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diff --git a/Documentation/git-rerere.txt b/Documentation/git-rerere.txt new file mode 100644 index 000000000..8b6b65123 --- /dev/null +++ b/Documentation/git-rerere.txt @@ -0,0 +1,177 @@ +git-rerere(1) +============= + +NAME +---- +git-rerere - Reuse recorded resolve + +SYNOPSIS +-------- +'git-rerere' + + +DESCRIPTION +----------- + +In a workflow that employs relatively long lived topic branches, +the developer sometimes needs to resolve the same conflict over +and over again until the topic branches are done (either merged +to the "release" branch, or sent out and accepted upstream). + +This command helps this process by recording conflicted +automerge results and corresponding hand-resolve results on the +initial manual merge, and later by noticing the same automerge +results and applying the previously recorded hand resolution. + +[NOTE] +You need to create `$GIT_DIR/rr-cache` directory to enable this +command. + +DISCUSSION +---------- + +When your topic branch modifies 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 pull . 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 pull . master + $ ... work on both topic and master branches + $ git checkout master + $ git pull . 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 pull . master + $ git reset --hard HEAD^ ;# rewind the test merge + $ ... work on both topic and master branches + $ git checkout master + $ git pull . 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, often this conflict is the +same conflict you resolved when you created the test merge you +blew away. `git-rerere` command helps you to resolve this final +conflicted merge using the information from your earlier hand +resolve. + +Running `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 records the resolved state of these +files. Suppose you did this when you created the test merge of +master into the topic branch. + +Next time, running `git-rerere` after seeing a conflicted +automerge, if the conflict is the same as the earlier one +recorded, it is noticed and a three-way merge between the +earlier conflicted automerge, the earlier manual resolution, and +the current conflicted automerge is performed by the command. +If this three-way merge resolves cleanly, the result is written +out to your working tree file, so you would 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 update-index` when you are +satisfied. + +As a convenience measure, `git-merge` automatically invokes +`git-rerere` when it exits with a failed automerge, which +records it if it is a new conflict, or reuses the earlier hand +resolve when it is not. `git-commit` also invokes `git-rerere` +when recording a merge result. What this means is that you do +not have to do anything special yourself (Note: you still have +to create `$GIT_DIR/rr-cache` directory to enable this command). + +In our example, when you did the test merge, the manual +resolution is recorded, and it will be reused when you do the +actual merge later with updated master and topic branch, as long +as the earlier 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 keep yourself +up-to-date even before your topic is ready to be sent upstream. +This would result in falling back to three-way merge, and it +would conflict the same way the test merge you resolved earlier. +`git-rerere` is run by `git rebase` to help you resolve this +conflict. + + +Author +------ +Written by Junio C Hamano <junkio@cox.net> + +GIT +--- +Part of the gitlink:git[7] suite |