restore: disable overlay mode by default

Overlay mode is considered confusing when the command is about
restoring files on worktree. Disable it by default. The user can still
turn it on, or use 'git checkout' which still has overlay mode on by
default.

While at it, make the check in checkout_branch() stricter. Neither
--overlay or --no-overlay should be accepted in branch switching mode.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -1274,9 +1274,9 @@ static int checkout_branch(struct checkout_opts *opts,
 		die(_("'%s' cannot be used with switching branches"),
 		    "--patch");
 
-	if (!opts->overlay_mode)
+	if (opts->overlay_mode != -1)
 		die(_("'%s' cannot be used with switching branches"),
-		    "--no-overlay");
+		    "--[no]-overlay");
 
 	if (opts->writeout_stage)
 		die(_("'%s' cannot be used with switching branches"),
@@ -1399,7 +1399,6 @@ static struct option *add_checkout_path_options(struct checkout_opts *opts,
 		OPT_BOOL('p', "patch", &opts->patch_mode, N_("select hunks interactively")),
 		OPT_BOOL(0, "ignore-skip-worktree-bits", &opts->ignore_skipworktree,
 			 N_("do not limit pathspecs to sparse entries only")),
-		OPT_BOOL(0, "overlay", &opts->overlay_mode, N_("use overlay mode (default)")),
 		OPT_END()
 	};
 	struct option *newopts = parse_options_concat(prevopts, options);
@@ -1419,7 +1418,6 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 	opts->overwrite_ignore = 1;
 	opts->prefix = prefix;
 	opts->show_progress = -1;
-	opts->overlay_mode = -1;
 
 	git_config(git_checkout_config, opts);
 
@@ -1593,6 +1591,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		OPT_BOOL('l', NULL, &opts.new_branch_log, N_("create reflog for new branch")),
 		OPT_BOOL(0, "guess", &opts.dwim_new_local_branch,
 			 N_("second guess 'git checkout <no-such-branch>' (default)")),
+		OPT_BOOL(0, "overlay", &opts.overlay_mode, N_("use overlay mode (default)")),
 		OPT_END()
 	};
 	int ret;
@@ -1607,6 +1606,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	opts.can_switch_when_in_progress = 1;
 	opts.orphan_from_empty_tree = 0;
 	opts.empty_pathspec_ok = 1;
+	opts.overlay_mode = -1;
 
 	options = parse_options_dup(checkout_options);
 	options = add_common_options(&opts, options);
@@ -1645,6 +1645,7 @@ int cmd_switch(int argc, const char **argv, const char *prefix)
 	opts.implicit_detach = 0;
 	opts.can_switch_when_in_progress = 0;
 	opts.orphan_from_empty_tree = 1;
+	opts.overlay_mode = -1;
 
 	options = parse_options_dup(switch_options);
 	options = add_common_options(&opts, options);
@@ -1663,6 +1664,7 @@ int cmd_restore(int argc, const char **argv, const char *prefix)
 	struct option restore_options[] = {
 		OPT_STRING('s', "source", &opts.from_treeish, "<tree-ish>",
 			   N_("where the checkout from")),
+		OPT_BOOL(0, "overlay", &opts.overlay_mode, N_("use overlay mode")),
 		OPT_END()
 	};
 	int ret;
@@ -1671,6 +1673,7 @@ int cmd_restore(int argc, const char **argv, const char *prefix)
 	opts.accept_ref = 0;
 	opts.accept_pathspec = 1;
 	opts.empty_pathspec_ok = 0;
+	opts.overlay_mode = 0;
 
 	options = parse_options_dup(restore_options);
 	options = add_common_options(&opts, options);