Strange panic when examining interface files

Hi!

This is what happened to me today:
I strolled around the file tree looking for some old code and I found it.
I noticed it was compiled and since there are (at least) six different
versions of ghc lying around here I wanted to know which one this was
compiled with (maybe I was luck and didn't need to recompile it). The
question was ofcourse: How do I find that out?

The answer, once it stuck me, seemed quite obvious: use --show-iface and
the compiler will either show me the interface (I used the compiler with
right version) or will complain and say that it expected number this and
that but found <the number I was looking for>. Sadly, when doing this with
both ghc v6.0 and v6.0.1 I got the following:

ghc-6.0: panic! (the `impossible' happened, GHC version 6.0):
        Ix{Int}.index: Index (16777216) out of range ((0,36))

Please report it as a compiler bug to glasgow-haskell-bugs@xxxxxxxxxxx,
or http://sourceforge.net/projects/ghc/.

ghc 5.04.3 behaved much better:
mismatched interface file versions: expected 5043, found 5040

I'm not sure this can even be classified as a bug but it would be nice if
ghc could tell me the version of the interface. At least it shouldn't
panic.

Cheers,

        /Josef