7b4d9e155f
Stabilize `impl_trait_projections` Closes #115659 ## TL;DR: This allows us to mention `Self` and `T::Assoc` in async fn and return-position `impl Trait`, as you would expect you'd be able to. Some examples: ```rust #![feature(return_position_impl_trait_in_trait, async_fn_in_trait)] // (just needed for final tests below) // ---------------------------------------- // struct Wrapper<'a, T>(&'a T); impl Wrapper<'_, ()> { async fn async_fn() -> Self { //^ Previously rejected because it returns `-> Self`, not `-> Wrapper<'_, ()>`. Wrapper(&()) } fn impl_trait() -> impl Iterator<Item = Self> { //^ Previously rejected because it mentions `Self`, not `Wrapper<'_, ()>`. std::iter::once(Wrapper(&())) } } // ---------------------------------------- // trait Trait<'a> { type Assoc; fn new() -> Self::Assoc; } impl Trait<'_> for () { type Assoc = (); fn new() {} } impl<'a, T: Trait<'a>> Wrapper<'a, T> { async fn mk_assoc() -> T::Assoc { //^ Previously rejected because `T::Assoc` doesn't mention `'a` in the HIR, // but ends up resolving to `<T as Trait<'a>>::Assoc`, which does rely on `'a`. // That's the important part -- the elided trait. T::new() } fn a_few_assocs() -> impl Iterator<Item = T::Assoc> { //^ Previously rejected for the same reason [T::new(), T::new(), T::new()].into_iter() } } // ---------------------------------------- // trait InTrait { async fn async_fn() -> Self; fn impl_trait() -> impl Iterator<Item = Self>; } impl InTrait for &() { async fn async_fn() -> Self { &() } //^ Previously rejected just like inherent impls fn impl_trait() -> impl Iterator<Item = Self> { //^ Previously rejected just like inherent impls [&()].into_iter() } } ``` ## Technical: Lifetimes in return-position `impl Trait` (and `async fn`) are duplicated as early-bound generics local to the opaque in order to make sure we are able to substitute any late-bound lifetimes from the function in the opaque's hidden type. (The [dev guide](https://rustc-dev-guide.rust-lang.org/return-position-impl-trait-in-trait.html#aside-opaque-lifetime-duplication) has a small section about why this is necessary -- this was written for RPITITs, but it applies to all RPITs) Prior to #103491, all of the early-bound lifetimes not local to the opaque were replaced with `'static` to avoid issues where relating opaques caused their *non-captured* lifetimes to be related. This `'static` replacement led to strange and possibly unsound behaviors (https://github.com/rust-lang/rust/issues/61949#issuecomment-508836314) (https://github.com/rust-lang/rust/issues/53613) when referencing the `Self` type alias in an impl or indirectly referencing a lifetime parameter via a projection type (via a `T::Assoc` projection without an explicit trait), since lifetime resolution is performed on the HIR, when neither `T::Assoc`-style projections or `Self` in impls are expanded. Therefore an error was implemented in #62849 to deny this subtle behavior as a known limitation of the compiler. It was attempted by `@cjgillot` to fix this in #91403, which was subsequently unlanded. Then it was re-attempted to much success (🎉) in #103491, which is where we currently are in the compiler. The PR above (#103491) fixed this issue technically by *not* replacing the opaque's parent lifetimes with `'static`, but instead using variance to properly track which lifetimes are captured and are not. The PR gated any of the "side-effects" of the PR behind a feature gate (`impl_trait_projections`) presumably to avoid having to involve T-lang or T-types in the PR as well. `@cjgillot` can clarify this if I'm misunderstanding what their intention was with the feature gate. Since we're not replacing (possibly *invariant*!) lifetimes with `'static` anymore, there are no more soundness concerns here. Therefore, this PR removes the feature gate. Tests: * `tests/ui/async-await/feature-self-return-type.rs` * `tests/ui/impl-trait/feature-self-return-type.rs` * `tests/ui/async-await/issues/issue-78600.rs` * `tests/ui/impl-trait/capture-lifetime-not-in-hir.rs` --- r? cjgillot on the impl (not much, just removing the feature gate) I'm gonna mark this as FCP for T-lang and T-types.
The Rust Programming Language
This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.
Note: this README is for users rather than contributors. If you wish to contribute to the compiler, you should read CONTRIBUTING.md instead.
Quick Start
Read "Installation" from The Book.
Installing from Source
The Rust build system uses a Python script called x.py to build the compiler,
which manages the bootstrapping process. It lives at the root of the project.
It also uses a file named config.toml to determine various configuration
settings for the build. You can see a full list of options in
config.example.toml.
The x.py command can be run directly on most Unix systems in the following
format:
./x.py <subcommand> [flags]
This is how the documentation and examples assume you are running x.py.
See the rustc dev guide if this does not work on your
platform.
More information about x.py can be found by running it with the --help flag
or reading the rustc dev guide.
Dependencies
Make sure you have installed the dependencies:
python3 or 2.7git- A C compiler (when building for the host,
ccis enough; cross-compiling may need additional compilers) curl(not needed on Windows)pkg-configif you are compiling on Linux and targeting Linuxlibiconv(already included with glibc on Debian-based distros)
To build Cargo, you'll also need OpenSSL (libssl-dev or openssl-devel on
most Unix distros).
If building LLVM from source, you'll need additional tools:
g++,clang++, or MSVC with versions listed on LLVM's documentationninja, or GNUmake3.81 or later (Ninja is recommended, especially on Windows)cmake3.13.4 or laterlibstdc++-staticmay be required on some Linux distributions such as Fedora and Ubuntu
On tier 1 or tier 2 with host tools platforms, you can also choose to download
LLVM by setting llvm.download-ci-llvm = true.
Otherwise, you'll need LLVM installed and llvm-config in your path.
See the rustc-dev-guide for more info.
Building on a Unix-like system
Build steps
-
Clone the source with
git:git clone https://github.com/rust-lang/rust.git cd rust
-
Configure the build settings:
./configureIf you plan to use
x.py installto create an installation, it is recommended that you set theprefixvalue in the[install]section to a directory:./configure --set install.prefix=<path> -
Build and install:
./x.py build && ./x.py installWhen complete,
./x.py installwill place several programs into$PREFIX/bin:rustc, the Rust compiler, andrustdoc, the API-documentation tool. By default, it will also include Cargo, Rust's package manager. You can disable this behavior by passing--set build.extended=falseto./configure.
Configure and Make
This project provides a configure script and makefile (the latter of which just
invokes x.py). ./configure is the recommended way to programatically
generate a config.toml. make is not recommended (we suggest using x.py
directly), but it is supported and we try not to break it unnecessarily.
./configure
make && sudo make install
configure generates a config.toml which can also be used with normal x.py
invocations.
Building on Windows
On Windows, we suggest using winget to install dependencies by running the following in a terminal:
winget install -e Python.Python.3
winget install -e Kitware.CMake
winget install -e Git.Git
Then edit your system's PATH variable and add: C:\Program Files\CMake\bin.
See
this guide on editing the system PATH
from the Java documentation.
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. Use the MSVC build of Rust to interop with software produced by Visual Studio and the GNU build to interop with GNU software built using the MinGW/MSYS2 toolchain.
MinGW
MSYS2 can be used to easily build Rust on Windows:
-
Download the latest MSYS2 installer and go through the installer.
-
Run
mingw32_shell.batormingw64_shell.batfrom the MSYS2 installation directory (e.g.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', 'cmake', # and 'ninja' 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-python \ mingw-w64-x86_64-cmake \ mingw-w64-x86_64-gcc \ mingw-w64-x86_64-ninja -
Navigate to Rust's source code (or clone it), then build it:
python x.py setup user && python x.py build && python x.py install
MSVC
MSVC builds of Rust additionally require an installation of Visual Studio 2017
(or later) so rustc can use its linker. The simplest way is to get
Visual Studio, check the "C++ build tools" and "Windows 10 SDK" workload.
(If you're installing CMake yourself, be careful that "C++ CMake tools for Windows" doesn't get included under "Individual components".)
With these dependencies installed, you can build the compiler in a cmd.exe
shell with:
python x.py setup user
python x.py build
Right now, building Rust only works with some known versions of Visual Studio. If you have a more recent version installed and the build system doesn't understand, 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\2019\Community\VC\Auxiliary\Build\vcvars64.bat"
python x.py build
Specifying an ABI
Each specific ABI can also be used from either environment (for example, using the GNU ABI in PowerShell) by using an explicit build triple. The available Windows build triples are:
- GNU ABI (using GCC)
i686-pc-windows-gnux86_64-pc-windows-gnu
- The MSVC ABI
i686-pc-windows-msvcx86_64-pc-windows-msvc
The build triple can be specified by either specifying --build=<triple> when
invoking x.py commands, or by creating a config.toml file (as described in
Building on a Unix-like system), and passing
--set build.build=<triple> to ./configure.
Building Documentation
If you'd like to build the documentation, it's almost the same:
./x.py doc
The generated documentation will appear under doc in the build directory for
the ABI used. That is, if the ABI was x86_64-pc-windows-msvc, the directory
will be build\x86_64-pc-windows-msvc\doc.
Notes
Since the Rust compiler is written in Rust, it must be built by a precompiled "snapshot" version of itself (made in an earlier stage of development). As such, source builds require an Internet connection to fetch snapshots, and an OS that can execute the available snapshot binaries.
See https://doc.rust-lang.org/nightly/rustc/platform-support.html for a list of supported platforms. Only "host tools" platforms have a pre-compiled snapshot binary available; to compile for a platform without host tools you must cross-compile.
You may find that other platforms work, but these are our officially supported build environments that are most likely to work.
Getting Help
See https://www.rust-lang.org/community for a list of chat platforms and forums.
Contributing
See CONTRIBUTING.md.
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.
Trademark
The Rust Foundation owns and protects the Rust and Cargo trademarks and logos (the "Rust Trademarks").
If you want to use these names or brands, please read the media guide.
Third-party logos may be subject to third-party copyrights and trademarks. See Licenses for details.