mpv/DOCS/contribute.md

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How to contribute
=================
General
-------
The main contact for mpv development is IRC, specifically #mpv
and #mpv-devel on Freenode. Github is used for code review and
long term discussions.
Sending patches
---------------
- Make a github pull request, or send a link to a plaintext patch created with
``git format-patch``.
- Plain diffs posted as pastebins are not acceptable! (Especially if the http
link returns HTML.) They only cause extra work for everyone, because they lack
commit message and authorship information.
- Never send patches to any of the developers email addresses.
- If your changes are not supposed to be merged immediately, mark them as
"[RFC]" in the commit message or the pull request title.
- Be sure to test your changes. If you didn't, please say so in the commit
message and the pull request text.
Copyright of contributions
--------------------------
- The copyright belongs to contributors. The project is a collaborative work. By
sending your changes, you agree to license your contributions according to the
requirements of this project.
- All new code must be LGPLv2.1+ licensed, or come with the implicit agreement
that it will be relicensed to LGPLv2.1+ later (see ``Copyright`` in the
repository root directory).
- 100% compatible licenses are allowed too.
- Changes in files with more liberal licenses (such as BSD, MIT, or ISC) are
assumed to be dual-licensed under LGPLv2.1+ and the license indicated in the
file header.
- You must be either the exclusive author of the patch, or acknowledge all
authors involved in the commit message. If you take 3rd party code, authorship
and copyright must be properly acknowledged. If you're making changes on
behalf of your employer, and the employer owns the copyright, you must mention
this. If the license of the code is not LGPLv2.1+, you must mention this.
- These license statements are legally binding.
- Don't use fake names (something that looks like an actual name, and may be
someone else's name, but is not your legal name). Using a pseudonyms is
allowed if it can be used to identify or contact you, even if whatever
account you used to submit the patch dies.
- Do not add your name to the license header. This convention is not used by
this project, and neither copyright law nor any of the used licenses require
it.
Write good commit messages
--------------------------
- Write informative commit messages. Use present tense to describe the
situation with the patch applied, and past tense for the situation before
the change.
- The subject line (the first line in a commit message) must contain a
prefix identifying the sub system, followed by a short description what
impact this commit has. This subject line and the commit message body
must not be longer than 72 characters per line, because it messes up the
output of many git tools otherwise.
For example, you fixed a crash in af_volume.c:
- Bad: ``fixed the bug (wtf?)``
- Good: ``af_volume: fix crash due to null pointer access``
Having a prefix gives context, and is especially useful when trying to find
a specific change by looking at the history, or when running ``git blame``.
- The first word after the ``:`` is lower case.
- Don't end the subject line with a ``.``.
- Put an empty line between the subject line and the commit message.
If this is missing, it will break display in common git tools.
- The body of the commit message (everything else after the subject line) must
be as informative as possible and contain everything that isn't obvious. Don't
hesitate to dump as much information as you can - it doesn't cost you
anything. Put some effort into it. If someone finds a bug months or years
later, and finds that it's caused by your commit (even though your commit was
supposed to fix another bug), it would be bad if there wasn't enough
information to test the original bug. The old bug might be reintroduced while
fixing the new bug.
The commit message must be wrapped on 72 characters per line, because git
tools usually do not break text automatically. On the other hand, you do not
need to break text that would be unnatural to break (like data for test cases,
or long URLs).
- Another summary of good conventions: https://chris.beams.io/posts/git-commit/
Split changes into multiple commits
-----------------------------------
- Follow git good practices, and split independent changes into several commits.
It's usually OK to put them into a single pull request.
- Try to separate cosmetic and functional changes. It's ok to make a few
additional cosmetic changes in the same file you're working on. But don't do
something like reformatting a whole file, and hiding an actual functional
change in the same commit.
- Splitting changes does _not_ mean that you should make them as fine-grained
as possible. Commits should form logical steps in development. The way you
split changes is important for code review and analyzing bugs.
Touching user-visible parts may require updating the mpv docs
-------------------------------------------------------------
- Most user-visible things are normally documented in DOCS/man/. If your commit
touches documented behavior, list of sub-options, etc., you need to adjust the
documentation.
- These changes usually go into the same commit that changes the code.
- Changes to command line options (addition/modification/removal) must be
documented in options.rst.
- Changes to input properties or input commands must be documented in input.rst.
- All incompatible changes to the user interface (options, properties, commands)
must be documented with a small note in interface-changes.rst. (Additions may
be documented there as well, but this isn't required.)
- Changes to the libmpv API must be reflected in the libmpv's headers doxygen,
and in client-api-changes.rst.
Code formatting
---------------
mpv uses C99 with K&R formatting, with some exceptions.
- Use the K&R indent style.
- Use 4 spaces of indentation, never use tabs (except in Makefiles).
- Add a single space between keywords and binary operators. There are some other
cases where spaces must be added. Example:
```C
if ((a * b) > c) {
// code
some_function(a, b, c);
}
```
- Break lines on 80 columns. There is a hard limit of 85 columns. You may ignore
this limit if there's a strong case that not breaking the line will increase
readability. Going over 85 columns might provoke endless discussions about
whether such a limit is needed or not, so avoid it.
- If the body of an if/for/while statement has more than 1 physical lines, then
always add braces, even if they're technically redundant.
Bad:
```C
if (a)
// do something if b
if (b)
do_something();
```
Good:
```C
if (a) {
// do something if b
if (b)
do_something();
}
```
- If the if has an else branch, both branches must use braces, even if they're
technically redundant.
Example:
```C
if (a) {
one_line();
} else {
one_other_line();
}
```
- If an if condition spans multiple physical lines, then put the opening brace
for the if body on the next physical line. (Also, preferably always add a
brace, even if technically none is needed.)
Example:
```C
if (very_long_condition_a &&
very_long_condition_b)
{
code();
} else {
...
}
```
(If the if body is simple enough, this rule can be skipped.)
- Remove any trailing whitespace.
- Do not make stray whitespaces changes.
Header #include statement order
-------------------------------
The order of ``#include`` statements in the source code is not very consistent.
New code must follow the following conventions:
- Put standard includes (``#include <stdlib.h>`` etc.) on the top,
- then after a blank line, add library includes (``#include <zlib.h>`` etc.)
- then after a blank line, add internal includes (``#include "player/core.h"``)
- sort them alphabetically within these sections
General coding
--------------
- Use C99. Also freely make use of C99 features if it's appropriate, such as
stdbool.h. (Except VLA and complex number types.)
- Don't use non-standard language (such as GNU C-only features). In some cases
they may be warranted, if they are optional (such as attributes enabling
printf-like format string checks). "#pragma once" is allowed as an exception.
But in general, standard C99 must be used.
- The same applies to libc functions. We have to be Windows-compatible too. Use
functions guaranteed by C99 or POSIX only, unless your use is guarded by a
configure check. There is some restricted use of C11 (ask on IRC for details).
- Prefer fusing declaration and initialization, rather than putting declarations
on the top of a block. Obvious data flow is more important than avoiding
mixing declarations and statements, which is just a C90 artifact.
- If you add features that require intrusive changes, discuss them on the dev
channel first. There might be a better way to add a feature and it can avoid
wasted work.
Code of Conduct
---------------
We have one, but the document describing it got lost accidentally.
Rules for git push access
-------------------------
Push access to the main git repository is handed out on an arbitrary basis. If
you got access, the following rules must be followed:
- You are expected to follow the general development rules as outlined in this
whole document.
- You must be present on the IRC dev channel when you push something.
- Anyone can push small fixes: typo corrections, small/obvious/uncontroversial
bug fixes, edits to the user documentation or code comments, and so on.
- You can freely make changes to parts of the code which you maintain. For
larger changes, it's recommended to let others review the changes first.
- You automatically maintain code if you wrote or modified most of it before
(e.g. you made larger changes to it before, did partial or full rewrites, did
major bug fixes, or you're the original author of the code). If there is more
than one maintainer, you may need to come to an agreement with the others how
to handle this to avoid conflict.
- If you make a pull requests (especially if it's to code you maintain), and you
want reviews, explicitly ping the people from which you expect reviews.
- As a maintainer, you can approve pull requests by others to "your" code.
- If you approve or merge 3rd party changes, make sure they follow the general
development rules.
- Changes to user interface and public API must always be approved by the
project leader.
- Seasoned project members are allowed to revert commits that broke the build,
or broke basic functionality in a catastrophic way, and the developer who
broke it is unavailable. (Depending on severity.)
- Adhere to the CoC.
- The project leader is not bound by these rules.