Add configuration option to set the default branch name for new repositories.

No documentation has been added, nor tests written, no any other checks done to see what this could break.

Author: Don Goodman-Wilson

builtin/init-db.c

@@ -258,15 +258,34 @@ static int create_default_files(const char *template_path,
 		die("failed to set up refs db: %s", err.buf);
 
 	/*
-	 * Create the default symlink from ".git/HEAD" to the "master"
-	 * branch, if it does not exist yet.
+	 * Create the default symlink from ".git/HEAD" to the default
+	 * branch name, if it does not exist yet.
 	 */
 	path = git_path_buf(&buf, "HEAD");
 	reinit = (!access(path, R_OK)
 		  || readlink(path, junk, sizeof(junk)-1) != -1);
 	if (!reinit) {
-		if (create_symref("HEAD", "refs/heads/master", NULL) < 0)
+		const char *branch_name;
+		char *prefixed;
+
+		/* get the default branch name from config, or failing that, env */
+		if (git_config_get_string_const("init.defaultbranchname", &branch_name))
+			branch_name = getenv("GIT_DEFAULT_BRANCH_NAME");
+
+		if (!branch_name) {
+			branch_name = "master";
+		}
+
+		/* prepend "refs/heads/" to the branch name */
+		prefixed = xstrfmt("refs/heads/%s", branch_name);
+		if(check_refname_format(prefixed, 0)) {
+			die(_("Invalid value for default branch name %s"), branch_name);
+		}
+
+		if (create_symref("HEAD", prefixed, NULL) < 0)
 			exit(1);
+
+		free(prefixed);
 	}
 
 	initialize_repository_version(fmt->hash_algo);

t/t0001-init.sh

@@ -464,4 +464,20 @@ test_expect_success MINGW 'redirect std handles' '
 	grep "Needed a single revision" output.txt
 '
 
+test_expect_success 'custom default branch name from config' '
+  git config --global init.defaultbranchname nmb &&
+	git init custom-config &&
+	git config --global --unset init.defaultbranchname &&
+	grep nmb custom-config/.git/HEAD
+'
+
+test_expect_success 'custom default branch name from env' '
+	GIT_DEFAULT_BRANCH_NAME=nmb git init custom-env &&
+	grep nmb custom-env/.git/HEAD
+'
+
+test_expect_fail 'invalid custom default branch name' '
+  GIT_DEFAULT_BRANCH_NAME=nmb. git init custom-invalid
+'
+
 test_done