mirror of
https://github.com/git/git
synced 2024-08-25 10:45:59 +00:00
![Justin Lebar](/assets/img/avatar_default.png)
Signed-off-by: Justin Lebar <jlebar@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
188 lines
7.6 KiB
Plaintext
188 lines
7.6 KiB
Plaintext
From: Junio C Hamano <gitster@pobox.com>
|
|
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>
|
|
|
|
How to revert 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 merge revert-c99 ;# 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(-)
|
|
------------------------------------------------
|
|
|
|
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.
|
|
* 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
|
|
* Applying: Document "git cherry-pick" and "git revert"
|
|
First trying simple merge strategy to cherry-pick.
|
|
* Applying: mailinfo and applymbox updates
|
|
First trying simple merge strategy to cherry-pick.
|
|
* Applying: Show commits in topo order and name all commits.
|
|
First trying simple merge strategy to cherry-pick.
|
|
* Applying: More documentation updates.
|
|
First trying simple merge strategy to 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
|
|
or tag anymore, so remove them:
|
|
|
|
------------------------------------------------
|
|
$ rm -f .git/refs/tags/pu-anchor
|
|
$ git branch -d 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
|
|
|
|
* commit-ish: 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: Add option to repack all objects.
|
|
* [rc] Merge refs/heads/master from .
|
|
---
|
|
+ [pu] git-repack: 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....
|
|
------------------------------------------------
|