1git-rerere(1) 2============= 3 4NAME 5---- 6git-rerere - Reuse recorded resolve 7 8SYNOPSIS 9-------- 10'git-rerere' 11 12 13DESCRIPTION 14----------- 15 16In a workflow that employs relatively long lived topic branches, 17the developer sometimes needs to resolve the same conflict over 18and over again until the topic branches are done (either merged 19to the "release" branch, or sent out and accepted upstream). 20 21This command helps this process by recording conflicted 22automerge results and corresponding hand-resolve results on the 23initial manual merge, and later by noticing the same automerge 24results and applying the previously recorded hand resolution. 25 26[NOTE] 27You need to create `$GIT_DIR/rr-cache` directory to enable this 28command. 29 30DISCUSSION 31---------- 32 33When your topic branch modifies overlapping area that your 34master branch (or upstream) touched since your topic branch 35forked from it, you may want to test it with the latest master, 36even before your topic branch is ready to be pushed upstream: 37 38------------ 39 o---*---o topic 40 / 41 o---o---o---*---o---o master 42------------ 43 44For such a test, you need to merge master and topic somehow. 45One way to do it is to pull master into the topic branch: 46 47------------ 48 $ git checkout topic 49 $ git pull . master 50 51 o---*---o---+ topic 52 / / 53 o---o---o---*---o---o master 54------------ 55 56The commits marked with `*` touch the same area in the same 57file; you need to resolve the conflicts when creating the commit 58marked with `+`. Then you can test the result to make sure your 59work-in-progress still works with what is in the latest master. 60 61After this test merge, there are two ways to continue your work 62on the topic. The easiest is to build on top of the test merge 63commit `+`, and when your work in the topic branch is finally 64ready, pull the topic branch into master, and/or ask the 65upstream to pull from you. By that time, however, the master or 66the upstream might have been advanced since the test merge `+`, 67in which case the final commit graph would look like this: 68 69------------ 70 $ git checkout topic 71 $ git pull . master 72 $ ... work on both topic and master branches 73 $ git checkout master 74 $ git pull . topic 75 76 o---*---o---+---o---o topic 77 / / \ 78 o---o---o---*---o---o---o---o---+ master 79------------ 80 81When your topic branch is long-lived, however, your topic branch 82would end up having many such "Merge from master" commits on it, 83which would unnecessarily clutter the development history. 84Readers of the Linux kernel mailing list may remember that Linus 85complained about such too frequent test merges when a subsystem 86maintainer asked to pull from a branch full of "useless merges". 87 88As an alternative, to keep the topic branch clean of test 89merges, you could blow away the test merge, and keep building on 90top of the tip before the test merge: 91 92------------ 93 $ git checkout topic 94 $ git pull . master 95 $ git reset --hard HEAD^ ;# rewind the test merge 96 $ ... work on both topic and master branches 97 $ git checkout master 98 $ git pull . topic 99 100 o---*---o-------o---o topic 101 / \ 102 o---o---o---*---o---o---o---o---+ master 103------------ 104 105This would leave only one merge commit when your topic branch is 106finally ready and merged into the master branch. This merge 107would require you to resolve the conflict, introduced by the 108commits marked with `*`. However, often this conflict is the 109same conflict you resolved when you created the test merge you 110blew away. `git-rerere` command helps you to resolve this final 111conflicted merge using the information from your earlier hand 112resolve. 113 114Running `git-rerere` command immediately after a conflicted 115automerge records the conflicted working tree files, with the 116usual conflict markers `<<<<<<<`, `=======`, and `>>>>>>>` in 117them. Later, after you are done resolving the conflicts, 118running `git-rerere` again records the resolved state of these 119files. Suppose you did this when you created the test merge of 120master into the topic branch. 121 122Next time, running `git-rerere` after seeing a conflicted 123automerge, if the conflict is the same as the earlier one 124recorded, it is noticed and a three-way merge between the 125earlier conflicted automerge, the earlier manual resolution, and 126the current conflicted automerge is performed by the command. 127If this three-way merge resolves cleanly, the result is written 128out to your working tree file, so you would not have to manually 129resolve it. Note that `git-rerere` leaves the index file alone, 130so you still need to do the final sanity checks with `git diff` 131(or `git diff -c`) and `git update-index` when you are 132satisfied. 133 134As a convenience measure, `git-merge` automatically invokes 135`git-rerere` when it exits with a failed automerge, which 136records it if it is a new conflict, or reuses the earlier hand 137resolve when it is not. `git-commit` also invokes `git-rerere` 138when recording a merge result. What this means is that you do 139not have to do anything special yourself (Note: you still have 140to create `$GIT_DIR/rr-cache` directory to enable this command). 141 142In our example, when you did the test merge, the manual 143resolution is recorded, and it will be reused when you do the 144actual merge later with updated master and topic branch, as long 145as the earlier resolution is still applicable. 146 147The information `git-rerere` records is also used when running 148`git-rebase`. After blowing away the test merge and continuing 149development on the topic branch: 150 151------------ 152 o---*---o-------o---o topic 153 / 154 o---o---o---*---o---o---o---o master 155 156 $ git rebase master topic 157 158 o---*---o-------o---o topic 159 / 160 o---o---o---*---o---o---o---o master 161------------ 162 163you could run `git rebase master topic`, to keep yourself 164up-to-date even before your topic is ready to be sent upstream. 165This would result in falling back to three-way merge, and it 166would conflict the same way the test merge you resolved earlier. 167`git-rerere` is run by `git rebase` to help you resolve this 168conflict. 169 170 171Author 172------ 173Written by Junio C Hamano <junkio@cox.net> 174 175GIT 176--- 177Part of the gitlink:git[7] suite