2 [contributing-to-rust]: #contributing-to-rust
4 Thank you for your interest in contributing to Rust! There are many ways to
5 contribute, and we appreciate all of them. This document is a bit long, so here's
6 links to the major sections:
8 * [Feature Requests](#feature-requests)
9 * [Bug Reports](#bug-reports)
10 * [The Build System](#the-build-system)
11 * [Pull Requests](#pull-requests)
12 * [Writing Documentation](#writing-documentation)
13 * [Issue Triage](#issue-triage)
14 * [Out-of-tree Contributions](#out-of-tree-contributions)
15 * [Helpful Links and Information](#helpful-links-and-information)
17 If you have questions, please make a post on [internals.rust-lang.org][internals] or
18 hop on the [Rust Discord server][rust-discord] or [Rust Zulip server][rust-zulip].
20 As a reminder, all contributors are expected to follow our [Code of Conduct][coc].
22 The [rustc-dev-guide] is your friend! It describes how the compiler works and how
23 to contribute to it in more detail than this document.
25 If this is your first time contributing, the [walkthrough] chapter of the guide
26 can give you a good example of how a typical contribution would go.
28 [internals]: https://internals.rust-lang.org
29 [rust-discord]: http://discord.gg/rust-lang
30 [rust-zulip]: https://rust-lang.zulipchat.com
31 [coc]: https://www.rust-lang.org/conduct.html
32 [rustc-dev-guide]: https://rustc-dev-guide.rust-lang.org/
33 [walkthrough]: https://rustc-dev-guide.rust-lang.org/walkthrough.html
36 [feature-requests]: #feature-requests
38 To request a change to the way the Rust language works, please head over
39 to the [RFCs repository](https://github.com/rust-lang/rfcs) and view the
40 [README](https://github.com/rust-lang/rfcs/blob/master/README.md)
44 [bug-reports]: #bug-reports
46 While bugs are unfortunate, they're a reality in software. We can't fix what we
47 don't know about, so please report liberally. If you're not sure if something
48 is a bug or not, feel free to file a bug anyway.
50 **If you believe reporting your bug publicly represents a security risk to Rust users,
51 please follow our [instructions for reporting security vulnerabilities](https://www.rust-lang.org/policies/security)**.
53 If you're using the nightly channel, please check if the bug exists in the
54 latest toolchain before filing your bug. It might be fixed already.
56 If you have the chance, before reporting a bug, please [search existing
57 issues](https://github.com/rust-lang/rust/search?q=&type=Issues&utf8=%E2%9C%93),
58 as it's possible that someone else has already reported your error. This doesn't
59 always work, and sometimes it's hard to know what to search for, so consider this
60 extra credit. We won't mind if you accidentally file a duplicate report.
62 Similarly, to help others who encountered the bug find your issue,
63 consider filing an issue with a descriptive title, which contains information that might be unique to it.
64 This can be the language or compiler feature used, the conditions that trigger the bug,
65 or part of the error message if there is any.
66 An example could be: **"impossible case reached" on lifetime inference for impl Trait in return position**.
68 Opening an issue is as easy as following [this
69 link](https://github.com/rust-lang/rust/issues/new) and filling out the fields.
70 Here's a template that you can use to file a bug, though it's not necessary to
73 <short summary of the bug>
77 <code sample that causes the bug>
79 I expected to see this happen: <explanation>
81 Instead, this happened: <explanation>
85 `rustc --version --verbose`:
89 All three components are important: what you did, what you expected, what
90 happened instead. Please include the output of `rustc --version --verbose`,
91 which includes important information about what platform you're on, what
92 version of Rust you're using, etc.
94 Sometimes, a backtrace is helpful, and so including that is nice. To get
95 a backtrace, set the `RUST_BACKTRACE` environment variable to a value
96 other than `0`. The easiest way
97 to do this is to invoke `rustc` like this:
100 $ RUST_BACKTRACE=1 rustc ...
105 For info on how to configure and build the compiler, please see [this
106 chapter][rustcguidebuild] of the rustc-dev-guide. This chapter contains info for
107 contributions to the compiler and the standard library. It also lists some
108 really useful commands to the build system (`./x.py`), which could save you a
111 [rustcguidebuild]: https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html
114 [pull-requests]: #pull-requests
116 Pull requests are the primary mechanism we use to change Rust. GitHub itself
117 has some [great documentation][about-pull-requests] on using the Pull Request feature.
118 We use the "fork and pull" model [described here][development-models], where
119 contributors push changes to their personal fork and create pull requests to
120 bring those changes into the source repository.
122 [about-pull-requests]: https://help.github.com/articles/about-pull-requests/
123 [development-models]: https://help.github.com/articles/about-collaborative-development-models/
125 Please make pull requests against the `master` branch.
127 Rust follows a no merge policy, meaning, when you encounter merge
128 conflicts you are expected to always rebase instead of merge.
129 E.g. always use rebase when bringing the latest changes from
130 the master branch to your feature branch.
131 Also, please make sure that fixup commits are squashed into other related
132 commits with meaningful commit messages.
134 GitHub allows [closing issues using keywords][closing-keywords]. This feature
135 should be used to keep the issue tracker tidy. However, it is generally preferred
136 to put the "closes #123" text in the PR description rather than the issue commit;
137 particularly during rebasing, citing the issue number in the commit can "spam"
138 the issue in question.
140 [closing-keywords]: https://help.github.com/en/articles/closing-issues-using-keywords
142 Please make sure your pull request is in compliance with Rust's style
143 guidelines by running
145 $ python x.py test tidy
147 Make this check before every pull request (and every new commit in a pull
148 request); you can add [git hooks](https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks)
149 before every push to make sure you never forget to make this check.
151 All pull requests are reviewed by another person. We have a bot,
152 [@rust-highfive][rust-highfive], that will automatically assign a random person to review your
155 If you want to request that a specific person reviews your pull request,
156 you can add an `r?` to the pull request description. For example, [Steve][steveklabnik] usually reviews
157 documentation changes. So if you were to make a documentation change, add
161 to the end of the pull request description, and [@rust-highfive][rust-highfive] will assign
162 [@steveklabnik][steveklabnik] instead of a random person. This is entirely optional.
164 After someone has reviewed your pull request, they will leave an annotation
165 on the pull request with an `r+`. It will look something like this:
169 This tells [@bors][bors], our lovable integration bot, that your pull request has
170 been approved. The PR then enters the [merge queue][merge-queue], where [@bors][bors]
171 will run all the tests on every platform we support. If it all works out,
172 [@bors][bors] will merge your code into `master` and close the pull request.
174 Depending on the scale of the change, you may see a slightly different form of `r+`:
178 The additional `rollup` tells [@bors][bors] that this change is eligible for to be
179 "rolled up". Changes that are rolled up are tested and merged at the same time, to
180 speed the process up. Typically only small changes that are expected not to conflict
181 with one another are rolled up.
183 [rust-highfive]: https://github.com/rust-highfive
184 [steveklabnik]: https://github.com/steveklabnik
185 [bors]: https://github.com/bors
186 [merge-queue]: https://buildbot2.rust-lang.org/homu/queue/rust
188 Speaking of tests, Rust has a comprehensive test suite. More information about
189 it can be found [here][rctd].
191 ### External Dependencies (subtree)
193 As a developer to this repository, you don't have to treat the following external projects
194 differently from other crates that are directly in this repo:
198 They are just regular files and directories. This is in contrast to `submodule` dependencies
199 (see below for those). Only tool authors will actually use any operations here.
201 #### Synchronizing a subtree
203 There are two synchronization directions: `subtree push` and `subtree pull`.
206 git subtree push -P src/tools/clippy git@github.com:your-github-name/rust-clippy sync-from-rust
209 takes all the changes that
210 happened to the copy in this repo and creates commits on the remote repo that match the local
211 changes. Every local commit that touched the subtree causes a commit on the remote repo, but is
212 modified to move the files from the specified directory to the tool repo root.
214 Make sure to not pick the `master` branch on the tool repo, so you can open a normal PR to the tool
215 to merge that subrepo push.
218 git subtree pull -P src/tools/clippy https://github.com/rust-lang/rust-clippy master
221 takes all changes since the last `subtree pull` from the tool repo
222 repo and adds these commits to the rustc repo + a merge commit that moves the tool changes into
223 the specified directory in the rust repository.
225 It is recommended that you always do a push first and get that merged to the tool master branch.
226 Then, when you do a pull, the merge works without conflicts.
227 While it's definitely possible to resolve conflicts during a pull, you may have to redo the conflict
228 resolution if your PR doesn't get merged fast enough and there are new conflicts. Do not try to
229 rebase the result of a `git subtree pull`, rebasing merge commits is a bad idea in general.
231 You always need to specify the `-P` prefix to the subtree directory and the corresponding remote
232 repository. If you specify the wrong directory or repository
233 you'll get very fun merges that try to push the wrong directory to the wrong remote repository.
234 Luckily you can just abort this without any consequences by throwing away either the pulled commits
235 in rustc or the pushed branch on the remote and try again. It is usually fairly obvious
236 that this is happening because you suddenly get thousands of commits that want to be synchronized.
238 #### Creating a new subtree dependency
240 If you want to create a new subtree dependency from an existing repository, call (from this
241 repository's root directory!)
244 git subtree add -P src/tools/clippy https://github.com/rust-lang/rust-clippy.git master
247 This will create a new commit, which you may not rebase under any circumstances! Delete the commit
248 and redo the operation if you need to rebase.
250 Now you're done, the `src/tools/clippy` directory behaves as if Clippy were part of the rustc
251 monorepo, so no one but you (or others that synchronize subtrees) actually needs to use `git subtree`.
254 ### External Dependencies (submodules)
256 Currently building Rust will also build the following external projects:
258 * [miri](https://github.com/rust-lang/miri)
259 * [rustfmt](https://github.com/rust-lang/rustfmt)
260 * [rls](https://github.com/rust-lang/rls/)
262 We allow breakage of these tools in the nightly channel. Maintainers of these
263 projects will be notified of the breakages and should fix them as soon as
266 After the external is fixed, one could add the changes with
269 git add path/to/submodule
272 outside the submodule.
274 In order to prepare your tool-fixing PR, you can run the build locally by doing
275 `./x.py build src/tools/TOOL`. If you will be editing the sources
276 there, you may wish to set `submodules = false` in the `config.toml`
277 to prevent `x.py` from resetting to the original branch.
279 Breakage is not allowed in the beta and stable channels, and must be addressed
280 before the PR is merged.
282 #### Breaking Tools Built With The Compiler
284 Rust's build system builds a number of tools that make use of the
285 internals of the compiler. This includes
286 [RLS](https://github.com/rust-lang/rls) and
287 [rustfmt](https://github.com/rust-lang/rustfmt). If these tools
288 break because of your changes, you may run into a sort of "chicken and egg"
289 problem. These tools rely on the latest compiler to be built so you can't update
290 them to reflect your changes to the compiler until those changes are merged into
291 the compiler. At the same time, you can't get your changes merged into the compiler
292 because the rust-lang/rust build won't pass until those tools build and pass their
295 That means that, in the default state, you can't update the compiler without first
296 fixing rustfmt, rls and the other tools that the compiler builds.
298 Luckily, a feature was [added to Rust's build](https://github.com/rust-lang/rust/issues/45861)
299 to make all of this easy to handle. The idea is that we allow these tools to be "broken",
300 so that the rust-lang/rust build passes without trying to build them, then land the change
301 in the compiler, wait for a nightly, and go update the tools that you broke. Once you're done
302 and the tools are working again, you go back in the compiler and update the tools
303 so they can be distributed again.
305 This should avoid a bunch of synchronization dances and is also much easier on contributors as
306 there's no need to block on rls/rustfmt/other tools changes going upstream.
308 Here are those same steps in detail:
310 1. (optional) First, if it doesn't exist already, create a `config.toml` by copying
311 `config.toml.example` in the root directory of the Rust repository.
312 Set `submodules = false` in the `[build]` section. This will prevent `x.py`
313 from resetting to the original branch after you make your changes. If you
314 need to [update any submodules to their latest versions](#updating-submodules),
315 see the section of this file about that for more information.
316 2. (optional) Run `./x.py test src/tools/rustfmt` (substituting the submodule
317 that broke for `rustfmt`). Fix any errors in the submodule (and possibly others).
318 3. (optional) Make commits for your changes and send them to upstream repositories as a PR.
319 4. (optional) Maintainers of these submodules will **not** merge the PR. The PR can't be
320 merged because CI will be broken. You'll want to write a message on the PR referencing
321 your change, and how the PR should be merged once your change makes it into a nightly.
322 5. Wait for your PR to merge.
323 6. Wait for a nightly
324 7. (optional) Help land your PR on the upstream repository now that your changes are in nightly.
325 8. (optional) Send a PR to rust-lang/rust updating the submodule.
327 #### Updating submodules
329 These instructions are specific to updating `rustfmt`, however they may apply
330 to the other submodules as well. Please help by improving these instructions
331 if you find any discrepancies or special cases that need to be addressed.
333 To update the `rustfmt` submodule, start by running the appropriate
334 [`git submodule` command](https://git-scm.com/book/en/v2/Git-Tools-Submodules).
335 For example, to update to the latest commit on the remote master branch,
338 git submodule update --remote src/tools/rustfmt
340 If you run `./x.py build` now, and you are lucky, it may just work. If you see
341 an error message about patches that did not resolve to any crates, you will need
342 to complete a few more steps which are outlined with their rationale below.
344 *(This error may change in the future to include more information.)*
346 error: failed to resolve patches for `https://github.com/rust-lang/rustfmt`
349 patch for `rustfmt-nightly` in `https://github.com/rust-lang/rustfmt` did not resolve to any crates
350 failed to run: ~/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo build --manifest-path ~/rust/src/bootstrap/Cargo.toml
353 If you haven't used the `[patch]`
354 section of `Cargo.toml` before, there is [some relevant documentation about it
355 in the cargo docs](http://doc.crates.io/manifest.html#the-patch-section). In
356 addition to that, you should read the
357 [Overriding dependencies](http://doc.crates.io/specifying-dependencies.html#overriding-dependencies)
358 section of the documentation as well.
360 Specifically, the following [section in Overriding dependencies](http://doc.crates.io/specifying-dependencies.html#testing-a-bugfix) reveals what the problem is:
362 > 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.
364 > 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!
366 This says that when we updated the submodule, the version number in our
367 `src/tools/rustfmt/Cargo.toml` changed. The new version is different from
368 the version in `Cargo.lock`, so the build can no longer continue.
370 To resolve this, we need to update `Cargo.lock`. Luckily, cargo provides a
371 command to do this easily.
374 $ cargo update -p rustfmt-nightly
377 This should change the version listed in `Cargo.lock` to the new version you updated
378 the submodule to. Running `./x.py build` should work now.
380 ## Writing Documentation
382 Documentation improvements are very welcome. The source of `doc.rust-lang.org`
383 is located in `src/doc` in the tree, and standard API documentation is generated
384 from the source code itself. Documentation pull requests function in the same way
385 as other pull requests.
387 To find documentation-related issues, sort by the [T-doc label][tdoc].
389 [tdoc]: https://github.com/rust-lang/rust/issues?q=is%3Aopen%20is%3Aissue%20label%3AT-doc
391 You can find documentation style guidelines in [RFC 1574][rfc1574].
393 [rfc1574]: https://github.com/rust-lang/rfcs/blob/master/text/1574-more-api-documentation-conventions.md#appendix-a-full-conventions-text
395 In many cases, you don't need a full `./x.py doc`, which will build the entire
396 stage 2 compiler and compile the various books published on
397 [doc.rust-lang.org]. When updating documentation for the standard library,
398 first try `./x.py doc --stage 0 src/libstd`. If that fails, or if you need to
399 see the output from the latest version of `rustdoc`, use `--stage 1` instead of
400 `--stage 0`. Results should appear in `build/$TARGET/crate-docs`.
402 [doc.rust-lang.org]: htts://doc.rust-lang.org
404 You can also use `rustdoc` directly to check small fixes. For example,
405 `rustdoc src/doc/reference.md` will render reference to `doc/reference.html`.
406 The CSS might be messed up, but you can verify that the HTML is right.
408 Additionally, contributions to the [rustc-dev-guide] are always welcome. Contributions
409 can be made directly at [the
410 rust-lang/rustc-dev-guide](https://github.com/rust-lang/rustc-dev-guide) repo. The issue
411 tracker in that repo is also a great way to find things that need doing. There
412 are issues for beginners and advanced compiler devs alike!
416 Sometimes, an issue will stay open, even though the bug has been fixed. And
417 sometimes, the original bug may go stale because something has changed in the
420 It can be helpful to go through older bug reports and make sure that they are
421 still valid. Load up an older issue, double check that it's still true, and
422 leave a comment letting us know if it is or is not. The [least recently
423 updated sort][lru] is good for finding issues like this.
425 Contributors with sufficient permissions on the Rust repo can help by adding
426 labels to triage issues:
428 * Yellow, **A**-prefixed labels state which **area** of the project an issue
431 * Magenta, **B**-prefixed labels identify bugs which are **blockers**.
433 * Dark blue, **beta-** labels track changes which need to be backported into
436 * Light purple, **C**-prefixed labels represent the **category** of an issue.
438 * Green, **E**-prefixed labels explain the level of **experience** necessary
441 * The dark blue **final-comment-period** label marks bugs that are using the
442 RFC signoff functionality of [rfcbot] and are currently in the final
445 * Red, **I**-prefixed labels indicate the **importance** of the issue. The
446 [I-nominated][inom] label indicates that an issue has been nominated for
447 prioritizing at the next triage meeting.
449 * The purple **metabug** label marks lists of bugs collected by other
452 * Purple gray, **O**-prefixed labels are the **operating system** or platform
453 that this issue is specific to.
455 * Orange, **P**-prefixed labels indicate a bug's **priority**. These labels
456 are only assigned during triage meetings, and replace the [I-nominated][inom]
459 * The gray **proposed-final-comment-period** label marks bugs that are using
460 the RFC signoff functionality of [rfcbot] and are currently awaiting
461 signoff of all team members in order to enter the final comment period.
463 * Pink, **regression**-prefixed labels track regressions from stable to the
466 * The light orange **relnotes** label marks issues that should be documented in
467 the release notes of the next release.
469 * Gray, **S**-prefixed labels are used for tracking the **status** of pull
472 * Blue, **T**-prefixed bugs denote which **team** the issue belongs to.
474 If you're looking for somewhere to start, check out the [E-easy][eeasy] tag.
476 [inom]: https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3AI-nominated
477 [eeasy]: https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3AE-easy
478 [lru]: https://github.com/rust-lang/rust/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-asc
479 [rfcbot]: https://github.com/anp/rfcbot-rs/
481 ## Out-of-tree Contributions
483 There are a number of other ways to contribute to Rust that don't deal with
486 Answer questions in the _Get Help!_ channels from the [Rust Discord server][rust-discord], on [users.rust-lang.org][users],
487 or on [StackOverflow][so].
489 Participate in the [RFC process](https://github.com/rust-lang/rfcs).
491 Find a [requested community library][community-library], build it, and publish
492 it to [Crates.io](http://crates.io). Easier said than done, but very, very
495 [rust-discord]: https://discord.gg/rust-lang
496 [users]: https://users.rust-lang.org/
497 [so]: http://stackoverflow.com/questions/tagged/rust
498 [community-library]: https://github.com/rust-lang/rfcs/labels/A-community-library
500 ## Helpful Links and Information
502 For people new to Rust, and just starting to contribute, or even for
503 more seasoned developers, some useful places to look for information
506 * The [rustc dev guide] contains information about how various parts of the compiler work and how to contribute to the compiler
507 * [Rust Forge][rustforge] contains additional documentation, including write-ups of how to achieve common tasks
508 * The [Rust Internals forum][rif], a place to ask questions and
509 discuss Rust's internals
510 * The [generated documentation for rust's compiler][gdfrustc]
511 * The [rust reference][rr], even though it doesn't specifically talk about Rust's internals, it's a great resource nonetheless
512 * Although out of date, [Tom Lee's great blog article][tlgba] is very helpful
513 * [rustaceans.org][ro] is helpful, but mostly dedicated to IRC
514 * The [Rust Compiler Testing Docs][rctd]
515 * For [@bors][bors], [this cheat sheet][cheatsheet] is helpful
516 (though you'll need to replace `@homu` with `@bors` in any commands)
517 * **Google!** ([search only in Rust Documentation][gsearchdocs] to find types, traits, etc. quickly)
518 * Don't be afraid to ask! The Rust community is friendly and helpful.
520 [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/about-this-guide.html
521 [gdfrustc]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/
522 [gsearchdocs]: https://www.google.com/search?q=site:doc.rust-lang.org+your+query+here
523 [rif]: http://internals.rust-lang.org
524 [rr]: https://doc.rust-lang.org/book/README.html
525 [rustforge]: https://forge.rust-lang.org/
526 [tlgba]: http://tomlee.co/2014/04/a-more-detailed-tour-of-the-rust-compiler/
527 [ro]: http://www.rustaceans.org/
528 [rctd]: https://rustc-dev-guide.rust-lang.org/tests/intro.html
529 [cheatsheet]: https://buildbot2.rust-lang.org/homu/