Leading underscore in path makes rust suggest to add a crate named `_` with edition >= 2018

[Veykril]

Code

use _::a;
use _::*;

fn main() {
    use _::a;
    use _::*;
}

Current output

⣿
Errors

Exited with status 101

Standard Error

   Compiling playground v0.0.1 (/playground)
error: expected identifier, found reserved identifier `_`
 --> src/main.rs:1:5
  |
1 | use _::a;
  |     ^ expected identifier, found reserved identifier

error: expected identifier, found reserved identifier `_`
 --> src/main.rs:2:5
  |
2 | use _::*;
  |     ^ expected identifier, found reserved identifier

error: expected identifier, found reserved identifier `_`
 --> src/main.rs:5:9
  |
5 |     use _::a;
  |         ^ expected identifier, found reserved identifier

error: expected identifier, found reserved identifier `_`
 --> src/main.rs:6:9
  |
6 |     use _::*;
  |         ^ expected identifier, found reserved identifier

error[E0432]: unresolved import `_`
 --> src/main.rs:2:5
  |
2 | use _::*;
  |     ^ use of unresolved module or unlinked crate `_`
  |
  = help: if you wanted to use a crate named `_`, use `cargo add _` to add it to your `Cargo.toml`

error[E0432]: unresolved import `_`
 --> src/main.rs:1:5
  |
1 | use _::a;
  |     ^ use of unresolved module or unlinked crate `_`
  |
  = help: if you wanted to use a crate named `_`, use `cargo add _` to add it to your `Cargo.toml`

error[E0432]: unresolved import `_`
 --> src/main.rs:5:9
  |
5 |     use _::a;
  |         ^ use of unresolved module or unlinked crate `_`
  |
  = help: if you wanted to use a crate named `_`, use `cargo add _` to add it to your `Cargo.toml`

error[E0432]: unresolved import `_`
 --> src/main.rs:6:9
  |
6 |     use _::*;
  |         ^ use of unresolved module or unlinked crate `_`
  |
  = help: if you wanted to use a crate named `_`, use `cargo add _` to add it to your `Cargo.toml`

For more information about this error, try `rustc --explain E0432`.
error: could not compile `playground` (bin "playground") due to 8 previous errors

Standard Output

Desired output

⣿
Errors

Exited with status 101

Standard Error

   Compiling playground v0.0.1 (/playground)
error: expected identifier, found reserved identifier `_`
 --> src/main.rs:1:5
  |
1 | use _::a;
  |     ^ expected identifier, found reserved identifier

error: expected identifier, found reserved identifier `_`
 --> src/main.rs:2:5
  |
2 | use _::*;
  |     ^ expected identifier, found reserved identifier

error: expected identifier, found reserved identifier `_`
 --> src/main.rs:5:9
  |
5 |     use _::a;
  |         ^ expected identifier, found reserved identifier

error: expected identifier, found reserved identifier `_`
 --> src/main.rs:6:9
  |
6 |     use _::*;
  |         ^ expected identifier, found reserved identifier

For more information about this error, try `rustc --explain E0432`.
error: could not compile `playground` (bin "playground") due to 8 previous errors

Standard Output

Rationale and extra context

crates cannot be named _ in Rust. Note this only happens with edition 2018 and beyond.

This was discovered by the ferrocene team while running the test suite with edition 2018, specifically with the test tests/ui/underscore-imports/issue-110164.rs output changing and showing this regression.

Other cases

Rust Version

rustc 1.87.0 (17067e9ac 2025-05-09)
binary: rustc
commit-hash: 17067e9ac6d7ecb70e50f92c1944e545188d2359
commit-date: 2025-05-09
host: x86_64-unknown-linux-gnu
release: 1.87.0
LLVM version: 20.1.1

Anything else?

No response

[JonathanBrouwer]

From what I'm seeing, crates can be named _ in Rust.
This succeeds:

cargo new _
cd _
cargo check

[Veykril]

Oh indeed, you can even specify it as a dependency, but naming that dependency is impossible in Rust. Interesting, well then I am not sure about this, I still think this suggestion is wrong given you cannot name a _ named dependency.