traverse_trees(): allow pruning with pathspec

The traverse_trees() machinery is primarily meant for merging two (or
more) trees, and because a merge is a full tree operation, it doesn't
support any pruning with pathspec.

Since d1f2d7e (Make run_diff_index() use unpack_trees(), not read_tree(),
2008-01-19), however, we use unpack_trees() to traverse_trees() callchain
to perform "diff-index", which could waste a lot of work traversing trees
outside the user-supplied pathspec, only to discard at the blob comparison
level in diff-lib.c::oneway_diff() which is way too late.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 34 insertions, 6 deletions

diff --git a/tree-walk.c b/tree-walk.c
index 33f749e1e..808bb55ba 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -309,6 +309,18 @@ static void free_extended_entry(struct tree_desc_x *t)
 	}
 }
 
+static inline int prune_traversal(struct name_entry *e,
+				  struct traverse_info *info,
+				  struct strbuf *base,
+				  int still_interesting)
+{
+	if (!info->pathspec || still_interesting == 2)
+		return 2;
+	if (still_interesting < 0)
+		return still_interesting;
+	return tree_entry_interesting(e, base, 0, info->pathspec);
+}
+
 int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 {
 	int ret = 0;
@@ -316,10 +328,18 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 	struct name_entry *entry = xmalloc(n*sizeof(*entry));
 	int i;
 	struct tree_desc_x *tx = xcalloc(n, sizeof(*tx));
+	struct strbuf base = STRBUF_INIT;
+	int interesting = 1;
 
 	for (i = 0; i < n; i++)
 		tx[i].d = t[i];
 
+	if (info->prev) {
+		strbuf_grow(&base, info->pathlen);
+		make_traverse_path(base.buf, info->prev, &info->name);
+		base.buf[info->pathlen-1] = '/';
+		strbuf_setlen(&base, info->pathlen);
+	}
 	for (;;) {
 		unsigned long mask, dirmask;
 		const char *first = NULL;
@@ -376,16 +396,22 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 			mask |= 1ul << i;
 			if (S_ISDIR(entry[i].mode))
 				dirmask |= 1ul << i;
+			e = &entry[i];
 		}
 		if (!mask)
 			break;
-		ret = info->fn(n, mask, dirmask, entry, info);
-		if (ret < 0) {
-			error = ret;
-			if (!info->show_all_errors)
-				break;
+		interesting = prune_traversal(e, info, &base, interesting);
+		if (interesting < 0)
+			break;
+		if (interesting) {
+			ret = info->fn(n, mask, dirmask, entry, info);
+			if (ret < 0) {
+				error = ret;
+				if (!info->show_all_errors)
+					break;
+			}
+			mask &= ret;
 		}
-		mask &= ret;
 		ret = 0;
 		for (i = 0; i < n; i++)
 			if (mask & (1ul << i))
@@ -395,6 +421,7 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 	for (i = 0; i < n; i++)
 		free_extended_entry(tx + i);
 	free(tx);
+	strbuf_release(&base);
 	return error;
 }
 
diff --git a/tree-walk.h b/tree-walk.h
index 39524b7db..0089581e1 100644
--- a/tree-walk.h
+++ b/tree-walk.h
@@ -44,6 +44,7 @@ struct traverse_info {
 	struct traverse_info *prev;
 	struct name_entry name;
 	int pathlen;
+	struct pathspec *pathspec;
 
 	unsigned long conflicts;
 	traverse_callback_t fn;