"Conflicting family instance declarations" error mentions code I did not write

I get an error message mentioning code that I did not write but results from desugaring when compiling the following program:

{-# LANGUAGE TypeFamilies, FlexibleInstances, OverlappingInstances #-}

class Stupid a where
  type F a

instance Stupid a where
  type F a = a

instance Stupid Int where
  type F Int = Bool

The error I get is:

families.hs:7:7:
    Conflicting family instance declarations:
      type instance F a -- Defined at families.hs:7:7
      type instance F Int -- Defined at families.hs:10:7

The error mentions "type instance F a", but it should say "type F a", because that is what I wrote in the source file. Or maybe "type F a in instance Stupid a" to make it clear that it's an instance declaration.

Trac metadata

Trac field	Value
Version	6.12.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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CC	rendel@informatik.uni-marburg.de
Operating system
Architecture