error[E0659]: `core` is ambiguous
  --> $DIR/issue-57539.rs:4:9
   |
LL |     use core;
   |         ^^^^ ambiguous name
   |
   = note: ambiguous because of multiple potential import sources
   = note: `core` could refer to a built-in crate
   = help: use `::core` to refer to this crate unambiguously
note: `core` could also refer to the module imported here
  --> $DIR/issue-57539.rs:5:9
   |
LL |     use crate::*;
   |         ^^^^^^^^
   = help: use `self::core` to refer to this module unambiguously

error: aborting due to previous error

For more information about this error, try `rustc --explain E0659`.