[perl #85026] Deleting the current iterator in void context

Looking at the delete code I see another strange thing. If the delete
of the current iterator is done with the G_DISCARD flag, the corres-
ponding value is not freed and survives until the lazy deleted entry
gets removed on the next hash iteration. This is easily demonstrated
like this:

perl -wle '
sub DESTROY { print "DESTROY" }
%a=(a=>bless[]);
each %a;
delete $a{a};
print "END"
'

This prints:

END
DESTROY

notice the difference with:

perl -wle '
sub DESTROY { print "DESTROY" }
%hash = (a => bless[]);
each %hash;
$dummy = delete $hash{a}; $dummy = 0;
print "END"
'

This prints:

DESTROY
END

This is easily solved by always replacing the deleted entry value with
&PL_sv_placeholder. It actually simplifies the code a bit except for the
fact that the mro_method_changed from free_hash_ent now has to be done
in hv_delete

Author: Ton Hospel

hv.c

@@ -1040,26 +1040,30 @@ S_hv_delete_common(pTHX_ HV *hv, SV *keysv, const char *key, STRLEN klen,
 		    mro_changes = 1;
 	}
 
-	if (d_flags & G_DISCARD)
-	    sv = NULL;
-	else {
-	    sv = sv_2mortal(HeVAL(entry));
-	    HeVAL(entry) = &PL_sv_placeholder;
-	}
+	if (d_flags & G_DISCARD) {
+	    sv = HeVAL(entry);
+	    if (sv) {
+		/* deletion of method from stash */
+		if (isGV(sv) && isGV_with_GP(sv) && GvCVu(sv)
+		 && HvENAME_get(hv))
+		    mro_method_changed_in(hv);
+		SvREFCNT_dec(sv);
+		sv = NULL;
+	    }
+	} else sv = sv_2mortal(HeVAL(entry));
+	HeVAL(entry) = &PL_sv_placeholder;
 
 	/*
 	 * If a restricted hash, rather than really deleting the entry, put
 	 * a placeholder there. This marks the key as being "approved", so
 	 * we can still access via not-really-existing key without raising
 	 * an error.
 	 */
-	if (SvREADONLY(hv)) {
-	    SvREFCNT_dec(HeVAL(entry));
-	    HeVAL(entry) = &PL_sv_placeholder;
+	if (SvREADONLY(hv))
 	    /* We'll be saving this slot, so the number of allocated keys
 	     * doesn't go down, but the number placeholders goes up */
 	    HvPLACEHOLDERS(hv)++;
-	} else {
+	else {
 	    *oentry = HeNEXT(entry);
 	    if (SvOOK(hv) && entry == HvAUX(hv)->xhv_eiter /* HvEITER(hv) */)
 		HvLAZYDEL_on(hv);