concrete5 version 8 won't run on PHP 7.3.
The reason is that concrete5 uses Doctrine ORM version 2.5, which is not compatible with PHP 7.3. We'd need to update ORM to the upcoming 2.6.3, but it requires PHP 7.1+ whereas concrete5 version 8 still supports PHP 5.5.9 (see doctrine/orm#7325 ).
I don't think that Doctrine 2.5 will be fixed, so we have 2 options:
- don't let concrete5 version 8 run on PHP 7.3
- create a fork of Doctrine
I'd go with 2...