duplicates:

• SR-4706 Name lookup in nested scopes is too restrictive

Issue Description:

Wording in title perhaps a bit confusing, so here's an example which I'd expect to work:

This works fine, I'm in Top.Middle.Hi and can use Middle however I want:

struct Top {
    struct Middle {
        struct Hi {
            func ret() -> Middle? { return nil }
        }
    }
}

Since the triple nesting gets pretty annoying, I refactor my code into an extension, like so:

extension Top.Middle.Hi {
    func nope() -> Middle? { return nil }
}
error: repl.swift:10:20: error: use of undeclared type 'Middle'
    func nope() -> Middle? { return nil }
                   ^~~~~~

which does not work, as suddenly I can't use Middle.

My current workaround is to define typealiases in the extension so the refactored code can use the short names... I would love to not have to do this. Visibility rules should not really change depending on if I declare the functions in the actual struct or in an extension IMO.

For context: we use nesting a lot for the sake of namespacing, so Top is more like "Namespace" so basically all code of larger modules already starts at one indentation level, then various types need to be in Middle and then have actual implementation specific types inside... This means this nesting pattern is quite common (or we end up polluting library user namespace with "popular names" which we'd like to avoid)