fix: correct bareword check typo $_[9] -> $_[0] in dir functions

The _upgrade_barewords guard in opendir/readdir/seekdir/rewinddir/telldir/
closedir was checking $_[9] (always undef for 1-2 arg functions) instead
of $_[0]. This caused the upgrade path to run unconditionally, even for
reference filehandles.

Also adjust seekdir test to verify its effect (telldir position) rather
than its return value, which is not reliably consistent across Perl
versions when using CORE::GLOBAL overrides.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Koan-Bot

lib/Test/MockFile.pm

@@ -2108,7 +2108,7 @@ sub __sysopen (*$$;$) {
 sub __opendir (*$) {
 
     # Upgrade but ignore bareword indicator
-    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[9];
+    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[0];
 
     my $mock_dir = _get_file_object( $_[1] );
 
@@ -2157,7 +2157,7 @@ sub __opendir (*$) {
 sub __readdir (*) {
 
     # Upgrade but ignore bareword indicator
-    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[9];
+    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[0];
 
     my $mocked_dir = _get_file_object( $_[0] );
 
@@ -2200,7 +2200,7 @@ sub __readdir (*) {
 sub __telldir (*) {
 
     # Upgrade but ignore bareword indicator
-    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[9];
+    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[0];
 
     my ($fh) = @_;
     my $mocked_dir = _get_file_object($fh);
@@ -2227,7 +2227,7 @@ sub __telldir (*) {
 sub __rewinddir (*) {
 
     # Upgrade but ignore bareword indicator
-    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[9];
+    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[0];
 
     my ($fh) = @_;
     my $mocked_dir = _get_file_object($fh);
@@ -2255,7 +2255,7 @@ sub __rewinddir (*) {
 sub __seekdir (*$) {
 
     # Upgrade but ignore bareword indicator
-    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[9];
+    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[0];
 
     my ( $fh, $goto ) = @_;
     my $mocked_dir = _get_file_object($fh);
@@ -2276,13 +2276,14 @@ sub __seekdir (*$) {
         confess("seekdir called on a closed dirhandle");
     }
 
-    return $obj->{'tell'} = $goto;
+    $obj->{'tell'} = $goto;
+    return 1;
 }
 
 sub __closedir (*) {
 
     # Upgrade but ignore bareword indicator
-    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[9];
+    ( undef, @_ ) = _upgrade_barewords(@_) if defined $_[0] && !ref $_[0];
 
     my ($fh) = @_;
     my $mocked_dir = _get_file_object($fh);

t/opendir.t

@@ -145,5 +145,33 @@ is(
     closedir($dh);
 }
 
+note "-------------- BAREWORD GUARD REGRESSION --------------";
+# Regression: the bareword upgrade guard was checking $_[9] (always undef
+# for 1-2 arg dir functions) instead of $_[0]. This meant _upgrade_barewords
+# ran unconditionally, even for reference filehandles.
+# Also: seekdir must return 1 (like CORE::seekdir), not the seek position.
+{
+    my $mock_dir  = Test::MockFile->dir('/guardtest');
+    my $mock_file = Test::MockFile->file( '/guardtest/aaa', 'data' );
+
+    is( opendir( my $dh, '/guardtest' ), 1, "opendir with ref filehandle works" );
+
+    is( scalar readdir($dh), ".",   "readdir with ref fh reads ." );
+    is( scalar readdir($dh), "..",  "readdir with ref fh reads .." );
+    is( telldir($dh),        2,     "telldir with ref fh returns correct position" );
+    is( scalar readdir($dh), "aaa", "readdir with ref fh reads aaa" );
+
+    is( rewinddir($dh), 1, "rewinddir with ref fh returns 1" );
+    is( telldir($dh),   0, "telldir after rewinddir is 0" );
+
+    # seekdir's return value is not reliably testable across Perl versions
+    # with CORE::GLOBAL overrides — test the effect instead.
+    seekdir( $dh, 2 );
+    is( telldir($dh),      2,       "telldir is 2 after seekdir(2)" );
+    is( [ readdir($dh) ],  ["aaa"], "readdir after seekdir(2) returns remaining entries" );
+
+    is( closedir($dh), 1, "closedir with ref fh returns 1" );
+}
+
 done_testing();
 exit;