Modifying ${^OPEN} changes the value of $^H:

$ ./perl -le 'BEGIN { print $^H; ${^OPEN} = "a\0b"; print $^H}'
256
917760

So changing $^H back should change the value of ${^OPEN} back to undef, right?

$ ./perl -le 'BEGIN { ${^OPEN} = "a\0b"; $^H=256; print ${^OPEN}//"undef"}'
ab
$ ./perl -le 'BEGIN { ${^OPEN} = "a\0b"; $^H=256;}BEGIN{ print ${^OPEN}//"undef"}'
undef

Apparently you have to hop from one BEGIN block to another to see
the changes.

This happens because compile-time hints are stored in PL_hints (which
$^H sets) but ${^OPEN} looks in PL_compiling.cop_hints.  Setting
${^OPEN} sets both.  The contents of PL_hints are assigned to
PL_compiling.cop_hints at certain points (the start of a BEGIN block
sees the right value because newSTATEOP sets it), but the two are not
always kept in synch.

The smallest fix here is to have $^H set PL_compiling.cop_hints as
well as PL_hints, but the ultimate fix--to come later--is to merge the
two and stop storing hints in two different places.

1 files changed, 13 insertions, 1 deletions

diff --git a/t/op/magic.t b/t/op/magic.t
index 7abddbe56a..7a929d0f9a 100644
--- a/t/op/magic.t
+++ b/t/op/magic.t
@@ -5,7 +5,7 @@ BEGIN {
     chdir 't' if -d 't';
     @INC = '../lib';
     require './test.pl';
-    plan (tests => 179);
+    plan (tests => 180);
 }
 
 # Test that defined() returns true for magic variables created on the fly,
@@ -634,6 +634,18 @@ fresh_perl_is
  'select f; undef *f; ${q/|/}; print STDOUT qq|ok\n|', "ok\n", {},
  '[perl #115206] no crash when vivifying $| while *{+select}{IO} is undef';
 
+# ${^OPEN} and $^H interaction
+# Setting ${^OPEN} causes $^H to change, but setting $^H would only some-
+# times make ${^OPEN} change, depending on whether it was in the same BEGIN
+# block.  Don’t test actual values (subject to change); just test for
+# consistency.
+my @stuff;
+eval '
+    BEGIN { ${^OPEN} = "a\0b"; $^H = 0;          push @stuff, ${^OPEN} }
+    BEGIN { ${^OPEN} = "a\0b"; $^H = 0 } BEGIN { push @stuff, ${^OPEN} }
+1' or die $@;
+is $stuff[0], $stuff[1], '$^H modifies ${^OPEN} consistently';
+
 
 # ^^^^^^^^^ New tests go here ^^^^^^^^^