Re: repeatable instance of "impossible" error

simonmar:
> On 21 October 2005 07:25, Seth Kurtzberg wrote:
> 
> > I have a case that produces the:
> > 
> > ghc-6.4.1: ghc-6.4.1: panic! (the `impossible' happened, GHC version
> >         6.4.1): unknown exception
> 
> The error message has a bug in it, it should be reporting an unknown
> package.  We fixed the bug in the error message, but you still have an
> unknown package in your build.  Unfortunately we can't easily find out
> which package GHC is looking for, but we could figure it out if you tell
> us what's in your package database and what command-line options you're
> giving to GHC.

Not sure if this is in fact an unknown package, as I'm only able to reproduce
it by installing Cabal-1.1.4 (and I think Seth is using 1.1.3, so 1.1.3 also
breaks the build) -- even though my package space doesn't change.

I've triggered this with both 6.4.1 and 6.5, but only if I use the darcs
version of Cabal.

To reproduce:

* Install hs-plugins and download yi+gtk. To save time we can edit yi's .cabal
file to skip the gtk2hs dependency. Note that the plugins dep is needed to
reproduce the bug (suspicious).

    $ darcs get http://www.cse.unsw.edu.au/~dons/code/hs-plugins
    $ cd hs-plugins
    $ chmod 700 configure
    $ runhaskell Setup.hs configure --prefix=/home/dons
    $ runhaskell Setup.hs build  
    $ runhaskell Setup.hs install

    $ darcs get http://scannedinavian.com/repos/yi  
    $ cd yi
    $ sed 's/\(Build-depends:\).*/\1 base, mtl, plugins/' yi.cabal > yi.cabal.1 
    $ mv yi.cabal.1 yi.cabal
    $ runhaskell Setup.lhs configure 
    $ runhaskell Setup.lhs build     

And it should stop with "Could not find module `Graphics.UI.Gtk'", which is OK
(we removed the gtk dep).  Now, to trigger a panic, install latest Cabal:

    $ darcs get http://cvs.haskell.org/darcs/cabal
    $ cd cabal    
    ... edit GNUMakefile for your environment ...
    $ make
    $ ghc-pkg unregister Cabal-1.0
    $ make install

Now, return to the build of yi:

    $ cd yi
    $ runhaskell Setup.lhs configure
    $ runhaskell Setup.lhs build -v9

    Preprocessing library yi-0.2...
    Preprocessing executables for yi-0.2...
    Building yi-0.2...
    Building library...
    /home/dons/bin/ghc -package-name yi --make -v -cpp -ffi -O 
-funbox-strict-fields -Wall -fglasgow-exts -hide-all-packages -i 
-idist/build/autogen -isrc -odir dist/build -hidir dist/build -package base-1.0 
-package mtl-1.0 -package plugins-0.9.10 Yi Yi.Buffer Yi.Char Yi.Core Yi.DLists 
Yi.Editor Yi.Gtk Yi.GtkBuffer Yi.Lexers Yi.MkTemp Yi.UI Yi.UTF8 Yi.Window 
Yi.Keymap.Ee Yi.Keymap.Emacs Yi.Keymap.Vim Yi.Plugin
    Glasgow Haskell Compiler, Version 6.5, for Haskell 98, compiled by GHC 
version 6.2.2
    Using package config file: /home/dons/lib/ghc-6.5/package.conf
    Using package config file: /home/dons/.ghc/i386-openbsd-6.5/package.conf
    *** Deleting temp files
    Deleting: 
    ghc-6.5: ghc-6.5: panic! (the `impossible' happened, GHC version 6.5):
            unknown exception

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

Typing the above cmd line by hand also causes the panic. What does the package
space look like?

    $ ghc-pkg list
    /home/dons/lib/ghc-6.5/package.conf:
        rts-1.0, base-1.0, haskell98-1.0, template-haskell-1.0, unix-1.0,
        parsec-2.0, haskell-src-1.0, network-1.0, QuickCheck-1.0,
        HUnit-1.1, mtl-1.0, fgl-5.2, X11-1.1, HGL-3.1, OpenGL-2.0, stm-1.0,
        readline-1.0, (lang-1.0), (concurrent-1.0), (posix-1.0),
        (util-1.0), (data-1.0), (text-1.0), (net-1.0), (hssource-1.0),
        (ghc-6.5), glib-0.9.9.6, gtk-0.9.9.6, mogul-0.9.9.6, glade-0.9.9.6,
        gconf-0.9.9.6, sourceview-0.9.9.6, (plugins-0.9.10), Cabal-1.1.4
    /home/dons/.ghc/i386-openbsd-6.5/package.conf:

Hmm, plugins is hidden?

    $ ghc-pkg expose plugins-0.9.10

Try again:    
    $ runhaskell Setup.lhs build    
    Preprocessing library yi-0.2...
    Preprocessing executables for yi-0.2...
    Building yi-0.2...
    ghc-6.5: ghc-6.5: panic! (the `impossible' happened, GHC version 6.5):
        unknown exception

    Please report it as a compiler bug to glasgow-haskell-bugs@xxxxxxxxxxx,
    or http://sourceforge.net/projects/ghc/.
     
What if we re-register Cabal-1.0?
    $ cd ~/src/ghc/cvs/build/libraries/Cabal 
    $ ghc-pkg unregister Cabal-1.1.4         
    $ ghc-pkg register package.conf.installed
   
And then yi builds ok.

-- Don