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+# Installing from Source
+
+**Note: This document describes _building_ Rust _from source_.
+This is _not recommended_ if you don't know what you're doing.
+If you just want to install Rust, check out the [README.md](README.md) instead.**
+
+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:
+
+```sh
+./x.py <subcommand> [flags]
+```
+
+This is how the documentation and examples assume you are running `x.py`.
+See the [rustc dev guide][rustcguidebuild] 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][rustcguidebuild].
+
+[gettingstarted]: https://rustc-dev-guide.rust-lang.org/getting-started.html
+[rustcguidebuild]: https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html#what-is-xpy
+
+## Dependencies
+
+Make sure you have installed the dependencies:
+
+* `python` 3 or 2.7
+* `git`
+* A C compiler (when building for the host, `cc` is enough; cross-compiling may
+  need additional compilers)
+* `curl` (not needed on Windows)
+* `pkg-config` if you are compiling on Linux and targeting Linux
+* `libiconv` (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 documentation](https://llvm.org/docs/GettingStarted.html#host-c-toolchain-both-compiler-and-standard-library)
+* `ninja`, or GNU `make` 3.81 or later (Ninja is recommended, especially on
+  Windows)
+* `cmake` 3.13.4 or later
+* `libstdc++-static` may 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][sysllvm].
+
+[sysllvm]: https://rustc-dev-guide.rust-lang.org/building/new-target.html#using-pre-built-llvm
+
+
+## Building on a Unix-like system
+
+### Build steps
+
+1. Clone the [source] with `git`:
+
+   ```sh
+   git clone https://github.com/rust-lang/rust.git
+   cd rust
+   ```
+
+[source]: https://github.com/rust-lang/rust
+
+2. Configure the build settings:
+
+   ```sh
+   ./configure
+   ```
+
+   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: `./configure --set install.prefix=<path>`
+
+3. Build and install:
+
+   ```sh
+   ./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. By default, it will also include [Cargo], Rust's
+   package manager. You can disable this behavior by passing
+   `--set build.extended=false` to `./configure`.
+
+[Cargo]: https://github.com/rust-lang/cargo
+
+### 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 programmatically
+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.
+
+```sh
+./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:
+
+```powershell
+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`](https://www.java.com/en/download/help/path.html)
+from the Java documentation.
+
+[winget]: https://github.com/microsoft/winget-cli
+
+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][msys2] can be used to easily build Rust on Windows:
+
+[msys2]: https://www.msys2.org/
+
+1. Download the latest [MSYS2 installer][msys2] and go through the installer.
+
+2. Run `mingw32_shell.bat` or `mingw64_shell.bat` from 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 run `msys2_shell.cmd
+   -mingw32` or `msys2_shell.cmd -mingw64` from the command line instead.)
+
+3. From this terminal, install the required tools:
+
+   ```sh
+   # 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
+   ```
+
+4. Navigate to Rust's source code (or clone it), then build it:
+
+   ```sh
+   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.
+
+[Visual Studio]: https://visualstudio.microsoft.com/downloads/
+
+(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:
+
+```sh
+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.
+
+```batch
+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 creating a `config.toml` file (as described in
+[Building on a Unix-like system](#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:
+
+```sh
+./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.