Merge branch 'js/default-branch-name' into pu

The name of the primary branch in existing repositories, and the
default name used for the first branch in newly created
repositories, is made configurable, so that we can eventually wean
ourselves off of the hardcoded 'master'.

* js/default-branch-name:
  Document how the default branch name can be overridden
  fmt-merge-msg: learn about the possibly-configured default branch name
  clone: learn about the possibly-configured default branch name
  submodule: use the (possibly overridden) default branch name
  testsvn: respect `core.defaultBranchName`
  send-pack/transport-helper: respect `core.defaultBranchName`
  remote: respect `core.defaultBranchName`
  init: allow overriding the default branch name for new repositories

Author: gitster

Documentation/config/core.txt

@@ -626,3 +626,7 @@ core.abbrev::
 	in your repository, which hopefully is enough for
 	abbreviated object names to stay unique for some time.
 	The minimum length is 4.
+
+core.defaultBranchName::
+	Allows overriding the default branch name e.g. when initializing
+	a new repository or when cloning an empty repository.

builtin/clone.c

@@ -1275,9 +1275,17 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 		remote_head_points_at = NULL;
 		remote_head = NULL;
 		option_no_checkout = 1;
-		if (!option_bare)
-			install_branch_config(0, "master", option_origin,
-					      "refs/heads/master");
+		if (!option_bare) {
+			char *default_branch = git_default_branch_name(0);
+			const char *nick;
+
+			if (!skip_prefix(default_branch, "refs/heads/", &nick))
+				BUG("unexpected default branch '%s'",
+				    default_branch);
+			install_branch_config(0, nick, option_origin,
+					      default_branch);
+			free(default_branch);
+		}
 	}
 
 	write_refspec_config(src_ref_prefix, our_head_points_at,

builtin/init-db.c

@@ -258,15 +258,17 @@ 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)
+		char *default_ref = git_default_branch_name(0);
+		if (create_symref("HEAD", default_ref, NULL) < 0)
 			exit(1);
+		free(default_ref);
 	}
 
 	initialize_repository_version(fmt->hash_algo);

builtin/submodule--helper.c

@@ -1980,8 +1980,14 @@ static const char *remote_submodule_branch(const char *path)
 		branch = sub->branch;
 	free(key);
 
-	if (!branch)
-		return "master";
+	if (!branch) {
+		static char *default_branch;
+
+		if (!default_branch)
+			default_branch = git_default_branch_name(1);
+
+		return default_branch;
+	}
 
 	if (!strcmp(branch, ".")) {
 		const char *refname = resolve_ref_unsafe("HEAD", 0, NULL, NULL);

fmt-merge-msg.c

@@ -407,7 +407,7 @@ static void fmt_merge_msg_title(struct strbuf *out,
 				const char *current_branch)
 {
 	int i = 0;
-	char *sep = "";
+	char *sep = "", *default_branch_name;
 
 	strbuf_addstr(out, "Merge ");
 	for (i = 0; i < srcs.nr; i++) {
@@ -451,10 +451,12 @@ static void fmt_merge_msg_title(struct strbuf *out,
 			strbuf_addf(out, " of %s", srcs.items[i].string);
 	}
 
-	if (!strcmp("master", current_branch))
+	default_branch_name = git_default_branch_name(1);
+	if (!strcmp(default_branch_name, current_branch))
 		strbuf_addch(out, '\n');
 	else
 		strbuf_addf(out, " into %s\n", current_branch);
+	free(default_branch_name);
 }
 
 static void fmt_tag_signature(struct strbuf *tagbuf,

refs.c

@@ -562,6 +562,40 @@ void expand_ref_prefix(struct argv_array *prefixes, const char *prefix)
 		argv_array_pushf(prefixes, *p, len, prefix);
 }
 
+char *git_default_branch_name(int short_name)
+{
+	const char *branch_name = getenv("GIT_TEST_DEFAULT_BRANCH_NAME");
+	char *from_config = NULL, *prefixed;
+
+	/*
+	 * If the default branch name was not specified via the environment
+	 * variable GIT_TEST_DEFAULT_BRANCH_NAME, retrieve it from the config
+	 * setting core.defaultBranchName. If neither are set, fall back to the
+	 * hard-coded default.
+	 */
+	if (!branch_name || !*branch_name) {
+		if (git_config_get_string("core.defaultbranchname",
+					  &from_config) < 0)
+			die(_("Could not retrieve `core.defaultBranchName`"));
+
+		if (from_config)
+			branch_name = from_config;
+		else
+			branch_name = "master";
+	}
+
+	if (short_name)
+		return from_config ? from_config : xstrdup(branch_name);
+
+	/* prepend "refs/heads/" to the branch name */
+	prefixed = xstrfmt("refs/heads/%s", branch_name);
+	if (check_refname_format(prefixed, 0))
+		die(_("invalid default branch name: '%s'"), branch_name);
+
+	free(from_config);
+	return prefixed;
+}
+
 /*
  * *string and *len will only be substituted, and *string returned (for
  * later free()ing) if the string passed in is a magic short-hand form

refs.h

@@ -154,6 +154,12 @@ int repo_dwim_log(struct repository *r, const char *str, int len, struct object_
 int dwim_ref(const char *str, int len, struct object_id *oid, char **ref);
 int dwim_log(const char *str, int len, struct object_id *oid, char **ref);
 
+/*
+ * Retrieves the name of the default branch. If `short_name` is non-zero, the
+ * branch name will be prefixed with "refs/heads/".
+ */
+char *git_default_branch_name(int short_name);
+
 /*
  * A ref_transaction represents a collection of reference updates that
  * should succeed or fail together.

remote-testsvn.c

@@ -13,7 +13,7 @@
 static const char *url;
 static int dump_from_file;
 static const char *private_ref;
-static const char *remote_ref = "refs/heads/master";
+static char *remote_ref;
 static const char *marksfilename, *notes_ref;
 struct rev_note { unsigned int rev_nr; };
 
@@ -286,14 +286,18 @@ int cmd_main(int argc, const char **argv)
 			private_ref_sb = STRBUF_INIT, marksfilename_sb = STRBUF_INIT,
 			notes_ref_sb = STRBUF_INIT;
 	static struct remote *remote;
-	const char *url_in;
+	const char *url_in, *default_branch;
 
 	setup_git_directory();
 	if (argc < 2 || argc > 3) {
 		usage("git-remote-svn <remote-name> [<url>]");
 		return 1;
 	}
 
+	remote_ref = git_default_branch_name(0);
+	if (!skip_prefix(remote_ref, "refs/heads/", &default_branch))
+		BUG("unexpected remote_ref '%s'", remote_ref);
+
 	remote = remote_get(argv[1]);
 	url_in = (argc == 3) ? argv[2] : remote->url[0];
 
@@ -306,7 +310,8 @@ int cmd_main(int argc, const char **argv)
 		url = url_sb.buf;
 	}
 
-	strbuf_addf(&private_ref_sb, "refs/svn/%s/master", remote->name);
+	strbuf_addf(&private_ref_sb, "refs/svn/%s/%s",
+		    remote->name, default_branch);
 	private_ref = private_ref_sb.buf;
 
 	strbuf_addf(&notes_ref_sb, "refs/notes/%s/revs", remote->name);

remote.c

@@ -256,7 +256,7 @@ static void read_remotes_file(struct remote *remote)
 
 static void read_branches_file(struct remote *remote)
 {
-	char *frag;
+	char *frag, *default_branch_name = NULL;
 	struct strbuf buf = STRBUF_INIT;
 	FILE *f = fopen_or_warn(git_path("branches/%s", remote->name), "r");
 
@@ -276,15 +276,15 @@ static void read_branches_file(struct remote *remote)
 
 	/*
 	 * The branches file would have URL and optionally
-	 * #branch specified.  The "master" (or specified) branch is
+	 * #branch specified.  The default (or specified) branch is
 	 * fetched and stored in the local branch matching the
 	 * remote name.
 	 */
 	frag = strchr(buf.buf, '#');
 	if (frag)
 		*(frag++) = '\0';
 	else
-		frag = "master";
+		frag = default_branch_name = git_default_branch_name(1);
 
 	add_url_alias(remote, strbuf_detach(&buf, NULL));
 	strbuf_addf(&buf, "refs/heads/%s:refs/heads/%s",
@@ -299,6 +299,7 @@ static void read_branches_file(struct remote *remote)
 	strbuf_addf(&buf, "HEAD:refs/heads/%s", frag);
 	refspec_append(&remote->push, buf.buf);
 	remote->fetch_tags = 1; /* always auto-follow */
+	free(default_branch_name);
 	strbuf_release(&buf);
 }
 
@@ -2149,7 +2150,10 @@ struct ref *guess_remote_head(const struct ref *head,
 
 	/* If refs/heads/master could be right, it is. */
 	if (!all) {
-		r = find_ref_by_name(refs, "refs/heads/master");
+		char *name = git_default_branch_name(0);
+
+		r = find_ref_by_name(refs, name);
+		free(name);
 		if (r && oideq(&r->old_oid, &head->old_oid))
 			return copy_ref(r);
 	}

send-pack.c

@@ -470,8 +470,12 @@ int send_pack(struct send_pack_args *args,
 	}
 
 	if (!remote_refs) {
+		char *branch_name = git_default_branch_name(1);
+
 		fprintf(stderr, "No refs in common and none specified; doing nothing.\n"
-			"Perhaps you should specify a branch such as 'master'.\n");
+			"Perhaps you should specify a branch such as '%s'.\n",
+			branch_name);
+		free(branch_name);
 		return 0;
 	}
 	if (args->atomic && !atomic_supported)

t/README

@@ -421,6 +421,10 @@ GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=<boolean>, when true (which is
 the default when running tests), errors out when an abbreviated option
 is used.
 
+GIT_TEST_DEFAULT_BRANCH_NAME allows overriding the default branch name
+that is used for example when initializing new repositories, or when
+cloning a repository that has no branches yet.
+
 Naming Tests
 ------------
 

t/t0001-init.sh

@@ -464,4 +464,24 @@ 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 core.defaultbranchname nmb &&
+	GIT_TEST_DEFAULT_BRANCH_NAME= git init custom-config &&
+	git config --global --unset core.defaultbranchname &&
+	git -C custom-config symbolic-ref HEAD >actual &&
+	grep nmb actual
+'
+
+test_expect_success 'custom default branch name from env' '
+	GIT_TEST_DEFAULT_BRANCH_NAME=nmb git init custom-env &&
+	git -C custom-env symbolic-ref HEAD >actual &&
+	grep nmb actual
+'
+
+test_expect_success 'invalid custom default branch name' '
+	test_must_fail env GIT_TEST_DEFAULT_BRANCH_NAME="with space" \
+		git init custom-invalid 2>err &&
+	test_i18ngrep "invalid default branch name" err
+'
+
 test_done

t/t5609-clone-branch.sh

@@ -67,4 +67,13 @@ test_expect_success 'clone -b not allowed with empty repos' '
 	test_must_fail git clone -b branch empty clone-branch-empty
 '
 
+test_expect_success 'chooses correct default branch name' '
+	GIT_TEST_DEFAULT_BRANCH_NAME= \
+		git -c core.defaultBranchName=up clone empty whats-up &&
+	test_write_lines refs/heads/up refs/heads/up >expect &&
+	git -C whats-up symbolic-ref HEAD >actual &&
+	git -C whats-up config branch.up.merge >>actual &&
+	test_cmp expect actual
+'
+
 test_done

t/t6200-fmt-merge-msg.sh

@@ -158,6 +158,14 @@ test_expect_success 'setup FETCH_HEAD' '
 	git fetch . left
 '
 
+test_expect_success 'with overridden default branch name' '
+	test_config core.defaultBranchName default &&
+	test_when_finished "git switch master" &&
+	git switch -c default &&
+	git fmt-merge-msg <.git/FETCH_HEAD >actual &&
+	! grep "into default" actual
+'
+
 test_expect_success 'merge.log=3 limits shortlog length' '
 	cat >expected <<-EOF &&
 	Merge branch ${apos}left${apos}

transport-helper.c

@@ -1099,9 +1099,13 @@ static int push_refs(struct transport *transport,
 	}
 
 	if (!remote_refs) {
+		char *branch_name = git_default_branch_name(1);
+
 		fprintf(stderr,
 			_("No refs in common and none specified; doing nothing.\n"
-			  "Perhaps you should specify a branch such as 'master'.\n"));
+			  "Perhaps you should specify a branch such as '%s'.\n"),
+			branch_name);
+		free(branch_name);
 		return 0;
 	}