list-objects: convert name_path to a strbuf

The "struct name_path" data is examined in only two places:
we generate it in process_tree(), and we convert it to a
single string in path_name(). Everyone else just passes it
through to those functions.

We can further note that process_tree() already keeps a
single strbuf with the leading tree path, for use with
tree_entry_interesting().

Instead of building a separate name_path linked list, let's
just use the one we already build in "base". This reduces
the amount of code (especially tricky code in path_name()
which did not check for integer overflows caused by deep
or large pathnames).

It is also more efficient in some instances.  Any time we
were using tree_entry_interesting, we were building up the
strbuf anyway, so this is an immediate and obvious win
there. In cases where we were not, we trade off storing
"pathname/" in a strbuf on the heap for each level of the
path, instead of two pointers and an int on the stack (with
one pointer into the tree object). On a 64-bit system, the
latter is 20 bytes; so if path components are less than that
on average, this has lower peak memory usage.  In practice
it probably doesn't matter either way; we are already
holding in memory all of the tree objects leading up to each
pathname, and for normal-depth pathnames, we are only
talking about hundreds of bytes.

This patch leaves "struct name_path" as a thin wrapper
around the strbuf, to avoid disrupting callbacks. We should
fix them, but leaving it out makes this diff easier to view.

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

1 files changed, 9 insertions, 13 deletions

diff --git a/list-objects.c b/list-objects.c
index 11732d938..4f60a3ea2 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -62,7 +62,6 @@ static void process_gitlink(struct rev_info *revs,
 static void process_tree(struct rev_info *revs,
 			 struct tree *tree,
 			 show_object_fn show,
-			 struct name_path *path,
 			 struct strbuf *base,
 			 const char *name,
 			 void *cb_data)
@@ -86,17 +85,14 @@ static void process_tree(struct rev_info *revs,
 			return;
 		die("bad tree object %s", oid_to_hex(&obj->oid));
 	}
+
 	obj->flags |= SEEN;
-	show(obj, path, name, cb_data);
-	me.up = path;
-	me.elem = name;
-	me.elem_len = strlen(name);
-
-	if (!match) {
-		strbuf_addstr(base, name);
-		if (base->len)
-			strbuf_addch(base, '/');
-	}
+	me.base = base;
+	show(obj, &me, name, cb_data);
+
+	strbuf_addstr(base, name);
+	if (base->len)
+		strbuf_addch(base, '/');
 
 	init_tree_desc(&desc, tree->buffer, tree->size);
 
@@ -113,7 +109,7 @@ static void process_tree(struct rev_info *revs,
 		if (S_ISDIR(entry.mode))
 			process_tree(revs,
 				     lookup_tree(entry.sha1),
-				     show, &me, base, entry.path,
+				     show, base, entry.path,
 				     cb_data);
 		else if (S_ISGITLINK(entry.mode))
 			process_gitlink(revs, entry.sha1,
@@ -220,7 +216,7 @@ void traverse_commit_list(struct rev_info *revs,
 			path = "";
 		if (obj->type == OBJ_TREE) {
 			process_tree(revs, (struct tree *)obj, show_object,
-				     NULL, &base, path, data);
+				     &base, path, data);
 			continue;
 		}
 		if (obj->type == OBJ_BLOB) {