git-rerere: reuse recorded resolve.
[git/git.git] / Documentation / git-rerere.txt
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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