errors using the latest beta

[mimoo]

Using the latest beta (4) I get the following errors:

warning: suffixes on a tuple index are invalid
   --> poseidon/src/sponge.rs:297:28
    |
297 |     #[derive(Debug, Clone, ocaml::ToValue, ocaml::FromValue, ocaml_gen::Struct)]
    |                            ^^^^^^^^^^^^^^ invalid suffix `usize`
    |
    = help: `usize` is *temporarily* accepted on tuple index fields as it was incorrectly accepted on stable for a few releases
    = help: on proc macros, you'll want to use `syn::Index::from` or `proc_macro::Literal::*_unsuffixed` for code that will desugar to tuple field access
    = help: see issue #60210 <https://github.com/rust-lang/rust/issues/60210> for more information
    = note: this warning originates in the derive macro `ocaml::ToValue` (in Nightly builds, run with -Z macro-backtrace for more info)

this one seems to be internal to ocaml-rs? Not sure

I'm also now getting errors that looks like the bounds are not added by the deriver:

error[E0277]: the trait bound `CamlF: ToValue` is not satisfied
   --> poseidon/src/sponge.rs:297:28
    |
297 |     #[derive(Debug, Clone, ocaml::ToValue, ocaml::FromValue, ocaml_gen::Struct)]
    |                            ^^^^^^^^^^^^^^ the trait `ToValue` is not implemented for `CamlF`
    |
    = note: required for `&CamlF` to implement `ToValue`
note: required by a bound in `Value::store_field`
   --> /Users/david/.cargo/registry/src/github.com-1ecc6299db9ec823/ocaml-1.0.0-beta.5/src/value.rs:420:34
    |
420 |     pub unsafe fn store_field<V: ToValue>(&mut self, rt: &Runtime, i: Size, val: V) {
    |                                  ^^^^^^^ required by this bound in `Value::store_field`
    = note: this error originates in the derive macro `ocaml::ToValue` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider restricting type parameter `CamlF`
    |
298 |     pub struct CamlScalarChallenge<CamlF: ocaml::ToValue>(pub CamlF);
    |                                         ++++++++++++++++

the code it points to, that used to work:

    #[derive(Debug, Clone, ocaml::ToValue, ocaml::FromValue, ocaml_gen::Struct)]
    pub struct CamlScalarChallenge<CamlF>(pub CamlF);

[zshipko]

Thanks! The first issue is an easy fix (I just pushed a commit for that one), but the bounds issue is a little more complicated. The ToValue macro is a little stricter and doesn't add any bounds for you. I can look for some solutions on my side but in the meantime you can add the bounds yourself:

#[derive(Debug, Clone, ocaml::ToValue, ocaml::FromValue, ocaml_gen::Struct)]
pub struct CamlScalarChallenge<CamlF>(pub CamlF)
where 
  CamlF: ocaml::ToValue + ocaml::FromValue;

[mimoo]

Yeah I wanted to avoid that if possible so I reverted back to latest stable. I'm wondering why it's a complicated issue to fix now :o (as it was successfully matching serde/debug/display/etc. behavior before)

[zshipko]

It's likely not too hard of problem to solve, but macros in Rust are hard to debug. I think I'll be able to get it to match the expected behavior but am pretty low on time at the moment!

[mimoo]

I just implemented this for another project here: https://github.com/o1-labs/proof-systems/blob/mimoo/snarky2/kimchi/snarky-deriver/src/lib.rs#L509 if this can help.

Basically the strategy was to look at all the fields of the struct, collect their types in a hashset, and add the bounds on them.