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diff --git a/Documentation/howto/revert-branch-rebase.txt b/Documentation/howto/revert-branch-rebase.txt new file mode 100644 index 000000000..1c9a36888 --- /dev/null +++ b/Documentation/howto/revert-branch-rebase.txt @@ -0,0 +1,199 @@ +From: Junio C Hamano <junkio@cox.net> +To: git@vger.kernel.org +Subject: [HOWTO] Reverting an existing commit +Abstract: In this article, JC gives a small real-life example of using + 'git revert' command, and using a temporary branch and tag for safety + and easier sanity checking. +Date: Mon, 29 Aug 2005 21:39:02 -0700 +Content-type: text/asciidoc +Message-ID: <7voe7g3uop.fsf@assigned-by-dhcp.cox.net> + +Reverting an existing commit +============================ + +One of the changes I pulled into the 'master' branch turns out to +break building GIT with GCC 2.95. While they were well intentioned +portability fixes, keeping things working with gcc-2.95 was also +important. Here is what I did to revert the change in the 'master' +branch and to adjust the 'pu' branch, using core GIT tools and +barebone Porcelain. + +First, prepare a throw-away branch in case I screw things up. + +------------------------------------------------ +$ git checkout -b revert-c99 master +------------------------------------------------ + +Now I am on the 'revert-c99' branch. Let's figure out which commit to +revert. I happen to know that the top of the 'master' branch is a +merge, and its second parent (i.e. foreign commit I merged from) has +the change I would want to undo. Further I happen to know that that +merge introduced 5 commits or so: + +------------------------------------------------ +$ git show-branch --more=4 master master^2 | head +! [master] Merge refs/heads/portable from http://www.cs.berkeley.... + ! [master^2] Replace C99 array initializers with code. +-- ++ [master] Merge refs/heads/portable from http://www.cs.berkeley.... +++ [master^2] Replace C99 array initializers with code. +++ [master^2~1] Replace unsetenv() and setenv() with older putenv(). +++ [master^2~2] Include sys/time.h in daemon.c. +++ [master^2~3] Fix ?: statements. +++ [master^2~4] Replace zero-length array decls with []. ++ [master~1] tutorial note about git branch +------------------------------------------------ + +The '--more=4' above means "after we reach the merge base of refs, +show until we display four more common commits". That last commit +would have been where the "portable" branch was forked from the main +git.git repository, so this would show everything on both branches +since then. I just limited the output to the first handful using +'head'. + +Now I know 'master^2~4' (pronounce it as "find the second parent of +the 'master', and then go four generations back following the first +parent") is the one I would want to revert. Since I also want to say +why I am reverting it, the '-n' flag is given to 'git revert'. This +prevents it from actually making a commit, and instead 'git revert' +leaves the commit log message it wanted to use in '.msg' file: + +------------------------------------------------ +$ git revert -n master^2~4 +$ cat .msg +Revert "Replace zero-length array decls with []." + +This reverts 6c5f9baa3bc0d63e141e0afc23110205379905a4 commit. +$ git diff HEAD ;# to make sure what we are reverting makes sense. +$ make CC=gcc-2.95 clean test ;# make sure it fixed the breakage. +$ make clean test ;# make sure it did not cause other breakage. +------------------------------------------------ + +The reverted change makes sense (from reading the 'diff' output), does +fix the problem (from 'make CC=gcc-2.95' test), and does not cause new +breakage (from the last 'make test'). I'm ready to commit: + +------------------------------------------------ +$ git commit -a -s ;# read .msg into the log, + # and explain why I am reverting. +------------------------------------------------ + +I could have screwed up in any of the above steps, but in the worst +case I could just have done 'git checkout master' to start over. +Fortunately I did not have to; what I have in the current branch +'revert-c99' is what I want. So merge that back into 'master': + +------------------------------------------------ +$ git checkout master +$ git resolve master revert-c99 fast ;# this should be a fast forward +Updating from 10d781b9caa4f71495c7b34963bef137216f86a8 to e3a693c... + cache.h | 8 ++++---- + commit.c | 2 +- + ls-files.c | 2 +- + receive-pack.c | 2 +- + server-info.c | 2 +- + 5 files changed, 8 insertions(+), 8 deletions(-) +------------------------------------------------ + +The 'fast' in the above 'git resolve' is not a magic. I knew this +'resolve' would result in a fast forward merge, and if not, there is +something very wrong (so I would do 'git reset' on the 'master' branch +and examine the situation). When a fast forward merge is done, the +message parameter to 'git resolve' is discarded, because no new commit +is created. You could have said 'junk' or 'nothing' there as well. + +There is no need to redo the test at this point. We fast forwarded +and we know 'master' matches 'revert-c99' exactly. In fact: + +------------------------------------------------ +$ git diff master..revert-c99 +------------------------------------------------ + +says nothing. + +Then we rebase the 'pu' branch as usual. + +------------------------------------------------ +$ git checkout pu +$ git tag pu-anchor pu +$ git rebase master +* Applying: Redo "revert" using three-way merge machinery. +First trying simple merge strategy to cherry-pick. +Finished one cherry-pick. +* Applying: Remove git-apply-patch-script. +First trying simple merge strategy to cherry-pick. +Simple cherry-pick fails; trying Automatic cherry-pick. +Removing Documentation/git-apply-patch-script.txt +Removing git-apply-patch-script +Finished one cherry-pick. +* Applying: Document "git cherry-pick" and "git revert" +First trying simple merge strategy to cherry-pick. +Finished one cherry-pick. +* Applying: mailinfo and applymbox updates +First trying simple merge strategy to cherry-pick. +Finished one cherry-pick. +* Applying: Show commits in topo order and name all commits. +First trying simple merge strategy to cherry-pick. +Finished one cherry-pick. +* Applying: More documentation updates. +First trying simple merge strategy to cherry-pick. +Finished one cherry-pick. +------------------------------------------------ + +The temporary tag 'pu-anchor' is me just being careful, in case 'git +rebase' screws up. After this, I can do these for sanity check: + +------------------------------------------------ +$ git diff pu-anchor..pu ;# make sure we got the master fix. +$ make CC=gcc-2.95 clean test ;# make sure it fixed the breakage. +$ make clean test ;# make sure it did not cause other breakage. +------------------------------------------------ + +Everything is in the good order. I do not need the temporary branch +nor tag anymore, so remove them: + +------------------------------------------------ +$ rm -f .git/refs/tags/pu-anchor .git/refs/heads/revert-c99 +------------------------------------------------ + +It was an emergency fix, so we might as well merge it into the +'release candidate' branch, although I expect the next release would +be some days off: + +------------------------------------------------ +$ git checkout rc +$ git pull . master +Packing 0 objects +Unpacking 0 objects + +* committish: e3a693c... refs/heads/master from . +Trying to merge e3a693c... into 8c1f5f0... using 10d781b... +Committed merge 7fb9b7262a1d1e0a47bbfdcbbcf50ce0635d3f8f + cache.h | 8 ++++---- + commit.c | 2 +- + ls-files.c | 2 +- + receive-pack.c | 2 +- + server-info.c | 2 +- + 5 files changed, 8 insertions(+), 8 deletions(-) +------------------------------------------------ + +And the final repository status looks like this: + +------------------------------------------------ +$ git show-branch --more=1 master pu rc +! [master] Revert "Replace zero-length array decls with []." + ! [pu] git-repack-script: Add option to repack all objects. + * [rc] Merge refs/heads/master from . +--- + + [pu] git-repack-script: Add option to repack all objects. + + [pu~1] More documentation updates. + + [pu~2] Show commits in topo order and name all commits. + + [pu~3] mailinfo and applymbox updates + + [pu~4] Document "git cherry-pick" and "git revert" + + [pu~5] Remove git-apply-patch-script. + + [pu~6] Redo "revert" using three-way merge machinery. + + [rc] Merge refs/heads/master from . ++++ [master] Revert "Replace zero-length array decls with []." + + [rc~1] Merge refs/heads/master from . ++++ [master~1] Merge refs/heads/portable from http://www.cs.berkeley.... +------------------------------------------------ |