Don't suppress warnings in the presence of errors

Consider this fragment of code (uses injective type families, not yet merged into HEAD):

type family Bar a = r | r -> a where
    Bar Int  = Bool
    Bar Bool = Int
    Bar Bool = Char

bar :: Bar a -> Bar a
bar x = x

barapp :: Char
barapp = bar 'c'

GHC rejects this with an error:

Couldn't match expected type ‘Bar a0’ with actual type ‘Char’
The type variable ‘a0’ is ambiguous
In the first argument of ‘bar’, namely ‘'c'’
In the expression: bar 'c'
In an equation for ‘barapp’: barapp = bar 'c'

The reason why this is rejected is that the last type family equation is not reachable. GHC warns about that if I comment out barapp:

Dropping overlapped type family instance equation:
  Bar Bool = Char

I believe that with that warning source of the error would be easier to find. So I propose that by default GHC does not suppress warnings in the presence of errors.

Trac metadata

Trac field	Value
Version	7.11
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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