[GHC] #11265: Internal error, using pattern synonym as instance head

[GHC]

#11265: Internal error, using pattern synonym as instance head
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by Iceland_jack:

Old description:

> {{{!#hs
> {-# LANGUAGE PatternSynonyms, DataKinds #-}
>
> pattern A = True
>
> class    F a
> instance F A
> }}}
>
> when loaded in ghci it results in an internal error
>
> {{{!#hs
> % g internal.hs
> GHCi, version 7.11.20151216: http://www.haskell.org/ghc/  :? for help
> [1 of 1] Compiling Main             ( internal.hs, interpreted )
>
> internal.hs:5:12: error:
>     • GHC internal error: ‘A’ is not in scope during type checking, but
> it passed the renamer
>       tcl_env of environment: []
>     • In the first argument of ‘F’, namely ‘A’
>       In the instance declaration for ‘F A’
> Failed, modules loaded: none.
> Prelude>
> }}}

New description:

 {{{#!hs
 {-# LANGUAGE PatternSynonyms, DataKinds #-}

 pattern A = True

 class    F a
 instance F A
 }}}

 when loaded in ghci it results in an internal error

 {{{#!hs
 % g internal.hs
 GHCi, version 7.11.20151216: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( internal.hs, interpreted )

 internal.hs:5:12: error:
     • GHC internal error: ‘A’ is not in scope during type checking, but it
 passed the renamer
       tcl_env of environment: []
     • In the first argument of ‘F’, namely ‘A’
       In the instance declaration for ‘F A’
 Failed, modules loaded: none.
 Prelude>
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11265#comment:1>
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