Contributing to Rust
Thank you for your interest in contributing to Rust! There are many ways to contribute, and we appreciate all of them. This document is a bit long, so here's links to the major sections:
- Feature Requests
- Bug Reports
- The Build System
- Pull Requests
- Writing Documentation
- Issue Triage
- Out-of-tree Contributions
- Helpful Links and Information
As a reminder, all contributors are expected to follow our Code of Conduct.
To request a change to the way that the Rust language works, please open an issue in the RFCs repository rather than this one. New features and other significant language changes must go through the RFC process.
While bugs are unfortunate, they're a reality in software. We can't fix what we don't know about, so please report liberally. If you're not sure if something is a bug or not, feel free to file a bug anyway.
If you believe reporting your bug publicly represents a security risk to Rust users, please follow our instructions for reporting security vulnerabilities.
If you have the chance, before reporting a bug, please search existing issues, as it's possible that someone else has already reported your error. This doesn't always work, and sometimes it's hard to know what to search for, so consider this extra credit. We won't mind if you accidentally file a duplicate report.
Opening an issue is as easy as following this link and filling out the fields. Here's a template that you can use to file a bug, though it's not necessary to use it exactly:
<short summary of the bug> I tried this code: <code sample that causes the bug> I expected to see this happen: <explanation> Instead, this happened: <explanation> ## Meta `rustc --version --verbose`: Backtrace:
All three components are important: what you did, what you expected, what
happened instead. Please include the output of
rustc --version --verbose,
which includes important information about what platform you're on, what
version of Rust you're using, etc.
Sometimes, a backtrace is helpful, and so including that is nice. To get
a backtrace, set the
RUST_BACKTRACE environment variable to a value
0. The easiest way
to do this is to invoke
rustc like this:
$ RUST_BACKTRACE=1 rustc ...
The Build System
Rust's build system allows you to bootstrap the compiler, run tests & benchmarks, generate documentation, install a fresh build of Rust, and more. It's your best friend when working on Rust, allowing you to compile & test your contributions before submission.
The build system lives in the
src/bootstrap directory in the
project root. Our build system is itself written in Rust and is based on Cargo
to actually build all the compiler's crates. If you have questions on the build
system internals, try asking in
Note: the build system was recently rewritten from a jungle of makefiles to the current incarnation you'll see in
src/bootstrap. If you experience bugs you can temporarily revert back to the makefiles with
Before you can start building the compiler you need to configure the build for
your system. In most cases, that will just mean using the defaults provided
for Rust. Configuring involves invoking the
configure script in the project
There are large number of options accepted by this script to alter the configuration used later in the build process. Some options to note:
--enable-debug- Build a debug version of the compiler (disables optimizations, which speeds up compilation of stage1 rustc)
--enable-optimize- Enable optimizations (can be used with
--enable-debugto make a debug build with optimizations)
--disable-valgrind-rpass- Don't run tests with valgrind
--enable-clang- Prefer clang to gcc for building dependencies (e.g., LLVM)
--enable-ccache- Invoke clang/gcc with ccache to re-use object files between builds
--enable-compiler-docs- Build compiler documentation
To see a full list of options, run
./configure script will generate a
Makefile, this is actually
just a thin veneer over the actual build system driver,
x.py. This file, at
the root of the repository, is used to build, test, and document various parts
of the compiler. You can execute it as:
python x.py build
On some systems you can also use the shorter version:
To learn more about the driver and top-level targets, you can execute:
python x.py --help
The general format for the driver script is:
python x.py <command> [<directory>]
Some example commands are
doc. These will build, test,
and document the specified directory. The second argument,
optional and defaults to working over the entire compiler. If specified,
however, only that specific directory will be built. For example:
# build the entire compiler python x.py build # build all documentation python x.py doc # run all test suites python x.py test # build only the standard library python x.py build src/libstd # test only one particular test suite python x.py test src/test/rustdoc # build only the stage0 libcore library python x.py build src/libcore --stage 0
You can explore the build system throught the various
--help pages for each
subcommand. For example to learn more about a command you can run:
python x.py build --help
To learn about all possible rules you can execute, run:
python x.py build --help --verbose
Some common invocations of
x.py build --help- show the help message and explain the subcommand
x.py build src/libtest --stage 1- build up to (and including) the first stage. For most cases we don't need to build the stage2 compiler, so we can save time by not building it. The stage1 compiler is a fully functioning compiler and (probably) will be enough to determine if your change works as expected.
x.py build src/rustc --stage 1- This will build just rustc, without libstd. This is the fastest way to recompile after you changed only rustc source code. Note however that the resulting rustc binary won't have a stdlib to link against by default. You can build libstd once with
x.py build src/libstd, but it is is only guaranteed to work if recompiled, so if there are any issues recompile it.
x.py test- build the full compiler & run all tests (takes a while). This is what gets run by the continuous integration system against your pull request. You should run this before submitting to make sure your tests pass & everything builds in the correct manner.
x.py test src/libstd --stage 1- test the standard library without recompiling stage 2.
x.py test src/test/run-pass --test-args TESTNAME- Run a matching set of tests.
TESTNAMEshould be a substring of the tests to match against e.g. it could be the fully qualified test name, or just a part of it.
x.py test src/test/run-pass --stage 1 --test-args <substring-of-test-name>- Run a single rpass test with the stage1 compiler (this will be quicker than running the command above as we only build the stage1 compiler, not the entire thing). You can also leave off the directory argument to run all stage1 test types.
x.py test src/libcore --stage 1- Run stage1 tests in
x.py test src/tools/tidy- Check that the source code is in compliance with Rust's style guidelines. There is no official document describing Rust's full guidelines as of yet, but basic rules like 4 spaces for indentation and no more than 99 characters in a single line should be kept in mind when writing code.
Pull requests are the primary mechanism we use to change Rust. GitHub itself has some great documentation on using the Pull Request feature. We use the 'fork and pull' model described there.
Please make pull requests against the
Compiling all of
make check can take a while. When testing your pull request,
consider using one of the more specialized
make targets to cut down on the
amount of time you have to wait. You need to have built the compiler at least
once before running these will work, but that’s only one full build rather than
one each time.
$ python x.py test --stage 1
is one such example, which builds just
rustc, and then runs the tests. If
you’re adding something to the standard library, try
$ python x.py test src/libstd --stage 1
Please make sure your pull request is in compliance with Rust's style guidelines by running
$ python x.py test src/tools/tidy
Make this check before every pull request (and every new commit in a pull request) ; you can add git hooks before every push to make sure you never forget to make this check.
All pull requests are reviewed by another person. We have a bot, @rust-highfive, that will automatically assign a random person to review your request.
If you want to request that a specific person reviews your pull request,
you can add an
r? to the message. For example, Steve usually reviews
documentation changes. So if you were to make a documentation change, add
to the end of the message, and @rust-highfive will assign @steveklabnik instead of a random person. This is entirely optional.
After someone has reviewed your pull request, they will leave an annotation
on the pull request with an
r+. It will look something like this:
@bors: r+ 38fe8d2
This tells @bors, our lovable integration bot, that your pull request has
been approved. The PR then enters the merge queue, where @bors
will run all the tests on every platform we support. If it all works out,
@bors will merge your code into
master and close the pull request.
Speaking of tests, Rust has a comprehensive test suite. More information about it can be found here.
Documentation improvements are very welcome. The source of
is located in
src/doc in the tree, and standard API documentation is generated
from the source code itself.
Documentation pull requests function in the same way as other pull requests,
though you may see a slightly different form of
@bors: r+ 38fe8d2 rollup
rollup tells @bors that this change is eligible for a 'rollup'.
To save @bors some work, and to get small changes through more quickly, when
@bors attempts to merge a commit that's rollup-eligible, it will also merge
the other rollup-eligible patches too, and they'll get tested and merged at
the same time.
To find documentation-related issues, sort by the A-docs label.
In many cases, you don't need a full
make doc. You can use
to check small fixes. For example,
rustdoc src/doc/reference.md will render
doc/reference.html. The CSS might be messed up, but you can
verify that the HTML is right.
Sometimes, an issue will stay open, even though the bug has been fixed. And sometimes, the original bug may go stale because something has changed in the meantime.
It can be helpful to go through older bug reports and make sure that they are still valid. Load up an older issue, double check that it's still true, and leave a comment letting us know if it is or is not. The least recently updated sort is good for finding issues like this.
Contributors with sufficient permissions on the Rust repo can help by adding labels to triage issues:
Yellow, A-prefixed labels state which area of the project an issue relates to.
Magenta, B-prefixed labels identify bugs which are blockers.
Green, E-prefixed labels explain the level of experience necessary to fix the issue.
Red, I-prefixed labels indicate the importance of the issue. The I-nominated label indicates that an issue has been nominated for prioritizing at the next triage meeting.
Orange, P-prefixed labels indicate a bug's priority. These labels are only assigned during triage meetings, and replace the I-nominated label.
Blue, T-prefixed bugs denote which team the issue belongs to.
Dark blue, beta- labels track changes which need to be backported into the beta branches.
The purple metabug label marks lists of bugs collected by other categories.
If you're looking for somewhere to start, check out the E-easy tag.
There are a number of other ways to contribute to Rust that don't deal with this repository.
Participate in the RFC process.
Helpful Links and Information
For people new to Rust, and just starting to contribute, or even for more seasoned developers, some useful places to look for information are:
- The Rust Internals forum, a place to ask questions and discuss Rust's internals
- The generated documentation for rust's compiler
- The rust reference, even though it doesn't specifically talk about Rust's internals, it's a great resource nonetheless
- Although out of date, Tom Lee's great blog article is very helpful
- rustaceans.org is helpful, but mostly dedicated to IRC
- The Rust Compiler Testing Docs
- For @bors, this cheat sheet is helpful (Remember to replace
@borsin the commands that you use.)
- Google! (search only in Rust Documentation to find types, traits, etc. quickly)
- Don't be afraid to ask! The Rust community is friendly and helpful.