developer.xml

<?xml version='1.0' encoding="utf-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
                      "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">

<book>
  <title>The Music Player Daemon - Developer's Manual</title>

  <chapter id="introduction">
    <title>Introduction</title>

    <para>
      This is a guide for those who wish to hack on the MPD source
      code.  MPD is an open project, and we are always happy about
      contributions.  So far, more than 150 people have contributed
      patches.
    </para>

    <para>
      This document is work in progress.  Most of it may be incomplete
      yet.  Please help!
    </para>
  </chapter>

  <chapter id="code_style">
    <title>Code Style</title>

    <itemizedlist>
      <listitem>
        <para>
          indent with tabs (width 8)
        </para>
      </listitem>

      <listitem>
        <para>
          don't write CPP when you can write C++: use inline
          functions and constexpr instead of macros
        </para>
      </listitem>

      <listitem>
        <para>
          comment your code, document your APIs
        </para>
      </listitem>

      <listitem>
        <para>
          the code should be C++14 compliant, and must compile with
          <application>GCC</application> 5.0 and
          <application>clang</application> 3.4
        </para>
      </listitem>

      <listitem>
        <para>
          report error conditions with C++ exceptions, preferable
          derived from <varname>std::runtime_error</varname>
        </para>
      </listitem>

      <listitem>
        <para>
          all code must be exception-safe
        </para>
      </listitem>

      <listitem>
        <para>
          classes and functions names use CamelCase; variables are
          lower-case with words separated by underscore
        </para>
      </listitem>

      <listitem>
        <para>
          Some example code:
        </para>

        <programlisting lang="C">static inline int
Foo(const char *abc, int xyz)
{
        if (abc == nullptr) {
                LogWarning("Foo happened!");
                return -1;
        }

        return xyz;
}
        </programlisting>
      </listitem>
    </itemizedlist>
  </chapter>

  <chapter id="hacking">
    <title>Hacking The Source</title>

    <para>
      MPD sources are managed in a git repository on <ulink
      url="https://github.com/MusicPlayerDaemon/">GitHub</ulink>.
    </para>

    <para>
      Always write your code against the latest git:
    </para>

    <programlisting>git clone git://github.com/MusicPlayerDaemon/MPD</programlisting>

    <para>
      If you already have a clone, update it:
    </para>

    <programlisting>git pull --rebase git://github.com/MusicPlayerDaemon/MPD master</programlisting>

    <para>
      You can do without "--rebase", but we recommend that you rebase
      your repository on the "master" repository all the time.
    </para>

    <para>
      Configure with the options <option>--enable-debug
      --enable-werror</option>.  Enable as many plugins as possible,
      to be sure that you don't break any disabled code.
    </para>

    <para>
      Don't mix several changes in one single patch.  Create a
      separate patch for every change.  Tools like
      <application>stgit</application> help you with that.  This way,
      we can review your patches more easily, and we can pick the
      patches we like most first.
    </para>


    <section>
      <title> Basic stgit usage</title>

      <para>
        stgit allows you to create a set of patches and refine all of
        them: you can go back to any patch at any time, and re-edit it
        (both the code and the commit message). You can reorder
        patches and insert new patches at any position. It encourages
        creating separate patches for tiny changes.
      </para>

      <para>
        stgit needs to be initialized on a git repository: stg init
      </para>

      <para>
        Before you edit the code, create a patch: stg new
        my-patch-name (stgit now asks you for the commit message).
      </para>

      <para>
        Now edit the code. Once you're finished, you have to "refresh"
        the patch, i.e. your edits are incorporated into the patch you
        have created: stg refresh
      </para>

      <para>
        You may now continue editing the same patch, and refresh it as
        often as you like. Create more patches, edit and refresh them.
      </para>

      <para>
        To view the list of patches, type stg series. To go back to a
        specific patch, type stg goto my-patch-name; now you can
        re-edit it (don't forget stg refresh when you're finished with
        that patch).
      </para>

      <para>
        When the whole patch series is finished, convert stgit patches
        to git commits: stg commit
      </para>
    </section>
  </chapter>

  <chapter id="submitting_patches">
    <title>Submitting Patches</title>

    <para>
      Send your patches to the mailing list:
      <email>mpd-devel@musicpd.org</email> (<ulink
      url="http://mailman.blarg.de/listinfo/mpd-devel">subscribe
      here</ulink>)
    </para>

    <para>
      <command>git pull</command> requests are preferred.
    </para>
  </chapter>

  <chapter id="tools">
    <title>Development Tools</title>

    <section>
      <title>Clang Static Analyzer</title>

      <para>
        The <ulink url="http://clang-analyzer.llvm.org/">clang static
        analyzer</ulink> is a tool that helps find bugs.  To run it on
        the MPD code base, install LLVM and clang.  Configure MPD to
        use clang:
      </para>

      <programlisting>./configure --enable-debug CXX=clang++ CC=clang ...</programlisting>

      <para>
        It is recommended to use <option>--enable-debug</option>,
        because the analyzer takes advantage of
        <function>assert()</function> calls, which are only enabled in
        the debug build.
      </para>

      <para>
        Now run the analyzer:
      </para>

      <programlisting>scan-build --use-c++=clang++ --use-cc=clang make</programlisting>

      <para>
        The options <option>--use-c++</option> and
        <option>--use-cc</option> are necessary because it invokes
        <command>cc</command> for actually compiling the sources by
        default.  That breaks, because MPD requires a C99 compiler.
      </para>
    </section>
  </chapter>
</book>