Hi,
I think I understand what's going on. If there are no net changes in one
of the two branches, the id of the merge commit will be the same as that
of the last commit on the other branch (pass the -d option to 'git subtree
split' to see the new commit id's of the split out commits). In that case,
git-subtree will drop the merge commit. I believe this is done because for
regular commits, this means that the commit does not make changes to files
in the subtree directory. I'm not sure I'm right about this, as I would
expect the merge commit's hash to depend on the hashes of its parent
commits.
I was thinking the solution would be to simply adjust the copy_or_skip
function to always copy merge commits. However, this may result in the
produced commit history to differ from before (unnecessary merge commits
were previously left out), leading to other problems.
A solution might be to check for the presence of such commit +
revert-commit branches. This can be done by checking for each parent of a
merge commit if it is the ancestor of any of the other parents (using git
merge-base --is-ancestor).
Best regards,
Brecht
On Tue, 27 Aug 2013 15:09:30 +0200, Machiels, Brecht
<Brecht.Machiels@xxxxxxxxxxxxxx> wrote:
Hello:
I'm running into the problem described in this mailing list post:
http://thread.gmane.org/gmane.comp.version-control.git/202645
'git subtree split' fails to reconstruct the history when a revert
commit is followed by a merge commit. I have slightly adjusted the test
script provided by Fabien in his mailing list post:
git init
# create a directory that is going to be split
mkdir doc
echo "TEST" > doc/README
git add doc
# commit A
git commit -a -m"first version"
# create a branch with a new commit (Z)
git checkout -b test
echo "TEST" > doc/README1
git add doc/README1
git commit -a -m"added README1"
git checkout master
# modify the README file (commit B)
echo "TEST_" > doc/README
git commit -a -m"second version"
# revert the change (commit C)
echo "TEST" > doc/README
git commit -a -m"revert second version"
# or use git revert HEAD^
# split
git subtree split --prefix="doc" --branch=TARGET
# add another commit (to a file *not* in the subtree dir)
echo "BLA" > BLA
git add BLA
git commit -a -m"third version"
# adding another commit to a file in the subtree dir will "fix" things
#echo "MEH" > doc/MEH
#git add doc
#git commit -a -m"fourth version"
# the log will show the 3 commits as expected (including B and C)
GIT_PAGER= git log --oneline TARGET
# merge the test branch
git merge -m"merged test" test
# attempt to re-split; this will fail
git subtree split --prefix="doc" --branch=TARGET
# see what history split generates
git subtree split --prefix="doc" --branch=TARGET2
I have discovered that if the revert commit is followed by another
commit that makes changes in the subtree directory, the split will work
as expected (see "fourth version" above).
See also this related SO question where I ask for a workaround:
http://stackoverflow.com/questions/18465867
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