Type is unknown to the importer module with strange workarounds

[wnats]

d.wybe

pub constructor empty 

pub type a is address {}

pub type c is address {}

b.wybe

use d

?b:d= empty:d

Compiling b.wybe yields:

Error detected during type checking of module(s) b
In unification, unknown type d
test/test/b.wybe:3:2: In unification, unknown type d
test/test/b.wybe:3:8: In unification, unknown type d

The issue could be avoided by one of the following:

1. Change the visibility of one of a or c to private
2. Remove one of a or c
3. Rename either a, c or d.

[jimbxb]

I havent yet trawled through the logs, but this is bizarre.

Two things that stick out as really odd are:

• changing the names of the types effects this -- that makes me think there's some caching issue, where some outdated .o file is being used
• the lack of location on the first type error -- I wonder where that is generated, and why it doesn't have a location.

On the lack of location, I believe it should always be possible to get a file-location, which would be nice to have as a fallback when we don't have a location for an error.

[pschachte]

Fixed by #443. Turned out to be a mangled Map that had multiple copies of the same key.