'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@xxxxxxxxx>
---
git-rebase--interactive.sh | 2 +-
t/t3409-rebase-preserve-merges.sh | 32 +++++++++++++++++++++++++++++++-
2 files changed, 32 insertions(+), 2 deletions(-)
diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 5873ba4..c308529 100755
--- 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 19341e5..08201e2 100755
--- 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
--
1.7.2.2
--
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