Add a new --rejoin option.

The idea is to join the new split branch back into this one, so future
splits can append themselves to the old split branch.  We mark the split
branch's history in our merge commit, so we can pull it back out later.

git-subtree.sh

@@ -2,10 +2,10 @@
 #
 # git-subtree.sh: split/join git repositories in subdirectories of this one
 #
-# Copyright (c) 2009 Avery Pennarun <apenwarr@gmail.com>
+# Copyright (C) 2009 Avery Pennarun <apenwarr@gmail.com>
 #
 OPTS_SPEC="\
-git subtree split <revisions> -- <subdir>
+git subtree split [--rejoin] [--onto rev] <commit...> -- <path>
 git subtree merge 
 
 git subtree does foo and bar!
@@ -13,6 +13,8 @@ git subtree does foo and bar!
 h,help   show the help
 q        quiet
 v        verbose
+onto=    existing subtree revision to connect, if any
+rejoin   merge the new branch back into HEAD
 "
 eval $(echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)
 . git-sh-setup
@@ -20,6 +22,8 @@ require_work_tree
 
 quiet=
 command=
+onto=
+rejoin=
 
 debug()
 {
@@ -42,9 +46,12 @@ assert()
 
 while [ $# -gt 0 ]; do
 	opt="$1"
+	debug "option: $1"
 	shift
 	case "$opt" in
 		-q) quiet=1 ;;
+		--onto) onto="$1"; shift ;;
+		--rejoin) rejoin=1 ;;
 		--) break ;;
 	esac
 done
@@ -93,7 +100,9 @@ cache_set()
 {
 	oldrev="$1"
 	newrev="$2"
-	if [ "$oldrev" != "latest" -a -e "$cachedir/$oldrev" ]; then
+	if [ "$oldrev" != "latest_old" \
+	     -a "$oldrev" != "latest_new" \
+	     -a -e "$cachedir/$oldrev" ]; then
 		die "cache for $oldrev already exists!"
 	fi
 	echo "$newrev" >"$cachedir/$oldrev"
@@ -111,12 +120,29 @@ copy_commit()
 		read GIT_COMMITTER_NAME
 		read GIT_COMMITTER_EMAIL
 		read GIT_COMMITTER_DATE
-		export GIT_AUTHOR_NAME GIT_AUTHOR_EMAIL GIT_AUTHOR_DATE
-		export GIT_COMMITTER_NAME GIT_COMMITTER_EMAIL GIT_COMMITTER_DATE
+		export  GIT_AUTHOR_NAME \
+			GIT_AUTHOR_EMAIL \
+			GIT_AUTHOR_DATE \
+			GIT_COMMITTER_NAME \
+			GIT_COMMITTER_EMAIL \
+			GIT_COMMITTER_DATE
 		git commit-tree "$2" $3  # reads the rest of stdin
 	) || die "Can't copy commit $1"
 }
 
+merge_msg()
+{
+	dir="$1"
+	latest_old="$2"
+	latest_new="$3"
+	cat <<-EOF
+		Split changes from '$dir/' into commit '$latest_new'
+		
+		git-subtree-dir: $dir
+		git-subtree-includes: $latest_old
+	EOF
+}
+
 cmd_split()
 {
 	debug "Splitting $dir..."
@@ -140,14 +166,23 @@ cmd_split()
 			newrev=$(copy_commit $rev $tree "$p") || exit $?
 			debug "  newrev is: $newrev"
 			cache_set $rev $newrev
-			cache_set latest $newrev
+			cache_set latest_new $newrev
+			cache_set latest_old $rev
 		done || exit $?
 	done || exit $?
-	latest=$(cache_get latest)
-	if [ -z "$latest" ]; then
+	latest_new=$(cache_get latest_new)
+	if [ -z "$latest_new" ]; then
 		die "No new revisions were found"
 	fi
-	echo $latest
+	
+	if [ -n "$rejoin" ]; then
+		debug "Merging split branch into HEAD..."
+		latest_old=$(cache_get latest_old)
+		git merge -s ours \
+			-m "$(merge_msg $dir $latest_old $latest_new)" \
+			$latest_new
+	fi
+	echo $latest_new
 	exit 0
 }