IDL generation fails on arrays where the size is an associated constant

[EquilateralDelta]

Checked with anchor-cli 0.24.2

const B: usize = 4;

#[account]
pub struct A {
    pub works: [(); 4],
    pub also_works: [(); B],
    pub does_not_work: [(); A::C],
}

impl A {
    const C: usize = 4;
}

In the case of the code below, anchor build successfully builds a contract, but on the IDL generation step build fails with

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ParseIntError { kind: InvalidDigit }', lang/syn/src/idl/mod.rs:204:76

If the field of does_not_work is commented out, everything works.

[Henry-E]

I feel like this is a known issue. Maybe the IDL generation needs to do a better job at correctly accessing constants but not entirely sure what the solution looks like tbh.

[EquilateralDelta]

I think it's not a critical problem to rewrite a code to use a regular constant instead of an associated one, but it can be very confusing for someone to find the culprit of this error. As a suggestion, maybe giving more meta information about a struct and field that causes IDL generation to fail would help locate a problem much more easily.

[Henry-E]

While fixing and improving IDL related generation stuff is a probably the number 3 anchor priority for me, I don't quite know when I'll be able to get to this. In the meantime PRs are welcome or maybe someone else more familiar with the IDL code could look into it.

[acheroncrypto]

Fixed by #2824.