interface - default mixed value

[ivyhjk]

Interfaces that contains methods with default parameters as mixed, breaks the generated code.

HHVM Reflection generate a HH\mixed value, but HHVM does not recognizes this
type as a mixed value, like HH\bool, HH\string, etc.

Test code:

use function Usox\HackMock\{mock, prospect};

interface InterfaceWithDefaultInput {
    public function mixedWithoutDefault(mixed $input): void;
}

class InterfaceWithDefaultInputTest extends \Usox\HackMock\HackMock {
    public function testWithDefault(): void {
        $stub = mock(InterfaceWithDefaultInput::class);

        prospect($stub, 'mixedWithoutDefault')->execute(vec['foo']);
    }
}

I think replacing value on-fly is a quick patch, but using Reflection (maybe custom reflection classes) or a Builder (for types) should be a better solution 🤔.

[usox]

This is somewhat related to facebook/hhvm#8254. A typemapper, which maps the reflection values to correct scalar type hints, should do the trick in the first place.
Maybe hhvm will drop/replace reflection in future, so it would be wise to think about a more generic solution for the next major version of hackmock.