Multiple candidate files were found for an out-of-line module.
Erroneous code example:
// file: ambiguous_module/mod.rs
fn foo() {}
// file: ambiguous_module.rs
fn foo() {}
// file: lib.rs
mod ambiguous_module; // error: file for module `ambiguous_module`
// found at both ambiguous_module.rs and
// ambiguous_module.rs/mod.rs
RunPlease remove this ambiguity by deleting/renaming one of the candidate files.