Merge branch 'jc/merge-bases'

Optimise the "merge-base" computation a bit, and also update its
users that do not need the full merge-base information to call a
cheaper subset.

* jc/merge-bases:
  reduce_heads(): reimplement on top of remove_redundant()
  merge-base: "--is-ancestor A B"
  get_merge_bases_many(): walk from many tips in parallel
  in_merge_bases(): use paint_down_to_common()
  merge_bases_many(): split out the logic to paint history
  in_merge_bases(): omit unnecessary redundant common ancestor reduction
  http-push: use in_merge_bases() for fast-forward check
  receive-pack: use in_merge_bases() for fast-forward check
  in_merge_bases(): support only one "other" commit

4 files changed, 26 insertions, 10 deletions

diff --git a/builtin/branch.c b/builtin/branch.c
index e61b0ece21..5cb6d78f2c 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -130,7 +130,7 @@ static int branch_merged(int kind, const char *name,
 	if (!reference_rev)
 		reference_rev = head_rev;
 
-	merged = in_merge_bases(rev, &reference_rev, 1);
+	merged = in_merge_bases(rev, reference_rev);
 
 	/*
 	 * After the safety valve is fully redefined to "check with
@@ -140,7 +140,7 @@ static int branch_merged(int kind, const char *name,
 	 * a gentle reminder is in order.
 	 */
 	if ((head_rev != reference_rev) &&
-	    in_merge_bases(rev, &head_rev, 1) != merged) {
+	    in_merge_bases(rev, head_rev) != merged) {
 		if (merged)
 			warning(_("deleting branch '%s' that has been merged to\n"
 				"         '%s', but not yet merged to HEAD."),
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 3f2ad7727f..97a849a9dc 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -323,7 +323,7 @@ static int update_local_ref(struct ref *ref,
 		return r;
 	}
 
-	if (in_merge_bases(current, &updated, 1)) {
+	if (in_merge_bases(current, updated)) {
 		char quickref[83];
 		int r;
 		strcpy(quickref, find_unique_abbrev(current->object.sha1, DEFAULT_ABBREV));
diff --git a/builtin/merge-base.c b/builtin/merge-base.c
index 2f223a6646..1bc7991048 100644
--- a/builtin/merge-base.c
+++ b/builtin/merge-base.c
@@ -26,6 +26,7 @@ static const char * const merge_base_usage[] = {
 	N_("git merge-base [-a|--all] <commit> <commit>..."),
 	N_("git merge-base [-a|--all] --octopus <commit>..."),
 	N_("git merge-base --independent <commit>..."),
+	N_("git merge-base --is-ancestor <commit> <commit>"),
 	NULL
 };
 
@@ -70,6 +71,20 @@ static int handle_octopus(int count, const char **args, int reduce, int show_all
 	return 0;
 }
 
+static int handle_is_ancestor(int argc, const char **argv)
+{
+	struct commit *one, *two;
+
+	if (argc != 2)
+		die("--is-ancestor takes exactly two commits");
+	one = get_commit_reference(argv[0]);
+	two = get_commit_reference(argv[1]);
+	if (in_merge_bases(one, two))
+		return 0;
+	else
+		return 1;
+}
+
 int cmd_merge_base(int argc, const char **argv, const char *prefix)
 {
 	struct commit **rev;
@@ -77,11 +92,14 @@ int cmd_merge_base(int argc, const char **argv, const char *prefix)
 	int show_all = 0;
 	int octopus = 0;
 	int reduce = 0;
+	int is_ancestor = 0;
 
 	struct option options[] = {
 		OPT_BOOLEAN('a', "all", &show_all, N_("output all common ancestors")),
 		OPT_BOOLEAN(0, "octopus", &octopus, N_("find ancestors for a single n-way merge")),
 		OPT_BOOLEAN(0, "independent", &reduce, N_("list revs not reachable from others")),
+		OPT_BOOLEAN(0, "is-ancestor", &is_ancestor,
+			    N_("is the first one ancestor of the other?")),
 		OPT_END()
 	};
 
@@ -89,6 +107,10 @@ int cmd_merge_base(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, options, merge_base_usage, 0);
 	if (!octopus && !reduce && argc < 2)
 		usage_with_options(merge_base_usage, options);
+	if (is_ancestor && (show_all | octopus | reduce))
+		die("--is-ancestor cannot be used with other options");
+	if (is_ancestor)
+		return handle_is_ancestor(argc, argv);
 	if (reduce && (show_all || octopus))
 		die("--independent cannot be used with other options");
 
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 2cb854feb4..9145f1a595 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -480,7 +480,6 @@ static const char *update(struct command *cmd)
 	    !prefixcmp(name, "refs/heads/")) {
 		struct object *old_object, *new_object;
 		struct commit *old_commit, *new_commit;
-		struct commit_list *bases, *ent;
 
 		old_object = parse_object(old_sha1);
 		new_object = parse_object(new_sha1);
@@ -493,12 +492,7 @@ static const char *update(struct command *cmd)
 		}
 		old_commit = (struct commit *)old_object;
 		new_commit = (struct commit *)new_object;
-		bases = get_merge_bases(old_commit, new_commit, 1);
-		for (ent = bases; ent; ent = ent->next)
-			if (!hashcmp(old_sha1, ent->item->object.sha1))
-				break;
-		free_commit_list(bases);
-		if (!ent) {
+		if (!in_merge_bases(old_commit, new_commit)) {
 			rp_error("denying non-fast-forward %s"
 				 " (you should pull first)", name);
 			return "non-fast-forward";