[commit: Cabal] : Workaround for 'cabal install world' problem with empty world file (076dde2)

[Ian Lynagh]

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

On branch  : 

http://hackage.haskell.org/trac/ghc/changeset/076dde2da0edb983fa7f344ac5dc060f92af29ae

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

commit 076dde2da0edb983fa7f344ac5dc060f92af29ae
Author: Duncan Coutts <duncan at haskell.org>
Date:   Mon May 10 03:30:51 2010 +0000

    Workaround for 'cabal install world' problem with empty world file
    The current dep resolver does not like an empty set of targets
    along with a non-empty set of constraints.

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

 cabal-install/Distribution/Client/Dependency.hs |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/cabal-install/Distribution/Client/Dependency.hs b/cabal-install/Distribution/Client/Dependency.hs
index 8971105..0d74d95 100644
--- a/cabal-install/Distribution/Client/Dependency.hs
+++ b/cabal-install/Distribution/Client/Dependency.hs
@@ -153,7 +153,12 @@ dependencyResolver
   -> [PackageName]
   -> Progress String String InstallPlan
 dependencyResolver resolver platform comp installed available
-                            pref constraints targets =
+                            pref constraints targets
+    -- TODO: the top down resolver chokes on the base constraints
+    -- below when there are no targets and thus no dep on base.
+    -- Need to refactor contraints separate from needing packages.
+  | null targets = return (toPlan [])
+  | otherwise    =
   let installed' = hideBrokenPackages installed
       -- If the user is not explicitly asking to upgrade base then lets
       -- prevent that from happening accidentally since it is usually not what