Support wild cards in data/type family instances

Handle anonymous wild cards in type or data family instance
declarations like
unnamed type variables. For instance (pun intented):

    type family F (a :: *) (b :: *) :: *
    type instance F Int _ = Int

Is now the same as:

    type family F (a :: *) (b :: *) :: *
    type instance F Int x = Int

Note that unlike wild cards in partial type signatures, no errors (or
warnings
with -XPartialTypeSignatures) are generated for these wild cards, as
there is
nothing interesting to report to the user, i.e. the inferred kind.

Only anonymous wild cards are supported here, named and
extra-constraints wild
card are not.

Test Plan: pass new tests

Reviewers: goldfire, austin, simonpj, bgamari

Reviewed By: simonpj, bgamari

Subscribers: goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D1092

GHC Trac Issues: #3699, #10586

0 files changed, 0 insertions, 0 deletions