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

'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>

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 5873ba4bc3b2a94cd7754ae572072fd745dc059d..c308529a9f1f668f02d63cfddcbac10770faa723 100755 (executable)
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -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"

diff --git a/t/t3409-rebase-preserve-merges.sh b/t/t3409-rebase-preserve-merges.sh
index 19341e5ca1c7f415afdf2c82f67930b8fed5478b..08201e2331d36af769d832e3d9551c48331b7033 100755 (executable)
--- a/t/t3409-rebase-preserve-merges.sh
+++ b/t/t3409-rebase-preserve-merges.sh
@@ -27,7 +27,17 @@ export GIT_AUTHOR_EMAIL
 #    \
 #     B2       <-- origin/topic
 #
-# In both cases, 'topic' is rebased onto 'origin/topic'.
+# Clone 3 (no-ff merge):
+#
+# A1--A2--B3   <-- origin/master
+#  \
+#   B1------M  <-- topic
+#    \     /
+#     \--A3    <-- topic2
+#      \
+#       B2     <-- origin/topic
+#
+# In all cases, 'topic' is rebased onto 'origin/topic'.
 
 test_expect_success 'setup for merge-preserving rebase' \
        'echo First > A &&
@@ -61,6 +71,16 @@ test_expect_success 'setup for merge-preserving rebase' \
                git commit -m "Merge origin/master into topic"
        ) &&
 
+       git clone ./. clone3 &&
+       (
+               cd clone3 &&
+               git checkout -b topic2 origin/topic &&
+               echo Sixth > A &&
+               git commit -a -m "Modify A3" &&
+               git checkout -b topic origin/topic &&
+               git merge --no-ff topic2
+       ) &&
+
        git checkout topic &&
        echo Fourth >> B &&
        git commit -a -m "Modify B2"
@@ -93,4 +113,14 @@ test_expect_success '--continue works after a conflict' '
        )
 '
 
+test_expect_success 'rebase -p preserves no-ff merges' '
+       (
+       cd clone3 &&
+       git fetch &&
+       git rebase -p origin/topic &&
+       test 3 = $(git rev-list --all --pretty=oneline | grep "Modify A" | wc -l) &&
+       test 1 = $(git rev-list --all --pretty=oneline | grep "Merge branch" | wc -l)
+       )
+'
+
 test_done