Fix solver-quickcheck failure.

cabal-install/tests/UnitTests/Distribution/Solver/Modular/QuickCheck.hs

@@ -258,11 +258,13 @@ arbitraryExDep db@(TestDb pkgs) level =
   let flag = ExFlag <$> arbitraryFlagName
                     <*> arbitraryDeps db
                     <*> arbitraryDeps db
-      other = [
-            ExAny . unPN <$> elements (map getName pkgs)
-
+      other =
+          -- Package checks require dependencies on "base" to have bounds.
+          let notBase = filter ((/= PN "base") . getName) pkgs
+          in [ExAny . unPN <$> elements (map getName notBase) | not (null notBase)]
+           ++ [
           -- existing version
-          , let fixed pkg = ExFix (unPN $ getName pkg) (unPV $ getVersion pkg)
+            let fixed pkg = ExFix (unPN $ getName pkg) (unPV $ getVersion pkg)
             in fixed <$> elements pkgs
 
           -- random version of an existing package
@@ -332,6 +334,7 @@ instance Arbitrary ExampleDependency where
   arbitrary = error "arbitrary not implemented: ExampleDependency"
 
   shrink (ExAny _) = []
+  shrink p@(ExFix "base" _) = [p] -- preserve bounds on base
   shrink (ExFix pn _) = [ExAny pn]
   shrink (ExFlag flag th el) =
          deps th ++ deps el