More flexible Rust<>Cairo types interface

[bilboquet]

From Ariel Elperin

• Support sending various uints (not just u8) to riscv call (potentially make it generic over the param type, where the param type has to implement some kind of Serde trait)
• User defined structs
• The endgame here could be something like a type definition by the dev, e.g. in a proto file, and a cli command that generates rust + cairo modules with those types. That way, you know that whatever is generated can be used as arguments/return values of the externalized rust functions and as arguments/return values of riscv_call

[bilboquet]

@damip please share your thoughts about this:

Let's focus on the use of a proto file to describe the interface between rust and cairo code.

On the rust side, we need

1. a proto to rust code generator which is used at compile time
2. a runtime support library written in rust to help serialize/deserialize data in protobuf format (that will be executed inside the riscv VM).
3. some basic code (the actual format of a risc_call is [u8]->[u8]).

Points 1 and 2 can be filled by https://docs.rs/micropb/0.1.0/micropb/ (and integration is almost complete).
Point 3 is not a big problem and can even be done manually by the project developer.

On the cairo side, we have the same requirements.
Should we start writing a proto for the cairo code generator (in rust) and the corresponding cairo runtime (in cairo)?

[damip]

OK For the rust side.

We need to check how proto works on the cairo side.
Looks like it is already used natively for hints: https://reilabs.io/blog/introducing-hints-in-cairo-programming-language/

https://github.com/reilabs/cairo-hints

In particular, here is the cairo proto codegen they use, conveniently written as a rust crate: https://github.com/reilabs/cairo-hints/tree/main/cairo-proto-build but let's make sure it generates the right version of cairo

[bilboquet]

@damip
Integration of cairo-proto-build went relatively fine.
But I just found that they are based on a different language edition (i.e. 2023_10) and that was the cause of the pain I had lately:

Something related to the visibility rules changed between edition 2023_10 and 2024_07:
given this cairo code:

// module mod1
struct A {
    a: u8,
}

// module main
mod mod1;
use mod1::A;

fn main2() -> bool {
    let x = A { a: 1 };
    x.a == 1
}

This code builds in edition 2023_10 but fails in edition 2024_07 because both A and A.a are not visible anymore.
This would work (but pub has to be added manually for the moment):

// module mod1
pub struct A {
    pub a: u8,
}

[bilboquet]

Added an issue to cairo-hints project reilabs/cairo-hints#35

[damip]

@bilboquet could we work on a fork and propose a PR upstream ? To avoid blocking our progress