@ramsey @cabbey Imagine the scenario. There's a new .phps format that allows advanced types, generics, etc. The engine can *not* consume it. Composer recognizes it and do erasure (the engine provides means to do it). If composer.json requires a library that "provides" types checks, Composer will use that library to check the code before erasure. This would have no impact on people who do not want to type-check, but would empower a lot people who want to use advanced types, etc.