Misleading error message "unresolved import. maybe a missing extern mod extra?"

[SimonSapin]

The following code does not build on Rust 0.7:

mod a {
    extern mod extra;
    use extra::json;
}

fn main() {}

Output:

/tmp/b.rc:4:8: 4:13 error: unresolved import. maybe a missing `extern mod extra`?
/tmp/b.rc:4     use extra::json;
                    ^~~~~
/tmp/b.rc:4:8: 4:19 error: failed to resolve import `extra::json`
/tmp/b.rc:4     use extra::json;
                    ^~~~~~~~~~~
error: aborting due to 2 previous errors

Moving extern mode extra; to the crate top level fixes the issue. The current error message is very confusing at best, especially if the module is a separate .rs file.

Please either change extern mod foo; to work in modules, or make it an error. Don’t ignore it silently.

UPDATE: See comments below.

[SimonSapin]

The weirder part is that stuff from extra can still be used with full names like extra::json::List!

[emberian]

Does use self::extra::json work? Imports are relative to the top of the crate, not the current mod.

[SimonSapin]

@cmr , yes it does work. So the extern mod extra line is not ignored, but I still find the error message on use misleading. I’ll update the issue title.

[emberian]

Dup of #7584, closing.