+static int checkout(void)
+{
+ unsigned char sha1[20];
+ char *head;
+ struct lock_file *lock_file;
+ struct unpack_trees_options opts;
+ struct tree *tree;
+ struct tree_desc t;
+ int err = 0, fd;
+
+ if (option_no_checkout)
+ return 0;
+
+ head = resolve_refdup("HEAD", sha1, 1, NULL);
+ if (!head) {
+ warning(_("remote HEAD refers to nonexistent ref, "
+ "unable to checkout.\n"));
+ return 0;
+ }
+ if (strcmp(head, "HEAD")) {
+ if (prefixcmp(head, "refs/heads/"))
+ die(_("HEAD not found below refs/heads!"));
+ }
+ free(head);
+
+ /* We need to be in the new work tree for the checkout */
+ setup_work_tree();
+
+ lock_file = xcalloc(1, sizeof(struct lock_file));
+ fd = hold_locked_index(lock_file, 1);
+
+ memset(&opts, 0, sizeof opts);
+ opts.update = 1;
+ opts.merge = 1;
+ opts.fn = oneway_merge;
+ opts.verbose_update = (option_verbosity > 0);
+ opts.src_index = &the_index;
+ opts.dst_index = &the_index;
+
+ tree = parse_tree_indirect(sha1);
+ parse_tree(tree);
+ init_tree_desc(&t, tree->buffer, tree->size);
+ unpack_trees(1, &t, &opts);
+
+ if (write_cache(fd, active_cache, active_nr) ||
+ commit_locked_index(lock_file))
+ die(_("unable to write new index file"));
+
+ err |= run_hook(NULL, "post-checkout", sha1_to_hex(null_sha1),
+ sha1_to_hex(sha1), "1", NULL);
+
+ if (!err && option_recursive)
+ err = run_command_v_opt(argv_submodule, RUN_GIT_CMD);
+
+ return err;
+}
+