Rustc behaviour mismatch with method resolution

[philberty]

Tried this test case: https://github.com/rust-lang/rust/blob/aa3ca1994904f2e056679fce1f185db8c7ed2703/src/test/ui/issue-10465.rs

pub mod a {
    pub trait A {
        fn foo(&self);
    }

}
pub mod b {
    use a::A;

    pub struct B;
    impl A for B { fn foo(&self) {} }

    pub mod c {
        use b::B;

        fn foo(b: &B) {
            b.foo(); //~ ERROR: no method named `foo` found
        }
    }

}

fn main() {}

We compile this fine: https://godbolt.org/z/e1c95Gj7e

[philberty]

Is this a valid piece of rust code? Or is gccrs doing dark magic

[flip1995]

The trait A cannot be seen inside of mod c.

error[E0599]: no method named `foo` found for reference `&B` in the current scope
  --> <source>:17:15
   |
17 |             b.foo(); //~ ERROR: no method named `foo` found
   |               ^^^ method not found in `&B`
   |
   = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope; perhaps add a `use` for it:
   |
14 |         use a::A;
   |