8eef79ca9a
Fix incorrect suggestions for E0605 Fixes #84598. Here is a simplified version of the problem presented in issue #84598: ```Rust #![allow(unused_variables)] #![allow(dead_code)] trait T { fn t(&self) -> i32; } unsafe fn foo(t: *mut dyn T) { (t as &dyn T).t(); } fn main() {} ``` The current output is: ``` error[E0605]: non-primitive cast: `*mut (dyn T + 'static)` as `&dyn T` --> src/main.rs:7:5 | 7 | (t as &dyn T).t(); | ^^^^^^^^^^^^^ invalid cast | help: borrow the value for the cast to be valid | 7 | (&t as &dyn T).t(); | ^ ``` This is incorrect, though: The cast will _not_ be valid when writing `&t` instead of `t`: ``` error[E0277]: the trait bound `*mut (dyn T + 'static): T` is not satisfied --> t4.rs:7:6 | 7 | (&t as &dyn T).t(); | ^^ the trait `T` is not implemented for `*mut (dyn T + 'static)` | = note: required for the cast to the object type `dyn T` ``` The correct suggestion is `&*t`, which I have implemented in this pull request. Of course, this suggestion will always require an unsafe block, but arguably, that's what the user really wants if they're trying to cast a pointer to a reference. In any case, claiming that the cast will be valid after implementing the suggestion is overly optimistic, as the coercion logic doesn't seem to resolve all nested obligations, i.e. the cast may still be invalid after implementing the suggestion. I have therefore rephrased the suggestion slightly ("consider borrowing the value" instead of "borrow the value for the cast to be valid"). Additionally, I have fixed another incorrect suggestion not mentioned in #84598, which relates to casting immutable references to mutable ones: ```rust fn main() { let mut x = 0; let m = &x as &mut i32; } ``` currently leads to ``` error[E0605]: non-primitive cast: `&i32` as `&mut i32` --> t5.rs:3:13 | 3 | let m = &x as &mut i32; | ^^^^^^^^^^^^^^ invalid cast | help: borrow the value for the cast to be valid | 3 | let m = &mut &x as &mut i32; | ^^^^ ``` which is obviously incorrect: ``` error[E0596]: cannot borrow data in a `&` reference as mutable --> t5.rs:3:13 | 3 | let m = &mut &x as &mut i32; | ^^^^^^^ cannot borrow as mutable ``` I've changed the suggestion to a note explaining the problem: ``` error[E0605]: non-primitive cast: `&i32` as `&mut i32` --> t5.rs:3:13 | 3 | let m = &x as &mut i32; | ^^^^^^^^^^^^^^ invalid cast | note: this reference is immutable --> t5.rs:3:13 | 3 | let m = &x as &mut i32; | ^^ note: trying to cast to a mutable reference type --> t5.rs:3:19 | 3 | let m = &x as &mut i32; | ^^^^^^^^ ``` In this example, it would have been even nicer to suggest replacing `&x` with `&mut x`, but this would be much more complex because we would have to take apart the expression to be cast (currently, we only look at its type), and `&x` could be stored in a variable, where such a suggestion would not even be directly applicable: ```rust fn main() { let mut x = 0; let r = &x; let m = r as &mut i32; } ``` My solution covers this case, too. |
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| Cargo.lock | ||
| Cargo.toml | ||
| CODE_OF_CONDUCT.md | ||
| config.toml.example | ||
| configure | ||
| CONTRIBUTING.md | ||
| COPYRIGHT | ||
| LICENSE-APACHE | ||
| LICENSE-MIT | ||
| README.md | ||
| RELEASES.md | ||
| rustfmt.toml | ||
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| x.py | ||
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 the Getting Started section of the rustc-dev-guide 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 in the root of the project.
The x.py command can be run directly on most systems in the following format:
./x.py <subcommand> [flags]
This is how the documentation and examples assume you are running x.py.
Systems such as Ubuntu 20.04 LTS do not create the necessary python command by default when Python is installed that allows x.py to be run directly. In that case you can either create a symlink for python (Ubuntu provides the python-is-python3 package for this), or run x.py using Python itself:
# Python 3
python3 x.py <subcommand> [flags]
# Python 2.7
python2.7 x.py <subcommand> [flags]
More information about x.py can be found
by running it with the --help flag or reading the rustc dev guide.
Building on a Unix-like system
-
Make sure you have installed the dependencies:
g++5.1 or later orclang++3.5 or laterpython3 or 2.7- GNU
make3.81 or later cmake3.13.4 or laterninjacurlgitsslwhich comes inlibssl-devoropenssl-develpkg-configif you are compiling on Linux and targeting Linux
-
Clone the source with
git:git clone https://github.com/rust-lang/rust.git cd rust
-
Configure the build settings:
The Rust build system uses a file named
config.tomlin the root of the source tree to determine various configuration settings for the build. Copy the defaultconfig.toml.exampletoconfig.tomlto get started.cp config.toml.example config.tomlIf you plan to use
x.py installto create an installation, it is recommended that you set theprefixvalue in the[install]section to a directory.Create install directory if you are not installing in default directory
-
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. This install does not include Cargo, Rust's package manager. To build and install Cargo, you may run./x.py install cargoor set thebuild.extendedkey inconfig.tomltotrueto build and install all tools.
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', '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:
./x.py build && ./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 the
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 build
Currently, 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 copying the config.toml file (as described
in Installing From Source), and modifying the
build option under the [build] section.
Configure and Make
While it's not the recommended build system, this project also provides a
configure script and makefile (the latter of which just invokes x.py).
./configure
make && sudo make install
When using the configure script, the generated config.mk file may override the
config.toml file. To go back to the config.toml file, delete the generated
config.mk file.
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. I.e., 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 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, 10, ...) | ✓ | ✓ |
| Linux (kernel 2.6.32, glibc 2.11 or later) | ✓ | ✓ |
| macOS (10.7 Lion or later) | (*) | ✓ |
(*): Apple dropped support for running 32-bit binaries starting from macOS 10.15 and iOS 11. Due to this decision from Apple, the targets are no longer useful to our users. Please read our blog post for more info.
You may find that other platforms work, but these are our officially supported build environments that are most likely to work.
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
If you are interested in contributing to the Rust project, please take a look at the Getting Started guide in the rustc-dev-guide.
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 programming language is an open source, community project governed by a core team. It is also sponsored by the Mozilla Foundation (“Mozilla”), which 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.