[Haskell-cafe] Re: unknown flags scramble

Simon Marlow marlowsd at gmail.com
Thu Aug 21 03:52:36 EDT 2008

Evan Laforge wrote:
> I've been getting a mysterious error for a while now.  It's come and
> gone, but seems to be showing up slightly more consistently now.
> Before I was on ghc 6.8.2 and now I'm on ghc 6.8.3, OS X 10.4 and now
> 10.5, i386 arch.  The problem is that randomly while compiling I get
> an error like this:
>     unknown flags in  {-# OPTIONS #-} pragma:
> -XDeriveDataTypeabl<Data/Array/IArray.hs" #<e Ui.Font ( TextStyle(..),
> Font(..), FontFace(..) ) where import qualified Data.Generics as
> <Data/Array/IArray.lhs.L<array-<Color as Color import
> Foreign import qualified Ui.Util as Util {-# LINE 14 "Ui/Font.hsc"
> It looks like somehow pragma parsing gets a bunch of random junk
> scrambled in.  In the past this would happen consistently until I did
> a make clean and rebuild, but more recently all I have to do is try
> again and it doesn't happen the second time.  I haven't gotten it
> while compiling for a while, but since I'm using hint which uses the
> ghc api to interpret haskell, I'm getting this quite frequently inside
> a GhcException when hint wants to interpret some code.  I've also
> gotten this from ghci occasionally, and the usual fix is just to do a
> reload, and the second time it works.
> Does this sound familiar to anyone?  It's not fatal since a retry
> clears things up, but it's a little worrying and would not look very
> good in released software.  I cast about a bit on the ghc trac and
> didn't find any open bugs like this.

This is one symptom of http://hackage.haskell.org/trac/ghc/ticket/1736, 
which turned out to be the same bug as 
http://hackage.haskell.org/trac/ghc/ticket/2240, and haunted us for a long 
time before we found it.

Sadly we found it after the 6.8.3 release, but you could backport the fix 
and build your own 6.8.3 if you are badly affected.


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