Support ref readonly parameters

[vzarytovskii]

Ref readonly are encoded as inrefs ([in] &T) with special attribute: https://github.com/jjonescz/csharplang/blob/5134bd7042bcd71dbddbdff618b9b63dc54775a0/proposals/ref-readonly-parameters.md#metadata-encoding

More info: https://discord.com/channels/143867839282020352/312132327348240384/1169766448063856650

Update 1: Intermediate ad-hoc fix (#16232) treats ref readonly as if it was inert in parameters. Proper fix should be introducing new byref type - readonlyref<_>, which should be a long-term fix.

cc @Tarmil @Sergio0694 @TIHan

[teo-tsirpanis]

My understanding is that inref<_> is already equivalent to C#'s ref readonly. You cannot pass an rvalue to an inref<_> for example.

If you want to fix inref and support passing rvalues to it, maybe the issue should be reworded accordingly.

[nodakai]

F# 8.0.100 sees a ref readonly parameter as a byref parameter, broke my code

Available overloads:
- Unsafe.AsRef<'T>(source: byref<'T>) : byref<'T> // Argument 'source' doesn't match
- Unsafe.AsRef<'T>(source: voidptr) : byref<'T> // Argument 'source' doesn't match

C.f. dotnet/runtime#93251 (comment)

https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.unsafe.asref?view=net-8.0#system-runtime-compilerservices-unsafe-asref-1(-0@)

[vzarytovskii]

My understanding is that inref<_> is already equivalent to C#'s ref readonly. You cannot pass an rvalue to an inref<_> for example.

If you want to fix inref and support passing rvalues to it, maybe the issue should be reworded accordingly.

Yeah. I actually think I'm going to close it now, since we have an ad-hoc fix which works, and it should be a small rfc if we want any additional support.

[vzarytovskii]

F# 8.0.100 sees a ref readonly parameter as a byref parameter, broke my code

Available overloads:

- Unsafe.AsRef<'T>(source: byref<'T>) : byref<'T> // Argument 'source' doesn't match

- Unsafe.AsRef<'T>(source: voidptr) : byref<'T> // Argument 'source' doesn't match

C.f. dotnet/runtime#93251 (comment)

https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.unsafe.asref?view=net-8.0#system-runtime-compilerservices-unsafe-asref-1(-0@)

Yes, it's known. BCL changed the API and we didn't have much time to revert or fix on F# side. 8.0.101 should have the fix with will treat ref readonly as inrefs.