git-debrebase: stitch: ff when possible

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

1 files changed, 13 insertions, 1 deletions

diff --git a/git-debrebase b/git-debrebase
index 93bf46b..c08af65 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -1199,8 +1199,20 @@ sub cmd_stitch () {
     if (!$prev) {
 	fail "No ffq-prev to stitch." unless $opt_noop_ok;
     }
-    fresh_workarea();
     my $old_head = get_head();
+    if (is_fast_fwd $old_head, $prev) {
+	my $differs = get_differs $old_head, $prev;
+	unless ($differs & ~D_PAT_ADD) {
+	    # ffq-prev is ahead of us, and the only tree changes it has
+	    # are possibly addition of things in debian/patches/.
+	    # Just wind forwards rather than making a pointless pseudomerge.
+	    update_head_checkout $old_head, $prev,
+		"debrebase: stitch (fast forward)";
+	    runcmd @git, qw(update-ref -d), $ffq_prev; # should be atomic
+	    return;
+	}
+    }
+    fresh_workarea();
     my $new_head = make_commit [ $old_head, $ffq_prev ], [
 	'Declare fast forward / record previous work',
         "[git-debrebase pseudomerge: stitch$prose]",