[perl #101738] Make sv_sethek set the UTF8 flag correctly

It was only ever turning it on, and not turning it off if the sv hap-
pened to have it on from its previous use.

This caused ref() (which uses sv_sethek(TARG,...)) to return a shared
scalar with the UTF8 flag on, even if it was supposed to be off.

For shared scalars, the UTF8 flag on ASCII strings does make a differ-
ence.  The pv *and* the flags are used in hash lookup, for speed.

So a scalar returned by ref() with the UTF8 flag on by mistake would
not work in hash lookups.  exists $classes{ref $foo} would return
false, even if there were an entry for that class.

2 files changed, 12 insertions, 1 deletions

diff --git a/sv.c b/sv.c
index 5ee48175b2..3efbc39ea7 100644
--- a/sv.c
+++ b/sv.c
@@ -4613,6 +4613,7 @@ Perl_sv_sethek(pTHX_ register SV *const sv, const HEK *const hek)
 	    sv_setpvn(sv, HEK_KEY(hek), HEK_LEN(hek));
 	    if (HEK_UTF8(hek))
 		SvUTF8_on(sv);
+	    else SvUTF8_off(sv);
             return;
 	}
         {
@@ -4624,6 +4625,7 @@ Perl_sv_sethek(pTHX_ register SV *const sv, const HEK *const hek)
 	    SvPOK_on(sv);
 	    if (HEK_UTF8(hek))
 		SvUTF8_on(sv);
+	    else SvUTF8_off(sv);
             return;
 	}
     }
diff --git a/t/op/ref.t b/t/op/ref.t
index 36371f7b73..e2ba10fca2 100644
--- a/t/op/ref.t
+++ b/t/op/ref.t
@@ -8,7 +8,7 @@ BEGIN {
 
 use strict qw(refs subs);
 
-plan(223);
+plan(224);
 
 # Test glob operations.
 
@@ -208,6 +208,15 @@ is (ref *STDOUT{IO}, 'IO::File', 'IO refs are blessed into IO::File');
 like (*STDOUT{IO}, qr/^IO::File=IO\(0x[0-9a-f]+\)$/,
     'stringify for IO refs');
 
+{ # Test re-use of ref's TARG [perl #101738]
+  my $obj = bless [], '____';
+  my $uniobj = bless [], chr 256;
+  my $get_ref = sub { ref shift };
+  my $dummy = &$get_ref($uniobj);
+     $dummy = &$get_ref($obj);
+  ok exists { ____ => undef }->{$dummy}, 'ref sets UTF8 flag correctly';
+}
+
 # Test anonymous hash syntax.
 
 $anonhash = {};