Type checker hangs

The following program gets GHC stuck in Renamer/typechecker. This compiles correctly in 7.6.3.

{-# LANGUAGE DeriveDataTypeable #-}

module Type.Type where

import Data.Data
import qualified Data.UnionFind.IO as UF

data SrcSpan = Span String | NoSpan String
    deriving (Eq, Ord, Data, Typeable)

data Located e = L SrcSpan e
    deriving (Eq, Ord, Data, Typeable)

Removing either the:

import qualified Data.UnionFind.IO as UF

or

data Located e = L SrcSpan e
    deriving (Eq, Ord, Data, Typeable)

or

Removing the Eq Ord from Located:

data Located e = L SrcSpan e
    deriving (Data, Typeable)

will allow it to terminate.

ddump-tc-trace shows it is related to the derived typeable instance.

The log is attached.

I am compiling with:

arm-apple-darwin10-ghc -staticlib -ddump-tc-trace Type/Type.hs -v -threaded

I don't have a x86 build of HEAD handy, I think if someone could try this program in HEAD then we will know if it is ARM / GHC iOS / stage1 specific or not.

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	MacOS X
Architecture

changed weight to 5

added Tbug Trac import labels

Attached file compile.log (download).

changed milestone to %7.8.1

changed weight to 10

assigned to @trac-dreixel

I can confirm this behavior with a copy of HEAD build from Friday (my HEAD is 7e91e5bf84c2b3f461934b43911c0defb61dd9c6.) This is obviously quite a problem.

José, will you take a look please?

Trac metadata

Trac field	Value
Priority	normal → highest
Operating system	MacOS X → Unknown/Multiple

Here is a smaller testcase. The bug is not related to Typeable.

File A.hs:

module A where

import Data.IORef

data Link a = Link !(IORef (Link a)) | X deriving Eq

File T.hs:

module T where

import A

data Located e = L () e deriving Eq

Run ghc-7.7 -O A.hs and then ghc-7.7 T.hs, the second command should hang.

While investigating this, I also found that compiling this contrived file with HEAD and -O hangs, while 7.6.3 succeeds. However, it is probably a different issue because deriving is not used:

module M where

data Link a = Link !(Link a)

mentioned in commit d3f002cc

mentioned in commit 4db3679c

Ugh. I'm on this.

mentioned in commit cab84ec1

closed

Great catch guys. There were indeed two bugs, both now fixed.

Simon

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	→ simplCore/should_compile/T8221,T8221b

added Phighest label