thodg/libgit2

diff --git a/include/git2/merge.h b/include/git2/merge.h
index 3563f35..cfec32f 100644
--- a/include/git2/merge.h
+++ b/include/git2/merge.h
@@ -191,7 +191,7 @@ GIT_EXTERN(int) git_merge_base(
  * @param repo the repository where the commits exist
  * @param length The number of commits in the provided `input_array`
  * @param input_array oids of the commits
- * @return 0 on success, GIT_ENOTFOUND if not found or error code
+ * @return Zero on success; GIT_ENOTFOUND or -1 on failure.
  */
 GIT_EXTERN(int) git_merge_base_many(
 	git_oid *out,
@@ -200,6 +200,21 @@ GIT_EXTERN(int) git_merge_base_many(
 	const git_oid input_array[]);
 
 /**
+ * Find a merge base in preparation for an octopus merge
+ *
+ * @param out the OID of a merge base considering all the commits
+ * @param repo the repository where the commits exist
+ * @param length The number of commits in the provided `input_array`
+ * @param input_array oids of the commits
+ * @return Zero on success; GIT_ENOTFOUND or -1 on failure.
+ */
+GIT_EXTERN(int) git_merge_base_octopus(
+	git_oid *out,
+	git_repository *repo,
+	size_t length,
+	const git_oid input_array[]);
+
+/**
  * Creates a `git_merge_head` from the given reference.  The resulting
  * git_merge_head must be freed with `git_merge_head_free`.
  *
diff --git a/src/merge.c b/src/merge.c
index 124e8c3..0b11c0d 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -114,6 +114,31 @@ cleanup:
 	return error;
 }
 
+int git_merge_base_octopus(git_oid *out, git_repository *repo, size_t length, const git_oid input_array[])
+{
+	git_oid result;
+	unsigned int i;
+	int error = -1;
+
+	assert(out && repo && input_array);
+
+	if (length < 2) {
+		giterr_set(GITERR_INVALID, "At least two commits are required to find an ancestor. Provided 'length' was %u.", length);
+		return -1;
+	}
+
+	result = input_array[0];
+	for (i = 1; i < length; i++) {
+		error = git_merge_base(&result, repo, &result, &input_array[i]);
+		if (error < 0)
+			return error;
+	}
+
+	*out = result;
+
+	return 0;
+}
+
 int git_merge_base(git_oid *out, git_repository *repo, const git_oid *one, const git_oid *two)
 {
 	git_revwalk *walk;
diff --git a/tests/revwalk/mergebase.c b/tests/revwalk/mergebase.c
index 2d01647..9766350 100644
--- a/tests/revwalk/mergebase.c
+++ b/tests/revwalk/mergebase.c
@@ -189,7 +189,6 @@ void test_revwalk_mergebase__many_no_common_ancestor_returns_ENOTFOUND(void)
 	assert_mergebase_many(NULL, 3, "e90810", "41bc8c", "a65fed");
 	assert_mergebase_many(NULL, 3, "e90810", "a65fed", "41bc8c");
 	assert_mergebase_many(NULL, 3, "a65fed", "e90810", "41bc8c");
-	assert_mergebase_many(NULL, 3, "a65fed", "e90810", "41bc8c");
 	assert_mergebase_many(NULL, 3, "a65fed", "41bc8c", "e90810");
 
 	assert_mergebase_many(NULL, 3, "e90810", "763d71", "a65fed");
@@ -209,6 +208,70 @@ void test_revwalk_mergebase__many_merge_branch(void)
 	assert_mergebase_many("5b5b025afb0b4c913b4c338a42934a3863bf3644", 5, "5b5b02", "763d71", "a4a7dc", "a65fed", "41bc8c");
 }
 
+static void assert_mergebase_octopus(const char *expected_sha, int count, ...)
+{
+	va_list ap;
+	int i;
+	git_oid *oids;
+	git_oid oid, expected;
+	char *partial_oid;
+	git_object *object;
+
+	oids = git__malloc(count * sizeof(git_oid));
+	cl_assert(oids != NULL);
+
+	memset(oids, 0x0, count * sizeof(git_oid));
+
+	va_start(ap, count);
+
+	for (i = 0; i < count; ++i) {
+		partial_oid = va_arg(ap, char *);
+		cl_git_pass(git_oid_fromstrn(&oid, partial_oid, strlen(partial_oid)));
+
+		cl_git_pass(git_object_lookup_prefix(&object, _repo, &oid, strlen(partial_oid), GIT_OBJ_COMMIT));
+		git_oid_cpy(&oids[i], git_object_id(object));
+		git_object_free(object);
+	}
+
+	va_end(ap);
+
+	if (expected_sha == NULL)
+		cl_assert_equal_i(GIT_ENOTFOUND, git_merge_base_octopus(&oid, _repo, count, oids));
+	else {
+		cl_git_pass(git_merge_base_octopus(&oid, _repo, count, oids));
+		cl_git_pass(git_oid_fromstr(&expected, expected_sha));
+
+		cl_assert(git_oid_cmp(&expected, &oid) == 0);
+	}
+
+	git__free(oids);
+}
+
+void test_revwalk_mergebase__octopus_no_common_ancestor_returns_ENOTFOUND(void)
+{
+	assert_mergebase_octopus(NULL, 3, "41bc8c", "e90810", "a65fed");
+	assert_mergebase_octopus(NULL, 3, "e90810", "41bc8c", "a65fed");
+	assert_mergebase_octopus(NULL, 3, "e90810", "a65fed", "41bc8c");
+	assert_mergebase_octopus(NULL, 3, "a65fed", "e90810", "41bc8c");
+	assert_mergebase_octopus(NULL, 3, "a65fed", "41bc8c", "e90810");
+
+	assert_mergebase_octopus(NULL, 3, "e90810", "763d71", "a65fed");
+
+	assert_mergebase_octopus(NULL, 3, "763d71", "e90810", "a65fed");
+	assert_mergebase_octopus(NULL, 3, "763d71", "a65fed", "e90810");
+
+	assert_mergebase_octopus(NULL, 5, "5b5b02", "763d71", "a4a7dc", "a65fed", "41bc8c");
+}
+
+void test_revwalk_mergebase__octopus_merge_branch(void)
+{
+	assert_mergebase_octopus("8496071c1b46c854b31185ea97743be6a8774479", 3, "a65fed", "763d71", "849607");
+
+	assert_mergebase_octopus("8496071c1b46c854b31185ea97743be6a8774479", 3, "a65fed", "763d71", "849607");
+	assert_mergebase_octopus("8496071c1b46c854b31185ea97743be6a8774479", 3, "a65fed", "849607", "763d71");
+	assert_mergebase_octopus("8496071c1b46c854b31185ea97743be6a8774479", 3, "849607", "a65fed", "763d71");
+}
+
 /*
  * testrepo.git $ git log --graph --all
  * * commit 763d71aadf09a7951596c9746c024e7eece7c7af