Diagnostic doesn't mention `cfg`-ed item referenced through glob import

[greeble-dev]

Code

pub mod original {
    #[cfg(FALSE)]
    pub mod gated {
        pub fn foo() {}
    }
}

pub mod reexport {
    pub use super::original::*;
}

pub fn main() {
    reexport::gated::foo();

    // A direct reference produces the desired output.
    //original::gated::foo();
}

Current output

error[E0433]: failed to resolve: could not find `gated` in `reexport`
  --> <source>:14:15
   |
14 |     reexport::gated::foo();
   |               ^^^^^ could not find `gated` in `reexport`

Desired output

error[E0433]: failed to resolve: could not find `gated` in `reexport`
  --> <source>:14:15
   |
17 |     reexport::gated::foo();
   |               ^^^^^ could not find `gated` in `reexport`
   |
note: found an item that was configured out
  --> <source>:3:13
   |
3  |     pub mod gated {
   |             ^^^^^
note: the item is gated here
  --> <source>:2:5
   |
2  |     #[cfg(FALSE)]
   |     ^^^^^^^^^^^^^

Rationale and extra context

If an item in a cfg gated module is directly referenced then the diagnostic will mention the gate. This does not happen if the gated module is re-exported through a glob import.

Rust Version

rustc 1.86.0 (05f9846f8 2025-03-31)
binary: rustc
commit-hash: 05f9846f893b09a1be1fc8560e33fc3c815cfecb
commit-date: 2025-03-31
host: x86_64-unknown-linux-gnu
release: 1.86.0
LLVM version: 19.1.7

rustc 1.89.0-nightly (777d37277 2025-05-17)
binary: rustc
commit-hash: 777d372772aa3b39ba7273fcb8208a89f2ab0afd
commit-date: 2025-05-17
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.4

Anything else?

Compiler Explorer: https://godbolt.org/z/d3rr35G4T

[Urgau]

For prioritization purpose: was this encountered in real code or is this more theoretical?

[greeble-dev]

@Urgau, this was encountered in real code. Roughly, an omnibus crate that wants to let users depend only on the omnibus crate and import omnibus::foo, omnibus::bar etc, even though behind the scenes foo and bar are from other crates that might be feature gated. One step in this chain is a glob import.

In case it's useful for context, here's a PR for the omnibus that adds some details and pitches a workaround: bevyengine/bevy#19297.

[alice-i-cecile]

Bevy maintainer here: this is real code, and users have tripped over this multiple times. It's easy to teach them what to do if they reach out for help, but the compiler should be the first line of defense here :) We have this setup due to our dynamic linking setup, which is in place to improve compile times.

[xizheyin]

That should be the problem, I need to investigate further.

rust/compiler/rustc_resolve/src/diagnostics.rs

Lines 2020 to 2042 in a8e4c68

	pub(crate) fn find_similarly_named_module_or_crate(
	&mut self,
	ident: Symbol,
	current_module: Module<'ra>,
	) -> Option<Symbol> {
	let mut candidates = self
	.extern_prelude
	.keys()
	.map(|ident| ident.name)
	.chain(
	self.module_map
	.iter()
	.filter(|(_, module)| {
	current_module.is_ancestor_of(**module) && current_module != **module
	})
	.flat_map(|(_, module)| module.kind.name()),
	)
	.filter(|c| !c.to_string().is_empty())
	.collect::<Vec<_>>();
	candidates.sort();
	candidates.dedup();
	find_best_match_for_name(&candidates, ident, None).filter(|sugg| *sugg != ident)
	}