1 files changed, 124 insertions, 0 deletions
diff --git a/builtin/merge-base.c b/builtin/merge-base.c
new file mode 100644
index 0000000000..0c4cd2f9f7
--- /dev/null
+++ b/builtin/merge-base.c
@@ -0,0 +1,124 @@
+#include "builtin.h"
+#include "cache.h"
+#include "commit.h"
+#include "parse-options.h"
+
+static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
+{
+	struct commit_list *result;
+
+	result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1, 0);
+
+	if (!result)
+		return 1;
+
+	while (result) {
+		printf("%s\n", sha1_to_hex(result->item->object.sha1));
+		if (!show_all)
+			return 0;
+		result = result->next;
+	}
+
+	return 0;
+}
+
+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
+};
+
+static struct commit *get_commit_reference(const char *arg)
+{
+	unsigned char revkey[20];
+	struct commit *r;
+
+	if (get_sha1(arg, revkey))
+		die("Not a valid object name %s", arg);
+	r = lookup_commit_reference(revkey);
+	if (!r)
+		die("Not a valid commit name %s", arg);
+
+	return r;
+}
+
+static int handle_octopus(int count, const char **args, int reduce, int show_all)
+{
+	struct commit_list *revs = NULL;
+	struct commit_list *result;
+	int i;
+
+	if (reduce)
+		show_all = 1;
+
+	for (i = count - 1; i >= 0; i--)
+		commit_list_insert(get_commit_reference(args[i]), &revs);
+
+	result = reduce ? reduce_heads(revs) : get_octopus_merge_bases(revs);
+
+	if (!result)
+		return 1;
+
+	while (result) {
+		printf("%s\n", sha1_to_hex(result->item->object.sha1));
+		if (!show_all)
+			return 0;
+		result = result->next;
+	}
+
+	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;
+	int rev_nr = 0;
+	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()
+	};
+
+	git_config(git_default_config, NULL);
+	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");
+
+	if (octopus || reduce)
+		return handle_octopus(argc, argv, reduce, show_all);
+
+	rev = xmalloc(argc * sizeof(*rev));
+	while (argc-- > 0)
+		rev[rev_nr++] = get_commit_reference(*argv++);
+	return show_merge_base(rev, rev_nr, show_all);
+}