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git-rebase--interactive.sh: preserve-merges fails on merges created with no-ff

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'git rebase' uses 'git merge' to preserve merges (-p).  This preserves
the original merge commit correctly, except when the original merge
commit was created by 'git merge --no-ff'.  In this case, 'git rebase'
will fail to preserve the merge, because during 'git rebase', 'git
merge' will simply fast-forward and skip the commit.  For example:

               B
              / \
             A---M
            /
    ---o---O---P---Q

If we try to rebase M onto P, we lose the merge commit and this happens:

                 A---B
                /
    ---o---O---P---Q

To correct this, we simply do a "no fast-forward" on all merge commits
when rebasing.  Since by the time we decided to do a 'git merge' inside
'git rebase', it means there was a merge originally, so 'git merge'
should always create a merge commit regardless of what the merge
branches look like. This way, when rebase M onto P from the above
example, we get:

                   B
                  / \
                 A---M
                /
    ---o---O---P---Q

Signed-off-by: Andrew Wong <andrew.kw.w@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Andrew Wong
2011-04-28 00:35:55 -04:00
committed by Junio C Hamano
parent 4fec83045b
commit c192f9c865
2 changed files with 32 additions and 2 deletions
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2
git-rebase--interactive.sh
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@ -339,7 +339,7 @@ pick_one_preserving_merges () {
# No point in merging the first parent, that's HEAD
new_parents=${new_parents# $first_parent}
if ! do_with_author output \
git merge $STRATEGY -m "$msg" $new_parents
git merge --no-ff $STRATEGY -m "$msg" $new_parents
then
printf "%s\n" "$msg" > "$GIT_DIR"/MERGE_MSG
die_with_patch $sha1 "Error redoing merge $sha1"