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, 1 insertions, 0 deletions

diff --git a/mg.c b/mg.c
index 0ce58ab5d2..b4c06923ee 100644
--- a/mg.c
+++ b/mg.c
@@ -2590,6 +2590,7 @@ Perl_magic_set(pTHX_ SV *sv, MAGIC *mg)
 	break;
     case '\010':	/* ^H */
 	PL_hints = SvIV(sv);
+	CopHINTS_set(&PL_compiling, PL_hints);
 	break;
     case '\011':	/* ^I */ /* NOT \t in EBCDIC */
 	Safefree(PL_inplace);