Add git_branch_name_is_valid

Signed-off-by: Sven Strickroth <email@cs-ware.de>

include/git2/branch.h

@@ -304,6 +304,18 @@ GIT_EXTERN(int) git_branch_remote_name(
  */
  GIT_EXTERN(int) git_branch_upstream_remote(git_buf *buf, git_repository *repo, const char *refname);
 
+/**
+ * Determine whether a branch name is valid, meaning that (when prefixed
+ * with `refs/heads/`) that it is a valid reference name, and that any
+ * additional branch name restrictions are imposed (eg, it cannot start
+ * with a `-`).
+ *
+ * @param valid output pointer to set with validity of given branch name
+ * @param name a branch name to test
+ * @return 0 on success or an error code
+ */
+GIT_EXTERN(int) git_branch_name_is_valid(int *valid, const char *name);
+
 /** @} */
 GIT_END_DECL
 #endif

src/branch.c

@@ -723,3 +723,32 @@ int git_branch_is_head(
 
 	return is_same;
 }
+
+int git_branch_name_is_valid(int *valid, const char *name)
+{
+	git_buf ref_name = GIT_BUF_INIT;
+	int error = 0;
+
+	GIT_ASSERT(valid);
+
+	*valid = 0;
+
+	/*
+	 * Discourage branch name starting with dash,
+	 * https://github.com/git/git/commit/6348624010888b
+	 * and discourage HEAD as branch name,
+	 * https://github.com/git/git/commit/a625b092cc5994
+	 */
+	if (!name || name[0] == '-' || !git__strcmp(name, "HEAD"))
+		goto done;
+
+	if ((error = git_buf_puts(&ref_name, GIT_REFS_HEADS_DIR)) < 0 ||
+	    (error = git_buf_puts(&ref_name, name)) < 0)
+		goto done;
+
+	error = git_reference_name_is_valid(valid, ref_name.ptr);
+
+done:
+	git_buf_dispose(&ref_name);
+	return error;
+}

tests/refs/branches/name.c

@@ -43,3 +43,20 @@ void test_refs_branches_name__error_when_ref_is_no_branch(void)
 	cl_git_pass(git_reference_lookup(&ref,repo,"refs/notes/fanout"));
 	cl_git_fail(git_branch_name(&name,ref));
 }
+
+static int name_is_valid(const char *name)
+{
+	int valid;
+	cl_git_pass(git_branch_name_is_valid(&valid, name));
+	return valid;
+}
+
+void test_refs_branches_is_name_valid(void)
+{
+	cl_assert_equal_i(true, name_is_valid("master"));
+	cl_assert_equal_i(true, name_is_valid("test/master"));
+
+	cl_assert_equal_i(false, name_is_valid(""));
+	cl_assert_equal_i(false, name_is_valid("HEAD"));
+	cl_assert_equal_i(false, name_is_valid("-dash"));
+}