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

59 files changed, 101 insertions, 32 deletions

diff --git a/src/libstd/ffi/os_str.rs b/src/libstd/ffi/os_str.rs
index 97bf33335b0..47b8230e430 100644
--- a/src/libstd/ffi/os_str.rs
+++ b/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;
diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs
index a879c2ebd73..62490bb9d08 100644
--- a/src/libstd/fs.rs
+++ b/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;
diff --git a/src/libstd/io/cursor.rs b/src/libstd/io/cursor.rs
index 980ec51c926..8033d77ff6a 100644
--- a/src/libstd/io/cursor.rs
+++ b/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};
diff --git a/src/libstd/io/impls.rs b/src/libstd/io/impls.rs
index 67bc45d3b62..864870a5905 100644
--- a/src/libstd/io/impls.rs
+++ b/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;
diff --git a/src/libstd/io/util.rs b/src/libstd/io/util.rs
index 6e651464c74..38e4b0d03e7 100644
--- a/src/libstd/io/util.rs
+++ b/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};
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 2e796004aab..a694a9280dc 100644
--- a/src/libstd/lib.rs
+++ b/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)]
diff --git a/src/libstd/net/udp.rs b/src/libstd/net/udp.rs
index 8212b8888d3..290aa6e2fda 100644
--- a/src/libstd/net/udp.rs
+++ b/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;
diff --git a/src/libstd/num/f32.rs b/src/libstd/num/f32.rs
index 73d6639cf00..64da75e94db 100644
--- a/src/libstd/num/f32.rs
+++ b/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;
diff --git a/src/libstd/num/f64.rs b/src/libstd/num/f64.rs
index 3911d276b0f..fcba821522e 100644
--- a/src/libstd/num/f64.rs
+++ b/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;
diff --git a/src/libstd/num/mod.rs b/src/libstd/num/mod.rs
index 9a52a0214e9..db7fd463e07 100644
--- a/src/libstd/num/mod.rs
+++ b/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;
diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index f5f8508e9aa..4a4db61c3b9 100644
--- a/src/libstd/path.rs
+++ b/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;
 
diff --git a/src/libstd/rand/mod.rs b/src/libstd/rand/mod.rs
index b806afc5951..df9cd98084b 100644
--- a/src/libstd/rand/mod.rs
+++ b/src/libstd/rand/mod.rs
@@ -57,6 +57,7 @@
 
 #![unstable(feature = "rand")]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use cell::RefCell;
diff --git a/src/libstd/rand/os.rs b/src/libstd/rand/os.rs
index 3f75c8bca83..9ae9455848e 100644
--- a/src/libstd/rand/os.rs
+++ b/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;
diff --git a/src/libstd/rand/reader.rs b/src/libstd/rand/reader.rs
index d19bc5b617f..665f423c3f1 100644
--- a/src/libstd/rand/reader.rs
+++ b/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;
 
diff --git a/src/libstd/rt/args.rs b/src/libstd/rt/args.rs
index 52697f00264..e77a2bbd0b9 100644
--- a/src/libstd/rt/args.rs
+++ b/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) {
diff --git a/src/libstd/rt/backtrace.rs b/src/libstd/rt/backtrace.rs
index 2eadf36a6b4..18d93cba8bc 100644
--- a/src/libstd/rt/backtrace.rs
+++ b/src/libstd/rt/backtrace.rs
@@ -12,6 +12,7 @@
 
 #![allow(non_camel_case_types)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use env;
diff --git a/src/libstd/sync/future.rs b/src/libstd/sync/future.rs
index b87a2756829..d0314da19d3 100644
--- a/src/libstd/sync/future.rs
+++ b/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;
diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
index d80d858e7a9..954edefcc45 100644
--- a/src/libstd/sync/mpsc/mod.rs
+++ b/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;
diff --git a/src/libstd/sync/mpsc/mpsc_queue.rs b/src/libstd/sync/mpsc/mpsc_queue.rs
index d6d173e5e7e..f45032d327f 100644
--- a/src/libstd/sync/mpsc/mpsc_queue.rs
+++ b/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;
diff --git a/src/libstd/sync/mpsc/oneshot.rs b/src/libstd/sync/mpsc/oneshot.rs
index 7e9c017617d..b84cb3b5472 100644
--- a/src/libstd/sync/mpsc/oneshot.rs
+++ b/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};
diff --git a/src/libstd/sync/mpsc/select.rs b/src/libstd/sync/mpsc/select.rs
index ee1516342ad..1d31ac165f6 100644
--- a/src/libstd/sync/mpsc/select.rs
+++ b/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;
diff --git a/src/libstd/sync/mpsc/shared.rs b/src/libstd/sync/mpsc/shared.rs
index 41c79dd52c8..8c019395d30 100644
--- a/src/libstd/sync/mpsc/shared.rs
+++ b/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;
diff --git a/src/libstd/sync/mpsc/spsc_queue.rs b/src/libstd/sync/mpsc/spsc_queue.rs
index 3cf75de5a46..5c0db521007 100644
--- a/src/libstd/sync/mpsc/spsc_queue.rs
+++ b/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;
diff --git a/src/libstd/sync/mpsc/stream.rs b/src/libstd/sync/mpsc/stream.rs
index 404814b4cd4..a9514da4698 100644
--- a/src/libstd/sync/mpsc/stream.rs
+++ b/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;
diff --git a/src/libstd/sync/mpsc/sync.rs b/src/libstd/sync/mpsc/sync.rs
index 904eab1fd7e..7c9298fff2a 100644
--- a/src/libstd/sync/mpsc/sync.rs
+++ b/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::*;
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index 0bda6a975a2..53191e14bec 100644
--- a/src/libstd/sync/once.rs
+++ b/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;
diff --git a/src/libstd/sys/common/backtrace.rs b/src/libstd/sys/common/backtrace.rs
index 00932712a07..17953d0af4e 100644
--- a/src/libstd/sys/common/backtrace.rs
+++ b/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::*;
 
diff --git a/src/libstd/sys/common/mod.rs b/src/libstd/sys/common/mod.rs
index 69c54f98917..b205b6df4cb 100644
--- a/src/libstd/sys/common/mod.rs
+++ b/src/libstd/sys/common/mod.rs
@@ -10,6 +10,7 @@
 
 #![allow(missing_docs)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 pub mod backtrace;
diff --git a/src/libstd/sys/common/poison.rs b/src/libstd/sys/common/poison.rs
index 065b1d6c9ac..196fe37d456 100644
--- a/src/libstd/sys/common/poison.rs
+++ b/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;
diff --git a/src/libstd/sys/common/thread_info.rs b/src/libstd/sys/common/thread_info.rs
index bb47c946e49..fb4e0ec70e0 100644
--- a/src/libstd/sys/common/thread_info.rs
+++ b/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;
diff --git a/src/libstd/sys/common/thread_local.rs b/src/libstd/sys/common/thread_local.rs
index 3b2cb00d8c4..2269a053874 100644
--- a/src/libstd/sys/common/thread_local.rs
+++ b/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};
diff --git a/src/libstd/sys/common/wtf8.rs b/src/libstd/sys/common/wtf8.rs
index 3d5d1f5e0eb..0a5f4563dea 100644
--- a/src/libstd/sys/common/wtf8.rs
+++ b/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;
diff --git a/src/libstd/sys/unix/backtrace.rs b/src/libstd/sys/unix/backtrace.rs
index ed6421f3670..ae8bfb07aaf 100644
--- a/src/libstd/sys/unix/backtrace.rs
+++ b/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::*;
 
diff --git a/src/libstd/sys/unix/condvar.rs b/src/libstd/sys/unix/condvar.rs
index beecb445e8d..9dd8df7524d 100644
--- a/src/libstd/sys/unix/condvar.rs
+++ b/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;
diff --git a/src/libstd/sys/unix/ext/fs.rs b/src/libstd/sys/unix/ext/fs.rs
index 4ee790b0161..dca7f6e829f 100644
--- a/src/libstd/sys/unix/ext/fs.rs
+++ b/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};
diff --git a/src/libstd/sys/unix/ext/process.rs b/src/libstd/sys/unix/ext/process.rs
index 63adae17581..71f83e7404b 100644
--- a/src/libstd/sys/unix/ext/process.rs
+++ b/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;
diff --git a/src/libstd/sys/unix/fd.rs b/src/libstd/sys/unix/fd.rs
index 026380027d2..bdbe120f79d 100644
--- a/src/libstd/sys/unix/fd.rs
+++ b/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};
diff --git a/src/libstd/sys/unix/fs.rs b/src/libstd/sys/unix/fs.rs
index 0c99a30f107..ddab24b133f 100644
--- a/src/libstd/sys/unix/fs.rs
+++ b/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::*;
 
diff --git a/src/libstd/sys/unix/mod.rs b/src/libstd/sys/unix/mod.rs
index 6fd20b940bb..85dc8752443 100644
--- a/src/libstd/sys/unix/mod.rs
+++ b/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};
diff --git a/src/libstd/sys/unix/mutex.rs b/src/libstd/sys/unix/mutex.rs
index 6eed403dfc0..a6132b37a66 100644
--- a/src/libstd/sys/unix/mutex.rs
+++ b/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;
diff --git a/src/libstd/sys/unix/os_str.rs b/src/libstd/sys/unix/os_str.rs
index 69d876a48a4..e21d88676e7 100644
--- a/src/libstd/sys/unix/os_str.rs
+++ b/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};
diff --git a/src/libstd/sys/unix/pipe.rs b/src/libstd/sys/unix/pipe.rs
index 140f0c042ba..2abd74bea1b 100644
--- a/src/libstd/sys/unix/pipe.rs
+++ b/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;
diff --git a/src/libstd/sys/unix/rwlock.rs b/src/libstd/sys/unix/rwlock.rs
index ee687f350f0..50b4907e6ca 100644
--- a/src/libstd/sys/unix/rwlock.rs
+++ b/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;
diff --git a/src/libstd/sys/unix/stack_overflow.rs b/src/libstd/sys/unix/stack_overflow.rs
index 62689c39255..ed4e50735a6 100644
--- a/src/libstd/sys/unix/stack_overflow.rs
+++ b/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};
diff --git a/src/libstd/sys/unix/stdio.rs b/src/libstd/sys/unix/stdio.rs
index fce52f8f92b..8542c660c26 100644
--- a/src/libstd/sys/unix/stdio.rs
+++ b/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;
diff --git a/src/libstd/sys/unix/thread_local.rs b/src/libstd/sys/unix/thread_local.rs
index 7238adfcc56..5626446b31c 100644
--- a/src/libstd/sys/unix/thread_local.rs
+++ b/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;
 
diff --git a/src/libstd/sys/windows/backtrace.rs b/src/libstd/sys/windows/backtrace.rs
index 3f595762fc7..d84513c5f95 100644
--- a/src/libstd/sys/windows/backtrace.rs
+++ b/src/libstd/sys/windows/backtrace.rs
@@ -24,6 +24,7 @@
 
 #![allow(dead_code)]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 use io::prelude::*;
 
diff --git a/src/libstd/sys/windows/condvar.rs b/src/libstd/sys/windows/condvar.rs
index 04d62200e9b..f3edcfd420c 100644
--- a/src/libstd/sys/windows/condvar.rs
+++ b/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;
diff --git a/src/libstd/sys/windows/ext/fs.rs b/src/libstd/sys/windows/ext/fs.rs
index f629e983ce5..e15d1f0ec15 100644
--- a/src/libstd/sys/windows/ext/fs.rs
+++ b/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};
diff --git a/src/libstd/sys/windows/fs.rs b/src/libstd/sys/windows/fs.rs
index 4ce6d53cf12..8d81d6576ff 100644
--- a/src/libstd/sys/windows/fs.rs
+++ b/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::*;
 
diff --git a/src/libstd/sys/windows/handle.rs b/src/libstd/sys/windows/handle.rs
index a566c5eff32..91fe131c251 100644
--- a/src/libstd/sys/windows/handle.rs
+++ b/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;
diff --git a/src/libstd/sys/windows/net.rs b/src/libstd/sys/windows/net.rs
index d58355ed1fe..f2aca8d1a6e 100644
--- a/src/libstd/sys/windows/net.rs
+++ b/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;
diff --git a/src/libstd/sys/windows/pipe.rs b/src/libstd/sys/windows/pipe.rs
index a7ece66e0f1..4044c429d49 100644
--- a/src/libstd/sys/windows/pipe.rs
+++ b/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;
diff --git a/src/libstd/sys/windows/rwlock.rs b/src/libstd/sys/windows/rwlock.rs
index 25865286db0..010ffe76fba 100644
--- a/src/libstd/sys/windows/rwlock.rs
+++ b/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;
diff --git a/src/libstd/sys/windows/stack_overflow.rs b/src/libstd/sys/windows/stack_overflow.rs
index 491b53c4ed9..bc8ee6619f1 100644
--- a/src/libstd/sys/windows/stack_overflow.rs
+++ b/src/libstd/sys/windows/stack_overflow.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 libc::types::os::arch::extra::{LPVOID, DWORD, LONG};
 use libc;
diff --git a/src/libstd/sys/windows/thread.rs b/src/libstd/sys/windows/thread.rs
index 42805c2ac52..a4131d4cada 100644
--- a/src/libstd/sys/windows/thread.rs
+++ b/src/libstd/sys/windows/thread.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 alloc::boxed::FnBox;
diff --git a/src/libstd/thread/local.rs b/src/libstd/thread/local.rs
index 9a6d68acb9f..a6ecd2d88d2 100644
--- a/src/libstd/thread/local.rs
+++ b/src/libstd/thread/local.rs
@@ -12,6 +12,7 @@
 
 #![unstable(feature = "thread_local_internals")]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use cell::UnsafeCell;
@@ -271,6 +272,7 @@ impl<T: 'static> LocalKey<T> {
           not(no_elf_tls)))]
 #[doc(hidden)]
 mod imp {
+    #[cfg(stage0)]
     use prelude::v1::*;
 
     use cell::{Cell, UnsafeCell};
diff --git a/src/libstd/thread/scoped_tls.rs b/src/libstd/thread/scoped_tls.rs
index cf2c5db8277..1ea33a01791 100644
--- a/src/libstd/thread/scoped_tls.rs
+++ b/src/libstd/thread/scoped_tls.rs
@@ -42,6 +42,7 @@
 
 #![unstable(feature = "thread_local_internals")]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 #[doc(hidden)]
@@ -249,6 +250,7 @@ mod imp {
           no_elf_tls))]
 #[doc(hidden)]
 mod imp {
+    #[cfg(stage0)]
     use prelude::v1::*;
 
     use cell::Cell;
@@ -278,6 +280,7 @@ mod imp {
 #[cfg(test)]
 mod tests {
     use cell::Cell;
+    #[cfg(stage0)]
     use prelude::v1::*;
 
     scoped_thread_local!(static FOO: u32);
diff --git a/src/libstd/time/duration.rs b/src/libstd/time/duration.rs
index 8001df29d1f..28eaed40da8 100644
--- a/src/libstd/time/duration.rs
+++ b/src/libstd/time/duration.rs
@@ -12,6 +12,7 @@
 
 #![unstable(feature = "duration", reason = "recently added API per RFC 1040")]
 
+#[cfg(stage0)]
 use prelude::v1::*;
 
 use fmt;