[commit: Cabal] master: treat ghc-prim like base as non-upgradeable in modular solver (24c6c70)

[Ian Lynagh]

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

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/24c6c70fef7fb7abb114642d21b9057a5c8e12d6

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

commit 24c6c70fef7fb7abb114642d21b9057a5c8e12d6
Author: Andres Loeh <andres at well-typed.com>
Date:   Tue Oct 25 06:38:20 2011 +0000

    treat ghc-prim like base as non-upgradeable in modular solver

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

 .../Client/Dependency/Modular/Solver.hs            |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/cabal-install/Distribution/Client/Dependency/Modular/Solver.hs b/cabal-install/Distribution/Client/Dependency/Modular/Solver.hs
index 778f706..9ae783b 100644
--- a/cabal-install/Distribution/Client/Dependency/Modular/Solver.hs
+++ b/cabal-install/Distribution/Client/Dependency/Modular/Solver.hs
@@ -46,5 +46,7 @@ solve sc idx userPrefs userConstraints userGoals =
     validationPhase  = P.enforcePackageConstraints userConstraints .
                        validateTree idx
     prunePhase       = (if avoidReinstalls sc then P.avoidReinstalls (const True) else id) .
-                       P.requireInstalled (== PackageName "base") -- never try to install a new "base"
+                       -- packages that can never be "upgraded":
+                       P.requireInstalled (`elem` [PackageName "base",
+                                                   PackageName "ghc-prim"])
     buildPhase       = buildTree idx (independentGoals sc) userGoals