Support ? operator

[franziskuskiefer]

The question mark operator is not supported.

The following Rust code

fn inner() -> Result<(), u8> {
    Err(1)
}

fn call_it() -> Result<(), u8> {
    inner()?;
    Ok(())
}

generates the following C code.

core_result_Result_55 eurydice_tests_call_it(void)
{
  KRML_HOST_EPRINTF("KaRaMeL abort at %s:%d\n%s\n",
    __FILE__,
    __LINE__,
    "Eurydice error: Failure(\"TODO: TraitTypes core::result::{core::ops::try_trait::Try for core::result::Result<T, E>[TraitClause@0, TraitClause@1]}#26<T@0, T@1>[TraitClause@0, TraitClause@1]::Residual\")\n");
  KRML_HOST_EXIT(255U);
}

[msprotz]

This boils down to support for associated types, which would require a little bit of feature work, to encode the associated types in trait parameters as type arguments to pre-monomorphized functions.

[Nadrieril]

You'll get support for associated types for free once we solve AeneasVerif/charon#127, which is at the top of my priority queue.

[msprotz]

Indeed, I was thinking of doing the same encoding at the eurydice level (types within traits as type parameters of the enclosing function), but if you're doing it in Charon, then indeed it should come "for free". Thanks!