stash: complain about unknown flags

The option parser for git-stash stuffs unknown flags into
the $FLAGS variable, where they can be accessed by the
individual commands. However, most commands do not even look
at these extra flags, leading to unexpected results like
this:

  $ git stash drop --help
  Dropped refs/stash@{0} (e6cf6d80faf92bb7828f7b60c47fc61c03bd30a1)

We should notice the extra flags and bail. Rather than
annotate each command to reject a non-empty $FLAGS variable,
we can notice that "stash show" is the only command that
actually _wants_ arbitrary flags. So we switch the default
mode to reject unknown flags, and let stash_show() opt into
the feature.

Reported-by: Vincent Legoll <vincent.legoll@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-stash.sh

@@ -301,6 +301,7 @@ list_stash () {
 }
 
 show_stash () {
+	ALLOW_UNKNOWN_FLAGS=t
 	assert_stash_like "$@"
 
 	git diff ${FLAGS:---stat} $b_commit $w_commit
@@ -332,13 +333,14 @@ show_stash () {
 #
 #   GIT_QUIET is set to t if -q is specified
 #   INDEX_OPTION is set to --index if --index is specified.
-#   FLAGS is set to the remaining flags
+#   FLAGS is set to the remaining flags (if allowed)
 #
 # dies if:
 #   * too many revisions specified
 #   * no revision is specified and there is no stash stack
 #   * a revision is specified which cannot be resolve to a SHA1
 #   * a non-existent stash reference is specified
+#   * unknown flags were set and ALLOW_UNKNOWN_FLAGS is not "t"
 #
 
 parse_flags_and_rev()
@@ -372,6 +374,8 @@ parse_flags_and_rev()
 				INDEX_OPTION=--index
 			;;
 			-*)
+				test "$ALLOW_UNKNOWN_FLAGS" = t ||
+					die "$(eval_gettext "unknown option: \$opt")"
 				FLAGS="${FLAGS}${FLAGS:+ }$opt"
 			;;
 		esac

t/t3903-stash.sh

@@ -93,6 +93,10 @@ test_expect_success 'unstashing in a subdirectory' '
 	)
 '
 
+test_expect_success 'stash drop complains of extra options' '
+	test_must_fail git stash drop --foo
+'
+
 test_expect_success 'drop top stash' '
 	git reset --hard &&
 	git stash list > stashlist1 &&