Rust error E0254: the name `core` is defined multiple times

What rustc prints

error[E0254]: the name `core` is defined multiple times
 --> main.rs:9:5
  |
1 | extern crate core;
  | ------------------ previous import of the extern crate `core` here
...
9 | use foo::core;  // error: an extern crate named `core` has already
  |     ^^^^^^^^^ `core` reimported here
  |
  = note: `core` must be defined only once in the type namespace of this module
help: you can use `as` to change the binding name of the import
  |
9 | use foo::core as other_core;  // error: an extern crate named `core` has already
  |               +++++++++++++

Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.

extern crate core;

mod foo {
    pub trait core {
        fn do_something();
    }
}

use foo::core;  // error: an extern crate named `core` has already
                //        been imported in this module

fn main() {}

extern crate core as libcore; // ok!

mod foo {
    pub trait core {
        fn do_something();
    }
}

use foo::core;

fn main() {}

Related errors

• E0425cannot find value in this scope
• E0603is private
• E0432unresolved import
• E0005refutable pattern in local binding
• E0130patterns aren't allowed in foreign function declarations
• E0252the name `baz` is defined multiple times
• E0255the name `foo` is defined multiple times
• E0259the name `core` is defined multiple times

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