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Guide to contributing to Coq

Foreword

As with any documentation, this guide is most useful if it's promptly updated to reflect changes in processes, development tools, or the Coq ecosystem. If you notice anything inaccurate or outdated, please signal it in a new issue, or fix it in a new pull request. If you find some parts are not sufficiently clear, you may open an issue as well.

Table of contents

Introduction

Thank you for your interest in contributing to Coq! There are many ways to contribute, and we appreciate all of them.

People often begin by making small contributions, and contributions to the ecosystem, before working their way up incrementally to the core parts of the system, and start to propose larger changes, or take an active role in maintaining the system. So this is the way this contributing guide is organized. However, it is by no means necessary that you go through these steps in this order. Feel free to use this guide as a reference and quickly jump to the part that is most relevant to you at the current time.

We want to make sure that contributing to Coq is a fun and positive experience for everyone, so please make sure you read and abide by our Code of Conduct.

Contributing to the ecosystem

In this section, we present all the ways to contribute to Coq outside of the Coq repository itself.

Asking and answering questions

One very important way of contributing is by asking and answering questions, in order to create a body of easily-browsable, problem-oriented, additional documentation.

There are many platforms for this purpose:

  • Our Zulip chat, which contains a main "#Coq users" stream, but also many other streams dedicated to specific Coq packages, such as Equations, MathComp, etc.
  • Our Discourse forum, which contains a main "Using Coq" category, but also categories dedicated to asking questions in other languages than English. They have yet to find their public, so do not hesitate to advertise them to people you know who might not be at ease with English.
  • The Proof Assistants Stack Exchange, a Q&A site for users of proof assistants, including Coq.
  • Other Stack Exchange sites, and particularly Stack Overflow, receive questions about Coq. Questions asked anywhere on Stack Exchange with the coq tag are automatically relayed to Zulip in a dedicated topic.

Other active places to answer questions include the Coq-Club mailing list, the Coq IRC channel, the /r/Coq subreddit, etc.

Writing tutorials and blog posts

Writing about Coq, in the form of tutorials or blog posts, is also a very important contribution. In particular, it can help new users get interested in Coq, and learn about it, and existing users learn about advance features. Our official resources, such as the reference manual are not suited for learning Coq, but serve as reference documentation to which you can link from your tutorials.

The Coq website has a page listing known tutorials and the wiki home page contains a list too. You can expand the former through a pull request on the Coq website repository, while the latter can be edited directly by anyone with a GitHub account.

At the current time, we do not have a way of aggregating blog posts on a single page (like OCaml planet), but this would probably be something useful to get, so do not hesitate if you want to create it. Some people use Reddit for this purpose.

Contributing to the wiki

Coq's wiki is an informal source of additional documentation which anyone with a GitHub account can edit directly. In particular, it contains the Coq FAQ which has not seen so many updates in the recent years. You should feel free to fix it, expand it, and even refactor it (if you are not sure if some changes would be welcome, you can open an issue to discuss them before performing them).

People who watch the Coq repository will see recent wiki edits in their GitHub feed. It is recommended to review them a posteriori to check no mistake was introduced. The wiki is also a standard git repository, so people can follow the changes using any standard git tool.

Coq's wiki is formatted using GitHub's flavored Markdown, with some wiki-specific extensions. See:

Creating and maintaining Coq packages

Note: this sub-section is about packages extending Coq, such as plugins or libraries. A different, but also very valuable, contribution is to package Coq for your preferred package manager (see Packaging Coq).

Sharing reusable assets in the form of new libraries, plugins, and tools is great so that others can start building new things on top. Having an extensive and healthy package ecosystem is key to the success of Coq.

Distribution of Coq packages

You can distribute your library or plugin through the Coq package index. Important packages and tools can be advertised on the Awesome Coq list. Some packages are distributed along Coq, within the Coq Platform. Check the Platform's charter if you consider adding your package to it.

Support for plugin and library authors

You can find advice and best practices about maintaining a Coq project on the coq-community wiki.

Learn how to write a Coq plugin, and about best practices, in the Coq plugin tutorial. This tutorial is still a work in progress, so do not hesitate to expand it, or ask questions.

If you want quick feedback on best practices, or how to talk to the Coq API, a good place to hang out is the Coq devs & plugin devs stream of our Zulip chat.

Finally, we strongly encourage authors of plugins to submit their plugins to join Coq's continuous integration (CI) early on. Indeed, the Coq API gets continuously reworked, so this is the best way of ensuring your plugin stays compatible with new Coq versions, as this means Coq developers will fix your plugin for you. Learn more about this in the CI README (user part).

Pure Coq libraries are also welcome to join Coq's CI, especially if they test underused / undertested features.

Standard libraries

There are many general purpose Coq libraries, so before you publish yours, consider whether you could contribute to an existing one instead (either the official standard library, or one of the many alternative standard libraries).

Maintaining existing packages in coq-community

Some Coq packages are not maintained by their initial authors anymore (for instance if they've moved on to new jobs or new projects) even if they were useful, or interesting. The coq-community organization is a place for volunteers to take over the maintenance of such packages.

If you want to contribute by becoming a maintainer, there is a list of packages waiting for a maintainer. You can also propose a package that is not listed. Find out more about coq-community in the manifesto's README.

Contributing to the editor support packages

Besides CoqIDE, whose sources are available in this repository, and to which you are welcome to contribute, there are a number of alternative user interfaces for Coq, more often as an editor support package.

Here are the URLs of the repositories of the various editor support packages:

And here are alternative user interfaces to be run in the web browser:

Each of them has their own contribution process.

Contributing to the website or the package archive

The website and the package archive have their own repositories:

You can contribute to them by using issues and pull requests on these repositories. These repositories should get their own contributing guides, but they don't have any at the time of writing this.

Other ways of creating content

There are many other ways of creating content and making the Coq community thrive, including many which we might not have thought about. Feel free to add more references / ideas to this sub-section.

You can tweet about Coq, you can give talks about Coq both in academic, and in non-academic venues (such as developer conferences).

Codewars is a platform where people can try to solve some programming challenges that were proposed by other community members. Coq is supported and the community is eager to get more challenges.

Issues

Reporting a bug, requesting an enhancement

Bug reports are enormously useful to identify issues with Coq; we can't fix what we don't know about. To report a bug, please open an issue in the Coq issue tracker (you'll need a GitHub account). You can file a bug for any of the following:

  • An anomaly. These are always considered bugs, so Coq will even ask you to file a bug report!
  • An error you didn't expect. If you're not sure whether it's a bug or intentional, feel free to file a bug anyway. We may want to improve the documentation or error message.
  • Missing or incorrect documentation. It's helpful to track where the documentation should be improved, so please file a bug if you can't find or don't understand some bit of documentation.
  • An error message that wasn't as helpful as you'd like. Bonus points for suggesting what information would have helped you.
  • Bugs in CoqIDE should also be filed in the Coq issue tracker. Bugs in the Emacs plugin should be filed against ProofGeneral, or against company-coq if they are specific to company-coq features.

It would help if you search the existing issues before reporting a bug. This can be difficult, so consider it extra credit. We don't mind duplicate bug reports. If unsure, you are always very welcome to ask on our Discourse forum or Zulip chat before, after, or while writing a bug report.

It is better if you can test that your bug is still present in the current testing or development version of Coq (see the next sub-section) before reporting it, but if you can't, it should not discourage you from reporting it.

When it applies, it's extremely helpful for bug reports to include sample code, and much better if the code is self-contained and complete. It's not necessary to minimize your bug or identify precisely where the issue is, since someone else can often do this if you include a complete example. We tend to include the code in the bug description itself, but if you have a very large input file then you can add it as an attachment.

If you want to minimize your bug (or help minimize someone else's) for more extra credit, then you can use the Coq bug minimizer (specifically, the bug minimizer is the find-bug.py script in that repo). Nowadays, the easiest way to use the Coq bug minimizer is to call it through @coqbot, as documented here.

Beta testing

Coq gets a new major release about every six months, which is then distributed through the Coq Platform. New major versions of Coq are first made available for beta-testing, before being declared stable and the new default version of the Coq Platform. You can help make by testing the beta version, and trying to port your projects to it. You should report any bug you notice, but also any change of behavior that is not documented in the changelog. Then Coq developers will be able to check if what you reported is a regression that needs to be fixed, or an expected change that needs to be mentioned in the changelog.

You can go even further by using the development version (master branch) of Coq on a day by day basis, and report problems as soon as you notice them. If you wish to do so, the easiest way to install Coq is through opam (using the dev version of the Coq package, available in the https://coq.inria.fr/opam/core-dev repository) or through Nix. The documentation of the development version is available online, including the unreleased changelog.

Helping triage existing issues

Coq has too many bug reports for its core developers alone to manage. You can help a lot by:

  • confirming that reported bugs are still active with the current version of Coq;
  • determining if the bug is a regression (new, and unexpected, behavior from a recent Coq version);
  • more generally, by reproducing a bug, on another system, configuration, another version of Coq, and by documenting what you did;
  • giving a judgement about whether the reported behavior is really a bug, or is expected but just improperly documented, or expected and already documented;
  • producing a trace if it is relevant and you know how to do it;
  • producing another example exhibiting the same bug, or minimizing the initial example using the bug minimizer mentioned above;
  • using git bisect to find the commit that introduced a regression;
  • fixing the bug if you have an idea of how to do so (see the following section).

Once you have some experience with the Coq issue tracker, you can request to join the @coq/contributors team (any member of the @coq/core team can give you access using this link). Being in this team will grant you the following access:

  • Updating labels: every open issue and pull request should ideally get one or several kind: and part: labels. In particular, valid issues should generally get either a kind: bug (the reported behavior can indeed be considered a bug, this can be completed with the kind: anomaly, and kind: regression labels), kind: documentation (e.g. if a reported behavior is expected but improperly documented), kind: enhancement (a request for enhancement of an existing feature), or kind: feature label (an idea for a new feature).
  • Creating new labels: if you feel a part: label is missing, do not hesitate to create it. If you are not sure, you may discuss it with other contributors and developers on Zulip first.
  • Closing issues: if a bug cannot be reproduced anymore, is a duplicate, or should not be considered a bug report in the first place, you should close it. When doing so, try putting an appropriate resolved: label to indicate the reason. If the bug has been fixed already, and you know in which version, you can add a milestone to it, even a milestone that's already closed, instead of a resolved: label. When closing a duplicate issue, try to add all the additional info that could be gathered to the original issue.
  • Editing issue titles: you may want to do so to better reflect the current understanding of the underlying issue.
  • Editing comments: feel free to do so to fix typos and formatting only (in particular, some old comments from the Bugzilla era or before are not properly formatted). You may also want to edit the OP's initial comment (a.k.a. body of the issue) to better reflect the current understanding of the issue, especially if the discussion is long. If you do so, only add to the original comment, and mark it clearly with an EDITED by @YourNickname:.
  • Hiding comments: when the discussion has become too long, this can be done to hide irrelevant comments (off-topic, outdated or resolved sub-issues).
  • Deleting things: please don't delete any comment or issue, our policy doesn't allow for comments to be deleted, unless done by the community moderators. You should hide them instead. An audit log is available to track deleted items if needed (but does not allow recovering them).

However, and contrary to most other repositories, it will not give you the ability to push new branches or tags to the repository. This is disabled because we prefer to use forks to work on feature branches.

Yet to be fully specified: use of priority, difficulty, help wanted, and good first issue labels, milestones, assignments, and GitHub projects.

Code changes

Using GitHub pull requests

If you want to contribute a documentation update, bug fix or feature yourself, pull requests (PRs) on the GitHub repository are the way to contribute directly to the Coq implementation (all changes, even the smallest changes from core developers, go through PRs). You will need to create a fork of the repository on GitHub and push your changes to a new "topic branch" in that fork (instead of using an existing branch name like master).

PRs should always target the master branch. Make sure that your copy of this branch is up-to-date before starting to do your changes, and that there are no conflicts before submitting your PR. If you need to fix conflicts, we generally prefer that you rebase your branch on top of master, instead of creating a merge commit.

If you are not familiar with git or GitHub, Sections Git documentation, tips and tricks, and GitHub documentation, tips and tricks, should be helpful (and even if you are, you might learn a few tricks).

Once you have submitted your PR, it may take some time to get feedback, in the form of reviews from maintainers, and test results from our continuous integration system. Our code owner system will automatically request reviews from relevant maintainers. Then, one maintainer should self-assign the PR (if that does not happen after a few days, feel free to ping the maintainers that were requested a review). The PR assignee will then become your main point of contact for handling the PR: they should ensure that everything is in order and merge when it is the case (you can ping them if the PR is ready from your side but nothing happens for a few days).

After your PR is accepted and merged, it may get backported to a release branch if appropriate, and will eventually make it to a release. You do not have to worry about this, it is the role of the assignee and the release manager to do so (see Section Release management). The milestone should give you an indication of when to expect your change to be released (this could be several months after your PR is merged). That said, you can start using the latest Coq master branch to take advantage of all the new features, improvements, and fixes.

Fixing bugs and performing small changes

Before fixing a bug, it is best to check that it was reported before:

  • If it was already reported and you intend to fix it, self-assign the issue (if you have the permission), or leave a comment marking your intention to work on it (and a contributor with write-access may then assign the issue to you).

  • If the issue already has an assignee, you should check with them if they still intend to work on it. If the assignment is several weeks, months, or even years (!) old, there are good chances that it does not reflect their current priorities.

  • If the bug has not been reported before, it can be a good idea to open an issue about it, while stating that you are preparing a fix. The issue can be the place to discuss about the bug itself while the PR will be the place to discuss your proposed fix.

It is generally a good idea to add a regression test to the test-suite. See the test-suite README for how to do so.

Small fixes do not need any documentation, or changelog update. New, or updated, user-facing features, and major bug fixes do. See the corresponding section for on how to contribute to the documentation, and the README in doc/changelog for how to add a changelog entry.

Proposing large changes: Coq Enhancement Proposals

Please refrain to open very large PRs without discussing them first. Indeed, you should be aware that the larger the change, the higher the chances it will take very long to review, and possibly never get merged.

So it is recommended that before spending a lot of time coding, you seek feedback from maintainers to see if your change would be supported, and if they have recommendations about its implementation. You can do this informally by opening an issue, or more formally by producing a design document as a Coq Enhancement Proposal.

Another recommendation is that you do not put several unrelated changes in the same PR (even if you produced them together). In particular, make sure you split bug fixes into separate PRs when this is possible. More generally, smaller-sized PRs, or PRs changing fewer components, are more likely to be reviewed and merged promptly.

Seeking early feedback on work-in-progress

You should always feel free to open your PR before the documentation, changelog entry and tests are ready. That's the purpose of the checkboxes in the PR template which you can leave unticked. This can be a way of getting reviewers' approval before spending time on writing the documentation (but you should still do it before your PR can be merged).

If even the implementation is not ready but you are still looking for early feedback on your code changes, please use the draft PR mechanism.

If you are looking for feedback on the design of your change, rather than on its implementation, then please refrain from opening a PR. You may open an issue to start a discussion, or create a Coq Enhancement Proposal if you have a clear enough view of the design to write a document about it.

Taking feedback into account

Understanding automatic feedback

When you open or update a PR, you get automatically some feedback: we have a bot whose job will be to push a branch to our GitLab mirror to run some continuous integration (CI) tests. The tests will run on a commit merging your branch with the base branch, so if there is a conflict and this merge cannot be performed automatically, the bot will put a needs: rebase label, and the tests won't run.

Otherwise, a suite of tests will be run on GitLab, plus some additional tests on GitHub Actions for Windows and macOS compatibility.

The complete suite of tests is no longer run by default to save resources. But it is still required before merging a PR, so this is why the bot will put a needs: full CI label if it has only run the lightweight tests. If you are a member of @coq/contributors, you can request a full run of the CI by putting the request: full CI label before pushing to your PR branch, or by commenting @coqbot: run full CI after having pushed. (In case you need to re-run the tests, e.g., because the results are outdated, you can also request the bot to do so by commenting @coqbot: run full CI or @coqbot: run light CI. If you comment @coqbot: run CI, the bot will decide whether to run the full or the lightweight tests based on the presence of the request: full CI label.)

If a test fails on GitLab, you will see in the GitHub PR interface, both the failure of the whole pipeline, and of the specific failed job. Most of these failures indicate problems that should be addressed, but some can still be due to synchronization issues out of your control. In particular, if you get a failure in one of the tested plugins but you didn't change the Coq API, it is probably a transient issue and you shouldn't have to worry about it. In case of doubt, ask the reviewers.

To re-run a specific failed job, you can use the Re-run jobs button in the GitHub interface (if you are a member of @coq/contributors). This won't create a new merge commits with the base branch, so if you need this, you can use the @coqbot: run ... CI commands instead.

Test-suite failures

If you broke the test-suite, you should get many failed jobs, because the test-suite is run multiple times in various settings. You should get the same failure locally by running make test-suite. It's helpful to run this locally and ensure the test-suite is not broken before submitting a PR as this will spare a lot of runtime on distant machines.

To learn more about the test-suite, you should refer to its README.

Linter failures

We have a linter that checks a few different things:

  • Every commit can build. This is an important requirement to allow the use of git bisect in the future. It should be possible to build every commit, and in principle even the test-suite should pass on every commit (but this isn't tested in CI because it would take too long). A good way to test this locally is to use git rebase master --exec "make check".

  • No tabs or end-of-line spaces on updated lines. We are trying to get rid of all tabs and all end-of-line spaces from the code base (except in some very special files that need them). This checks not only that you didn't introduce new ones, but also that updated lines are clean (even if they were there before). You can avoid worrying about tabs and end-of-line spaces by installing our pre-commit git hook, which will fix these issues at commit time. Running ./configure once will install this hook automatically unless you already have a pre-commit hook installed. If you are encountering these issues nonetheless, you can fix them by rebasing your branch with git rebase --whitespace=fix.

  • All files should end with a single newline. See the section Style guide for additional style recommendations.

  • Documented syntax is up-to-date. If you update the grammar, you should run make doc_gram_rsts to update the documented syntax. You should then update the text describing the syntax in the documentation and commit the changes. In some cases, the documented syntax is edited to make the documentation more readable. In this case, you may have to edit doc/tools/docgram/common.edit_mlg to make doc_gram_rsts pass. See doc_grammar's README for details.

    Note that in the case where you added new commands or tactics, you will have to manually insert them in the documentation, the tool won't do that for you, although it should detect in most cases if you have forgotten to add documentation for your new command or tactic, or if the documentation is not consistent with the parser.

  • .opam files are up to date. Coq's *.opam files are generated automatically from metadata in dune-project. If the meta-data becomes out of sync, the linter will complain. This can be fixed doing dune build *.opam at the root of Coq's repository.

You may run the linter yourself with dev/lint-repository.sh.

Plugin failures

If you did change the Coq API, then you may have broken a plugin. After ensuring that the failure comes from your change, you will have to provide a fix to the plugin, and the PR assignee will have to ensure that this fix is merged in the plugin simultaneously with your PR on the Coq repository.

If your changes to the API are not straightforward, you should also document them in dev/doc/changes.md.

The CI README (developer part) contains more information on how to fix plugins, test and submit your changes, and how you can anticipate the results of the CI before opening a PR.

Library failures

Such a failure can indicate either a bug in your branch, or a breaking change that you introduced voluntarily. All such breaking changes should be properly documented in the user changelog. Furthermore, a backward-compatible fix should be found, properly documented in the changelog when non-obvious, and this fix should be merged in the broken projects before your PR to the Coq repository can be.

Note that once the breaking change is well understood, it should not feel like it is your role to fix every project that is affected: as long as reviewers have approved and are ready to integrate your breaking change, you are entitled to (politely) request project authors / maintainers to fix the breakage on their own, or help you fix it. Obviously, you should leave enough time for this to happen (you cannot expect a project maintainer to allocate time for this as soon as you request it) and you should be ready to listen to more feedback and reconsider the impact of your change.

If you need help figuring out why your PR is breaking a tested project, you may consider requesting automatic minimization of the failure with the bot. In principle, the bot should automatically propose this option to you if it is available (it needs to detect a failure in a Coq file and it needs to confirm that the failure was not already present in the base branch to propose to run the minimization process).

Understanding reviewers' feedback

The reviews you get are highly dependent on the kind of changes you did. In any case, you should always remember that reviewers are friendly volunteers that do their best to help you get your changes in (and should abide by our Code of Conduct). But at the same time, they try to ensure that code that is introduced or updated is of the highest quality and will be easy to maintain in the future, and that's why they may ask you to perform small or even large changes. If you need a clarification, do not hesitate to ask.

Here are a few labels that reviewers may add to your PR to track its status. In general, this will come in addition to comments from the reviewers, with specific requests.

  • needs: fixing indicates the PR needs a fix, as discussed in the comments.
  • needs: documentation indicates the PR introduces changes that should be documented before it can be merged. This label may be used to reflect that the corresponding checkbox is not yet checked in the PR template (so that we don't forget when we intend to merge the PR).
  • needs: changelog entry indicates the PR introduces changes that should be documented in the user changelog. Similarly to the previous label, this may be used to reflect that the corresponding checkbox is not yet checked in the PR template.
  • needs: test-suite update indicates that tests should be added to the test-suite / modified to ensure that the changes are properly tested. Similarly to the previous two labels, this may be used to reflect that the corresponding checkbox is not yet checked in the PR template.
  • needs: benchmarking and needs: testing indicate the PR needs testing beyond what the test suite can handle. For example, performance benchmarking is currently performed with a different infrastructure (documented in the wiki). Unless some followup is specifically requested, you aren't expected to do this additional testing.

More generally, such labels should come with a description that should allow you to understand what they mean.

Fixing your branch

If you have changes to perform before your PR can be merged, you might want to do them in separate commits at first to ease the reviewers' task, but we generally appreciate that they are squashed with the commits that they fix before merging. This is especially true of commits fixing previously introduced bugs or failures.

Improving the official documentation

The documentation is usually a good place to start contributing, because you can get used to the pull request submitting and review process, without needing to learn about the code source of Coq at the same time.

The official documentation is formed of two components:

The sources of the reference manual are located in the doc/sphinx directory. They are written in rst (Sphinx) format with some Coq-specific extensions, which are documented in the README in the above directory. This README was written to be read from begin to end. As soon as your edits to the documentation are more than changing the textual content, we strongly encourage you to read this document.

The documentation of the standard library is generated with coqdoc from the comments in the sources of the standard library.

The README in the doc directory contains more information about the documentation's build dependencies, and the make targets.

You can browse through the list of open documentation issues using the kind: documentation label, or the user documentation GitHub project (you can look in particular at the "Writing" and "Fixing" columns).

Contributing to the standard library

Contributing to the standard library is also made easier by not having to learn about Coq's internals, and its implementation language.

Due to the compatibility constraints created by the many projects that depend on it, proposing breaking changes, will usually require to go through a specific process, with a deprecation phase. Additions, such as contributing new lemmas on existing definitions, and clean-ups of existing proofs are easier contributions to start with. In case of doubt, ask in an issue before spending too much time preparing your PR.

If you create a new file, it needs to be listed in doc/stdlib/index-list.html.

Add coqdoc comments to extend the standard library documentation. See the coqdoc documentation to learn more.

Becoming a maintainer

Reviewing pull requests

You can start reviewing PRs as soon as you feel comfortable doing so (anyone can review anything, although some designated reviewers will have to give a final approval before a PR can be merged, as is explained in the next sub-section).

Reviewers should ensure that the code that is changed or introduced is in good shape and will not be a burden to maintain, is unlikely to break anything, or the compatibility-breakage has been identified and validated, includes documentation, changelog entries, and test files when necessary. Reviewers can use needs: labels, or change requests to further emphasize what remains to be changed before they can approve the PR. Once reviewers are satisfied (regarding the part they reviewed), they should formally approve the PR, possibly stating what they reviewed.

That being said, reviewers should also make sure that they do not make the contributing process harder than necessary: they should make it clear which comments are really required to perform before approving, and which are just suggestions. They should strive to reduce the number of rounds of feedback that are needed by posting most of their comments at the same time. If they are opposed to the change, they should clearly say so from the beginning to avoid the contributor spending time in vain. They should avoid making nitpick comments when in fact, they have larger concerns that should be addressed first (these larger concerns should then be made very clear).

Furthermore, when reviewing a first contribution (GitHub highlights first-time contributors), be extra careful to be welcoming, whatever the decision on the PR is. When approving a PR, consider thanking the newcomer for their contribution, even if it is a very small one (in cases where, if the PR had come from a regular contributor, it would have felt OK to just merge it without comment). When rejecting a PR, take some extra steps to explain the reasons, so that it doesn't feel hurtful. Don't hesitate to still thank the contributor and possibly redirect them to smaller tasks that might be more appropriate for a newcomer.

Collaborating on a pull request

Beyond making suggestions to a PR author during the review process, you may want to collaborate further by checking out the code, making changes, and pushing them. There are two main ways of doing this:

  • Pull requests on pull requests: You can checkout the PR branch (GitHub provides the link to the remote to pull from and the branch name on the top and the bottom of the PR discussion thread), checkout a new personal branch from there, do some changes, commit them, push to your fork, and open a new PR on the PR author's fork.
  • Pushing to the PR branch: If the PR author has not unchecked the "Allow edit from maintainers" checkbox, and you have write-access to the repository (i.e. you are in the @coq/contributors team), then you can also push (and even force-push) directly to the PR branch, on the main author's fork. Obviously, don't do it without coordinating with the PR author first (in particular, in case you need to force-push).

When several people have co-authored a single commit (e.g. because someone fixed something in a commit initially authored by someone else), this should be reflected by adding "Co-authored-by:" tags at the end of the commit message. The line should contain the co-author name and committer e-mail address.

Merging pull requests

Our CODEOWNERS file associates a team of maintainers to each component. When a PR is opened (or a draft PR is marked as ready for review), GitHub will automatically request reviews to maintainer teams of affected components. As soon as it is the case, one available member of a team that was requested a review should self-assign the PR, and will act as its shepherd from then on.

The PR assignee is responsible for making sure that all the proposed changes have been reviewed by relevant maintainers (at least one reviewer for each component that is significantly affected), that change requests have been implemented, that CI is passing, and eventually will be the one who merges the PR.

The PR assignee may use their own judgement to decide to merge a PR that has not received reviews from all maintainers of affected components, depending on how large or controversial the changes to these components are. It is also admissible to have an assignee who is not a maintainer of any of the affected components, in case relevant maintainers are not available, and as long as the assignee is a member of the @coq/pushers team and is able to understand the changes in the PR.

If you have already frequently contributed to a component, we would be happy to have you join one of the maintainer teams. See the section below on joining / leaving maintainer teams.

The complete list of maintainer teams is available here (link only accessible to people who are already members of the Coq organization, because of a limitation of GitHub).

Additional notes for pull request reviewers and assignees

  • NEVER USE GITHUB'S MERGE BUTTON. Instead, you should either:

    • post a comment containing "@coqbot: merge now"; This is the recommended method and more convenient than the previous script based method (see next bullet) e.g. for developers who do not have a GPG key and for when you do not have access to a console. "coqbot" will not check CI status - it is expected that the merger does this manually upfront, but coqbot will deny the merge with an error response in the following cases:

      • no assignee
      • no milestone
      • no kind label
      • left-over needs labels
      • you try to merge a PR which you authored (this is decided by the creator of the PR - reviewers can still do minor changes and merge)

    • alternatively run the dev/tools/merge-pr.sh script; Since "coqbot" this method is deprecated with a few exceptions, like merges to release branches - which only release managers do. This requires having configured gpg with git.

  • PR authors or co-authors cannot review, self-assign, or merge the PR they contributed to. However, reviewers may push small fixes to the PR branch to facilitate the PR integration.

  • PRs are merged when there is consensus. Consensus is defined by an explicit approval from at least one maintainer for each component that is significantly affected and an absence of dissent. As soon as a developer opposes a PR, it should not be merged without being discussed first (usually in a call or working group).

  • Sometimes (especially for large or potentially controversial PRs), it is a good practice to announce the intent to merge, one or several days in advance, when unsure that everyone had a chance to voice their opinion, or to finish reviewing the PR.

  • Only PRs targetting the master branch can be merged by a maintainer. For PRs targetting an actively maintained release branch, the assignee should always be the release manager. For older release branches, any @coq/core member can merge any PR (but such PRs should be limited to fixing build issues).

  • Before merging, the assignee must also select a milestone for the PR (see also Section Release management).

  • To know which files you are a maintainer of, you can look for black shields icons in the "Files changed" tab.

    shield icon

  • When a PR has overlays, then:

    • the overlays that are backward-compatible (normally the case for overlays fixing Coq code) should have been merged before the PR can be merged; it might be a good idea to ask the PR author to remove the overlay information from the PR to get a fresh CI run and ensure that all the overlays have been merged; the PR assignee may also push a commit removing the overlay information (in that case the assignee is not considered a co-author, hence no need to change the assignee)

    • the overlays that are not backward-compatible (normally only the case for overlays fixing OCaml code) should be merged just after the PR has been merged (and thus the assignee should ping the maintainers of the affected projects to ask them to merge the overlays).

Joining / leaving maintainer teams

We are always happy to have more people involved in the PR reviewing and merging process, so do not hesitate to propose yourself if you already have experience on a component.

Maintainers can leave teams at any time (and core members can also join any team where they feel able to help) but you should always announce it to other maintainers when you do join or leave a team.

Core development team

The core developers are the active developers with a lengthy and significant contribution track record. They are the ones with admin powers over the Coq organization, and the ones who take part in votes in case of conflicts to take a decision (rare). One of them is designated as a development coordinator, and has to approve the changes in the core team membership (until we get a more formal joining and leaving process).

The core developers are the members of the @coq/core team (member list only visible to the Coq organization members because of a limitation of GitHub). They are also listed on the Coq Team page.

Release management

Coq's major release cycles generally span about six months, with about 4-5 months of development, and 1-2 months of stabilization / release candidates. The release manager (RM) role is a rolling position among core developers. The release plan is published on the wiki.

Development of new features, refactorings, deprecations and clean-ups always happens on master. Stabilization starts by branching (creating a new v... release branch from the current master), which marks the beginning of a feature freeze (new features will continue to be merged into master but won't make it for the upcoming major release, but only for the next one).

After branching, most changes are introduced in the release branch by a backporting process. PR authors and assignee can signal a desire to have a PR backported by selecting an appropriate milestone. Most of the time, the choice of milestone is between two options: the next major version that has yet to branch from master, or the next version (rc, final, or patch-level release) of the active release branch. In the end, it is the RM who decides whether to follow or not the recommendation of the PR assignee, and who backports PRs to the release branch.

Very specific changes that are only relevant for the release branch and not for the master branch can result in a PR targetting the release branch instead of master. In this case, the RM is the only one who can merge the PR, and they may even do so if they are the author of the PR. Examples of such PRs include bug fixes to a feature that has been removed in master, and PRs from the RM changing the version number in preparation for the next release.

Some automation is in place to help the RM in their task: a GitHub project is created at branching time to manage PRs to backport; when a PR is merged in a milestone corresponding to the release branch, our bot will add this PR in a "Request inclusion" column in this project; the RM can browse through the list of PRs waiting to be backported in this column, possibly reject some of them by simply removing the PR from the column (in which case, the bot will update the PR milestone), and proceed to backport others; when a backported PR is pushed to the release branch, the bot moves the PR from the "Request inclusion" column to a "Shipped" column.

More information about the RM tasks can be found in the release process checklist.

Packaging Coq

The RM role does not include the task of making Coq available through the various package managers out there: several contributors (most often external to the development team) take care of this, and we thank them for this. If your preferred package manager does not include Coq, it is a very worthy contribution to make it available there. But be careful not to let a package get outdated, as this could lead some users to install an outdated version of Coq without even being aware of it. Beyond packaging Coq, you might want to consider packaging the rest of Coq packages available to users through the Coq Platform. In this case, it would be helpful if you try to favor the same versions as in the Coq Platform.

This Repology page lists the versions of Coq which are packaged in many repositories, although it is missing information on some repositories, like opam.

The Windows and macOS installers are created as part of the preparation of the Coq Platform.

Additional resources

Developer documentation

Where to find the resources

  • You can find developer resources in the dev directory, and more specifically developer documentation in dev/doc. The README in the dev directory lists what's available.

    For example, dev/doc/README.md is a beginner's guide to hacking Coq, and documentation on debugging Coq can be found in dev/doc/debugging.md.

  • When it makes sense, the documentation is kept even closer to the sources, in README files in various directories (e.g. the test-suite README or the refman README).

  • Documentation of the Coq API is written directly in comments in .mli files. You can browse it on the Coq website, or rebuild it locally (make apidoc, requires odoc and dune).

  • A plugin tutorial is located in doc/plugin_tutorial.

  • The Coq wiki contains additional developer resources.

Building Coq

The list of dependencies can be found in the first section of the INSTALL.md file.

Coq is built using the dune build system. Run make to get help on the various available targets. Additional documentation can be found in dev/doc/build-system.dune.md, and in the official Dune documentation.

Continuous integration

Continuous integration (CI) testing is key in ensuring that the master branch is kept in a well-functioning state at all times, and that no accidental compatibility breakages are introduced. Our CI is quite extensive since it includes testing many external projects, some of them taking more than an hour to compile. However, you can get partial results much more quickly (when our CI is not overloaded). Nowadays, the full CI is not run by default as already explained in Understanding automatic feedback.

The main documentation resources on our CI are:

Preparing an overlay (i.e. a patch to an external project that we test in our CI, to make it compile with the modified version of Coq in your branch) is a step that everyone goes through at some point. All you need to know to prepare an overlay manually is in the README in the user-overlays directory. You might want to use some additional tooling such as the make ci-* targets of Makefile.ci, the Nix support for getting the dependencies of the external projects (see the README in dev/ci/nix, and the (so far undocumented) dev/tools/create_overlays.sh script.

More work is to be done on understanding how each developer proceeds to prepare overlays, and propose a simplified and documented procedure.

We also have a benchmarking infrastructure, which is documented on the wiki.

Restarting failed jobs

When CI has a few failures which look spurious, restarting the corresponding jobs is a good way to ensure this was indeed the case. Most failed jobs can be restarted directly from the "Checks" tab on GitHub. In case you need to restart a job on GitLab CI using the GitLab interface, then you should sign into GitLab (this can be done using a GitHub account) and join the Coq GitLab organization.

Code owners, issue and pull request templates

These files can be found in the .github directory. The templates are particularly useful to remind contributors what information we need for them, and, in the case of PRs, to update the documentation, changelog, and test-suite when relevant.

GitHub now supports setting up multiple issue templates, and we could use this to define distinct requirements for various kind of bugs, enhancement and feature requests.

Style guide

There exists an old style guide whose content is still mostly relevant. Yet to be done: extract the parts that are most relevant, and put them in this section instead.

We don't use a code formatter at the current time, and we are reluctant to merge changes to parts of the code that are unchanged aside from formatting. However, it is still a good idea if you don't know how to format a block of code to use the formatting that ocamlformat would give

OCaml resources

You can find lots of OCaml resources on http://ocaml.org/, including documentation, a Discourse forum, the package archive, etc. You may also want to refer to the Dune documentation.

Another ressource is https://ocamlverse.github.io/, especially its community page, which lists the various OCaml discussion platforms.

Git documentation, tips and tricks

Lots of resources about git, the version control system, are available on the web, starting with the official website.

We recommend a setup with two configured remotes, one for the official Coq repository, called upstream, and one for your fork, called origin. Here is a way to do this for a clean clone:

git clone https://github.com/coq/coq -o upstream
cd coq
git remote add origin [email protected]:$YOURNAME/coq
# Make sure you click the fork button on GitHub so that this repository exists
cp dev/tools/pre-commit .git/hooks/ # Setup the pre-commit hook

Then, if you want to prepare a fix:

# Make sure we start from an up-to-date master
git checkout master
git pull --ff-only # If this fails, then your master branch is messy
git checkout -b my-topic-branch
# Modify some files
git add .
# Every untracked or modified file will be included in the next commit
# You can also replace the dot with an explicit list of files
git commit -m "My commit summary.

You can add more information on multiple lines,
but you need to skip a line first."
git push -u origin my-topic-branch
# Next time, you push to this branch, you can just do git push

When you push a new branch for the first time, GitHub gives you a link to open a PR.

If you need to fix the last commit in your branch (typically, if your branch has a single commit on top of master), you can do so with

git add .
git commit --amend --no-edit

If you need to fix another commit in your branch, or if you need to fix a conflict with master, you will need to learn about git rebase. GitHub provides a short introduction to git rebase.

GitHub documentation, tips and tricks

GitHub has extensive documentation about everything you can do on the platform, and tips about using git as well. See in particular, how to configure your commit e-mail address and how to open a PR from a fork.

Watching the repository

"Watching" this repository can result in a very large number of notifications. We recommend you, either, configure your mailbox to handle incoming notifications efficiently, or you read your notifications within a web browser. You can configure how you receive notifications in your GitHub settings, you can use the GitHub interface to mark as read, save for later or mute threads. Nowadays, you have also the option to watch only part of the activity (only issues, only PRs, only releases, etc.).

Draft pull requests

Draft PRs are a mechanism proposed by GitHub to open a pull request before it is ready for review.

Opening a draft PR is a way of announcing a change and seeking early feedback without formally requesting maintainers' reviews. Indeed, you should avoid cluttering our maintainers' review request lists before a change is ready on your side.

When opening a draft PR, make sure to give it a descriptive enough title so that interested developers still notice it in their notification feed. You may also advertise it by talking about it in our developer chat. If you know which developer would be able to provide useful feedback to you, you may also ping them.

Turning a PR into draft mode

If a PR was opened as ready for review, but it turns out that it still needs work, it can be transformed into a draft PR.

In this case, previous review requests won't be removed automatically. Someone with write access to the repository should remove them manually. Afterwards, upon marking the PR as ready for review, someone with write access will have to manually add the review requests that were previously removed.

GitLab documentation, tips and tricks

We use GitLab mostly for its CI service. The Coq organization on GitLab hosts a number of CI/CD-only mirrors. If you are a regular contributor, you can request access to it from the organization page, although in most cases, you won't need this.

GitLab too has extensive documentation, in particular on configuring CI.

Merge script dependencies

Nowadays, most assignees should use the @coqbot: merge now command instead of the merge script. However, the merge script is still available, and is still needed to merge PRs into release branches.

The merge script passes option -S to git merge to ensure merge commits are signed. Consequently, it depends on the GnuPG command utility being installed and a GPG key being available. Here is a short documentation on how to use GPG, git & GitHub: https://help.github.com/articles/signing-commits-with-gpg/.

The script depends on a few other utilities. If you are a Nix user, the simplest way of getting them is to run nix-shell first.

Note for homebrew (MacOS) users: it has been reported that installing GnuPG is not out of the box. Installing explicitly pinentry-mac seems important for typing of passphrase to work correctly (see also this Stack Overflow Q-and-A).

Coqbot

Our bot sources can be found at https://github.com/coq/bot. Its documentation is still a work-in-progress.

Online forum and chat to talk to developers

We have a Discourse forum (see in particular the Coq development category) and a Zulip chat (see in particular the Coq devs & plugin devs stream). Feel free to join any of them and ask questions. People are generally happy to help and very reactive.

Obviously, the issue tracker is also a good place to ask questions, especially if the development processes are unclear, or the developer documentation should be improved.

Coq calls

We try to gather every week for one hour through video-conference to discuss current and urgent matters. When longer discussions are needed, topics are left out for the next working group. See the wiki for more information about Coq calls, as well as notes of past ones.

Coq remote working groups

We semi-regularly (up to every month) organize remote working groups, which can be accessed through video-conference, and are most often live streamed on YouTube. Summary notes and announcements of the next working group can be found on the wiki

These working groups are where important decisions are taken, most often by consensus, but also, if it is needed, by a vote of core developers.

Coq Users and Developers Workshops

We have an annual gathering late Spring in France where most core developers are present, and whose objective is to help new contributors get started with the Coq codebase, provide help to plugin and library authors, and more generally have fun together.

The list of past (and upcoming, when it's already planned) workshops can be found on the wiki.