[PATCH v2 07/12] init: allow specifying the main branch name for the new repository

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

There is a growing number of projects trying to avoid the non-inclusive
name `master` in their repositories: The `master`/`slave` terminology is
insensitive and perpetuates injustice. This `master`/`slave` idea is
actually where Git's naming comes from, as it was inherited from
BitKeeper which uses the term in exactly this way, see
https://mail.gnome.org/archives/desktop-devel-list/2019-May/msg00066.html

To change that branch name for new repositories, currently the only way
to do that automatically is by copying all of Git's template directory,
then hard-coding the desired default branch name into the `.git/HEAD`
file, and then configuring `init.templateDir` to point to those copied
template files.

To make this process much less cumbersome, let's introduce a new option:
`--main-branch=<branch-name>`.

This will not only initialize the repository with the specified initial
branch; It will also record that branch name in `core.mainBranch`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 Documentation/git-init.txt |  7 +++++++
 builtin/clone.c            |  3 ++-
 builtin/init-db.c          | 34 +++++++++++++++++++++++++++-------
 cache.h                    |  2 +-
 t/t0001-init.sh            | 15 +++++++++++++++
 5 files changed, 52 insertions(+), 9 deletions(-)

diff --git a/Documentation/git-init.txt b/Documentation/git-init.txt
index adc6adfd380..011a7ff4d76 100644
--- a/Documentation/git-init.txt
+++ b/Documentation/git-init.txt
@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git init' [-q | --quiet] [--bare] [--template=<template_directory>]
 	  [--separate-git-dir <git dir>] [--object-format=<format]
+	  [-b <branch-name> | --main-branch=<branch-name>]
 	  [--shared[=<permissions>]] [directory]
 
 
@@ -67,6 +68,12 @@ repository.
 +
 If this is reinitialization, the repository will be moved to the specified path.
 
+-b <branch-name::
+--main-branch=<branch-name>::
+
+Use the specified name for the main (or: initial) branch in the newly created
+repository. If not specified, fall back to the default name: `master`.
+
 --shared[=(false|true|umask|group|all|world|everybody|0xxx)]::
 
 Specify that the Git repository is to be shared amongst several users.  This
diff --git a/builtin/clone.c b/builtin/clone.c
index cb48a291caf..487b0a42d75 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1108,7 +1108,8 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 		}
 	}
 
-	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN, INIT_DB_QUIET);
+	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN, NULL,
+		INIT_DB_QUIET);
 
 	if (real_git_dir)
 		git_dir = real_git_dir;
diff --git a/builtin/init-db.c b/builtin/init-db.c
index 0b7222e7188..287cdafaab1 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -203,6 +203,7 @@ void initialize_repository_version(int hash_algo)
 
 static int create_default_files(const char *template_path,
 				const char *original_git_dir,
+				const char *main_branch,
 				const struct repository_format *fmt)
 {
 	struct stat st1;
@@ -258,16 +259,29 @@ 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 *ref;
+
+		if (!main_branch)
+			main_branch = "master";
+
+		ref = xstrfmt("refs/heads/%s", main_branch);
+		if (check_refname_format(ref, 0) < 0)
+			die(_("invalid main branch name: '%s'"), main_branch);
+
+		if (create_symref("HEAD", ref, NULL) < 0)
 			exit(1);
-	}
+		free(ref);
+
+		git_config_set("core.mainbranch", main_branch);
+	} else if (main_branch)
+		warning(_("re-init: ignoring --main-branch=%s"), main_branch);
 
 	initialize_repository_version(fmt->hash_algo);
 
@@ -383,7 +397,8 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 }
 
 int init_db(const char *git_dir, const char *real_git_dir,
-	    const char *template_dir, int hash, unsigned int flags)
+	    const char *template_dir, int hash, const char *main_branch,
+	    unsigned int flags)
 {
 	int reinit;
 	int exist_ok = flags & INIT_DB_EXIST_OK;
@@ -425,7 +440,8 @@ int init_db(const char *git_dir, const char *real_git_dir,
 
 	validate_hash_algorithm(&repo_fmt, hash);
 
-	reinit = create_default_files(template_dir, original_git_dir, &repo_fmt);
+	reinit = create_default_files(template_dir, original_git_dir,
+				      main_branch, &repo_fmt);
 
 	create_object_directory();
 
@@ -528,6 +544,7 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 	const char *template_dir = NULL;
 	unsigned int flags = 0;
 	const char *object_format = NULL;
+	const char *main_branch = NULL;
 	int hash_algo = GIT_HASH_UNKNOWN;
 	const struct option init_db_options[] = {
 		OPT_STRING(0, "template", &template_dir, N_("template-directory"),
@@ -541,6 +558,8 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 		OPT_BIT('q', "quiet", &flags, N_("be quiet"), INIT_DB_QUIET),
 		OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
 			   N_("separate git dir from working tree")),
+		OPT_STRING('b', "main-branch", &main_branch, N_("name"),
+			   N_("override the name of the main branch")),
 		OPT_STRING(0, "object-format", &object_format, N_("hash"),
 			   N_("specify the hash algorithm to use")),
 		OPT_END()
@@ -652,5 +671,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 	UNLEAK(work_tree);
 
 	flags |= INIT_DB_EXIST_OK;
-	return init_db(git_dir, real_git_dir, template_dir, hash_algo, flags);
+	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
+		       main_branch, flags);
 }
diff --git a/cache.h b/cache.h
index 0f0485ecfe2..afd5ad3121f 100644
--- a/cache.h
+++ b/cache.h
@@ -628,7 +628,7 @@ int path_inside_repo(const char *prefix, const char *path);
 
 int init_db(const char *git_dir, const char *real_git_dir,
 	    const char *template_dir, int hash_algo,
-	    unsigned int flags);
+	    const char *main_branch, unsigned int flags);
 void initialize_repository_version(int hash_algo);
 
 void sanitize_stdfds(void);
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 1edd5aeb8f0..5d8e321a703 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -464,4 +464,19 @@ test_expect_success MINGW 'redirect std handles' '
 	grep "Needed a single revision" output.txt
 '
 
+test_expect_success '--main-branch' '
+	git init --main-branch=hello main-branch-option &&
+	git -C main-branch-option symbolic-ref HEAD >actual &&
+	echo refs/heads/hello >expect &&
+	test_cmp expect actual &&
+
+	: re-initializing should not change the main branch name &&
+	git init --main-branch=ignore main-branch-option 2>err &&
+	test_i18ngrep "ignoring --main-branch" err &&
+	git -C main-branch-option symbolic-ref HEAD >actual &&
+	grep hello actual &&
+	git -C main-branch-option config core.mainBranch >actual &&
+	grep hello actual
+'
+
 test_done
-- 
gitgitgadget