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<!DOCTYPE html><html><head><meta charset="utf-8" /><meta content="noarchive" name="robots" /><title>Automatic merge conflict resolution for git-rebase(1) - The Terminal Programmer</title><meta content="2016-01-03T22:31:05-08:00" name="DCTERMS.created" /><meta content="2016-07-15T10:51:12-07:00" name="DCTERMS.modified" /><meta content="Suraj N. Kurapati" name="author" /><meta content="tool, git, shell, script" name="keywords" /><meta content="width=device-width, initial-scale=1" name="viewport" /><meta content="Readably https://github.com/sunaku/readably" name="generator" /><link href="style.css" rel="stylesheet" type="text/css" /><link href="index.atom" rel="alternate" title="feed" type="application/atom+xml" /><script src="js/jquery.slim.min.js"></script></head><body><article data-entry-id="git-rebase-autocon" id="body"><header><div class="navigation"><a class="rootlink" href="index.html#git-rebase-autocon" title="The Terminal Programmer"><span>The Terminal Programmer</span></a></div><h1 class="title">Automatic merge conflict resolution for git-rebase(1)</h1><div class="author">Suraj N. Kurapati</div><time class="date" datetime="2016-01-03T22:31:05-08:00"> 3 January 2016 <span class="update_count"><a href="#updates" title="3 updates">···→</a></span> 15 July 2016</time></header><hr /><div class="description"></div><div class="content"><ol class="table-of-contents"><li><a id="__problem__" href="#problem" class="downlink">Problem</a><ol></ol></li><li><a id="__solution__" href="#solution" class="downlink">Solution</a><ol><li><a id="__bin-git-rebase-autocon__" href="#bin-git-rebase-autocon" class="downlink">~/bin/git-rebase-autocon</a><ol></ol></li></ol></li></ol>
<div id="problem" class="section"></div><h1 class="heading">Problem<a href="#problem" class="permalink" title="Permalink"></a><a href="#__problem__" class="uplink" title="Contents"></a></h1>
<p>Let’s say you have a copy of some software (a clone of a Git repository, to be
precise) that you’ve modified in some way, locally. Some time later, that
software is changed upstream, thereby rendering your local copy <em>out of date</em>.
How can you bring your local copy up to date <em>while also</em> retaining your
local modifications?</p>
<p>The answer is to <a href="http://git-scm.com/book/ch3-6.html">use git-rebase(1)</a>.
However, if your local modifications conflict with any upstream changes, then
you’ll need to <a href="http://git-scm.com/book/en/v2/Git-Branching-Basic-Branching-and-Merging#Basic-Merge-Conflicts">resolve those conflicts</a>
manually: a cumbersome process that can be daunting for inexperienced users.</p>
<p>This is particularly problematic for configurable software distributed through
Git, such as my <a href="https://github.com/sunaku/.vim#readme">text editor</a> and
<a href="https://github.com/sunaku/wmiirc#readme">window manager</a> configurations,
where the occasional need for manual conflict resolution greatly impedes users
who aren’t technically inclined or lack the time necessary to manually resolve
such conflicts.</p>
<div id="solution" class="section"></div><h1 class="heading">Solution<a href="#solution" class="permalink" title="Permalink"></a><a href="#__solution__" class="uplink" title="Contents"></a></h1>
<p>The following shell script automates conflict resolution for git-rebase(1) by
simply <em>setting aside</em> local modifications that conflict with upstream changes
and by offering users a means of easily undoing such actions, through <code>git
reset --hard</code>.</p>
<p>Afterwards, the user may choose to inspect the automatically set-aside
conflicts, recorded in empty-tree commits labeled “fixup!”, and restore
portions thereof: thereby enacting manual conflict resolution, but willingly
performed at one’s leisure.</p>
<div id="bin-git-rebase-autocon" class="section"></div><h2 class="heading">~/bin/git-rebase-autocon<a href="#bin-git-rebase-autocon" class="permalink" title="Permalink"></a><a href="#__bin-git-rebase-autocon__" class="uplink" title="Contents"></a></h2>
<div class="highlight"><pre class="highlight shell"><code><span class="c">#!/bin/sh -e</span>
<span class="c">#</span>
<span class="c"># Usage: git-rebase-autocon [TARGET] [ARGUMENTS_FOR_GIT_REBASE...]</span>
<span class="c">#</span>
<span class="c"># Rebases the given TARGET while automatically resolving conflicts</span>
<span class="c"># by substituting empty-tree commits labeled "fixup!" that log all</span>
<span class="c"># conflicting hunks in their commit messages in git-diff(1) format.</span>
<span class="c">#</span>
<span class="c"># If TARGET is not specified, the upstream tracking branch is used.</span>
<span class="c"># Optional ARGUMENTS_FOR_GIT_REBASE... are passed to git-rebase(1).</span>
<span class="c">#</span>
<span class="c"># Written in 2010 by Suraj N. Kurapati <https://github.com/sunaku></span>
<span class="c"># Documented at <https://sunaku.github.io/git-rebase-autocon.html></span>
<span class="c"># ensure working tree is clean</span>
git rebase HEAD <span class="nt">--quiet</span>
<span class="nv">commit</span><span class="o">=</span><span class="si">$(</span>git rev-parse <span class="nt">--short</span> HEAD<span class="si">)</span>
<span class="c"># parse command-line arguments</span>
<span class="nb">test</span> <span class="nv">$# </span><span class="nt">-gt</span> 0 <span class="o">&&</span> <span class="nv">target</span><span class="o">=</span><span class="nv">$1</span> <span class="o">&&</span> <span class="nb">shift</span> <span class="o">||</span> <span class="nv">target</span><span class="o">=</span><span class="s1">'@{u}'</span>
<span class="nv">target</span><span class="o">=</span><span class="si">$(</span>git name-rev <span class="nt">--name-only</span> <span class="s2">"</span><span class="nv">$target</span><span class="s2">"</span><span class="si">)</span>
<span class="nv">target</span><span class="o">=</span><span class="k">${</span><span class="nv">target</span><span class="p">#remotes/</span><span class="k">}</span>
<span class="c"># rebase target and ensure that only merge conflicts made it fail</span>
git rebase <span class="nt">--fork-point</span> <span class="s2">"</span><span class="nv">$target</span><span class="s2">"</span> <span class="s2">"</span><span class="nv">$@</span><span class="s2">"</span> <span class="o">&&</span> <span class="nb">exit</span> <span class="o">||</span> <span class="nb">test</span> <span class="nt">-d</span> .git/rebase-apply
<span class="c"># solve merge conflicts by absorbing leftover commits from prior</span>
<span class="c"># versions of the target or by setting aside conflicting commits</span>
<span class="nb">trap</span> <span class="s1">'git rebase --abort'</span> TERM INT
<span class="k">while </span><span class="nb">test</span> <span class="nt">-d</span> .git/rebase-apply<span class="p">;</span> <span class="k">do
</span><span class="nv">headline</span><span class="o">=</span><span class="si">$(</span><span class="nb">head</span> <span class="nt">-1</span> .git/rebase-apply/final-commit<span class="si">)</span>
<span class="nv">conflict</span><span class="o">=</span><span class="si">$(</span><span class="nb">cat</span> .git/rebase-apply/original-commit<span class="si">)</span>
<span class="nv">shortish</span><span class="o">=</span><span class="si">$(</span>git rev-parse <span class="nt">--short</span> <span class="s2">"</span><span class="nv">$conflict</span><span class="s2">"</span><span class="si">)</span>
<span class="c"># in place of each conflicting commit, record an empty commit whose</span>
<span class="c"># message contains the changes introduced by the conflicting commit</span>
git reset <span class="nt">--mixed</span> <span class="nt">--quiet</span> <span class="c"># empty the index so we can make a commit</span>
git commit <span class="nt">--allow-empty</span> <span class="nt">--reuse-message</span><span class="o">=</span><span class="s2">"</span><span class="nv">$conflict</span><span class="s2">"</span> <span class="nt">--quiet</span>
<span class="o">{</span>
<span class="nb">printf</span> <span class="s1">'fixup! %s %s\n\n'</span> <span class="s2">"</span><span class="nv">$shortish</span><span class="s2">"</span> <span class="s2">"</span><span class="nv">$headline</span><span class="s2">"</span>
git format-patch <span class="nt">--stdout</span> <span class="s2">"</span><span class="nv">$conflict</span><span class="s2">~..</span><span class="nv">$conflict</span><span class="s2">"</span>
<span class="o">}</span> |
git commit <span class="nt">--amend</span> <span class="nt">--allow-empty</span> <span class="nt">--file</span><span class="o">=</span>-
git rebase <span class="nt">--skip</span> <span class="o">></span>/dev/null 2>&1 <span class="o">||</span> :
<span class="k">done
</span><span class="nb">cat</span> <span class="o"><<</span><span class="no">END</span><span class="sh">
+-------------------------IMPORTANT!----------------------------+
| |
| Some of YOUR COMMITS WERE SET ASIDE to solve merge conflicts: |
| empty commits labeled as "fixup!" have now taken their place. |
| But rest assured, THEY STILL EXIST in Git history at </span><span class="nv">$commit</span><span class="sh">, |
| and your working tree has all changes from those commits too! |
| |
| You can UNDO THIS REBASE at any time by running this command: |
| |
| git reset --hard </span><span class="nv">$commit</span><span class="sh"> |
| |
| You can SEE WHAT CHANGED from before by running this command: |
| |
| git diff </span><span class="nv">$commit</span><span class="sh"> |
| |
+-------------------------IMPORTANT!----------------------------+
</span><span class="no">
END
</span></code></pre></div></div><hr /><h1 id="updates">Updates<a class="permalink" href="#updates" title="Permalink"></a></h1><aside class="update"><dl><dt class="title"><time datetime="2016-07-15T10:51:12-07:00">15 July 2016: </time></dt><dd class="content"><p>Commits that were set aside had empty message bodies, caused by Git > 2.3.6
producing no output when <code>--</code> was specified just before the revision range.</p>
</dd></dl></aside><aside class="update"><dl><dt class="title"><time datetime="2016-06-24T21:28:06-07:00">24 June 2016: </time></dt><dd class="content"><p>Use <code>--fork-point</code> option for <code>git rebase</code> instead of detecting leftovers.</p>
</dd></dl></aside><aside class="update"><dl><dt class="title"><time datetime="2016-06-17T21:34:06-07:00">17 June 2016: </time></dt><dd class="content"><ul>
<li>When a conflicting commit originates from a prior version of the target,
we can safely absorb it via <code>git rebase --skip</code> to resolve the conflict.</li>
<li>Apply proper patch(1) formatting when setting aside conflicting commits.</li>
<li>Only show “important” message if any conflicting commits were set aside.</li>
<li>Gracefully abort rebase when the script is terminated prematurely.</li>
<li>Don’t summarize any differences after rebasing: do one thing well.</li>
</ul>
</dd></dl></aside><div class="comments" id="comments"><script>var disqus_container_id = 'comments';
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