Feature request

• Remove built-in type-specifying extensions in favour of stubs: https://github.com/phpstan/phpstan-src/tree/1.9.x/src/Type/Php (a nicer list is here https://apiref.phpstan.org/1.9.x/PHPStan.Type.FunctionTypeSpecifyingExtension.html)
  • An interesting gotcha here is that if you remove an extension for a function mentioned here https://github.com/phpstan/phpstan-src/blob/1.9.x/src/Type/Php/TypeSpecifyingFunctionsDynamicReturnTypeExtension.php without adding a stub, PHPStan ends in an infinite recursion. But after adding a @phpstan-assert stub it's fine again. This might be worth investigation and maybe fixing it.
• Maybe we can simplify phpstan-phpunit, phpstan-beberlei-assert, phpstan-webmozart-assert since these libraries already have @psalm-assert annotations.
  • BUT: It already happened that PHPStan extension was more correct and precise than these annotations so we need to keep the tests
  • BUT: We need to investigate which version of these libraries added those annotations. I'd say if it's longer than three years we can safely remove redundant extensions, otherwise not.
  • We can definitely remove extensions for new methods in these libraries that were already added with those assert annotations.
• UnionTypeMethodReflection::getAssertions() needs to be fixed. The logic to compute which annotations to use might be non-trivial.
• IntersectionTypeMethodReflection::getAssertions() needs to be fixed. The logic to compute which annotations to use might be non-trivial.
• Documentation at https://phpstan.org/writing-php-code/narrowing-types#custom-type-checking-functions-and-methods