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author | Junio C Hamano <gitster@pobox.com> | 2010-07-08 18:55:50 -0700 |
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committer | Junio C Hamano <gitster@pobox.com> | 2010-07-08 18:55:50 -0700 |
commit | 037c43c68e220739e690540de89a6d5835fefe73 (patch) | |
tree | 3e201f833fc63e48db6983e45ce2425d884408db /Documentation/howto/revert-a-faulty-merge.txt | |
parent | Fix "read-tree -m A B" priming the cache-tree (diff) | |
parent | Git 1.7.2-rc2 (diff) | |
download | tgif-037c43c68e220739e690540de89a6d5835fefe73.tar.xz |
Merge remote branch 'ko/master' into jc/read-tree-cache-tree-fix
* ko/master: (2325 commits)
Git 1.7.2-rc2
backmerge a few more fixes to 1.7.1.X series
fix git branch -m in presence of cross devices
t/t0006: specify timezone as EST5 not EST to comply with POSIX
add missing && to submodule-merge testcase
t/README: document more test helpers
test-date: fix sscanf type conversion
xdiff: optimise for no whitespace difference when ignoring whitespace.
gitweb: Move evaluate_gitweb_config out of run_request
parse_date: fix signedness in timezone calculation
t0006: test timezone parsing
rerere.txt: Document forget subcommand
t/README: proposed rewording...
t/README: Document the do's and don'ts of tests
t/README: Add a section about skipping tests
t/README: Document test_expect_code
t/README: Document test_external*
t/README: Document the prereq functions, and 3-arg test_*
t/README: Typo: paralell -> parallel
t/README: The trash is in 't/trash directory.$name'
...
Conflicts:
builtin-read-tree.c
Diffstat (limited to 'Documentation/howto/revert-a-faulty-merge.txt')
-rw-r--r-- | Documentation/howto/revert-a-faulty-merge.txt | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/Documentation/howto/revert-a-faulty-merge.txt b/Documentation/howto/revert-a-faulty-merge.txt index 3b4a390005..ff5c0bc27a 100644 --- a/Documentation/howto/revert-a-faulty-merge.txt +++ b/Documentation/howto/revert-a-faulty-merge.txt @@ -142,6 +142,8 @@ different resolution strategies: revert of a merge was rebuilt from scratch (i.e. rebasing and fixing, as you seem to have interpreted), then re-merging the result without doing anything else fancy would be the right thing to do. + (See the ADDENDUM below for how to rebuild a branch from scratch + without changing its original branching-off point.) However, there are things to keep in mind when reverting a merge (and reverting such a revert). @@ -177,3 +179,91 @@ the answer is: "oops, I really shouldn't have merged it, because it wasn't ready yet, and I really need to undo _all_ of the merge"). So then you really should revert the merge, but when you want to re-do the merge, you now need to do it by reverting the revert. + +ADDENDUM + +Sometimes you have to rewrite one of a topic branch's commits *and* you can't +change the topic's branching-off point. Consider the following situation: + + P---o---o---M---x---x---W---x + \ / + A---B---C + +where commit W reverted commit M because it turned out that commit B was wrong +and needs to be rewritten, but you need the rewritten topic to still branch +from commit P (perhaps P is a branching-off point for yet another branch, and +you want be able to merge the topic into both branches). + +The natural thing to do in this case is to checkout the A-B-C branch and use +"rebase -i P" to change commit B. However this does not rewrite commit A, +because "rebase -i" by default fast-forwards over any initial commits selected +with the "pick" command. So you end up with this: + + P---o---o---M---x---x---W---x + \ / + A---B---C <-- old branch + \ + B'---C' <-- naively rewritten branch + +To merge A-B'-C' into the mainline branch you would still have to first revert +commit W in order to pick up the changes in A, but then it's likely that the +changes in B' will conflict with the original B changes re-introduced by the +reversion of W. + +However, you can avoid these problems if you recreate the entire branch, +including commit A: + + A'---B'---C' <-- completely rewritten branch + / + P---o---o---M---x---x---W---x + \ / + A---B---C + +You can merge A'-B'-C' into the mainline branch without worrying about first +reverting W. Mainline's history would look like this: + + A'---B'---C'------------------ + / \ + P---o---o---M---x---x---W---x---M2 + \ / + A---B---C + +But if you don't actually need to change commit A, then you need some way to +recreate it as a new commit with the same changes in it. The rebase commmand's +--no-ff option provides a way to do this: + + $ git rebase [-i] --no-ff P + +The --no-ff option creates a new branch A'-B'-C' with all-new commits (all the +SHA IDs will be different) even if in the interactive case you only actually +modify commit B. You can then merge this new branch directly into the mainline +branch and be sure you'll get all of the branch's changes. + +You can also use --no-ff in cases where you just add extra commits to the topic +to fix it up. Let's revisit the situation discussed at the start of this howto: + + P---o---o---M---x---x---W---x + \ / + A---B---C----------------D---E <-- fixed-up topic branch + +At this point, you can use --no-ff to recreate the topic branch: + + $ git checkout E + $ git rebase --no-ff P + +yielding + + A'---B'---C'------------D'---E' <-- recreated topic branch + / + P---o---o---M---x---x---W---x + \ / + A---B---C----------------D---E + +You can merge the recreated branch into the mainline without reverting commit W, +and mainline's history will look like this: + + A'---B'---C'------------D'---E' + / \ + P---o---o---M---x---x---W---x---M2 + \ / + A---B---C |