git‐rerere − Reuse recorded resolution of conflicted merges

git rerere [clear|forget <pathspec>|diff|remaining|status|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.


     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.

     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>.

     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

     Print paths with conflicts whose merge resolution
     rerere will record.


     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.

     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

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

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