`E0365` newly triggers on `pub(crate)` reexports (cannot be re-exported outside)

[mkrasnitski]

I have had trouble creating a minimal repro for this, however I do think this is potentially unwanted breakage. On the latest nightly, I tried compiling the latest version of the serenity crate (v0.12.5) and received a compiler error:

error[E0365]: `Result` is only public within the crate, and cannot be re-exported outside
   --> src/lib.rs:185:9
    |
185 |         model::prelude::*,
    |         ^^^^^^^^^^^^^^^^^ re-export of crate public `Result`
    |
    = note: consider declaring type or module `Result` with `pub`

error[E0365]: `Error` is only public within the crate, and cannot be re-exported outside
   --> src/lib.rs:185:9
    |
185 |         model::prelude::*,
    |         ^^^^^^^^^^^^^^^^^ re-export of crate public `Error`
    |
    = note: consider declaring type or module `Error` with `pub`

Code

I tried creating a minimal repro, but no luck. However, the relevant module structure in serenity is described below:

mod error {
    pub enum Error {
        // ...
    }
    pub type Result<T, E = Error> = std::result::Result<T, E>;
}

mod internal {
    pub mod prelude {
        pub use crate::error::{Error, Result};
        // ...
    }
}

pub mod model {
    pub mod prelude {
        pub(crate) use crate::internal::prelude::*;
        // ...
    }
}

pub use crate::error::{Error, Result};

pub mod all {
    pub use crate::model::prelude::*;
    // ...
}

This code by itself is not a repro, however the important thing to note is that the error::{Result, Error} types are exported publicly at the root level of the crate, and additionally exported as part of the internal prelude that is re-exported within the model::prelude, but only at the pub(crate) level. This lets other modules within the crate obtain the contents of the interal::prelude module by importing module::prelude::*.

Something to do with this code causes serenity to no longer compile on nightly-2026-05-06. I was able to bisect down to #156014, specifically this code which is responsible for the error being emitted.

Version it worked on

It most recently worked on nightly-2026-05-05:

rustc 1.97.0-nightly (cb40c25f6 2026-05-04)
binary: rustc
commit-hash: cb40c25f6aebb637163d26bf76a680ed6e5d1eda
commit-date: 2026-05-04
host: x86_64-unknown-linux-gnu
release: 1.97.0-nightly
LLVM version: 22.1.4

Version with regression

The most recent nightly fails to build the crate:

rustc 1.97.0-nightly (e95e73209 2026-05-05)
binary: rustc
commit-hash: e95e73209faf6ead2bc5c7636e45e589a751b79b
commit-date: 2026-05-05
host: x86_64-unknown-linux-gnu
release: 1.97.0-nightly
LLVM version: 22.1.4

@rustbot modify labels: +regression-from-stable-to-nightly -regression-untriaged

[petrochenkov]

If macros 2.0 (the macro keyword) are not involved, then something is indeed going wrong and these errors should not appear.
I'll look into this in a few days, but it would still be very useful to have some minimized reproduction until then.

[cyrgani]

the above example is actually almost correct; the following compiles on stable but not on nightly

mod error {
    pub enum Error {
        // ...
    }
    pub type Result<T, E = Error> = std::result::Result<T, E>;
}

mod internal {
    pub mod prelude {
        pub use crate::error::{Error, Result};
        // ...
    }
}

pub mod model {
    pub mod prelude {
        pub(crate) use crate::internal::prelude::*;
        // ...
    }
}

pub use crate::error::{Error, Result};

pub mod all {
    pub use crate::{model::prelude::*, *}; // note this extra *
}

or smaller:

mod error {
    pub struct Error;
}

pub mod prelude {
    pub(crate) use crate::error::*;
}

pub use crate::error::Error;

pub mod all {
    pub use crate::{prelude::*, *};
}

[petrochenkov]

Fixed in #156284.