Inaccessible equations in a closed type family should be a warning, not an error

If I say

foo _     = ()
foo False = ()

I get

/Users/rae/temp/Bug.hs:2:1: Warning:
    Pattern match(es) are overlapped
    In an equation for ‘foo’: foo False = ...

But, if I say

{-# LANGUAGE TypeFamilies #-}

type family Foo a where
  Foo x    = ()
  Foo Bool = ()

I get

/Users/rae/temp/Bug.hs:5:3:
    Inaccessible family instance equation:
      Foo Bool = ()
    In the equations for closed type family ‘Foo’
    In the type family declaration for ‘Foo’

If this issues a warning at the term level, it probably should do the same at the type level.

This was my design decision that I'm changing, and I will fix. The warning will be controlled by the same flag that controls the term-level version.

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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