Macro ambiguity with #![no_implicit_prelude]

[Slickis]

Code

I tried this code:

#![no_std]
#![no_implicit_prelude]

mod foo {
    use crate::*;
    fn bar() {
        unreachable!();
    }
}

#[macro_export]
macro_rules! unreachable {
    () => {
        loop {}
    };
}

I expected to see this happen: The code should compile (no name-resolution ambiguity).

Instead, this happened: The compiler reports an ambiguity error for unreachable!() claiming a conflict between a name from a glob import and an outer scope (the prelude).

error[E0659]: `unreachable` is ambiguous
  --> src/lib.rs:7:9
   |
 7 |         unreachable!();
   |         ^^^^^^^^^^^ ambiguous name
   |
   = note: ambiguous because of a conflict between a name from a glob import and an outer scope during import or macro resolution
note: `unreachable` could refer to the macro imported here
  --> src/lib.rs:5:9
   |
 5 |     use crate::*;
   |         ^^^^^^^^
   = help: consider adding an explicit import of `unreachable` to disambiguate
   = help: or use `self::unreachable` to refer to this macro unambiguously
note: `unreachable` could also refer to the macro defined here
  --> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/prelude/mod.rs:59:13
   |
59 |     pub use super::v1::*;
   |             ^^^^^^^^^

Version it worked on

It most recently worked on: 1.93.0-beta.8

Version with regression

rustc --version --verbose:

rustc 1.94.0-beta.1 (9b1f8ff42 2026-01-19)
binary: rustc
commit-hash: 9b1f8ff42d110b0ca138116745be921df5dc97e7
commit-date: 2026-01-19
host: x86_64-unknown-linux-gnu
release: 1.94.0-beta.1
LLVM version: 21.1.8

Notes / additional observations:

Rust Playground:
https://play.rust-lang.org/?version=nightly&edition=2024&gist=23b9e8aa365dc3f6b4bffb840ac0c700

Removing #![no_implicit_prelude] yields the same error.
Swapping order (define macro before mod foo) makes the code compile successfully.

[SpriteOvO]

Bisection points to #139493. CC @Voultapher

[Voultapher]

I'm afraid that's en expected breakage because panic and unreachable are now always part of the prelude even if #![no_implicit_prelude] is set, as was already the case for column|concat|file|line|module_path|stringify since they count as compiler built-ins. It should be easy for users to explicitly import the one they want, this only happens with glob imports.