[pod] unable to compile with other newer dependencies

[therealdannzor]

When building spl-pod together with the other Solana dependencies as part of the 2.x crates and anchor 0.31.0, the compilation fails like so:

error[E0276]: impl has stricter requirements than trait
  --> /Users/dkf/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/spl-pod-0.5.1/src/error.rs:40:15
   |
40 |             + DecodeError<E>
   |               ^^^^^^^^^^^^^^ impl has extra requirement `E: DecodeError<E>`

   Compiling oid-registry v0.6.1
   Compiling rustls-platform-verifier v0.5.1
   Compiling num-rational v0.2.4
   Compiling rand v0.9.0
For more information about this error, try `rustc --explain E0276`.

The core reason seem to be in the error message, that there are versions of spl-pod still being used that does not have this strict requirement.

The commit for the change was more than three months ago.

Any thoughts on a workaround for this? I can only think of relaxing the trait requirement in order to get past this as of now.

[therealdannzor]

Similarly to anza-xyz/solana-sdk#124, I strongly suspect it has to do with being on a newer Rust version, here 1.85.0, which seems to have increasingly more sensitive type system.

Edit: I notice the repo is already on 1.84.1 and that I'm pulling old code so this issue might likely be outdated and is a problem with the dependency tree. I'll have to try to compile with the current master version to confirm if it's still a problem.

[joncinque]

Note that I wasn't able to reproduce this against master with 1.79, 1.84.1, or 1.85.1, so maybe some other sets of deps are messed up

[therealdannzor]

Note that I wasn't able to reproduce this against master with 1.79, 1.84.1, or 1.85.1, so maybe some other sets of deps are messed up

This should demonstrate the unintended compile error that has been introduced in 1.84.0 as part of the stricter trait checker:

src/main.rs:

use spl_pod::error::PodSliceError;

trait DecodeError<E> {
    fn type_of() -> &'static str;
}

trait PrintProgramError {
    fn print<E>(&self)
    where
        E: 'static;
}

// Triggers E0276 — stricter bounds than the trait.
impl PrintProgramError for PodSliceError {
    fn print<E>(&self)
    where
        E: 'static
            + std::error::Error
            + DecodeError<E>
            + PrintProgramError
            + num_traits::FromPrimitive,
    {
        println!("PodSliceError");
    }
}

fn main() {
    let err = PodSliceError::CalculationFailure;
    err.print::<PodSliceError>();
}

Cargo.toml:

[package]
name = "pod-trait-error"
version = "0.1.0"
edition = "2021"

[dependencies]
num-traits = "0.2"
spl-pod = { git = "https://github.com/solana-program/libraries", branch = "main" }

[therealdannzor]

Having anza-xyz/solana-sdk#104 in this repo would resolve this, too