php7 7.1.12-r1 bug "Fixed bug in type inference" - fix already available by PHP
The current release of PHP on edge has the bug Fixed bug
https://bugs.php.net/bug.php?id=75570&edit=1 - as fix has already been
supplied on the 28th of November 2017 and should be applied to the
Alpine packages.
Fix:
https://github.com/php/php-src/commit/776bef8447f2848c043e4716a1e08c4ac5a88fdb
(from redmine: issue id 8436, created on 2018-01-28, closed on 2018-08-10)