[GHC] #13806: Invalid usage of TypeFamilies cause GHC Internal Error

[GHC]

#13806: Invalid usage of TypeFamilies cause GHC Internal Error
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        Reporter:  utdemir           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by utdemir:

@@ -1,3 +1,3 @@
- I couldn't be able to reproduce this with a valid program, but seeing "GHC
- internal error" was surprising. Only the second error should be enough in
- this case.
+ I couldn't be able to reproduce this with a valid program, but even on an
+ invalid program seeing "GHC internal error" is unexpected. Only the second
+ error should be enough in this case.

New description:

 I couldn't be able to reproduce this with a valid program, but even on an
 invalid program seeing "GHC internal error" is unexpected. Only the second
 error should be enough in this case.

 {{{
 $ cat test.hs
 {-# LANGUAGE TypeFamilies #-}

 data Foo value
   = Foo (T value)

 class Cl t where
   type T
   mk :: t -> T

 main :: IO ()
 main = undefined


 $ runhaskell test.hs

 test.hs:4:10: error:
     • GHC internal error: ‘T’ is not in scope during type checking, but it
 passed the renamer
       tcl_env of environment: [a10K :-> Type variable ‘value’ = value,
                                r10F :-> ATcTyCon Foo, r10G :->
 APromotionErr RecDataConPE]
     • In the type ‘T value’
       In the definition of data constructor ‘Foo’
       In the data declaration for ‘Foo’

 test.hs:6:1: error:
     • The associated type ‘T’
       mentions none of the type or kind variables of the class ‘Cl t’
     • In the class declaration for ‘Cl’


 $ runhaskell --version
 runghc 8.0.2
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13806#comment:1>
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