ghc panic kindFunResult with template haskell 'isInstance'

--TH.hs

{-# OPTIONS_GHC -Wall #-}
{-# LANGUAGE TemplateHaskell #-}

module TH
       ( SomeClass
       , doThStuff
       ) where

import Control.Monad ( void )
import Language.Haskell.TH

class SomeClass a where

doThStuff :: Name -> Q [Dec]
doThStuff name = reify name >>= go

go :: Info -> Q [Dec]
go (TyConI (DataD [] _ _ [(NormalC _ [(_,typ)])] _)) = do
  void (isInstance ''SomeClass [typ])  -- THIS LINE CRASHES GHC
  return []
go _ = fail "wrong info"

-- Bug.hs

{-# OPTIONS_GHC -Wall #-}
{-# LANGUAGE TemplateHaskell #-}

module Bug
       ( Bar(..)
       ) where

import TH

data Foo a = Foo a
instance SomeClass (Foo a)

data Bar f = Bar (Foo (f Int))
doThStuff ''Bar

I get this error:

$ runghc -ddump-splices Bug.hs 

Bug.hs:1:1:
    Exception when trying to run compile-time code:
      ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.3 for x86_64-unknown-linux):
	kindFunResult

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

    Code: doThStuff ''Bar

If I comment out either instance SomeClass (Foo a) or void (isInstance ''SomeClass [typ]), the crash does not occur.

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
Test case
Differential revisions
BlockedBy
Related
Blocking
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Operating system
Architecture

changed weight to 5

added Tbug TemplateHaskell Trac import labels

closed

This bug is fixed in 8.0.

To make your code work with 8.0, you will have to make the following change to TH.hs (see also wiki:Migration/8.0):

- go (TyConI (DataD [] _ _ [(NormalC _ [(_,typ)])] _)) = do
+ go (TyConI (DataD [] _ _ _ [(NormalC _ [(_,typ)])] _)) = do

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedDuplicate
Related	- → #11694 (closed)

added compiler crash label

added Pnormal label