rev-list: allow bitmaps when counting objects

The prior commit taught "--count --objects" to work without bitmaps. We
should be able to get the same answer much more quickly with bitmaps.

Note that we punt on the max_count case here. This perhaps _could_ be
made to work if we find all of the boundary commits and treat them as
UNINTERESTING, subtracting them (and their reachable objects) from the
set we return. That implies an actual commit traversal, but we'd still
be faster due to avoiding opening up any trees. Given the complexity and
the fact that anyone is unlikely to want this, it makes sense to just
fall back to the non-bitmap case for now.

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

builtin/rev-list.c

@@ -374,7 +374,10 @@ static inline int parse_missing_action_value(const char *value)
 
 static int try_bitmap_count(struct rev_info *revs)
 {
-	uint32_t commit_count;
+	uint32_t commit_count = 0,
+		 tag_count = 0,
+		 tree_count = 0,
+		 blob_count = 0;
 	int max_count;
 	struct bitmap_index *bitmap_git;
 
@@ -389,6 +392,15 @@ static int try_bitmap_count(struct rev_info *revs)
 	if (revs->left_right || revs->cherry_mark)
 		return -1;
 
+	/*
+	 * If we're counting reachable objects, we can't handle a max count of
+	 * commits to traverse, since we don't know which objects go with which
+	 * commit.
+	 */
+	if (revs->max_count >= 0 &&
+	    (revs->tag_objects || revs->tree_objects || revs->blob_objects))
+		return -1;
+
 	/*
 	 * This must be saved before doing any walking, since the revision
 	 * machinery will count it down to zero while traversing.
@@ -399,11 +411,14 @@ static int try_bitmap_count(struct rev_info *revs)
 	if (!bitmap_git)
 		return -1;
 
-	count_bitmap_commit_list(bitmap_git, &commit_count, NULL, NULL, NULL);
+	count_bitmap_commit_list(bitmap_git, &commit_count,
+				 revs->tree_objects ? &tree_count : NULL,
+				 revs->blob_objects ? &blob_count : NULL,
+				 revs->tag_objects ? &tag_count : NULL);
 	if (max_count >= 0 && max_count < commit_count)
 		commit_count = max_count;
 
-	printf("%d\n", commit_count);
+	printf("%d\n", commit_count + tree_count + blob_count + tag_count);
 	free_bitmap_index(bitmap_git);
 	return 0;
 }

t/t5310-pack-bitmaps.sh

@@ -74,6 +74,12 @@ rev_list_tests() {
 		test_cmp expect actual
 	'
 
+	test_expect_success "counting objects via bitmap ($state)" '
+		git rev-list --count --objects HEAD >expect &&
+		git rev-list --use-bitmap-index --count --objects HEAD >actual &&
+		test_cmp expect actual
+	'
+
 	test_expect_success "enumerate --objects ($state)" '
 		git rev-list --objects --use-bitmap-index HEAD >tmp &&
 		cut -d" " -f1 <tmp >tmp2 &&