DOCS: remove coding-style.md to contribute.md

I wonder if this is better. The intention is to make the instructions
for sending patches more visible.

1 files changed, 141 insertions, 0 deletions

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+Coding style
+============
+
+mpv uses C99 with K&R formatting, with some exceptions.
+
+General formatting
+------------------
+
+- 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 should 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 body of an if statement uses braces, the else branch should also
+  use braces (and reverse).
+
+  Example:
+
+    ```C
+    if (a) {
+        // do something
+        something();
+        something_else();
+    } else {
+        one_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();
+    }
+    ```
+- Remove any trailing whitespace.
+- If the file you're editing uses formatting different from from what is
+  described here, it's probably an old file from times when nobody followed a
+  consistent style. You're free to use the existing style, or the new style, or
+  to send a patch to reformat the file to the new style before making functional
+  changes.
+
+General coding
+--------------
+
+- Use C99. Also freely make use of C99 features if it's appropriate, such as
+  stdbool.h.
+- Don't use GNU-only features. In some cases they may be warranted, if they
+  are optional (such as attributes enabling printf-like format string checks).
+  But in general, standard C99 should 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.
+- 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.
+- tech-overview.txt might help to get an overview how mpv is structured.
+- 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.
+
+Sending patches
+---------------
+
+- Make a github pull request, or send a link to a plaintext patch created with
+  ``git format-patch``. diffs posted as pastebins (especially if the http link
+  returns HTML) just cause extra work for everyone, because they lack commit
+  message and authorship information.
+- 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) should contain a
+  prefix identifying the sub system, followed by a short description what
+  impact this commit has. This subject line shouldn't be longer than 72
+  characters, 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 body of the commit message (everything else after the subject line) should
+  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 should 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).
+
+  Important: put an empty line between the subject line and the commit message.
+  If this is missing, it will break display in common git tools.
+- 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.
+- If you add a new command line option, document it in options.rst. If you
+  add a new input property, document it in input.rst.