[PATCH] rebase --preserve-merges keeps empty merge commits

From: Phil Hord <hordp@cisco.com>
Date: Jan 12, 2013, 20:46 UTC
Message-ID: <1358023561-26773-1-git-send-email-hordp@cisco.com>

Since 90e1818f9a (git-rebase: add keep_empty flag, 2012-04-20) 'git rebase --preserve-merges' fails to preserve empty merge commits unless --keep-empty is also specified. Merge commits should be preserved in order to preserve the structure of the rebased graph, even if the merge commit does not introduce changes to the parent.

Teach rebase not to drop merge commits only because they are empty.

A special case which is not handled by this change is for a merge commit
whose parents are now the same commit because all the previous different
parents have been dropped as a result of this rebase or some previous
operation.
---
 git-rebase--interactive.sh | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 44901d5..8ed7fcc 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -190,6 +190,11 @@ is_empty_commit() {
 	test "$tree" = "$ptree"
 }
 
+is_merge_commit()
+{
+	git rev-parse --verify --quiet "$1"^2 >/dev/null 2>&1
+}
+
 # Run command with GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL, and
 # GIT_AUTHOR_DATE exported from the current environment.
 do_with_author () {
@@ -874,7 +879,7 @@ git rev-list $merges_option --pretty=oneline --abbrev-commit \
 while read -r shortsha1 rest
 do
 
-	if test -z "$keep_empty" && is_empty_commit $shortsha1
+	if test -z "$keep_empty" && is_empty_commit $shortsha1 && ! is_merge_commit $shortsha1
 	then
 		comment_out="# "
 	else

-- 
1.8.1.dirty