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Date: Sat, 13 Aug 2005 22:16:02 -0700 (PDT)
From: Linus Torvalds <torvalds@osdl.org>
To: Steve French <smfrench@austin.rr.com>
cc: git@vger.kernel.org
Subject: Re: sending changesets from the middle of a git tree
Abstract: In this article, Linus demonstrates how a broken commit
in a sequence of commits can be removed by rewinding the head and
reapplying selected changes.
On Sat, 13 Aug 2005, Linus Torvalds wrote:
> That's correct. Same things apply: you can move a patch over, and create a
> new one with a modified comment, but basically the _old_ commit will be
> immutable.
Let me clarify.
You can entirely _drop_ old branches, so commits may be immutable, but
nothing forces you to keep them. Of course, when you drop a commit, you'll
always end up dropping all the commits that depended on it, and if you
actually got somebody else to pull that commit you can't drop it from
_their_ repository, but undoing things is not impossible.
For example, let's say that you've made a mess of things: you've committed
three commits "old->a->b->c", and you notice that "a" was broken, but you
want to save "b" and "c". What you can do is
# Create a branch "broken" that is the current code
# for reference
git branch broken
# Reset the main branch to three parents back: this
# effectively undoes the three top commits
git reset HEAD^^^
git checkout -f
# Check the result visually to make sure you know what's
# going on
gitk --all
# Re-apply the two top ones from "broken"
#
# First "parent of broken" (aka b):
git-diff-tree -p broken^ | git-apply --index
git commit --reedit=broken^
# Then "top of broken" (aka c):
git-diff-tree -p broken | git-apply --index
git commit --reedit=broken
and you've now re-applied (and possibly edited the comments) the two
commits b/c, and commit "a" is basically gone (it still exists in the
"broken" branch, of course).
Finally, check out the end result again:
# Look at the new commit history
gitk --all
to see that everything looks sensible.
And then, you can just remove the broken branch if you decide you really
don't want it:
# remove 'broken' branch
rm .git/refs/heads/broken
# Prune old objects if you're really really sure
git prune
And yeah, I'm sure there are other ways of doing this. And as usual, the
above is totally untested, and I just wrote it down in this email, so if
I've done something wrong, you'll have to figure it out on your own ;)
Linus
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