Fix FFI specs on release builds

[HertzDevil]

Should fix #12592.

[straight-shoota]

Wouldn't it make sense to move that constant into the actual code in the FFI namespace?

[HertzDevil]

Crystal::FFI is not public yet and the interpreter itself doesn't need this type, so all this does is requiring longer qualified type names in that spec file.

[straight-shoota]

In the specs we could just use Int64 everywhere without needing ffi_arg at all. That should promote correctly.

[HertzDevil]

In case someone else or ourselves later try to publicize FFI based on what is already in the repository, it is a good idea to remind them of ffi_arg's existence.

[straight-shoota]

Yes, that's exactly why I suggested to move it out of the spec into the implementation.
The current solution feels some middle ground compromise partly acknowledging, but not entirely. I'd either go full and move ffi_sarg to the implementation, or avoid it entirely (but mention it in a comment).

[beta-ziliani]

@straight-shoota am I getting it right that you meant to move the code for the Sarg type to ./src/compiler/crystal/ffi/ffi.cr, instead of being in the spec as it is now?

[straight-shoota]

Yes, either that or remove it entirely (because it's only used in the spec and there we can simply just use the bigger type with Int64 and then there's no need for it).

[straight-shoota]

Regardless of that, I'm fine with merging it as is - or with changes in either of the directions I suggested.
I'd like to get this fix into 1.6.1 and not hold up the release for long.

[asterite]

But this can be done after 1.6.1. Just don't run the specs in release mode. I think ffi has been there since 1.5.0

[HertzDevil]

In theory we cannot take an Int64*, pass it to FFI as a Void*, and then have FFI reinterpret it as an Int32* because that would break on big-endian systems. So it is good practice to always use ffi_sarg and never assume Int64 fits everything.

[straight-shoota]

I don't want to reinterpret Int64 as Int32. I just want to switch the return type to Int64 entirely.

[straight-shoota]

Thank you ❤️