GHC crash (panic) with -O2 and nonexistent .hi

[mornfall]

14:13:47 | morn@ald:~/dev/darcs/prims-v3 -> ghc test.hs   
[1 of 1] Compiling Test             ( test.hs, test.o )
14:13:51 | morn@ald:~/dev/darcs/prims-v3 -> ghc -O2 test.hs
14:13:52 | morn@ald:~/dev/darcs/prims-v3 -> rm test.{hi,o} 
14:14:03 | morn@ald:~/dev/darcs/prims-v3 -> ghc -O2 test.hs
[1 of 1] Compiling Test             ( test.hs, test.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.0.3 for i386-unknown-linux):
        funResultTy
    <pred>main:Test.ApplyState{tc rrv} p{tv aBn} [sk]
            ~
          hashed-storage-0.5.7:Storage.Hashed.Tree.Tree{tc r4Y}

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

I am attaching the test.hs that causes this. It needs hashed-storage and mtl from hackage to build, but otherwise it should be fairly minimal. I suppose I could cut it down further to only need mtl, but I already spent an hour tracking this down instead of getting work done. If you do need a further cutdown, let me know though, and I can try.

14:12:26 | morn@ald:~ -> ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.0.3

(GHC installed from Debian packages)

[mornfall]

(sorry about the formatting, but trac won't let me edit it now... let me try again)

14:13:51 | morn@ald:~/dev/darcs/prims-v3 -> ghc -O2 test.hs
14:13:52 | morn@ald:~/dev/darcs/prims-v3 -> rm test.{hi,o} 
14:14:03 | morn@ald:~/dev/darcs/prims-v3 -> ghc -O2 test.hs
[1 of 1] Compiling Test             ( test.hs, test.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.0.3 for i386-unknown-linux):
        funResultTy
    <pred>main:Test.ApplyState{tc rrv} p{tv aBn} [sk]
            ~
          hashed-storage-0.5.7:Storage.Hashed.Tree.Tree{tc r4Y}

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

[simonmar]

confirmed:

$ ghc -O2 5303.hs 
[1 of 1] Compiling Test             ( 5303.hs, 5303.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.0.3 for x86_64-unknown-linux):
        funResultTy
    <pred>main:Test.ApplyState{tc rrv} p{tv aBn} [sk]
            ~
          hashed-storage-0.5.6:Storage.Hashed.Tree.Tree{tc r4V}

unfortunately I can't test with HEAD because hashed-storage doesn't install:

$ cabal install hashed-storage
Resolving dependencies...
cabal: cannot configure dataenc-0.14. It requires base >=3.0.0 && <4.4
For the dependency on base >=3.0.0 && <4.4 there are these packages:
base-3.0.3.1, base-3.0.3.2, base-4.0.0.0, base-4.1.0.0, base-4.2.0.0,
base-4.2.0.1, base-4.2.0.2, base-4.3.0.0 and base-4.3.1.0. However none of
them are available.

[mornfall]

Ok, I distilled the test case further (still crashing for me):

{-# LANGUAGE KindSignatures, GADTs, TypeFamilies, MultiParamTypeClasses, FlexibleContexts, ScopedTypeVariables, TypeSynonymInstances, FlexibleInstances #-}
module Test( showContextSeries ) where

import Control.Monad.State.Strict( StateT )
import Control.Monad.Trans ( lift )

data Tree m = Tree {}

data FL (a :: * -> * -> *) x z where
    (:>:) :: a x y -> FL a y z -> FL a x z
    NilFL :: FL a x x

class (Functor m, Monad m) => ApplyMonad m (state :: (* -> *) -> *)

class Apply (p :: * -> * -> *) where
    type ApplyState p :: (* -> *) -> *
    apply :: ApplyMonad m (ApplyState p) => p x y -> m ()

class (Functor m, Monad m, ApplyMonad (ApplyMonadOver m state) state)
      => ApplyMonadTrans m (state :: (* -> *) -> *) where
  type ApplyMonadOver m state :: * -> *
  runApplyMonad :: (ApplyMonadOver m state) x -> state m -> m (x, state m)

instance (Functor m, Monad m) => ApplyMonadTrans m Tree where
  type ApplyMonadOver m Tree = TreeMonad m
  runApplyMonad = virtualTreeMonad

instance (Functor m, Monad m) => ApplyMonad (TreeMonad m) Tree

-- | Internal state of the 'TreeIO' monad. Keeps track of the current Tree
-- content, unsync'd changes and a current working directory (of the monad).
data TreeState m = TreeState { tree :: !(Tree m) }
type TreeMonad m = StateT (TreeState m) m
type TreeIO = TreeMonad IO

virtualTreeMonad :: (Functor m, Monad m) => TreeMonad m a -> Tree m -> m (a, Tree m)
virtualTreeMonad action t = undefined

applyToState :: forall p m x y. (Apply p, ApplyMonadTrans m (ApplyState p))
             => p x y -> (ApplyState p) m -> m ((ApplyState p) m)
applyToState _ _ = snd `fmap` runApplyMonad undefined undefined

showContextSeries :: (Apply p, ApplyState p ~ Tree) => FL p x y -> TreeIO ()
showContextSeries (p:>:_) = (undefined >>= lift . applyToState p) >> return ()

Still needs MTL, but you could at least in theory get rid of that as well. Whether it is practical, I can't say without trying.

[simonpj]

I believe that, despite the commit message, this patch fixes the bug

commit e91c7ea8afb81f0ed184437f3eef840e5faf047c
Author: Simon Peyton Jones <simonpj@microsoft.com>
Date:   Fri Jul 15 17:14:10 2011 +0100

    A bit more work to to keep the right in-scope set around
    
    This change gets rid of a debug WARNING; it wasn't
    actually making anything go wrong, but it's best to
    have the correct in-scope set.

 compiler/typecheck/TcInstDcls.lhs |    6 ++-
 compiler/types/Coercion.lhs       |   18 +++----
 compiler/types/OptCoercion.lhs    |   98 +++++++++++++++++++------------------
 3 files changed, 61 insertions(+), 61 deletions(-)

I think I just forgot what I had fixed! Anyway, it certainly works now, and I've added a test. Thanks for reporting it.

Pls merge to 7.2

Simon

[igloo]

Merged as changeset:2b6a6e88dfea7aa7f9372683e618ee73d0790c1b.