[commit: Cabal] : When selecting paired packages, select both. (6c2e259)

[Ian Lynagh]

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

On branch  : 

http://hackage.haskell.org/trac/ghc/changeset/6c2e2598d1c17eb9cd74e5ffcaf3751634875e81

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

commit 6c2e2598d1c17eb9cd74e5ffcaf3751634875e81
Author: Duncan Coutts <duncan at haskell.org>
Date:   Sun Oct 5 05:38:04 2008 +0000

    When selecting paired packages, select both.

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

 .../Distribution/Client/Dependency/TopDown.hs      |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/cabal-install/Distribution/Client/Dependency/TopDown.hs b/cabal-install/Distribution/Client/Dependency/TopDown.hs
index 31b4291..cd54be2 100644
--- a/cabal-install/Distribution/Client/Dependency/TopDown.hs
+++ b/cabal-install/Distribution/Client/Dependency/TopDown.hs
@@ -152,7 +152,13 @@ searchSpace configure constraints selected changes next =
             constraints' selected' (newSelected, newDiscarded) next'
         where
           selected' = foldl' (flip PackageIndex.insert) selected newSelected
-          newSelected = [pkg']
+          newSelected =
+            case Constraints.isPaired constraints (packageId pkg) of
+              Nothing     -> [pkg']
+              Just pkgid' -> [pkg', pkg'']
+                where
+                  Just pkg'' = fmap (\(InstalledOnly p) -> InstalledOnly p)
+                    (PackageIndex.lookupPackageId available pkgid')
 
           newPkgs   = [ name'
                       | dep <- packageConstraints pkg'