<chapter id="gbp.releases">
    <title>Releases and Snapshots</title>
    <para>When branching and merging frequently, the different Debian changelog
    entries on the different branches tend to get into the way of the automatic
    merge and the the merge fails - leaving the (pathological) merge to the
    committer. In order to avoid this &gbp-dch; offers a way for creating
    changelog entries from &git; commits before doing a
    release or anytime between releases.</para> 
    <para>
    The simplest way is doing all the changes to the
    <option>debian-branch</option> without touching
    <emphasis>debian/changelog</emphasis> at all. Then, when done, do:
    </para>
<screen>
&gbp-dch; <option>--release</option>
</screen>
    <para> This will look up the latest released version in the changelog,
    increment the version in the &debian; changelog, generate changelog
    messages from the corresponding &git; commit id up to the branch head and
    finally spawns an editor for final changelog file editing by invoking &dch;
    <option>--release</option>.</para>
    <para>
    But what if you want to have an (unreleased) snapshot for intermediate testing:
    </para>
<screen>
&gbp-dch; <option>--snapshot</option>
</screen>
   <para>will generate a snapshot release with a specially crafted version number
   and a warning in the changelog that this is a snapshort release:
   </para>
<programlisting>
git-buildpackage (0.3.7~1.gbp470ce2) UNRELEASED; urgency=low

  ** SNAPSHOT build @470ce29ec7877705c844474a2fd89869aea0406d **

  * add support for automatic snapshot 
</programlisting>
   <para>During subsequent calls with <option>--snapshot</option> this version
   number will continue to increase. Since the snapshot banners contains the
   commit id of the current branch head, &gbp-dch; can figure out what to
   append to the changelog by itself:
<screen>
&gbp-dch; <option>--snapshot</option> <option>--auto</option>
</screen>
   will fetch the commit id and add changelog entries from that point to the
   current HEAD - again auto incrementing the version number. If you don't want
   to start at that commit id, you can specify any id or tag with:</para>
<screen>
&gbp-dch; <option>--since</option>=<replaceable>e76a6a180a57701ae4ae381f74523cacb3152780</replaceable> <option>--snapshot</option>
</screen>
   <para>
   After testing you can remove the snapshot header by a final &gbp-dch; call:
   </para>
<screen>
&gbp-dch; <option>--since</option>=<replaceable>HEAD</replaceable> <option>--release</option>
</screen>
   <para>
   This will add no further entries but simply remove the specially crafted
   version number and the snapshort header. Again you can use any commit id
   or tag instead of <option>HEAD</option> if you want to add further changelog
   entries - or you can (of course) use <option>--auto</option> again.
   </para>
<sect1 id="gbp.release.numbers">
    <title>Customizing snapshot numbers</title>
    <para>If the auto incrementing of the snapshot number doesn't suite you needs you
    can give any python expression that evaluates to a positive integer to
    calculate the new snapshot number:</para>
<screen>
&gbp-dch; <option>-S</option> <option>-a</option> <option>--snapshot-number</option>=<replaceable>1</replaceable>
&gbp-dch; <option>-S</option> <option>-a</option> <option>--snapshot-number</option>=<replaceable>'snapshot + 2'</replaceable>
&gbp-dch; <option>-S</option> <option>-a</option> <option>--snapshot-number</option>=<replaceable>'os.popen("git-log --pretty=oneline | wc -l").readlines()[0]'</replaceable>
&gbp-dch; <option>-S</option> <option>-a</option> <option>--snapshot-number</option>=<replaceable>`git-log --pretty=oneline debian/0.3.3 | wc -l`</replaceable>
</screen>
<para>
You can also add the snapshot-number calculation to <filename>gbp.conf</filename>:
</para>
<programlisting>
[DEFAULT]
snapshot-number = os.popen("git-log --pretty=oneline | wc -l").readlines()[0]
</programlisting>
</sect1>
<sect1 id="gbp.release.commit">
    <title>More on commit messages</title>
    <para>You can use <option>--full</option> to include the full commit
    message in the changelog, note that you will lose the formatting though,
    since &dch; wraps lines by itself.</para>
    <para>Additionally there are tags <option>Closes:</option> and
<option>Thanks:</option> available to customize the commit message. Each tag
has to start at the beginning of a single line. For example the git commit message
<screen>
New upstream version

Closes: #1000
Thanks: cool upstream
</screen>
    would result in a changelog entry:
<screen>
    * New upstream version (Closes: #1000) - thanks to cool upstream
</screen>
You can use the <option>Closes:</option> tag multiple times.
</para>
<para>
There are several tags to further customize what (and how) commit messages get
included into the changelog:
</para><para>
To exclude a commit from the generated changelog use:
</para><para>
<screen>
Git-Dch: Ignore
</screen>
This is e.g. useful if you're just fixing up a previous commit and couldn't
ammend it or for other janitorial commits that really don't need to end up in
the changelog. For example, the following git commit message
<screen>
Set correct branchnames in debian/gbp.conf

Git-Dch: Ignore
</screen>
will not show up in the generated changelog in any way.
</para>
<para>
To include the full commit message in the changelog use:
<screen>
Git-Dch: Full
</screen>
</para>
<para>
To only include the short description in the changelog and skip the body use:
<screen>
Git-Dch: Short
</screen>
The latter only takes effect when running &gbp-dch; with the
<option>--full</option> option, since including only the short
description is the default.
</para>
<para>
Usually changelog entries should correspond to a single &git; commit. In this case it's
convenient to include the commit id in the changelog entry. 
This has the advantage that it's easy for people to identify changes without
having to write very extensive changelog messages - the link back to Git can be
automated via the <option>Vcs-Browser</option> and <option>Vcs-Git</option>
fields in <filename>debian/control</filename>. See <ulink url="https://honk.sigxcpu.org/cl2vcs">
Cl2vcs</ulink> for how this looks.
</para>
<para>
The inclusion of the commit id can be done automatically
via &gbp-dch;'s <option>--id-length</option> option. Using
<option>--id-length</option>=<replaceable>7</replaceable>  would change the above example to:
<screen>
    * [571bfd4] New upstream version (Closes: #1000) - thanks to cool upstream
</screen>
This makes it much easier to see which commit actually fixed bug #1000.
</para>
</sect1>
</chapter>
