Oddity with 'cabal install' in GHC 7.4.1

Conal Elliott conal at conal.net
Sun Feb 5 00:36:54 CET 2012

Since upgrading to 7.4.1, if I 'cabal install' successfully and then 'cabal
install' a second time without first doing a 'ghc-pkg unregister
<package-name>', I get the following complaint:

cabal: The install plan contains reinstalls which can break your GHC
> installation. You can try --solver=modular for the new modular solver that
> chooses such reinstalls less often and also offers the --avoid-reinstalls
> option. You can also ghc-pkg unregister the affected packages and run
> ghc-pkg
> check to see the effect on reverse dependencies. If you know what you are
> doing you can use the --force-reinstalls option to override this reinstall
> check.

The only path I've found so far that's willing to rebuild or even say
nothing needs rebuilding (when nothing does) is to 'ghc-pkg unregister' and
then 'cabal install' again. I'm getting the same behavior on Red Hat 5 and
Mac OS 10.6.8, both compiled from sources.

Does anyone know what's going on here?

-- Conal
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