Auto merge of #21988 - kmcallister:no-std, r=sfackler

Fixes #21833.

[breaking-change]

r? @alexcrichton 

The tests in #21912 will also need `#[feature(no_std)]`. If you're okay with both PRs, I can merge and test them.

Author: bors

Diff for: src/doc/reference.md

@@ -2467,6 +2467,12 @@ The currently implemented features of the reference compiler are:
 
 * `associated_types` - Allows type aliases in traits. Experimental.
 
+* `no_std` - Allows the `#![no_std]` crate attribute, which disables the implicit
+             `extern crate std`. This typically requires use of the unstable APIs
+             behind the libstd "facade", such as libcore and libcollections. It
+             may also cause problems when using syntax extensions, including
+             `#[derive]`.
+
 If a feature is promoted to a language feature, then all existing programs will
 start to receive compilation warnings about #[feature] directives which enabled
 the new feature (because the directive is no longer necessary). However, if a

Diff for: src/doc/trpl/unsafe.md

@@ -433,6 +433,7 @@ attribute attached to the crate.
 ```ignore
 // a minimal library
 #![crate_type="lib"]
+#![feature(no_std)]
 #![no_std]
 # // fn main() {} tricked you, rustdoc!
 ```
@@ -446,8 +447,8 @@ The function marked `#[start]` is passed the command line parameters
 in the same format as C:
 
 ```
+#![feature(lang_items, start, no_std)]
 #![no_std]
-#![feature(lang_items, start)]
 
 // Pull in the system libc library for what crt0.o likely requires
 extern crate libc;
@@ -473,6 +474,7 @@ correct ABI and the correct name, which requires overriding the
 compiler's name mangling too:
 
 ```ignore
+#![feature(no_std)]
 #![no_std]
 #![no_main]
 #![feature(lang_items, start)]
@@ -528,8 +530,8 @@ As an example, here is a program that will calculate the dot product of two
 vectors provided from C, using idiomatic Rust practices.
 
 ```
+#![feature(lang_items, start, no_std)]
 #![no_std]
-#![feature(lang_items, start)]
 
 # extern crate libc;
 extern crate core;
@@ -576,10 +578,6 @@ extern fn panic_fmt(args: &core::fmt::Arguments,
 #[lang = "eh_personality"] extern fn eh_personality() {}
 # #[start] fn start(argc: isize, argv: *const *const u8) -> isize { 0 }
 # fn main() {}
-# mod std {  // for-loops
-#     pub use core::iter;
-#     pub use core::option;
-# }
 ```
 
 Note that there is one extra lang item here which differs from the examples
@@ -656,8 +654,8 @@ and one for deallocation. A freestanding program that uses the `Box`
 sugar for dynamic allocations via `malloc` and `free`:
 
 ```
+#![feature(lang_items, box_syntax, start, no_std)]
 #![no_std]
-#![feature(lang_items, box_syntax, start)]
 
 extern crate libc;
 

Diff for: src/liballoc/lib.rs

@@ -65,6 +65,7 @@
        html_favicon_url = "http://www.rust-lang.org/favicon.ico",
        html_root_url = "http://doc.rust-lang.org/nightly/")]
 
+#![feature(no_std)]
 #![no_std]
 #![feature(lang_items, unsafe_destructor)]
 #![feature(box_syntax)]
@@ -126,7 +127,8 @@ pub fn oom() -> ! {
 #[doc(hidden)]
 pub fn fixme_14344_be_sure_to_link_to_collections() {}
 
-#[cfg(not(test))]
+// NOTE: remove after next snapshot
+#[cfg(all(stage0, not(test)))]
 #[doc(hidden)]
 mod std {
     pub use core::fmt;

Diff for: src/libstd/fmt.rs renamed to src/libcollections/fmt.rs

@@ -1,4 +1,4 @@
-// Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -134,7 +134,7 @@
 //! * `E` ⇒ `UpperExp`
 //!
 //! What this means is that any type of argument which implements the
-//! `std::fmt::Binary` trait can then be formatted with `{:b}`. Implementations
+//! `fmt::Binary` trait can then be formatted with `{:b}`. Implementations
 //! are provided for these traits for a number of primitive types by the
 //! standard library as well. If no format is specified (as in `{}` or `{:6}`),
 //! then the format trait used is the `Display` trait.
@@ -146,7 +146,7 @@
 //! # use std::fmt;
 //! # struct Foo; // our custom type
 //! # impl fmt::Display for Foo {
-//! fn fmt(&self, f: &mut std::fmt::Formatter) -> fmt::Result {
+//! fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 //! # write!(f, "testing, testing")
 //! # } }
 //! ```
@@ -403,8 +403,6 @@
 
 #![unstable(feature = "std_misc")]
 
-use string;
-
 pub use core::fmt::{Formatter, Result, Writer, rt};
 pub use core::fmt::{Show, String, Octal, Binary};
 pub use core::fmt::{Display, Debug};
@@ -413,6 +411,8 @@ pub use core::fmt::{LowerExp, UpperExp};
 pub use core::fmt::Error;
 pub use core::fmt::{ArgumentV1, Arguments, write, radix, Radix, RadixFmt};
 
+use string;
+
 /// The format function takes a precompiled format string and a list of
 /// arguments, to return the resulting formatted string.
 ///
@@ -434,3 +434,15 @@ pub fn format(args: Arguments) -> string::String {
     let _ = write!(&mut output, "{}", args);
     output
 }
+
+#[cfg(test)]
+mod tests {
+    use prelude::*;
+    use fmt;
+
+    #[test]
+    fn test_format() {
+        let s = fmt::format(format_args!("Hello, {}!", "world"));
+        assert_eq!(s.as_slice(), "Hello, world!");
+    }
+}

Diff for: src/libcollections/lib.rs

@@ -33,6 +33,7 @@
 #![cfg_attr(test, feature(test))]
 #![cfg_attr(test, allow(deprecated))] // rand
 
+#![feature(no_std)]
 #![no_std]
 
 #[macro_use]
@@ -68,6 +69,7 @@ mod bit;
 mod btree;
 pub mod dlist;
 pub mod enum_set;
+pub mod fmt;
 pub mod ring_buf;
 pub mod slice;
 pub mod str;
@@ -107,15 +109,16 @@ pub fn fixme_14344_be_sure_to_link_to_collections() {}
 
 #[cfg(not(test))]
 mod std {
-    pub use core::fmt;      // necessary for panic!()
-    pub use core::option;   // necessary for panic!()
-    pub use core::clone;    // derive(Clone)
-    pub use core::cmp;      // derive(Eq, Ord, etc.)
-    pub use core::marker;   // derive(Copy)
-    pub use core::hash;     // derive(Hash)
+    // NOTE: remove after next snapshot
+    #[cfg(stage0)] pub use core::clone;    // derive(Clone)
+    #[cfg(stage0)] pub use core::cmp;      // derive(Eq, Ord, etc.)
+    #[cfg(stage0)] pub use core::marker;   // derive(Copy)
+    #[cfg(stage0)] pub use core::hash;     // derive(Hash)
+    #[cfg(stage0)] pub use core::iter;
+    #[cfg(stage0)] pub use core::fmt;      // necessary for panic!()
+    #[cfg(stage0)] pub use core::option;   // necessary for panic!()
+
     pub use core::ops;      // RangeFull
-    // for-loops
-    pub use core::iter;
 }
 
 #[cfg(test)]

Diff for: src/libcollections/macros.rs

@@ -22,3 +22,19 @@ macro_rules! vec {
     );
     ($($x:expr,)*) => (vec![$($x),*])
 }
+
+/// Use the syntax described in `std::fmt` to create a value of type `String`.
+/// See `std::fmt` for more information.
+///
+/// # Example
+///
+/// ```
+/// format!("test");
+/// format!("hello {}", "world!");
+/// format!("x = {}, y = {y}", 10, y = 30);
+/// ```
+#[macro_export]
+#[stable(feature = "rust1", since = "1.0.0")]
+macro_rules! format {
+    ($($arg:tt)*) => ($crate::fmt::format(format_args!($($arg)*)))
+}

Diff for: src/libcollections/ring_buf.rs

@@ -27,8 +27,8 @@ use core::ops::{Index, IndexMut};
 use core::ptr;
 use core::raw::Slice as RawSlice;
 
-use std::hash::{Writer, Hash, Hasher};
-use std::cmp;
+use core::hash::{Writer, Hash, Hasher};
+use core::cmp;
 
 use alloc::heap;
 

Diff for: src/libcore/iter.rs

@@ -67,7 +67,7 @@ use num::{ToPrimitive, Int};
 use ops::{Add, Deref, FnMut};
 use option::Option;
 use option::Option::{Some, None};
-use std::marker::Sized;
+use marker::Sized;
 use usize;
 
 /// An interface for dealing with "external iterators". These types of iterators

Diff for: src/libcore/lib.rs

@@ -56,6 +56,7 @@
        html_root_url = "http://doc.rust-lang.org/nightly/",
        html_playground_url = "http://play.rust-lang.org/")]
 
+#![feature(no_std)]
 #![no_std]
 #![allow(raw_pointer_derive)]
 #![deny(missing_docs)]
@@ -148,17 +149,25 @@ mod array;
 mod core {
     pub use panicking;
     pub use fmt;
+    #[cfg(not(stage0))] pub use clone;
+    #[cfg(not(stage0))] pub use cmp;
+    #[cfg(not(stage0))] pub use hash;
+    #[cfg(not(stage0))] pub use marker;
+    #[cfg(not(stage0))] pub use option;
+    #[cfg(not(stage0))] pub use iter;
 }
 
 #[doc(hidden)]
 mod std {
-    pub use clone;
-    pub use cmp;
-    pub use fmt;
-    pub use hash;
-    pub use marker;
+    // NOTE: remove after next snapshot
+    #[cfg(stage0)] pub use clone;
+    #[cfg(stage0)] pub use cmp;
+    #[cfg(stage0)] pub use hash;
+    #[cfg(stage0)] pub use marker;
+    #[cfg(stage0)] pub use option;
+    #[cfg(stage0)] pub use fmt;
+    #[cfg(stage0)] pub use iter;
+
+    // range syntax
     pub use ops;
-    pub use option;
-    // for-loops
-    pub use iter;
 }

Diff for: src/liblibc/lib.rs

@@ -16,6 +16,7 @@
 #![cfg_attr(not(feature = "cargo-build"), staged_api)]
 #![cfg_attr(not(feature = "cargo-build"), feature(core))]
 #![feature(int_uint)]
+#![feature(no_std)]
 #![no_std]
 #![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "http://www.rust-lang.org/favicon.ico",
@@ -5729,8 +5730,9 @@ pub fn issue_14344_workaround() {} // FIXME #14344 force linkage to happen corre
 
 #[test] fn work_on_windows() { } // FIXME #10872 needed for a happy windows
 
+// NOTE: remove after next snapshot
 #[doc(hidden)]
-#[cfg(not(test))]
+#[cfg(all(stage0, not(test)))]
 mod std {
     pub use core::marker;
 }

Diff for: src/librand/lib.rs

@@ -23,6 +23,7 @@
        html_root_url = "http://doc.rust-lang.org/nightly/",
        html_playground_url = "http://play.rust-lang.org/")]
 #![feature(int_uint)]
+#![feature(no_std)]
 #![no_std]
 #![unstable(feature = "rand")]
 #![feature(staged_api)]
@@ -496,7 +497,8 @@ pub struct Open01<F>(pub F);
 /// ```
 pub struct Closed01<F>(pub F);
 
-#[cfg(not(test))]
+// NOTE: remove after next snapshot
+#[cfg(all(stage0, not(test)))]
 mod std {
     pub use core::{option, fmt}; // panic!()
     pub use core::clone; // derive Clone

Diff for: src/librustc_bitflags/lib.rs

@@ -12,6 +12,7 @@
 #![feature(staged_api)]
 #![staged_api]
 #![crate_type = "rlib"]
+#![feature(no_std)]
 #![no_std]
 #![unstable(feature = "rustc_private")]
 
@@ -281,6 +282,13 @@ 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 {

Diff for: src/librustc_driver/test.rs

@@ -43,7 +43,7 @@ struct RH<'a> {
     sub: &'a [RH<'a>]
 }
 
-static EMPTY_SOURCE_STR: &'static str = "#![no_std]";
+static EMPTY_SOURCE_STR: &'static str = "#![feature(no_std)] #![no_std]";
 
 struct ExpectErrorEmitter {
     messages: Vec<String>

Diff for: src/libstd/lib.rs

@@ -124,6 +124,7 @@
 #![cfg_attr(test, feature(test))]
 
 // Don't link to std. We are std.
+#![feature(no_std)]
 #![no_std]
 
 #![deny(missing_docs)]
@@ -137,7 +138,7 @@
 extern crate core;
 
 #[macro_use]
-#[macro_reexport(vec)]
+#[macro_reexport(vec, format)]
 extern crate "collections" as core_collections;
 
 #[allow(deprecated)] extern crate "rand" as core_rand;
@@ -180,6 +181,7 @@ pub use core::error;
 #[cfg(not(test))] pub use alloc::boxed;
 pub use alloc::rc;
 
+pub use core_collections::fmt;
 pub use core_collections::slice;
 pub use core_collections::str;
 pub use core_collections::string;
@@ -245,7 +247,6 @@ pub mod thread_local;
 
 pub mod dynamic_lib;
 pub mod ffi;
-pub mod fmt;
 pub mod old_io;
 pub mod io;
 pub mod os;
@@ -285,11 +286,12 @@ mod tuple;
 // can be resolved within libstd.
 #[doc(hidden)]
 mod std {
+    // NOTE: remove after next snapshot
     // mods used for deriving
-    pub use clone;
-    pub use cmp;
-    pub use hash;
-    pub use default;
+    #[cfg(stage0)] pub use clone;
+    #[cfg(stage0)] pub use cmp;
+    #[cfg(stage0)] pub use hash;
+    #[cfg(stage0)] pub use default;
 
     pub use sync; // used for select!()
     pub use error; // used for try!()
@@ -312,5 +314,6 @@ mod std {
 
     pub use boxed; // used for vec![]
     // for-loops
-    pub use iter;
+    // NOTE: remove after next snapshot
+    #[cfg(stage0)] pub use iter;
 }