git-init: set core.worktree if GIT_WORK_TREE is specified

Now you can do the following to create a repository which
has a separate working tree:

    /tmp/foo$ export GIT_DIR=/tmp/bar
    /tmp/foo$ git --work-tree . init
    Initialized empty Git repository in /tmp/bar/
    /tmp/foo$ git config core.worktree
    /tmp/foo

Signed-off-by: Matthias Lederhofer <matled@gmx.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-init-db.c

@@ -174,7 +174,36 @@ static void copy_templates(const char *git_dir, int len, const char *template_di
 	closedir(dir);
 }
 
-static int create_default_files(const char *git_dir, const char *template_path)
+/*
+ * Get the full path to the working tree specified in $GIT_WORK_TREE
+ * or NULL if no working tree is specified.
+ */
+static const char *get_work_tree(void)
+{
+	const char *git_work_tree;
+	char cwd[PATH_MAX];
+	static char worktree[PATH_MAX];
+
+	git_work_tree = getenv(GIT_WORK_TREE_ENVIRONMENT);
+	if (!git_work_tree)
+		return NULL;
+	if (!getcwd(cwd, sizeof(cwd)))
+		die("Unable to read current working directory");
+	if (chdir(git_work_tree))
+		die("Cannot change directory to specified working tree '%s'",
+			git_work_tree);
+	if (git_work_tree[0] != '/') {
+		if (!getcwd(worktree, sizeof(worktree)))
+			die("Unable to read current working directory");
+		git_work_tree = worktree;
+	}
+	if (chdir(cwd))
+		die("Cannot come back to cwd");
+	return git_work_tree;
+}
+
+static int create_default_files(const char *git_dir, const char *git_work_tree,
+	const char *template_path)
 {
 	unsigned len = strlen(git_dir);
 	static char path[PATH_MAX];
@@ -253,14 +282,16 @@ static int create_default_files(const char *git_dir, const char *template_path)
 	}
 	git_config_set("core.filemode", filemode ? "true" : "false");
 
-	if (is_bare_repository()) {
+	if (is_bare_repository() && !git_work_tree) {
 		git_config_set("core.bare", "true");
 	}
 	else {
 		git_config_set("core.bare", "false");
 		/* allow template config file to override the default */
 		if (log_all_ref_updates == -1)
 		    git_config_set("core.logallrefupdates", "true");
+		if (git_work_tree)
+			git_config_set("core.worktree", git_work_tree);
 	}
 	return reinit;
 }
@@ -277,6 +308,7 @@ static const char init_db_usage[] =
 int cmd_init_db(int argc, const char **argv, const char *prefix)
 {
 	const char *git_dir;
+	const char *git_work_tree;
 	const char *sha1_dir;
 	const char *template_dir = NULL;
 	char *path;
@@ -297,6 +329,8 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			usage(init_db_usage);
 	}
 
+	git_work_tree = get_work_tree();
+
 	/*
 	 * Set up the default .git directory contents
 	 */
@@ -312,7 +346,7 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 	 */
 	check_repository_format();
 
-	reinit = create_default_files(git_dir, template_dir);
+	reinit = create_default_files(git_dir, git_work_tree, template_dir);
 
 	/*
 	 * And set up the object store.