Multiple different versions note when using main.rs + lib.rs and use crate_name

[Ved-s]

Code

// main.rs

// mentioning `use testing` is important
use testing::{};

struct S1 {}

struct S2 {}

fn main() {
    <S1 as MainTrait>::test();
}

// :Sized + return Self and no Sized and Box<Self> still trigger this
trait MainTrait {
    fn test();
}

impl MainTrait for S2 {
    fn test() {
        todo!()
    }
}

// lib.rs

pub trait LibTrait {}

Current output

Checking testing v0.1.0 (/home/ved-s/code/Rust/testing)
warning: unused import: `testing::{}`
 --> src/main.rs:1:5
  |
1 | use testing::{};
  |     ^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error[E0277]: the trait bound `S1: MainTrait` is not satisfied
  --> src/main.rs:8:6
   |
8  |     <S1 as MainTrait>::test();
   |      ^^ the trait `MainTrait` is not implemented for `S1`
   |
note: there are multiple different versions of crate `testing` in the dependency graph
  --> src/main.rs:12:1
   |
1  | use testing::{};
   |     ------- one version of crate `testing` used here, as a direct dependency of the current crate
2  |
3  | struct S1 {}
   | --------- this type doesn't implement the required trait
...
12 | trait MainTrait {
   | ^^^^^^^^^^^^^^^ this is the required trait
   |
  ::: /home/ved-s/code/Rust/testing/src/lib.rs:1:1
   |
1  | pub trait LibTrait {}
   | ------------------ this is the found trait
   = help: you can use `cargo tree` to explore your dependency tree

For more information about this error, try `rustc --explain E0277`.
warning: `testing` (bin "testing") generated 1 warning
error: could not compile `testing` (bin "testing") due to 1 previous error; 1 warning emitted

Desired output

no `multiple different versions` note and pointing to the first trait in the lib.rs

Rationale and extra context

No response

Other cases

Rust Version

rustc 1.86.0-nightly (854f22563 2025-01-31)
binary: rustc
commit-hash: 854f22563c8daf92709fae18ee6aed52953835cd
commit-date: 2025-01-31
host: x86_64-unknown-linux-gnu
release: 1.86.0-nightly
LLVM version: 19.1.7

Anything else?

No response

[hanna-kruppe]

This does not reproduce 1.83 but does reproduce on 1.84, so it's a stable-to-stable regression. The note about there being multiple crates called testing is technically correct but unhelpful in this case.

Note that the unused import warning can be avoided while still reproducing the regression by writing extern crate testing; instead of use testing::{};.

[Ved-s]

@hanna-kruppe what about it pointing to the first trait in the lib.rs?

   |
1  | pub trait LibTrait {}
   | ------------------ this is the found trait

[Ved-s]

Also i had a compiler panic in the same place in the crate i was making, which then got replaced by this after updating from 1.84 nightly to 1.86 nightly, i can attach a crash log it made if that may be relevant

[hanna-kruppe]

@hanna-kruppe what about it pointing to the first trait in the lib.rs?

   |
1  | pub trait LibTrait {}
   | ------------------ this is the found trait

The full output with 1.83, using main.rs exactly as in the issue except for use -> extern crate, is:

error[E0277]: the trait bound `S1: MainTrait` is not satisfied
 --> src/main.rs:9:6
  |
9 |     <S1 as MainTrait>::test();
  |      ^^ the trait `MainTrait` is not implemented for `S1`
  |
  = help: the trait `MainTrait` is implemented for `S2`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `testing` (bin "testing") due to 1 previous error