os::unix::raw::{uid_t, gid_t};
 use os::unix::io::{FromRawFd, RawFd, AsRawFd, IntoRawFd};
+#[cfg(stage0)]
 use prelude::v1::*;
 use process;
 use sys;

src/libstd/sys/unix/fd.rs

@@ -8,7 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use io;
 use libc::{self, c_int, size_t, c_void};

src/libstd/sys/unix/fs.rs

@@ -8,7 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 use io::prelude::*;
 use os::unix::prelude::*;
 

src/libstd/sys/unix/mod.rs

@@ -11,6 +11,7 @@
 #![allow(missing_docs)]
 #![allow(non_camel_case_types)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use io::{self, ErrorKind};

src/libstd/sys/unix/mutex.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use cell::UnsafeCell;

src/libstd/sys/unix/os_str.rs

@@ -11,7 +11,8 @@
 /// The underlying OsString/OsStr implementation on Unix systems: just
 /// a `Vec<u8>`/`[u8]`.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 
 use borrow::Cow;
 use fmt::{self, Debug};

src/libstd/sys/unix/pipe.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use sys::fd::FileDesc;

src/libstd/sys/unix/rwlock.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use libc;

src/libstd/sys/unix/stack_overflow.rs

@@ -8,8 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
+use core::prelude::v1::*;
+
 use libc;
-use core::prelude::*;
 use self::imp::{make_handler, drop_handler};
 
 pub use self::imp::{init, cleanup};

src/libstd/sys/unix/stdio.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use io;

src/libstd/sys/unix/thread.rs

@@ -166,6 +166,7 @@ impl Drop for Thread {
           not(target_os = "netbsd"),
           not(target_os = "openbsd")))]
 pub mod guard {
+    #[cfg(stage0)]
     use prelude::v1::*;
 
     pub unsafe fn current() -> Option<usize> { None }

src/libstd/sys/unix/thread_local.rs

@@ -10,6 +10,7 @@
 
 #![allow(dead_code)] // sys isn't exported yet
 
+#[cfg(stage0)]
 use prelude::v1::*;
 use libc::c_int;
 

src/libstd/sys/windows/backtrace.rs

@@ -24,6 +24,7 @@
 
 #![allow(dead_code)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 use io::prelude::*;
 

src/libstd/sys/windows/condvar.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use cell::UnsafeCell;

src/libstd/sys/windows/ext/fs.rs

@@ -12,6 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use fs::{OpenOptions, Metadata};

src/libstd/sys/windows/fs.rs

@@ -8,7 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::prelude::*;
+#[cfg(stage0)]
+use core::prelude::v1::*;
 use io::prelude::*;
 use os::windows::prelude::*;
 

src/libstd/sys/windows/handle.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use io::ErrorKind;

src/libstd/sys/windows/net.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use io;

src/libstd/sys/windows/pipe.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use io;

src/libstd/sys/windows/rwlock.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use cell::UnsafeCell;