For those looking forward to PHP 7, there's a new series of posts from Damien Seguy that can help you with some of the newer error messages and what might be causing them.
The first step to prepare for PHP 7 is to lint it : using the command line instruction 'php -l script.php', one can easily check that every file in a current application compile with PHP 7. The second step is to run the application and the unit tests : in short, execute it with PHP 7. And this is where we'll learn about the new errors that PHP has prepared for us. In order to be one step ahead of the migration, this article will help you prepare here is a panorama on PHP error messages.
In part one he looks at some of the most often raised errors including the incorrect use of "$this" and undefined offsets. Part two gets into a few more complex messages about return type hinting, the constant scalar expression and using temporary expressions in a write context. Finally, part three looks at messaging around redefinition of identical parameters, bit shifting by a negative number, named constructor deprecation and strict typing. Each part of the series covers a few more than just the ones listed here too, so be sure to check each for more helpful error messages and solutions.