[Fedora-haskell-list] Revised Haskell Guidelines 2008.08.13

[Tom Moertel]

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