Stop pos() from being confused by changing utf8ness

The value of pos() is stored as a byte offset.  If it is stored on a
tied variable or a reference (or glob), then the stringification could
change, resulting in pos() now pointing to a different character off-
set or pointing to the middle of a character:

$ ./perl -Ilib -le '$x = bless [], chr 256; pos $x=1; bless $x, a; print pos $x'
2
$ ./perl -Ilib -le '$x = bless [], chr 256; pos $x=1; bless $x, "\x{1000}"; print pos $x'
Malformed UTF-8 character (unexpected end of string) in match position at -e line 1.
0

So pos() should be stored as a character offset.

The regular expression engine expects byte offsets always, so allow it
to store bytes when possible (a pure non-magical string) but use char-
acters otherwise.

This does result in more complexity than I should like, but the alter-
native (always storing a character offset) would slow down regular
expressions, which is a big no-no.

1 files changed, 1 insertions, 0 deletions

diff --git a/regexp.h b/regexp.h
index 9c8fd30225..fd6425f403 100644
--- a/regexp.h
+++ b/regexp.h
@@ -606,6 +606,7 @@ typedef struct {
     STRLEN  subcoffset; /* saved subcoffset field from rex */
     MAGIC   *pos_magic; /* pos() magic attached to $_ */
     I32     pos;        /* the original value of pos() in pos_magic */
+    U8      pos_flags;  /* flags to be restored; currently only MGf_BYTES*/
 } regmatch_info_aux_eval;