Description:
------------
Split off from bug #81190:

<?php
$str = "foo";
null?->{$str . "bar"};

leaks the property name. The opcodes look like this:

0000 ASSIGN CV0($str) string("foo")
0001 T2 = CONCAT CV0($str) string("bar")
0002 T3 = JMP_NULL null 0004
0003 T3 = FETCH_OBJ_R null T2
0004 FREE T3
0005 RETURN int(1)

Note that the CONCAT happens before the JMP_NULL. This is JMP_NULL is part of the delayed opline stack.

Possibly we could get away with not using delayed oplines with nullsafe, because nullsafe cannot be used in write context, so not delaying should be safe. It will result in different evaluation order than non-nullsafe properties though.