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weston/CONTRIBUTING.md

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Contributing to Weston

Sending patches

Patches should be sent to wayland-devel@lists.freedesktop.org, using git send-email. See git documentation for help.

The first line of a commit message should contain a prefix indicating what part is affected by the patch followed by one sentence that describes the change. For examples:

compositor-drm: Support modifiers for drm_fb

and

input: do not forward unmatched touch-ups

If in doubt what prefix to use, look at other commits that change the same file(s) as the patch being sent.

The body of the commit message should describe what the patch changes and why, and also note any particular side effects. This shouldn't be empty on most of the cases. It shouldn't take a lot of effort to write a commit message for an obvious change, so an empty commit message body is only acceptable if the questions "What?" and "Why?" are already answered on the one-line summary.

The lines of the commit message should have at most 76 characters, to cope with the way git log presents them.

See notes on commit messages for a recommended reading on writing commit messages.

Your patches should also include a Signed-off-by line with your name and email address. If you're not the patch's original author, you should also gather S-o-b's by them (and/or whomever gave the patch to you.) The significance of this is that it certifies that you created the patch, that it was created under an appropriate open source license, or provided to you under those terms. This lets us indicate a chain of responsibility for the copyright status of the code.

We won't reject patches that lack S-o-b, but it is strongly recommended.

When you re-send patches, revised or not, it would be very good to document the changes compared to the previous revision in the commit message and/or the cover letter. If you have already received Reviewed-by or Acked-by tags, you should evaluate whether they still apply and include them in the respective commit messages. Otherwise the tags may be lost, reviewers miss the credit they deserve, and the patches may cause redundant review effort.

Tracking patches and following up

Wayland Patchwork is used for tracking patches to Wayland and Weston. Xwayland patches are tracked with the Xorg project instead. Libinput patches, even though they use the same mailing list as Wayland, are not tracked in the Wayland Patchwork.

The following applies only to Wayland and Weston.

If a patch is not found in Patchwork, there is a high possibility for it to be forgotten. Patches attached to bug reports or not arriving to the mailing list because of e.g. subscription issues will not be in Patchwork because Patchwork only collects patches sent to the list.

When you send a revised version of a patch, it would be very nice to mark your old patch as superseded (or rejected, if that is applicable). You can change the status of your own patches by registering to Patchwork - ownership is identified by email address you use to register. Updating your patch status appropriately will help maintainer work.

The following patch states are found in Patchwork:

  • New: Patches under discussion or not yet processed.

  • Under review: Mostly unused state.

  • Accepted: The patch is merged in the master branch upstream, as is or slightly modified.

  • Rejected: The idea or approach is rejected and cannot be fixed by revising the patch.

  • RFC: Request for comments, not meant to be merged as is.

  • Not applicable: The email was not actually a patch, or the patch is not for Wayland or Weston. Libinput patches are usually automatically ignored by Wayland Patchwork, but if they get through, they will be marked as Not applicable.

  • Changes requested: Reviewers determined that changes to the patch are needed. The submitter is expected to send a revised version. (You should not wait for your patch to be set to this state before revising, though.)

  • Awaiting upstream: Mostly unused as the patch is waiting for upstream actions but is not shown in the default list, which means it is easy to overlook.

  • Superseded: A revised version of the patch has been submitted.

  • Deferred: Used mostly during freeze periods before releases, to temporarily hide patches that cannot be merged during a freeze.

Note, that in the default listing, only patches in New or Under review are shown.

There is also a command line interface to Patchwork called pwclient, see http://patchwork.freedesktop.org/project/wayland/ for links where to get it and the sample .pwclientrc for Wayland/Weston.

Coding style

You should follow the style of the file you're editing. In general, we try to follow the rules below.

Note: this file uses spaces due to markdown rendering issues for tabs. Code must be implemented using tabs.

  • indent with tabs, and a tab is always 8 characters wide
  • opening braces are on the same line as the if statement;
  • no braces in an if-body with just one statement;
  • if one of the branches of an if-else condition has braces, then the other branch should also have braces;
  • there is always an empty line between variable declarations and the code;
static int
my_function(void)
{
        int a = 0;

        if (a)
                b();
        else
                c();

        if (a) {
                b();
                c();
        } else {
                d();
        }
}
  • lines should be less than 80 characters wide;
  • when breaking lines with functions calls, the parameters are aligned with the opening parentheses;
  • when assigning a variable with the result of a function call, if the line would be longer we break it around the equal '=' sign if it makes sense;
        long_variable_name =
                function_with_a_really_long_name(parameter1, parameter2,
                                                 parameter3, parameter4);

        x = function_with_a_really_long_name(parameter1, parameter2,
                                             parameter3, parameter4);

Conduct

As a freedesktop.org project, Wayland follows the Contributor Covenant, found at: https://www.freedesktop.org/wiki/CodeOfConduct

Please conduct yourself in a respectful and civilised manner when interacting with community members on mailing lists, IRC, or bug trackers. The community represents the project as a whole, and abusive or bullying behaviour is not tolerated by the project.

Licensing

Weston is licensed with the intention to be usable anywhere X.org is. Originally, X.org was covered under the MIT X11 license, but changed to the MIT Expat license. Similarly, Weston was covered initially as MIT X11 licensed, but changed to the MIT Expat license, following in X.org's footsteps. Other than wording, the two licenses are substantially the same, with the exception of a no-advertising clause in X11 not included in Expat.

New source code files should specify the MIT Expat license in their boilerplate, as part of the copyright statement.

Review

All patches, even trivial ones, require at least one positive review (Reviewed-by). Additionally, if no Reviewed-by's have been given by people with commit access, there needs to be at least one Acked-by from someone with commit access. A person with commit access is expected to be able to evaluate the patch with respect to the project scope and architecture.

The below review guidelines are intended to be interpreted in spirit, not by the letter. There may be circumstances where some guidelines are better ignored. We rely very much on the judgement of reviewers and commit rights holders.

During review, the following matters should be checked:

  • The commit message explains why the change is being made.

  • The code fits the project's scope.

  • The code license is the same MIT licence the project generally uses.

  • Stable ABI or API is not broken.

  • Stable ABI or API additions must be justified by actual use cases, not only by speculation. They must also be documented, and it is strongly recommended to include tests excercising the additions in the test suite.

  • The code fits the existing software architecture, e.g. no layering violations.

  • The code is correct and does not introduce new failures for existing users, does not add new corner-case bugs, and does not introduce new compiler warnings.

  • The patch does what it says in the commit message and changes nothing else.

  • The patch is a single logical change. If the commit message addresses multiple points, it is a hint that the commit might need splitting up.

  • A bug fix should target the underlying root cause instead of hiding symptoms. If a complete fix is not practical, partial fixes are acceptable if they come with code comments and filed Gitlab issues for the remaining bugs.

  • The bug root cause rule applies to external software components as well, e.g. do not work around kernel driver issues in userspace.

  • The test suite passes.

  • The code does not depend on API or ABI which has no working free open source implementation.

  • The code is not dead or untestable. E.g. if there are no free open source software users for it then it is effectively dead code.

  • The code is written to be easy to understand, or if code cannot be clear enough on its own there are code comments to explain it.

  • The code is minimal, i.e. prefer refactor and re-use when possible unless clarity suffers.

  • The code adheres to the style guidelines.

  • In a patch series, every intermediate step adheres to the above guidelines.

Commit rights

Commit rights will be granted to anyone who requests them and fulfills the below criteria:

  • Submitted some (10 as a rule of thumb) non-trivial (not just simple spelling fixes and whitespace adjustment) patches that have been merged already.

  • Are actively participating in public discussions about their work (on the mailing list or IRC). This should not be interpreted as a requirement to review other peoples patches but just make sure that patch submission isn't one-way communication. Cross-review is still highly encouraged.

  • Will be regularly contributing further patches. This includes regular contributors to other parts of the open source graphics stack who only do the occasional development in this project.

  • Agrees to use their commit rights in accordance with the documented merge criteria, tools, and processes.

To apply for commit rights, create a new issue in gitlab for the respective project and give it the "accounts" label.

Committers are encouraged to request their commit rights get removed when they no longer contribute to the project. Commit rights will be reinstated when they come back to the project.

Maintainers and committers should encourage contributors to request commit rights, especially junior contributors tend to underestimate their skills.

Stabilising for releases

A release cycle ends with a stable release which also starts a new cycle and lifts any code freezes. Gradual code freezing towards a stable release starts with an alpha release. The release stages of a cycle are:

  • Alpha release: Signified by version number #.#.91. Major features must have landed before this. Major features include invasive code motion and refactoring, high risk changes, and new stable library ABI.

  • Beta release: Signified by version number #.#.92. Minor features must have landed before this. Minor features include all new features that are not major, low risk changes, clean-ups, and documentation. Stable ABI that was new in the alpha release can be removed before a beta release if necessary.

  • Release candidates (RC): Signified by version number #.#.93 and up to #.#.99. Bug fixes that are not release critical must have landed before this. Release critical bug fixes can still be landed after this, but they may call for another RC.

  • Stable release: Signified by version number #.#.0. Ideally no changes since the last RC.

Mind that version #.#.90 is never released. It is used during development when no code freeze is in effect. Stable branches and point releases are not covered by the above.