allow using --branch with existing branches if it makes sense

diff --git a/git-subtree.sh b/git-subtree.sh
index 96118735b2c9da6867579dd19ae314add87f8b6d..09992e39d5897698daaf6c6db2ef0b23460a58b1 100755 (executable)
--- a/git-subtree.sh
+++ b/git-subtree.sh
@@ -161,6 +161,20 @@ rev_exists()
        fi
 }
 
+rev_is_descendant_of_branch()
+{
+       newrev="$1"
+       branch="$2"
+       branch_hash=$(git rev-parse $branch)
+       match=$(git rev-list $newrev | grep $branch_hash)
+
+       if [ -n "$match" ]; then
+               return 0
+       else
+               return 1
+       fi
+}
+
 # if a commit doesn't have a parent, this might not work.  But we only want
 # to remove the parent from the rev-list, and since it doesn't exist, it won't
 # be there anyway, so do nothing in that case.
@@ -476,10 +490,6 @@ cmd_add()
 
 cmd_split()
 {
-       if [ -n "$branch" ] && rev_exists "refs/heads/$branch"; then
-               die "Branch '$branch' already exists."
-       fi
-
        debug "Splitting $dir..."
        cache_setup || exit $?
        
@@ -510,7 +520,8 @@ cmd_split()
        eval "$grl" |
        while read rev parents; do
                revcount=$(($revcount + 1))
-               say -n "$revcount/$revmax ($createcount)\r"
+               say -n "$revcount/$revmax ($createcount)
+"
                debug "Processing commit: $rev"
                exists=$(cache_get $rev)
                if [ -n "$exists" ]; then
@@ -548,9 +559,16 @@ cmd_split()
                        $latest_new >&2 || exit $?
        fi
        if [ -n "$branch" ]; then
-               git update-ref -m 'subtree split' "refs/heads/$branch" \
-                       $latest_new "" || exit $?
-               say "Created branch '$branch'"
+               if rev_exists "refs/heads/$branch"; then
+                       if ! rev_is_descendant_of_branch $latest_new $branch; then
+                               die "Branch '$branch' is not an ancestor of commit '$latest_new'."
+                       fi
+                       action='Updated'
+               else
+                       action='Created'
+               fi
+               git update-ref -m 'subtree split' "refs/heads/$branch" $latest_new || exit $?
+               say "$action branch '$branch'"
        fi
        echo $latest_new
        exit 0