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>

builtin/pack-objects.c

@@ -2284,21 +2284,11 @@ static void show_commit(struct commit *commit, void *data)
 		index_commit_for_bitmap(commit);
 }
 
-static void show_object(struct object *obj,
+static void show_object(struct object *obj, const char *name, void *data)
-			struct strbuf *path, const char *last,
-			void *data)
 {
-	char *name = path_name(path, last);
-
 	add_preferred_base_object(name);
 	add_object_entry(obj->sha1, obj->type, name, 0);
 	obj->flags |= OBJECT_ADDED;
-
-	/*
-	 * We will have generated the hash from the name,
-	 * but not saved a pointer to it - we can free it
-	 */
-	free((char *)name);
 }
 
 static void show_edge(struct commit *commit)
@@ -2480,8 +2470,7 @@ static int get_object_list_from_bitmap(struct rev_info *revs)
 }
 
 static void record_recent_object(struct object *obj,
-				 struct strbuf *path,
+				 const char *name,
-				 const char *last,
 				 void *data)
 {
 	sha1_array_append(&recent_objects, obj->sha1);

builtin/rev-list.c

@@ -177,9 +177,7 @@ static void finish_commit(struct commit *commit, void *data)
 	free_commit_buffer(commit);
 }
 
-static void finish_object(struct object *obj,
+static void finish_object(struct object *obj, const char *name, void *cb_data)
-			  struct strbuf *path, const char *name,
-			  void *cb_data)
 {
 	struct rev_list_info *info = cb_data;
 	if (obj->type == OBJ_BLOB && !has_sha1_file(obj->sha1))
@@ -188,15 +186,13 @@ static void finish_object(struct object *obj,
 		parse_object(obj->sha1);
 }
 
-static void show_object(struct object *obj,
+static void show_object(struct object *obj, const char *name, void *cb_data)
-			struct strbuf *path, const char *component,
-			void *cb_data)
 {
 	struct rev_list_info *info = cb_data;
-	finish_object(obj, path, component, cb_data);
+	finish_object(obj, name, cb_data);
 	if (info->flags & REV_LIST_QUIET)
 		return;
-	show_object_with_name(stdout, obj, path, component);
+	show_object_with_name(stdout, obj, name);
 }
 
 static void show_edge(struct commit *commit)

list-objects.c

@@ -16,6 +16,7 @@ static void process_blob(struct rev_info *revs,
 			 void *cb_data)
 {
 	struct object *obj = &blob->object;
+	size_t pathlen;
 
 	if (!revs->blob_objects)
 		return;
@@ -24,7 +25,11 @@ static void process_blob(struct rev_info *revs,
 	if (obj->flags & (UNINTERESTING | SEEN))
 		return;
 	obj->flags |= SEEN;
-	show(obj, path, name, cb_data);
+
+	pathlen = path->len;
+	strbuf_addstr(path, name);
+	show(obj, path->buf, cb_data);
+	strbuf_setlen(path, pathlen);
 }
 
 /*
@@ -86,9 +91,8 @@ static void process_tree(struct rev_info *revs,
 	}
 
 	obj->flags |= SEEN;
-	show(obj, base, name, cb_data);
-
 	strbuf_addstr(base, name);
+	show(obj, base->buf, cb_data);
 	if (base->len)
 		strbuf_addch(base, '/');
 
@@ -207,7 +211,7 @@ void traverse_commit_list(struct rev_info *revs,
 			continue;
 		if (obj->type == OBJ_TAG) {
 			obj->flags |= SEEN;
-			show_object(obj, NULL, name, data);
+			show_object(obj, name, data);
 			continue;
 		}
 		if (!path)
@@ -219,7 +223,7 @@ void traverse_commit_list(struct rev_info *revs,
 		}
 		if (obj->type == OBJ_BLOB) {
 			process_blob(revs, (struct blob *)obj, show_object,
-				     NULL, path, data);
+				     &base, path, data);
 			continue;
 		}
 		die("unknown pending object %s (%s)",

list-objects.h

@@ -2,7 +2,7 @@
 #define LIST_OBJECTS_H
 
 typedef void (*show_commit_fn)(struct commit *, void *);
-typedef void (*show_object_fn)(struct object *, struct strbuf *, const char *, void *);
+typedef void (*show_object_fn)(struct object *, const char *, void *);
 void traverse_commit_list(struct rev_info *, show_commit_fn, show_object_fn, void *);
 
 typedef void (*show_edge_fn)(struct commit *);

pack-bitmap-write.c

@@ -148,8 +148,7 @@ static uint32_t find_object_pos(const unsigned char *sha1)
 	return entry->in_pack_pos;
 }
 
-static void show_object(struct object *object, struct strbuf *path,
+static void show_object(struct object *object, const char *name, void *data)
-			const char *last, void *data)
 {
 	struct bitmap *base = data;
 	bitmap_set(base, find_object_pos(object->sha1));

pack-bitmap.c

@@ -422,19 +422,15 @@ 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,
+static void show_object(struct object *object, const char *name, void *data)
-			const char *last, void *data)
 {
 	struct bitmap *base = data;
 	int bitmap_pos;
 
 	bitmap_pos = bitmap_position(object->sha1);
 
-	if (bitmap_pos < 0) {
+	if (bitmap_pos < 0)
-		char *name = path_name(path, last);
 		bitmap_pos = ext_index_add_object(object, name);
-		free(name);
-	}
 
 	bitmap_set(base, bitmap_pos);
 }
@@ -902,9 +898,8 @@ struct bitmap_test_data {
 	size_t seen;
 };
 
-static void test_show_object(struct object *object,
+static void test_show_object(struct object *object, const char *name,
-			     struct strbuf *path,
+			     void *data)
-			     const char *last, void *data)
 {
 	struct bitmap_test_data *tdata = data;
 	int bitmap_pos;

reachable.c

@@ -36,15 +36,14 @@ static int add_one_ref(const char *path, const unsigned char *sha1, int flag, vo
  * The traversal will have already marked us as SEEN, so we
  * only need to handle any progress reporting here.
  */
-static void mark_object(struct object *obj, struct strbuf *path,
+static void mark_object(struct object *obj, const char *name, void *data)
-			const char *name, void *data)
 {
 	update_progress(data);
 }
 
 static void mark_commit(struct commit *c, void *data)
 {
-	mark_object(&c->object, NULL, NULL, data);
+	mark_object(&c->object, NULL, data);
 }
 
 struct recent_data {

revision.c

@@ -21,27 +21,14 @@
 
 volatile show_early_output_fn_t show_early_output;
 
-char *path_name(struct strbuf *path, const char *name)
+void show_object_with_name(FILE *out, struct object *obj, const char *name)
 {
-	struct strbuf ret = STRBUF_INIT;
+	const char *p;
-	if (path)
-		strbuf_addbuf(&ret, path);
-	strbuf_addstr(&ret, name);
-	return strbuf_detach(&ret, NULL);
-}
-
-void show_object_with_name(FILE *out, struct object *obj,
-			   struct strbuf *path, const char *component)
-{
-	char *name = path_name(path, component);
-	char *p;
 
 	fprintf(out, "%s ", sha1_to_hex(obj->sha1));
 	for (p = name; *p && *p != '\n'; p++)
 		fputc(*p, out);
 	fputc('\n', out);
-
-	free(name);
 }
 
 static void mark_blob_uninteresting(struct blob *blob)

revision.h

@@ -258,8 +258,7 @@ extern void mark_tree_uninteresting(struct tree *tree);
 
 char *path_name(struct strbuf *path, const char *name);
 
-extern void show_object_with_name(FILE *, struct object *,
+extern void show_object_with_name(FILE *, struct object *, const char *);
-				  struct strbuf *, const char *);
 
 extern void add_pending_object(struct rev_info *revs,
 			       struct object *obj, const char *name);