Re: [Fedora-haskell-list] Revised Haskell Guidelines 2008.08.13

[Tom Moertel <tmoertel gmail com>]

Jens Petersen wrote:
> I don't quite understand %ghc_preinst_script and %ghc_postun_script: why 
> do we need them?

Here's the rationale for those bits:

http://www.serpentine.com/blog/2007/02/20/haskell-cabal-now-with-extra-crunchy-rpm-goodness/#comment-20132

Quoting:

    Let me point out a wrinkle I encountered when registering
    RPM-installed packages with GHC.  When upgrading an RPM file that
    contains the same Cabal name+version of a package as the
    previously installed version (say with only an RPM release being
    different), the %pre, %post, %preun, and %postun scripts will all
    be asking GHC to register/unregister what it thinks are the same
    library.  As a result, when the %preun script is called, which
    occurs *after* the new package is installed but before the old
    package is removed, its unregister script will actually unregister
    the newly installed library, leaving the new library unregistered
    with GHC.

    To test for the problem, take the existing spec file for an
    already-installed package, bump its RPM release, rebuild the RPMs,
    and then try to upgrade to the new version. After the upgrade, GHC
    will no longer know about the package.

    To avoid this problem, I’ve worked out the following spec-script
    dance...

Cheers,
Tom