git-rerere - Reuse recorded resolution of conflicted merges
git rerere [clear | forget <pathspec>... | diff | status | remaining | gc]
In a workflow employing relatively long lived topic branches, the developer
sometimes needs to resolve the same conflicts over and over again until the
topic branches are done (either merged to the "release" branch, or
sent out and accepted upstream).
This command assists the developer in this process by recording conflicted
automerge results and corresponding hand resolve results on the initial manual
merge, and applying previously recorded hand resolutions to their
corresponding automerge results.
Note
You need to set the configuration variable
rerere.enabled in order to
enable this command.
Normally,
git rerere is run without arguments or user-intervention.
However, it has several commands that allow it to interact with its working
state.
clear
Reset the metadata used by rerere if a merge
resolution is to be aborted. Calling git am [--skip|--abort] or git
rebase [--skip|--abort] will automatically invoke this command.
forget <pathspec>
Reset the conflict resolutions which rerere
has recorded for the current conflict in <pathspec>.
diff
Display diffs for the current state of the
resolution. It is useful for tracking what has changed while the user is
resolving conflicts. Additional arguments are passed directly to the system
diff command installed in PATH.
status
Print paths with conflicts whose merge
resolution rerere will record.
remaining
Print paths with conflicts that have not been
autoresolved by rerere. This includes paths whose resolutions cannot be
tracked by rerere, such as conflicting submodules.
gc
Prune records of conflicted merges that
occurred a long time ago. By default, unresolved conflicts older than 15 days
and resolved conflicts older than 60 days are pruned. These defaults are
controlled via the gc.rerereUnresolved and gc.rerereResolved
configuration variables respectively.
When your topic branch modifies an overlapping area that your master branch (or
upstream) touched since your topic branch forked from it, you may want to test
it with the latest master, even before your topic branch is ready to be pushed
upstream:
o---*---o topic
/
o---o---o---*---o---o master
For such a test, you need to merge master and topic somehow. One way to do it is
to pull master into the topic branch:
$ git switch topic
$ git merge master
o---*---o---+ topic
/ /
o---o---o---*---o---o master
The commits marked with
* touch the same area in the same file; you need
to resolve the conflicts when creating the commit marked with
+. Then
you can test the result to make sure your work-in-progress still works with
what is in the latest master.
After this test merge, there are two ways to continue your work on the topic.
The easiest is to build on top of the test merge commit
+, and when
your work in the topic branch is finally ready, pull the topic branch into
master, and/or ask the upstream to pull from you. By that time, however, the
master or the upstream might have been advanced since the test merge
+,
in which case the final commit graph would look like this:
$ git switch topic
$ git merge master
$ ... work on both topic and master branches
$ git switch master
$ git merge topic
o---*---o---+---o---o topic
/ / \
o---o---o---*---o---o---o---o---+ master
When your topic branch is long-lived, however, your topic branch would end up
having many such "Merge from master" commits on it, which would
unnecessarily clutter the development history. Readers of the Linux kernel
mailing list may remember that Linus complained about such too frequent test
merges when a subsystem maintainer asked to pull from a branch full of
"useless merges".
As an alternative, to keep the topic branch clean of test merges, you could blow
away the test merge, and keep building on top of the tip before the test
merge:
$ git switch topic
$ git merge master
$ git reset --hard HEAD^ ;# rewind the test merge
$ ... work on both topic and master branches
$ git switch master
$ git merge topic
o---*---o-------o---o topic
/ \
o---o---o---*---o---o---o---o---+ master
This would leave only one merge commit when your topic branch is finally ready
and merged into the master branch. This merge would require you to resolve the
conflict, introduced by the commits marked with
*. However, this
conflict is often the same conflict you resolved when you created the test
merge you blew away.
git rerere helps you resolve this final conflicted
merge using the information from your earlier hand resolve.
Running the
git rerere command immediately after a conflicted automerge
records the conflicted working tree files, with the usual conflict markers
<<<<<<<,
=======, and
>>>>>>> in them. Later, after you are done
resolving the conflicts, running
git rerere again will record the
resolved state of these files. Suppose you did this when you created the test
merge of master into the topic branch.
Next time, after seeing the same conflicted automerge, running
git rerere
will perform a three-way merge between the earlier conflicted automerge, the
earlier manual resolution, and the current conflicted automerge. If this
three-way merge resolves cleanly, the result is written out to your working
tree file, so you do not have to manually resolve it. Note that
git
rerere leaves the index file alone, so you still need to do the final
sanity checks with
git diff (or
git diff -c) and
git add
when you are satisfied.
As a convenience measure,
git merge automatically invokes
git
rerere upon exiting with a failed automerge and
git rerere records
the hand resolve when it is a new conflict, or reuses the earlier hand resolve
when it is not.
git commit also invokes
git rerere when
committing a merge result. What this means is that you do not have to do
anything special yourself (besides enabling the rerere.enabled config
variable).
In our example, when you do the test merge, the manual resolution is recorded,
and it will be reused when you do the actual merge later with the updated
master and topic branch, as long as the recorded resolution is still
applicable.
The information
git rerere records is also used when running
git
rebase. After blowing away the test merge and continuing development on
the topic branch:
o---*---o-------o---o topic
/
o---o---o---*---o---o---o---o master
$ git rebase master topic
o---*---o-------o---o topic
/
o---o---o---*---o---o---o---o master
you could run
git rebase master topic, to bring yourself up to date
before your topic is ready to be sent upstream. This would result in falling
back to a three-way merge, and it would conflict the same way as the test
merge you resolved earlier.
git rerere will be run by
git rebase
to help you resolve this conflict.
[NOTE]
git rerere relies on the conflict markers in the file to detect
the conflict. If the file already contains lines that look the same as lines
with conflict markers,
git rerere may fail to record a conflict
resolution. To work around this, the
conflict-marker-size setting in
gitattributes(5) can be used.
Part of the
git(1) suite