list-objects: pass full pathname to callbacks

When we find a blob at "a/b/c", we currently pass this to
our show_object_fn callbacks as two components: "a/b/" and
"c". Callbacks which want the full value then call
path_name(), which concatenates the two. But this is an
inefficient interface; the path is a strbuf, and we could
simply append "c" to it temporarily, then roll back the
length, without creating a new copy.

So we could improve this by teaching the callsites of
path_name() this trick (and there are only 3). But we can
also notice that no callback actually cares about the
broken-down representation, and simply pass each callback
the full path "a/b/c" as a string. The callback code becomes
even simpler, then, as we do not have to worry about freeing
an allocated buffer, nor rolling back our modification to
the strbuf.

This is theoretically less efficient, as some callbacks
would not bother to format the final path component. But in
practice this is not measurable. Since we use the same
strbuf over and over, our work to grow it is amortized, and
we really only pay to memcpy a few bytes.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 9 deletions

diff --git a/pack-bitmap.c b/pack-bitmap.c
index 51f790e7c..b949e5171 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -414,19 +414,15 @@ static int ext_index_add_object(struct object *object, const char *name)
 	return bitmap_pos + bitmap_git.pack->num_objects;
 }
 
-static void show_object(struct object *object, struct strbuf *path,
-			const char *last, void *data)
+static void show_object(struct object *object, const char *name, void *data)
 {
 	struct bitmap *base = data;
 	int bitmap_pos;
 
 	bitmap_pos = bitmap_position(object->oid.hash);
 
-	if (bitmap_pos < 0) {
-		char *name = path_name(path, last);
+	if (bitmap_pos < 0)
 		bitmap_pos = ext_index_add_object(object, name);
-		free(name);
-	}
 
 	bitmap_set(base, bitmap_pos);
 }
@@ -894,9 +890,8 @@ struct bitmap_test_data {
 	size_t seen;
 };
 
-static void test_show_object(struct object *object,
-			     struct strbuf *path,
-			     const char *last, void *data)
+static void test_show_object(struct object *object, const char *name,
+			     void *data)
 {
 	struct bitmap_test_data *tdata = data;
 	int bitmap_pos;