[GHC] #13251: Must perform family consistency check on non-imported identifiers

[GHC]

#13251: Must perform family consistency check on non-imported identifiers
-------------------------------------+-------------------------------------
        Reporter:  ezyang            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by rwbarton):

 This plan sounds generally good.

 Nitpick:

 > Less obviously, the use of a wired-in `TyCon` to deal with built-in
 syntax (e.g. overloaded lists) may add a new instance provider that was
 not (transitively) imported. A particular case is `GHC.Exts`.

 The things involved in overloaded lists are `fromListN` and the `IsList`
 type class, both of which are known-key things, not wired-in. (The built-
 in list type is not the issue here.) Then "Tracking instance providers"
 needs to include this case as well.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13251#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler