Suggest `use self::Thing::OtherThing` when using `use Thing::OtherThing`

[jonas-schievink]

This frequently happens for code like this:

mod m {
    enum MyEnum {
        MyVariant
    }

    // Import all variants:
    use MyEnum::*;
}

fn main() {}

Since this will compile when putting ms contents into the main module, this can be quite confusing (for example when refactoring some code into it's own module).

Currently, this yields error: unresolved import MyEnum::*. Maybe a missing extern crate MyEnum?. When this case is detected, the Maybe a missing extern crate MyEnum? probably shouldn't be printed.

[jseyfried]

cc me

[euclio]

I'd like to work on this.

I'm thinking: if we detect that adding "self" to the import resolves it, then a help message suggesting that is added. Otherwise, we add a help message that suggests extern crate. Does that make sense?

[jseyfried]

@euclio Yeah, that makes sense -- I think that's a good idea.

I would check whether prefixing self fixes the import in finalize_import (resolve_imports.rs).
If resolve_module_path fails, try resolve_module_path_from_root with a root of self.current_module (EDIT: nevermind).
If that succeeds, prefixing self would fix it and you can return Failed(Some(span, "Try prepending self::")).