Support for initializing tuple-structs

[bonzini]

Is your feature request related to a problem? Please describe.
Currently, pin-init does not support initializing tuple structs, which could be useful to write concise wrappers like

#[pin_data]
struct Gadget(#[pin] Opaque<bindings::Gadget>);

(Optional) Solution Implementation
Implementation should not be hard, since C code can expand the field numbers and pass them to the internal Rust macros. The Rust macros need to change the fields from $field:ident to $field:tt.

Additional context
This is especially useful in order to implement PinnedDrop for the wrapper.

[BennoLossin]

Yeah this is on my todo-list as well. But I'd really prefer to wait with this until we have syn...

The implementation on the declarative macro side would be very expensive, as #[pin_data] generates a lot of stuff that needs valid identifiers and with tuple structs we need to use the index instead (which is very cumbersome to generate).

[bonzini]

Yeah this is on my todo-list as well. But I'd really prefer to wait with this until we have syn...

Ok, I wasn't sure if that was still being considered.

The implementation on the declarative macro side would be very expensive, as #[pin_data] generates a lot of stuff that needs valid identifiers and with tuple structs we need to use the index instead (which is very cumbersome to generate).

My idea was to start by making concat_idents a bit more lenient, and accept numeric literals as the second argument. This should keep the changes to the declarative macro relatively small.

[BennoLossin]

My idea was to start by making concat_idents a bit more lenient, and accept numeric literals as the second argument. This should keep the changes to the declarative macro relatively small.

I'm not using concat_idents, I'm using paste!.

But that's not the issue, the problem is how do you get the index of the field in a declarative macro.

[bonzini]

Ah, and now that you've integrated pin projection that wouldn't really work anyway.

[BennoLossin]

Yeah, but it is possible with syn & we want to have it for the kernel as well :)