[FR]: Add WhenStaticCastTo matcher

[dkaszews]

Does the feature exist in the most recent commit?

No

Why do we need this feature?

The existing (Safe)MatcherCast and WhenDynamicCastTo do not work well for pointers such as void*, since the former requires the underlying types to be convertible (void => T) and the second simply does not allow void* as the argument.

This is especially needed when mocking APIs which type-erase their arguments as void*, e.g. something like int api(enum message_type type, void* arg).

Example usage:

const auto matcher = WhenStaticCastTo<ReadMessage*>(Field(&ReadMessage::length, 10));
EXPECT_CALL(mock, api(ReadMessageId, matcher)).WillOnce(Return(0));

Describe the proposal.

I was perfectly able to get the expected behavior by simply duplicating all of WhenDynamicCastTo with its underlying implementation and just switching dynamic_cast to static_cast with the corresponding message. Real implementation should probably avoid such duplication and instead just abstract away the casting into something like:

struct static_caster {
    static constexpr const char* name = "static";
    template <typename To, typename From>
    To cast(From* from) { return static_cast<To>(from); }
    // plus overload references
};

// same for dynamic

Other types of casts such as reinterpret, const and C++20 bit should also be considered.

Is the feature specific to an operating system, compiler, or build system version?

No