repo: honor the init.defaultBranch setting

As part of a push towards more inclusive language, git is reconsidering
using "master" as the default branch name.  As a first step, this
setting will be configurable with the `init.defaultBranch` configuration
option.  Honor this during repository initialization.

During initialization, we will create an initial branch:

1. Using the `initial_head` setting, if specified;
2. Using the `HEAD` configured in a template, if it exists;
3. Using the `init.defaultBranch` configuration option, if it is set; or
4. Using `master` in the absence of additional configuration.

src/repository.c

@@ -70,7 +70,7 @@ static int check_extensions(git_config *config, int version);
 
 #define GIT_FILE_CONTENT_PREFIX "gitdir:"
 
-#define GIT_BRANCH_MASTER "master"
+#define GIT_BRANCH_DEFAULT "master"
 
 #define GIT_REPO_VERSION 0
 #define GIT_REPO_MAX_VERSION 1
@@ -1408,9 +1408,6 @@ int git_repository_create_head(const char *git_dir, const char *ref_name)
 	    (error = git_filebuf_open(&ref, ref_path.ptr, 0, GIT_REFS_FILE_MODE)) < 0)
 		goto out;
 
-	if (!ref_name)
-		ref_name = GIT_BRANCH_MASTER;
-
 	if (git__prefixcmp(ref_name, GIT_REFS_DIR) == 0)
 		fmt = "ref: %s\n";
 	else
@@ -2061,6 +2058,43 @@ static int repo_init_directories(
 	return error;
 }
 
+static int repo_init_head(const char *repo_dir, const char *given)
+{
+	git_config *cfg = NULL;
+	git_buf head_path = GIT_BUF_INIT, cfg_branch = GIT_BUF_INIT;
+	const char *initial_head = NULL;
+	int error;
+
+	if ((error = git_buf_joinpath(&head_path, repo_dir, GIT_HEAD_FILE)) < 0)
+		goto out;
+
+	/*
+	 * A template may have set a HEAD; use that unless it's been
+	 * overridden by the caller's given initial head setting.
+	 */
+	if (git_path_exists(head_path.ptr) && !given)
+		goto out;
+
+	if (given) {
+		initial_head = given;
+	} else if ((error = git_config_open_default(&cfg)) >= 0 &&
+	           (error = git_config_get_string_buf(&cfg_branch, cfg, "init.defaultbranch")) >= 0) {
+		initial_head = cfg_branch.ptr;
+	}
+
+	if (!initial_head)
+		initial_head = GIT_BRANCH_DEFAULT;
+
+	error = git_repository_create_head(repo_dir, initial_head);
+
+out:
+	git_config_free(cfg);
+	git_buf_dispose(&head_path);
+	git_buf_dispose(&cfg_branch);
+
+	return error;
+}
+
 static int repo_init_create_origin(git_repository *repo, const char *url)
 {
 	int error;
@@ -2091,7 +2125,7 @@ int git_repository_init_ext(
 	git_repository_init_options *opts)
 {
 	git_buf repo_path = GIT_BUF_INIT, wd_path = GIT_BUF_INIT,
-		common_path = GIT_BUF_INIT, head_path = GIT_BUF_INIT;
+		common_path = GIT_BUF_INIT;
 	const char *wd;
 	bool is_valid;
 	int error;
@@ -2125,16 +2159,7 @@ int git_repository_init_ext(
 	} else {
 		if ((error = repo_init_structure(repo_path.ptr, wd, opts)) < 0 ||
 		    (error = repo_init_config(repo_path.ptr, wd, opts->flags, opts->mode)) < 0 ||
-		    (error = git_buf_joinpath(&head_path, repo_path.ptr, GIT_HEAD_FILE)) < 0)
-			goto out;
-
-		/*
-		 * Only set the new HEAD if the file does not exist already via
-		 * a template or if the caller has explicitly supplied an
-		 * initial HEAD value.
-		 */
-		if ((!git_path_exists(head_path.ptr) || opts->initial_head) &&
-		    (error = git_repository_create_head(repo_path.ptr, opts->initial_head)) < 0)
+		    (error = repo_init_head(repo_path.ptr, opts->initial_head)) < 0)
 			goto out;
 	}
 
@@ -2146,7 +2171,6 @@ int git_repository_init_ext(
 		goto out;
 
 out:
-	git_buf_dispose(&head_path);
 	git_buf_dispose(&common_path);
 	git_buf_dispose(&repo_path);
 	git_buf_dispose(&wd_path);

tests/repo/init.c

@@ -665,3 +665,19 @@ void test_repo_init__unwriteable_directory(void)
 	clar__skip();
 #endif
 }
+
+void test_repo_init__defaultbranch_config(void)
+{
+	git_reference *head;
+
+	cl_set_cleanup(&cleanup_repository, "repo");
+
+	create_tmp_global_config("tmp_global_path", "init.defaultbranch", "my_default_branch");
+
+	cl_git_pass(git_repository_init(&_repo, "repo", 0));
+	cl_git_pass(git_reference_lookup(&head, _repo, "HEAD"));
+
+	cl_assert_equal_s("refs/heads/my_default_branch", git_reference_symbolic_target(head));
+
+	git_reference_free(head);
+}