problems building ghc 6.4.1_pre using 6.4 with multiple cabal versions installed

[Duncan Coutts]

All,

With our current 6.4.1 snapshot 20050819, we have problems building when
we've got more than over version of cabal registered.

That is we build it using ghc 6.4 and we have cabal-1.0 and cabal-1.1.2
installed. Then it complains that multiple packages match "-package
cabal".

It also has problems when no version of cabal is registered.

There is no problem building with ghc 6.2.2 with no cabal installed.

I think it would be much more reliable if ghc did not rely on the
version of cabal installed and registered with ghc 6.4. Since it has to
work without cabal anyway (for the 6.2.2 case), wouldn't it be possible
to make it ignore any installed version of cabal even when building with
ghc 6.4?

At the moment, it looks like we're going to have problems on gentoo
upgrading users from ghc 6.4 to 6.4.1. Our current idea is to unregister
the Cabal-1.0 package that ghc 6.4 comes with and use a later version
(Cabal-1.1.2 at the moment) however it's not clear that ghc will cope
with using the later version. We need to install the later version
anyway for other reasons (version 1.0 has bugs and lacks some features
we need for reasonable packaging) and ghc 6.4 does not cope very well
with having multiple versions of a package installed (this is improved
in 6.4.1), hence the rationale for unregistering the 1.0 version
entirely.

Duncan