[PATCH v2 14/21] checkout: support checking out into a new working directory

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-checkout.txt         |  6 +++
 Documentation/gitrepository-layout.txt |  3 +-
 builtin/checkout.c                     | 94 ++++++++++++++++++++++++++++++++++
 path.c                                 |  3 +-
 4 files changed, 104 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 91294f8..06076c8 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -225,6 +225,12 @@ This means that you can use `git checkout -p` to selectively discard
 edits from your current working tree. See the ``Interactive Mode''
 section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 
+--to=<path>::
+	Check out a new branch in a separate working directory at
+	`<path>`. A new repository is initialized at `<path>` that
+	shares everything with the current repository except working
+	directory specific files.
+
 <branch>::
 	Branch to checkout; if it refers to a branch (i.e., a name that,
 	when prepended with "refs/heads/", is a valid ref), then that
diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index 7ce31d4..3c6149e 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -222,7 +222,8 @@ repos/<id>::
 	If a repository's .git is a file contains two lines `gitsuper:
 	<path>` and `repo: <id>`. The directory `<path>/repos/<id>`
 	contains the real non-shared part of .git directory of the
-	repository in question (e.g. HEAD or index).
+	repository in question (e.g. HEAD or index). Such .git files
+	are created by `git checkout --to`.
 
 SEE ALSO
 --------
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 904fd71..95a1a61 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -48,6 +48,9 @@ struct checkout_opts {
 	const char *prefix;
 	struct pathspec pathspec;
 	struct tree *source_tree;
+
+	const char *new_worktree;
+	const char **saved_argv;
 };
 
 static int post_checkout_hook(struct commit *old, struct commit *new,
@@ -250,6 +253,9 @@ static int checkout_paths(const struct checkout_opts *opts,
 		die(_("Cannot update paths and switch to branch '%s' at the same time."),
 		    opts->new_branch);
 
+	if (opts->new_worktree)
+		die(_("'%s' cannot be used with updating paths"), "--to");
+
 	if (opts->patch_mode)
 		return run_add_interactive(revision, "--patch=checkout",
 					   &opts->pathspec);
@@ -808,6 +814,82 @@ static int switch_branches(const struct checkout_opts *opts,
 	return ret || writeout_error;
 }
 
+static void write_to_file(const char *path, const char *fmt, ...)
+{
+	va_list params;
+	FILE *fp = fopen(path, "w");
+	if (!fp)
+		die_errno(_("could not create file '%s'"), path);
+	va_start(params, fmt);
+	vfprintf(fp, fmt, params);
+	va_end(params);
+	fclose(fp);
+}
+
+static int checkout_new_worktree(const struct checkout_opts *opts,
+				 struct branch_info *new)
+{
+	struct strbuf sb_git = STRBUF_INIT, sb_repo = STRBUF_INIT;
+	struct strbuf sb = STRBUF_INIT;
+	const char *path = opts->new_worktree;
+	struct stat st;
+	const char *name;
+	struct child_process cp;
+	int counter = 0, len;
+
+	if (!new->commit)
+		die(_("no branch specified"));
+
+	len = strlen(path);
+	if (!len || is_dir_sep(path[len - 1]))
+		die(_("'--to' argument '%s' cannot end with a slash"), path);
+
+	for (name = path + len - 1; name > path; name--)
+		if (is_dir_sep(*name)) {
+			name++;
+			break;
+		}
+	strbuf_addstr(&sb_repo, git_path("repos/%s", name));
+	len = sb_repo.len;
+	if (safe_create_leading_directories_const(sb_repo.buf))
+		die_errno(_("could not create leading directories of '%s'"),
+			  sb_repo.buf);
+	while (!stat(sb_repo.buf, &st)) {
+		counter++;
+		strbuf_setlen(&sb_repo, len);
+		strbuf_addf(&sb_repo, "%d", counter);
+	}
+	name = sb_repo.buf + len - strlen(name);
+	if (mkdir(sb_repo.buf, 0777))
+		die_errno(_("could not create directory of '%s'"), sb_repo.buf);
+
+	strbuf_addf(&sb_git, "%s/.git", path);
+	if (safe_create_leading_directories_const(sb_git.buf))
+		die_errno(_("could not create leading directories of '%s'"),
+			  sb_git.buf);
+
+	write_to_file(sb_git.buf, "gitsuper: %s\ngitdir: %s\n",
+		      real_path(get_git_dir()), name);
+	strbuf_addf(&sb, "%s/HEAD", sb_repo.buf);
+	write_to_file(sb.buf, "%s\n", sha1_to_hex(new->commit->object.sha1));
+
+	if (!opts->quiet)
+		fprintf_ln(stderr, _("Enter %s (identifier %s)"), path, name);
+
+	/*
+	 * Rerun checkout in the new worktree. This way is safer than
+	 * set_git_dir() because a path relative to cwd could have
+	 * been cached somewhere undetected.
+	 */
+	setenv("GIT_CHECKOUT_NEW_WORKTREE", "1", 1);
+	setenv(GIT_DIR_ENVIRONMENT, sb_git.buf, 1);
+	setenv(GIT_WORK_TREE_ENVIRONMENT, path, 1);
+	memset(&cp, 0, sizeof(cp));
+	cp.git_cmd = 1;
+	cp.argv = opts->saved_argv;
+	return run_command(&cp);
+}
+
 static int git_checkout_config(const char *var, const char *value, void *cb)
 {
 	if (!strcmp(var, "diff.ignoresubmodules")) {
@@ -1069,6 +1151,9 @@ static int checkout_branch(struct checkout_opts *opts,
 		die(_("Cannot switch branch to a non-commit '%s'"),
 		    new->name);
 
+	if (opts->new_worktree)
+		return checkout_new_worktree(opts, new);
+
 	if (!new->commit && opts->new_branch) {
 		unsigned char rev[20];
 		int flag;
@@ -1111,6 +1196,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 			 N_("do not limit pathspecs to sparse entries only")),
 		OPT_HIDDEN_BOOL(0, "guess", &dwim_new_local_branch,
 				N_("second guess 'git checkout no-such-branch'")),
+		OPT_STRING(0, "to", &opts.new_worktree, N_("path"),
+			   N_("check a branch out in a separate working directory")),
 		OPT_END(),
 	};
 
@@ -1119,6 +1206,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	opts.overwrite_ignore = 1;
 	opts.prefix = prefix;
 
+	opts.saved_argv = xmalloc(sizeof(const char *) * (argc + 2));
+	memcpy(opts.saved_argv, argv, sizeof(const char *) * (argc + 1));
+
 	gitmodules_config();
 	git_config(git_checkout_config, &opts);
 
@@ -1127,6 +1217,10 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, options, checkout_usage,
 			     PARSE_OPT_KEEP_DASHDASH);
 
+	if (getenv("GIT_CHECKOUT_NEW_WORKTREE"))
+		/* recursive execution from checkout_new_worktree() */
+		opts.new_worktree = NULL;
+
 	if (conflict_style) {
 		opts.merge = 1; /* implied */
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
diff --git a/path.c b/path.c
index e51fc35..1a2478a 100644
--- a/path.c
+++ b/path.c
@@ -93,7 +93,8 @@ static void update_super_dir(char *buf, size_t n, int git_dir_len)
 {
 	const char *super_dir_list[] = {
 		"branches", "hooks", "info", "logs", "modules",
-		"objects", "refs", "remotes", "rr-cache", "svn", NULL
+		"objects", "refs", "remotes", "repos", "rr-cache",
+		"svn", NULL
 	};
 	const char *super_top_file_list[] = {
 		"config", "packed-refs", "shallow", NULL
-- 
1.8.5.1.77.g42c48fa