"./Setup.hs configure" does not find older Cabal version when a newer one is installed

[guest]

I tried to configure a package with

  Cabal-Version: >= 1.2 && < 1.3

in its cabal file. "ghc-pkg list" states i have both "Cabal-1.2.4.0" and "Cabal-1.4.0.1" installed. The configuration ("runghc Setup.lhs configure") fails with the following message:

  Warning: grapefruit-frp.cabal: This package requires Cabal version: >=1.2 &&
  <1.3
  Configuring grapefruit-frp-0.0.0.0...
  Error: This package requires Cabal version: >=1.2 && <1.3

After "ghc-pkg unregister Cabal-1.4.0.1" everything works.

(I stumbled upon this trying to compile grapefruit-frp ( http://softbase.org/grapefruit/darcs/main/).)

[duncan]

The problem here is that by the time you're running runghc Setup.hs you've already fixed the version of the Cabal library that you are using and Cabal has no choice in the matter.

This is solved by cabal-install because it is a program and builds Setup.hs using an appropriate version of the Cabal lib.

So I don't think we can really fix it. The workaround is to use cabal-install or runghc -package Cabal-1.2.4.0 Setup.hs.