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    Optimize counting digits in line numbers during error reporting further
    This one-ups #82248 by switching the strategy: Instead of dividing the value by 10 repeatedly, we compare with a limit that we multiply by 10 repeatedly. In my benchmarks, this took between 50% and 25% of the original time. The reasons for being faster are:
    1. While LLVM is able to replace a division by constant with a multiply + shift, a plain multiplication is still faster. However, this doesn't even factor, because
    2. Multiplication, unlike division, is const. We also use a simple for-loop instead of a more complex loop + break, which allows
    3. rustc to const-fold the whole loop, and indeed the assembly output simply shows a series of comparisons.


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    Feb 26, 2021


    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. More information about it can be found by running ./x.py --help or reading the rustc dev guide.

    Building on a Unix-like system

    1. Make sure you have installed the dependencies:

      • g++ 5.1 or later or clang++ 3.5 or later
      • python 3 or 2.7
      • GNU make 3.81 or later
      • cmake 3.4.3 or later
      • ninja
      • curl
      • git
      • ssl which comes in libssl-dev or openssl-devel
      • pkg-config if you are compiling on Linux and targeting Linux
    2. Clone the source with git:

      git clone http://www.shanzhaw.com/rust-lang/rust.git
      cd rust
    1. Configure the build settings:

      The Rust build system uses a file named config.toml in the root of the source tree to determine various configuration settings for the build. Copy the default config.toml.example to config.toml to get started.

      cp config.toml.example config.toml

      If you plan to use x.py install to create an installation, it is recommended that you set the prefix value in the [install] section to a directory.

      Create install directory if you are not installing in default directory

    2. Build and install:

      ./x.py build && ./x.py install

      When complete, ./x.py install will place several programs into $PREFIX/bin: rustc, the Rust compiler, and rustdoc, 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 cargo or set the build.extended key in config.toml to true to 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.


    MSYS2 can be used to easily build Rust on Windows:

    1. Grab the latest MSYS2 installer and go through the installer.

    2. Run mingw32_shell.bat or mingw64_shell.bat from 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 run msys2_shell.cmd -mingw32 or msys2_shell.cmd -mingw64 from the command line instead)

    3. 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 \
    4. Navigate to Rust's source code (or clone it), then build it:

      ./x.py build && ./x.py install


    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-gnu
      • x86_64-pc-windows-gnu
    • The MSVC ABI
      • i686-pc-windows-msvc
      • x86_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).

    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.


    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:


    If you are interested in contributing to the Rust project, please take a look at the Getting Started guide in the rustc-dev-guide.


    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.



    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.