Internal Compiler Error deriving `Debug` on packed `zero_copy` structs

[Lbqds]

Description

When using declare_program! to generate a program that includes #[zero_copy(unsafe)] structs, Anchor automatically derives Debug and marks these structs with #[repr(Rust, packed)].

This triggers a Rust Internal Compiler Error because the derived Debug implementation creates references to fields in a packed struct:

error: internal compiler error: compiler/rustc_mir_transform/src/check_packed_ref.rs:49:17: builtin derive created an unaligned reference

Reproduction

You can run cargo build in the demo repository to reproduce this issue.

[spellsaif]

Did you try overriding Derive manually? I mean, Anchor allows that I guess. This will prevent Anchor auto adding Debug. Give it a try.

example:

#[zero_copy(unsafe)]
#[derive(Copy, Clone)]
pub struct Anime {
    pub total_watched: u64,
}

[Lbqds]

Did you try overriding Derive manually? I mean, Anchor allows that I guess. This will prevent Anchor auto adding Debug. Give it a try.

example:

#[zero_copy(unsafe)]
#[derive(Copy, Clone)]
pub struct Anime {
pub total_watched: u64,
}

Thanks for the suggestion, but it doesn’t solve the issue, because the problem isn’t on the contract side. it happens when calling declare_program to generate Rust code from the IDL.

As you can see, Anchor always derives Debug in this case:

anchor/lang/attribute/program/src/declare_program/common.rs

Line 127 in b8f96b3

let debug_attr = quote!(#[derive(Debug)]);

For repr(Rust, packed) structs, Debug should either not be derived, or be implemented manually.

[spellsaif]

Did you try overriding Derive manually? I mean, Anchor allows that I guess. This will prevent Anchor auto adding Debug. Give it a try.
example:
#[zero_copy(unsafe)]
#[derive(Copy, Clone)]
pub struct Anime {
pub total_watched: u64,
}

Thanks for the suggestion, but it doesn’t solve the issue, because the problem isn’t on the contract side. it happens when calling declare_program to generate Rust code from the IDL.

As you can see, Anchor always derives Debug in this case:

anchor/lang/attribute/program/src/declare_program/common.rs

Line 127 in b8f96b3

let debug_attr = quote!(#[derive(Debug)]);
For repr(Rust, packed) structs, Debug should either not be derived, or be implemented manually.

You are so right. Anchor adds Debug as default anyway regardless of what you do. I don't know if there is any other workaround. If there is not we might fix it and create a PR