0f49616a53
Perform lifetime elision (more) syntactically, before type-checking. The *initial* goal of this patch was to remove the (contextual) `&RegionScope` argument passed around `rustc_typeck::astconv` and allow converting arbitrary (syntactic) `hir::Ty` to (semantic) `Ty`. I've tried to closely match the existing behavior while moving the logic to the earlier `resolve_lifetime` pass, and [the crater report](https://gist.github.com/eddyb/4ac5b8516f87c1bfa2de528ed2b7779a) suggests none of the changes broke real code, but I will try to list everything: There are few cases in lifetime elision that could trip users up due to "hidden knowledge": ```rust type StaticStr = &'static str; // hides 'static trait WithLifetime<'a> { type Output; // can hide 'a } // This worked because the type of the first argument contains // 'static, although StaticStr doesn't even have parameters. fn foo(x: StaticStr) -> &str { x } // This worked because the compiler resolved the argument type // to <T as WithLifetime<'a>>::Output which has the hidden 'a. fn bar<'a, T: WithLifetime<'a>>(_: T::Output) -> &str { "baz" } ``` In the two examples above, elision wasn't using lifetimes that were in the source, not even *needed* by paths in the source, but rather *happened* to be part of the semantic representation of the types. To me, this suggests they should have never worked through elision (and they don't with this PR). Next we have an actual rule with a strange result, that is, the return type here elides to `&'x str`: ```rust impl<'a, 'b> Trait for Foo<'a, 'b> { fn method<'x, 'y>(self: &'x Foo<'a, 'b>, _: Bar<'y>) -> &str { &self.name } } ``` All 3 of `'a`, `'b` and `'y` are being ignored, because the `&self` elision rule only cares that the first argument is "`self` by reference". Due implementation considerations (elision running before typeck), I've limited it in this PR to a reference to a primitive/`struct`/`enum`/`union`, but not other types, but I am doing another crater run to assess the impact of limiting it to literally `&self` and `self: &Self` (they're identical in HIR). It's probably ideal to keep an "implicit `Self` for `self`" type around and *only* apply the rule to `&self` itself, but that would result in more bikeshed, and #21400 suggests some people expect otherwise. Another decent option is treating `self: X, ... -> Y` like `X -> Y` (one unique lifetime in `X` used for `Y`). The remaining changes have to do with "object lifetime defaults" (see RFCs [599](https://github.com/rust-lang/rfcs/blob/master/text/0599-default-object-bound.md) and [1156](https://github.com/rust-lang/rfcs/blob/master/text/1156-adjust-default-object-bounds.md)): ```rust trait Trait {} struct Ref2<'a, 'b, T: 'a+'b>(&'a T, &'b T); // These apply specifically within a (fn) body, // which allows type and lifetime inference: fn main() { // Used to be &'a mut (Trait+'a) - where 'a is one // inference variable - &'a mut (Trait+'b) in this PR. let _: &mut Trait; // Used to be an ambiguity error, but in this PR it's // Ref2<'a, 'b, Trait+'c> (3 inference variables). let _: Ref2<Trait>; } ``` What's happening here is that inference variables are created on the fly by typeck whenever a lifetime has no resolution attached to it - while it would be possible to alter the implementation to reuse inference variables based on decisions made early by `resolve_lifetime`, not doing that is more flexible and works better - it can compile all testcases from #38624 by not ending up with `&'static mut (Trait+'static)`. The ambiguity specifically cannot be an early error, because this is only the "default" (typeck can still pick something better based on the definition of `Trait` and whether it has any lifetime bounds), and having an error at all doesn't help anyone, as we can perfectly infer an appropriate lifetime inside the `fn` body. **TODO**: write tests for the user-visible changes. cc @nikomatsakis @arielb1
The Rust Programming Language
This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.
Quick Start
Read "Installing Rust" from The Book.
Building from Source
-
Make sure you have installed the dependencies:
g++4.7 or later orclang++3.xpython2.7 (but not 3.x)- GNU
make3.81 or later cmake3.4.3 or latercurlgit
-
Clone the source with
git:$ git clone https://github.com/rust-lang/rust.git $ cd rust
-
Build and install:
$ ./configure $ make && sudo make installNote: Install locations can be adjusted by passing a
--prefixargument toconfigure. Various other options are also supported – pass--helpfor more information on them.When complete,
sudo make installwill place several programs into/usr/local/bin:rustc, the Rust compiler, andrustdoc, the API-documentation tool. This install does not include Cargo, Rust's package manager, which you may also want to build.
Building on Windows
There are two prominent ABIs in use on Windows: the native (MSVC) ABI used by Visual Studio, and the GNU ABI used by the GCC toolchain. Which version of Rust you need depends largely on what C/C++ libraries you want to interoperate with: for interop with software produced by Visual Studio use the MSVC build of Rust; for interop with GNU software built using the MinGW/MSYS2 toolchain use the GNU build.
MinGW
MSYS2 can be used to easily build Rust on Windows:
-
Grab the latest MSYS2 installer and go through the installer.
-
Run
mingw32_shell.batormingw64_shell.batfrom wherever you installed MSYS2 (i.e.C:\msys64), depending on whether you want 32-bit or 64-bit Rust. (As of the latest version of MSYS2 you have to runmsys2_shell.cmd -mingw32ormsys2_shell.cmd -mingw64from the command line instead) -
From this terminal, install the required tools:
# Update package mirrors (may be needed if you have a fresh install of MSYS2) $ pacman -Sy pacman-mirrors # Install build tools needed for Rust. If you're building a 32-bit compiler, # then replace "x86_64" below with "i686". If you've already got git, python, # or CMake installed and in PATH you can remove them from this list. Note # that it is important that you do **not** use the 'python2' and 'cmake' # packages from the 'msys2' subsystem. The build has historically been known # to fail with these packages. $ pacman -S git \ make \ diffutils \ tar \ mingw-w64-x86_64-python2 \ mingw-w64-x86_64-cmake \ mingw-w64-x86_64-gcc -
Navigate to Rust's source code (or clone it), then configure and build it:
$ ./configure $ make && make install
MSVC
MSVC builds of Rust additionally require an installation of Visual Studio 2013
(or later) so rustc can use its linker. Make sure to check the “C++ tools”
option.
With these dependencies installed, you can build the compiler in a cmd.exe
shell with:
> python x.py build
If you're running inside of an msys shell, however, you can run:
$ ./configure --build=x86_64-pc-windows-msvc
$ make && make install
Currently building Rust only works with some known versions of Visual Studio. If you have a more recent version installed the build system doesn't understand then you may need to force rustbuild to use an older version. This can be done by manually calling the appropriate vcvars file before running the bootstrap.
CALL "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64\vcvars64.bat"
python x.py build
Building Documentation
If you’d like to build the documentation, it’s almost the same:
$ ./configure
$ make docs
The generated documentation will appear in a top-level doc directory,
created by the make rule.
Notes
Since the Rust compiler is written in Rust, it must be built by a precompiled "snapshot" version of itself (made in an earlier state of development). As such, source builds require a connection to the Internet, to fetch snapshots, and an OS that can execute the available snapshot binaries.
Snapshot binaries are currently built and tested on several platforms:
| Platform / Architecture | x86 | x86_64 |
|---|---|---|
| Windows (7, 8, Server 2008 R2) | ✓ | ✓ |
| Linux (2.6.18 or later) | ✓ | ✓ |
| OSX (10.7 Lion or later) | ✓ | ✓ |
You may find that other platforms work, but these are our officially supported build environments that are most likely to work.
Rust currently needs between 600MiB and 1.5GiB to build, depending on platform. If it hits swap, it will take a very long time to build.
There is more advice about hacking on Rust in CONTRIBUTING.md.
Getting Help
The Rust community congregates in a few places:
- Stack Overflow - Direct questions about using the language.
- users.rust-lang.org - General discussion and broader questions.
- /r/rust - News and general discussion.
Contributing
To contribute to Rust, please see CONTRIBUTING.
Rust has an IRC culture and most real-time collaboration happens in a variety of channels on Mozilla's IRC network, irc.mozilla.org. The most popular channel is #rust, a venue for general discussion about Rust. And a good place to ask for help would be #rust-beginners.
License
Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.
See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.