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 PATH.

       Print paths with conflicts whose merge resolution rerere will

       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 checkout 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 checkout topic
               $ git merge master
               $ ... work on both topic and master branches
               $ git checkout 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 checkout topic
               $ git merge master
               $ git reset --hard HEAD^ ;# rewind the test merge
               $ ... work on both topic and master branches
               $ git checkout 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.


   Part of the git(1) suite


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