fix for [perl #72604] @DB::args and win32 fork

A previous fix for [perl #66108] (7fa38291524c327a3cb23bfe94979e1537743cac)
stopped cloning PL_dbargs, on the grounds that it was usually filled with
garbage (it contains an un-refcounted copy of @_'s elements; once the
function has returned, these may have been freed or reassigned). However,
the fix instead recreated PL_dbargs as a new empty AV that *wasn't* then
associated with the DB::args glob; so modifications to PL_dbargs weren't
seen via @DB::args.

The fix is to simply set it to null when cloning; pp_caller() will
recreate it again if necessary when it is needed.

1 files changed, 18 insertions, 0 deletions

diff --git a/t/op/fork.t b/t/op/fork.t
index 9fe8107cfa..fc9c58fc06 100644
--- a/t/op/fork.t
+++ b/t/op/fork.t
@@ -462,3 +462,21 @@ sub { @_ = 3; fork ? die "1\n" : die "1\n" }->(2);
 EXPECT
 1
 1
+########
+# [perl #72604] @DB::args stops working across Win32 fork
+$|=1;
+sub f {
+    if ($pid = fork()) {
+	print "waitpid() returned ok\n" if waitpid($pid,0) == $pid;
+    }
+    else {
+	package DB;
+	my @c = caller(0);
+	print "child: called as [$c[3](", join(',',@DB::args), ")]\n";
+	exit(0);
+    }
+}
+f("foo", "bar");
+EXPECT
+child: called as [main::f(foo,bar)]
+waitpid() returned ok