Compiler panic in the presence of cyclic imports

A.hs

module A where

import {-# SOURCE #-} B

data X = X Y

B.hs-boot

module B where

data Y

B.hs

module B where

import A

data Y = Y Int Int

thing :: X -> a
thing (X (Y a b)) = thing (X (Y a b))

C.hs

module C where

import A
import B

panic :: Int -> a
panic x = thing (X (Y x x))

Now try to compile module C:

$ ghc-stage2 -O C
[1 of 4] Compiling B[boot]          ( B.hs-boot, B.o-boot )
[2 of 4] Compiling A                ( A.hs, A.o )
[3 of 4] Compiling B                ( B.hs, B.o )
[4 of 4] Compiling C                ( C.hs, C.o )
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.7.20130826 for x86_64-unknown-linux):
        applyTypeToArgs
    main:B.$wthing{v rsQ} [gid]
      @ a{tv ivX} [tv] ww_iwm{v} [lid] ww_iwn{v} [lid]
    a{tv ivX} [tv]

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

I encountered this bug when attempting to compile GHC with GHC -O2 --make.

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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