[commit: Cabal] master: Don't add installed constraints system packages that are not installed (af47510)

[Ian Lynagh]

Repository : ssh://darcs.haskell.org//srv/darcs/packages/Cabal

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/af47510e62b4cbaa1981accecc59dda71b9a658f

>---------------------------------------------------------------

commit af47510e62b4cbaa1981accecc59dda71b9a658f
Author: Duncan Coutts <duncan at haskell.org>
Date:   Wed Jan 14 14:35:40 2009 +0000

    Don't add installed constraints system packages that are not installed
    In particular fixes a problem (ticket #439) where we required the
    installed version of ghc-prim with compilers that do not have that
    package such as ghc-6.8 and older, hugs, nhc, lhc etc.

>---------------------------------------------------------------

 cabal-install/Distribution/Client/Dependency.hs |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/cabal-install/Distribution/Client/Dependency.hs b/cabal-install/Distribution/Client/Dependency.hs
index 84d9cfe..b5e2710 100644
--- a/cabal-install/Distribution/Client/Dependency.hs
+++ b/cabal-install/Distribution/Client/Dependency.hs
@@ -165,11 +165,11 @@ dependencyResolver resolver platform comp installed available
       -- prevent that from happening accidentally since it is usually not what
       -- you want and it probably does not work anyway. We do it by adding a
       -- constraint to only pick an installed version of base and ghc-prim.
-      extraConstraints
+      extraConstraints =
+        [ PackageInstalledConstraint pkgname
         | all (/=PackageName "base") targets
-        = [ PackageInstalledConstraint (PackageName "base")
-          , PackageInstalledConstraint (PackageName "ghc-prim") ]
-        | otherwise = []
+        , pkgname <-  [ PackageName "base", PackageName "ghc-prim" ]
+        , not (null (PackageIndex.lookupPackageName installed pkgname)) ]
       preferences = interpretPackagesPreference (Set.fromList targets) pref
    in fmap toPlan
     $ resolver platform comp installed' available