[perl #118651] don't overwrite $! in readdir()

POSIX expects readdir() to leave errno alone when it reaches end of
directory without an error so that case can be detected.  Do the same
in perl.

2 files changed, 19 insertions, 1 deletions

diff --git a/pp_sys.c b/pp_sys.c
index 6f4c198d49..74b65f7b67 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -3858,7 +3858,7 @@ PP(pp_readdir)
     } while (gimme == G_ARRAY);
 
     if (!dp && gimme != G_ARRAY)
-        goto nope;
+        RETPUSHUNDEF;
 
     RETURN;
 
diff --git a/t/op/readdir.t b/t/op/readdir.t
index 528a0f1e0c..8515d1d9d0 100644
--- a/t/op/readdir.t
+++ b/t/op/readdir.t
@@ -67,4 +67,22 @@ fresh_perl_like(<<'EOP', qr/^no crash/, {}, 'RT #68182');
   print "no crash";
 EOP
 
+SKIP:
+{ # [perl #118651]
+  # test that readdir doesn't modify errno on successfully reaching the end of the list
+  # in scalar context, POSIX requires that readdir() not modify errno on end-of-directory
+  my @s;
+  ok(opendir(OP, "op"), "opendir op");
+  $! = 0;
+  while (defined(my $f = readdir OP)) {
+    push @s, $f
+      if $f =~ /^[^\.].*\.t$/i;
+  }
+  my $errno = $! + 0;
+  closedir OP;
+  is(@s, @D, "should be the same number of files, scalar or list")
+    or skip "mismatch on file count - presumably a readdir error", 1;
+  is($errno, 0, "errno preserved");
+}
+
 done_testing();