git-rebase: add keep_empty flag

Add a command line switch to git-rebase to allow a user the ability to specify
that they want to keep any commits in a series that are empty.

When git-rebase's type is am, then this option will automatically keep any
commit that has a tree object identical to its parent.

This patch changes the default behavior of interactive rebases as well.  With
this patch, git-rebase -i will produce a revision set passed to
git-revision-editor, in which empty commits are commented out.  Empty commits
may be kept manually by uncommenting them.  If the new --keep-empty option is
used in an interactive rebase the empty commits will automatically all be
uncommented in the editor.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 32 insertions, 3 deletions

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 5812222eb..70538bb20 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -167,6 +167,14 @@ has_action () {
 	sane_grep '^[^#]' "$1" >/dev/null
 }
 
+is_empty_commit() {
+	tree=$(git rev-parse -q --verify "$1"^{tree} 2>/dev/null ||
+		die "$1: not a commit that can be picked")
+	ptree=$(git rev-parse -q --verify "$1"^^{tree} 2>/dev/null ||
+		ptree=4b825dc642cb6eb9a060e54bf8d69288fbee4904)
+	test "$tree" = "$ptree"
+}
+
 # Run command with GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL, and
 # GIT_AUTHOR_DATE exported from the current environment.
 do_with_author () {
@@ -191,12 +199,19 @@ git_sequence_editor () {
 
 pick_one () {
 	ff=--ff
+
 	case "$1" in -n) sha1=$2; ff= ;; *) sha1=$1 ;; esac
 	case "$force_rebase" in '') ;; ?*) ff= ;; esac
 	output git rev-parse --verify $sha1 || die "Invalid commit name: $sha1"
+
+	if is_empty_commit "$sha1"
+	then
+		empty_args="--allow-empty"
+	fi
+
 	test -d "$rewritten" &&
 		pick_one_preserving_merges "$@" && return
-	output git cherry-pick $ff "$@"
+	output git cherry-pick $empty_args $ff "$@"
 }
 
 pick_one_preserving_merges () {
@@ -780,9 +795,17 @@ git rev-list $merges_option --pretty=oneline --abbrev-commit \
 	sed -n "s/^>//p" |
 while read -r shortsha1 rest
 do
+
+	if test -z "$keep_empty" && is_empty_commit $shortsha1
+	then
+		comment_out="# "
+	else
+		comment_out=
+	fi
+
 	if test t != "$preserve_merges"
 	then
-		printf '%s\n' "pick $shortsha1 $rest" >> "$todo"
+		printf '%s\n' "${comment_out}pick $shortsha1 $rest" >>"$todo"
 	else
 		sha1=$(git rev-parse $shortsha1)
 		if test -z "$rebase_root"
@@ -801,7 +824,7 @@ do
 		if test f = "$preserve"
 		then
 			touch "$rewritten"/$sha1
-			printf '%s\n' "pick $shortsha1 $rest" >> "$todo"
+			printf '%s\n' "${comment_out}pick $shortsha1 $rest" >>"$todo"
 		fi
 	fi
 done
@@ -851,6 +874,12 @@ cat >> "$todo" << EOF
 #
 EOF
 
+if test -z "$keep_empty"
+then
+	echo "# Note that empty commits are commented out" >>"$todo"
+fi
+
+
 has_action "$todo" ||
 	die_abort "Nothing to do"