error[E0583]: file not found for module `missing`
  --> $DIR/foo.rs:3:1
   |
LL | mod missing;
   | ^^^^^^^^^^^^
   |
   = help: to create the module `missing`, create file "$DIR/foo/missing.rs" or "$DIR/foo/missing/mod.rs"
   = note: if there is a `mod missing` elsewhere in the crate already, import it with `use crate::...` instead

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0583`.