Thank you for your interest in contributing to Rust! There are many ways to contribute, and we appreciate all of them.
- Feature Requests
- Bug Reports
- 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.
Feature requests need to go through a process to be approved by the relevant teams. Usually this requires a Final Comment Period (FCP) or even a Request for Comments (RFC). See Getting Started for more information about these processes.
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're using the nightly channel, please check if the bug exists in the latest toolchain before filing your bug. It might be fixed already.
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.
Similarly, to help others who encountered the bug find your issue, consider filing an issue with a descriptive title, which contains information that might be unique to it. This can be the language or compiler feature used, the conditions that trigger the bug, or part of the error message if there is any. An example could be: "impossible case reached" on lifetime inference for impl Trait in return position.
Opening an issue is as easy as following this link and filling out the fields in the appropriate provided template.
Pull requests (or PRs for short) 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 here, where contributors push changes to their personal fork and create pull requests to bring those changes into the source repository. We have more info about how to use git when contributing to Rust under the git section.
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 pull request description. For example,
Steve usually reviews documentation changes. So if you were to
make a documentation change, add
In addition to being reviewed by a human, pull requests are automatically tested thanks to continuous integration (CI). Basically, every time you open and update a pull request, CI builds the compiler and tests it against the compiler test suite, and also performs other tests such as checking that your pull request is in compliance with Rust's style guidelines.
Running continuous integration tests allows PR authors to catch mistakes early without going through a first review cycle, and also helps reviewers stay aware of the status of a particular pull request.
Rust has plenty of CI capacity, and you should never have to worry about wasting
computational resources each time you push a change. It is also perfectly fine
(and even encouraged!) to use the CI to test your changes if it can help your
productivity. In particular, we don't recommend running the full
x.py test suite locally,
since it takes a very long time to execute.
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:
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.
Depending on the scale of the change, you may see a slightly different form of
@bors r+ rollup
rollup tells @bors that this change should always be "rolled up".
Changes that are rolled up are tested and merged alongside other PRs, to
speed the process up. Typically only small changes that are expected not to conflict
with one another are marked as "always roll up".
You are now ready to file a pull request? Great! Here are a few points you should be aware of.
All pull requests should be filed against the
master branch, except in very
particular scenarios. Unless you know for sure that you should target another
master will be the right choice (it's also the default).
Make sure your pull request is in compliance with Rust's style guidelines by running
$ ./x.py test tidy --bless
We recommend to 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. The CI will also run tidy and will fail if tidy fails.
Rust follows a no merge-commit policy, meaning, when you encounter merge conflicts you are expected to always rebase instead of merging. E.g. always use rebase when bringing the latest changes from the master branch to your feature branch. Also, please make sure that fixup commits are squashed into other related commits with meaningful commit messages.
If you encounter merge conflicts or when a reviewer asks you to perform some
changes, your PR will get marked as
S-waiting-on-author. When you resolve
them, you should use
@rustbot to mark it as
@rustbot label -S-waiting-on-author +S-waiting-on-review
See this chapter for more details.
GitHub allows closing issues using keywords. This feature should be used to keep the issue tracker tidy. However, it is generally preferred to put the "closes #123" text in the PR description rather than the issue commit; particularly during rebasing, citing the issue number in the commit can "spam" the issue in question.
As a developer to this repository, you don't have to treat the following external projects differently from other crates that are directly in this repo:
They are just regular files and directories. This is in contrast to
(see below for those). Only tool authors will actually use any operations here.
There are two synchronization directions:
subtree push and
git subtree push -P src/tools/clippy email@example.com:your-github-name/rust-clippy sync-from-rust
takes all the changes that happened to the copy in this repo and creates commits on the remote repo that match the local changes. Every local commit that touched the subtree causes a commit on the remote repo, but is modified to move the files from the specified directory to the tool repo root.
Make sure to not pick the
master branch on the tool repo, so you can open a normal PR to the tool
to merge that subrepo push.
git subtree pull -P src/tools/clippy https://github.com/rust-lang/rust-clippy master
takes all changes since the last
subtree pull from the tool repo
and adds these commits to the rustc repo + a merge commit that moves the tool changes into
the specified directory in the rust repository.
It is recommended that you always do a push first and get that merged to the tool master branch.
Then, when you do a pull, the merge works without conflicts.
While it's definitely possible to resolve conflicts during a pull, you may have to redo the conflict
resolution if your PR doesn't get merged fast enough and there are new conflicts. Do not try to
rebase the result of a
git subtree pull, rebasing merge commits is a bad idea in general.
You always need to specify the
-P prefix to the subtree directory and the corresponding remote
repository. If you specify the wrong directory or repository
you'll get very fun merges that try to push the wrong directory to the wrong remote repository.
Luckily you can just abort this without any consequences by throwing away either the pulled commits
in rustc or the pushed branch on the remote and try again. It is usually fairly obvious
that this is happening because you suddenly get thousands of commits that want to be synchronized.
If you want to create a new subtree dependency from an existing repository, call (from this repository's root directory!)
git subtree add -P src/tools/clippy https://github.com/rust-lang/rust-clippy.git master
This will create a new commit, which you may not rebase under any circumstances! Delete the commit and redo the operation if you need to rebase.
Now you're done, the
src/tools/clippy directory behaves as if Clippy were
part of the rustc monorepo, so no one but you (or others that synchronize
subtrees) actually needs to use
Currently building Rust will also build the following external projects:
We allow breakage of these tools in the nightly channel. Maintainers of these projects will be notified of the breakages and should fix them as soon as possible.
After the external is fixed, one could add the changes with
git add path/to/submodule
outside the submodule.
In order to prepare your tool-fixing PR, you can run the build locally by doing
./x.py build src/tools/TOOL. If you will be editing the sources
there, you may wish to set
submodules = false in the
x.py from resetting to the original branch.
Breakage is not allowed in the beta and stable channels, and must be addressed before the PR is merged.
Rust's build system builds a number of tools that make use of the internals of the compiler and that are hosted in a separate repository, and included in Rust via git submodules. This includes RLS and Miri. If these tools break because of your changes, you may run into a sort of "chicken and egg" problem. These tools rely on the latest compiler to be built so you can't update them (in their own repositories) to reflect your changes to the compiler until those changes are merged into the compiler. At the same time, you can't get your changes merged into the compiler because the rust-lang/rust build won't pass until those tools build and pass their tests.
Luckily, a feature was added to Rust's build to make all of this easy to handle. The idea is that we allow these tools to be "broken", so that the rust-lang/rust build passes without trying to build them, then land the change in the compiler, and go update the tools that you broke. Some tools will require waiting for a nightly release before this can happen, while others use the builds uploaded after each bors merge and thus can be updated immediately (check the tool's documentation for details). Once you're done and the tools are working again, you go back in the compiler and update the tools so they can be distributed again.
This should avoid a bunch of synchronization dances and is also much easier on contributors as there's no need to block on rls/miri/other tools changes going upstream.
Here are those same steps in detail:
- (optional) First, if it doesn't exist already, create a
config.toml.examplein the root directory of the Rust repository. Set
submodules = falsein the
[build]section. This will prevent
x.pyfrom resetting to the original branch after you make your changes. If you need to update any submodules to their latest versions, see the section of this file about that for more information.
- (optional) Run
./x.py test src/tools/rls(substituting the submodule that broke for
rls). Fix any errors in the submodule (and possibly others).
- (optional) Make commits for your changes and send them to upstream repositories as a PR.
- (optional) Maintainers of these submodules will not merge the PR. The PR can't be merged because CI will be broken. You'll want to write a message on the PR referencing your change, and how the PR should be merged once your change makes it into a nightly.
- Wait for your PR to merge.
- Wait for a nightly
- (optional) Help land your PR on the upstream repository now that your changes are in nightly.
- (optional) Send a PR to rust-lang/rust updating the submodule.
These instructions are specific to updating
rls, however they may apply
to the other submodules as well. Please help by improving these instructions
if you find any discrepancies or special cases that need to be addressed.
To update the
rls submodule, start by running the appropriate
git submodule command.
For example, to update to the latest commit on the remote master branch,
you may want to run:
git submodule update --remote src/tools/rls
If you run
./x.py build now, and you are lucky, it may just work. If you see
an error message about patches that did not resolve to any crates, you will need
to complete a few more steps which are outlined with their rationale below.
(This error may change in the future to include more information.)
error: failed to resolve patches for `https://github.com/rust-lang/rls` Caused by: patch for `rls` in `https://github.com/rust-lang/rls` did not resolve to any crates failed to run: ~/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo build --manifest-path ~/rust/src/bootstrap/Cargo.toml
Specifically, the following section in Overriding dependencies reveals what the problem is:
Next up we need to ensure that our lock file is updated to use this new version of uuid so our project uses the locally checked out copy instead of one from crates.io. The way
[patch]works is that it'll load the dependency at ../path/to/uuid and then whenever crates.io is queried for versions of uuid it'll also return the local version.
This means that the version number of the local checkout is significant and will affect whether the patch is used. Our manifest declared uuid = "1.0" which means we'll only resolve to >= 1.0.0, < 2.0.0, and Cargo's greedy resolution algorithm also means that we'll resolve to the maximum version within that range. Typically this doesn't matter as the version of the git repository will already be greater or match the maximum version published on crates.io, but it's important to keep this in mind!
This says that when we updated the submodule, the version number in our
src/tools/rls/Cargo.toml changed. The new version is different from
the version in
Cargo.lock, so the build can no longer continue.
To resolve this, we need to update
Cargo.lock. Luckily, cargo provides a
command to do this easily.
$ cargo update -p rls
This should change the version listed in
Cargo.lock to the new version you updated
the submodule to. Running
./x.py build should work now.
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 (e.g.
lib.rs). Documentation pull requests function
in the same way as other pull requests.
To find documentation-related issues, sort by the T-doc label.
You can find documentation style guidelines in RFC 1574.
In many cases, you don't need a full
./x.py doc --stage 2, which will build
the entire stage 2 compiler and compile the various books published on
doc.rust-lang.org. When updating documentation for the standard library,
./x.py doc library/std. If that fails, or if you need to
see the output from the latest version of
Results should appear in
You can also use
rustdoc directly to check small fixes. For example,
rustdoc src/doc/reference.md will render reference to
The CSS might be messed up, but you can verify that the HTML is right.
Contributions to the rustc-dev-guide are always welcome, and can be made directly at the rust-lang/rustc-dev-guide repo. The issue tracker in that repo is also a great way to find things that need doing. There are issues for beginners and advanced compiler devs alike!
Just a few things to keep in mind:
Please limit line length to 100 characters. This is enforced by CI, and you can run the checks locally with
When contributing text to the guide, please contextualize the information with some time period and/or a reason so that the reader knows how much to trust or mistrust the information. Aim to provide a reasonable amount of context, possibly including but not limited to:
A reason for why the data may be out of date other than "change", as change is a constant across the project.
The date the comment was added, e.g. instead of writing "Currently, ..." or "As of now, ...", consider writing "As of January 2021, ...". Try to format the date as
<MONTH> <YEAR>to ease search.
Additionally, include a machine-readable comment of the form
<!-- date: 2021-01 -->(if the current month is January 2021). We have an automated tool that uses these (in
So, for the month of January 2021, the comment would look like:
As of <!-- date: 2021-01 --> January 2021. Make sure to put the comment between
January 2021; see PR #1066 for the rationale.
A link to a relevant WG, tracking issue,
rustcrustdoc page, or similar, that may provide further explanation for the change process or a way to verify that the information is not outdated.
If a text grows rather long (more than a few page scrolls) or complicated (more than four subsections) it might benefit from having a Table of Contents at the beginning, which you can auto-generate by including the
<!-- toc -->marker.
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.
@rustbot, anyone can help triage issues by adding
appropriate labels to issues that haven't been triaged yet:
Yellow, A-prefixed labels state which area of the project an issue relates to.
Magenta, B-prefixed labels identify bugs which are blockers.
Dark blue, beta- labels track changes which need to be backported into the beta branches.
Light purple, C-prefixed labels represent the category of an issue.
Green, E-prefixed labels explain the level of experience necessary to fix the issue.
The dark blue final-comment-period label marks bugs that are using the RFC signoff functionality of rfcbot and are currently in the final comment period.
Red, I-prefixed labels indicate the importance of the issue. The I-nominated label indicates that an issue has been nominated for discussion at the next meeting of the team tagged using a T-prefixed label. Similarly, the I-prioritize indicates that an issue has been requested to be prioritized by the appropriate team.
The purple metabug label marks lists of bugs collected by other categories.
Purple gray, O-prefixed labels are the operating system or platform that this issue is specific to.
Orange, P-prefixed labels indicate a bug's priority. These labels can be assigned by anyone that understand the issue and is able to prioritize it, and replace the I-prioritize label.
The gray proposed-final-comment-period label marks bugs that are using the RFC signoff functionality of rfcbot and are currently awaiting signoff of all team members in order to enter the final comment period.
Pink, regression-prefixed labels track regressions from stable to the release channels.
The light orange relnotes label marks issues that should be documented in the release notes of the next release.
Gray, S-prefixed labels are used for tracking the status of pull requests.
Blue, T-prefixed bugs denote which team the issue belongs to.
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 rust-lang/rust:
- Answer questions in the Get Help! channels on the Rust Discord server, on users.rust-lang.org, or on StackOverflow.
- Participate in the RFC process.
- Find a requested community library, build it, and publish it to Crates.io. Easier said than done, but very, very valuable!
For people new to Rust, and just starting to contribute, or even for more seasoned developers, some useful places to look for information are:
- This guide contains information about how various parts of the compiler work and how to contribute to the compiler
- Rust Forge contains additional documentation, including write-ups of how to achieve common tasks
- 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, is 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
- Google is always helpful when programming. You can search all Rust documentation (the standard library, the compiler, the books, the references, and the guides) to quickly find information about the language and compiler.
- You can also use Rustdoc's built-in search feature to find documentation on
types and functions within the crates you're looking at. You can also search
by type signature! For example, searching for
* -> vecshould find all functions that return a
Vec<T>. Hint: Find more tips and keyboard shortcuts by typing
?on any Rustdoc page!
- Don't be afraid to ask! The Rust community is friendly and helpful.