restore: fault --staged --worktree with merge opts

The 'restore' command already rejects the --merge, --conflict, --ours
and --theirs options when combined with --staged, but accepts them when
--worktree is added as well.

Unfortunately that doesn't appear to do anything useful. The --ours and
--theirs options seem to be ignored when both --staged and --worktree
are given, whereas with --merge or --conflict, the command has the same
effect as if the --staged option wasn't present.

So reject those options with '--staged --worktree' as well, using
opts->accept_ref to distinguish restore from checkout.

Add test for both '--staged' and '--staged --worktree'.

Signed-off-by: Andy Koppe <andy.koppe@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -487,15 +487,28 @@ static int checkout_paths(const struct checkout_opts *opts,
 		die(_("'%s' must be used when '%s' is not specified"),
 		    "--worktree", "--source");
 
-	if (opts->checkout_index && !opts->checkout_worktree &&
-	    opts->writeout_stage)
-		die(_("'%s' or '%s' cannot be used with %s"),
-		    "--ours", "--theirs", "--staged");
+	/*
+	 * Reject --staged option to the restore command when combined with
+	 * merge-related options. Use the accept_ref flag to distinguish it
+	 * from the checkout command, which does not accept --staged anyway.
+	 *
+	 * `restore --ours|--theirs --worktree --staged` could mean resolving
+	 * conflicted paths to one side in both the worktree and the index,
+	 * but does not currently.
+	 *
+	 * `restore --merge|--conflict=<style>` already recreates conflicts
+	 * in both the worktree and the index, so adding --staged would be
+	 * meaningless.
+	 */
+	if (!opts->accept_ref && opts->checkout_index) {
+		if (opts->writeout_stage)
+			die(_("'%s' or '%s' cannot be used with %s"),
+			    "--ours", "--theirs", "--staged");
 
-	if (opts->checkout_index && !opts->checkout_worktree &&
-	    opts->merge)
-		die(_("'%s' or '%s' cannot be used with %s"),
-		    "--merge", "--conflict", "--staged");
+		if (opts->merge)
+			die(_("'%s' or '%s' cannot be used with %s"),
+			    "--merge", "--conflict", "--staged");
+	}
 
 	if (opts->patch_mode) {
 		const char *patch_mode;

t/t2070-restore.sh

@@ -137,4 +137,20 @@ test_expect_success 'restore --staged invalidates cache tree for deletions' '
 	test_must_fail git rev-parse HEAD:new1
 '
 
+test_expect_success 'restore with merge options rejects --staged' '
+	for opts in \
+		"--staged --ours" \
+		"--staged --theirs" \
+		"--staged --merge" \
+		"--staged --conflict=diff3" \
+		"--staged --worktree --ours" \
+		"--staged --worktree --theirs" \
+		"--staged --worktree --merge" \
+		"--staged --worktree --conflict=zdiff3"
+	do
+		test_must_fail git restore $opts . 2>err &&
+		grep "cannot be used with --staged" err || return
+	done
+'
+
 test_done