Source file that compiled fine no longer compiles after touching it.

In the following session, t.hs first compiles fine, then after being touched, no longer does:

  eelis ~/sand : cat M.hs
  {-# LANGUAGE TypeFamilies #-}
  module M where
  class C a where data D :: * -> *

  eelis ~/sand : cat t.hs
  {-# LANGUAGE TypeFamilies #-}
  import M
  data Bla = Bla
  instance C Bla where data D a = D
  main = return ()

  eelis ~/sand : ghc --make t.hs
  [1 of 2] Compiling M                ( M.hs, M.o )
  [2 of 2] Compiling Main             ( t.hs, t.o )
  Linking t ...

  eelis ~/sand : touch t.hs

  eelis ~/sand : ghc --make t.hs
  [2 of 2] Compiling Main             ( t.hs, t.o )

  t.hs:4:21:
      Type indexes must match class instance head
      Found a but expected Bla
      In the associated type instance for `D'
      In the instance declaration for `C Bla'

It seems to me that t.hs should either compile both times, or not compile at all, but not only part of the time.

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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