Update error message and comments

Cabal/Distribution/PackageDescription/Configuration.hs

@@ -199,8 +199,9 @@ data BT a = BT a [BT a] -- very simple binary tree
 -- resulting data, the associated dependencies, and the chosen flag
 -- assignments.
 --
--- In case of failure, the _smallest_ number of of missing dependencies is
--- returned. [TODO: Could also be specified with a function argument.]
+-- In case of failure, the union of the dependencies that led to backtracking
+-- on all branches is returned.
+-- [TODO: Could also be specified with a function argument.]
 --
 -- TODO: The current algorithm is rather naive.  A better approach would be to:
 --
@@ -472,9 +473,10 @@ instance Monoid PDTagged where
 --
 -- This function will fail if it cannot find a flag assignment that leads to
 -- satisfiable dependencies.  (It will not try alternative assignments for
--- explicitly specified flags.)  In case of failure it will return a /minimum/
--- number of dependencies that could not be satisfied.  On success, it will
--- return the package description and the full flag assignment chosen.
+-- explicitly specified flags.)  In case of failure it will return the missing
+-- dependencies that it encountered when trying different flag assignments.
+-- On success, it will return the package description and the full flag
+-- assignment chosen.
 --
 finalizePackageDescription ::
      FlagAssignment  -- ^ Explicitly specified flag assignments

Cabal/Distribution/Simple/Configure.hs

@@ -470,7 +470,7 @@ configure (pkg_descr0, pbi) cfg
                        pkg_descr0''
                 of Right r -> return r
                    Left missing ->
-                       die $ "At least one of the following dependencies is missing:\n"
+                       die $ "Encountered missing dependencies:\n"
                          ++ (render . nest 4 . sep . punctuate comma
                                     . map (disp . simplifyDependency)
                                     $ missing)