concretizer: get rid of last maximize directive in concretize.lp

- [x] Get rid of forgotten maximize directive.
- [x] Simplify variant handling
- [x] Fix bug in treatment of defaults on externals (don't count
      non-default variants on externals against them)

lib/spack/spack/solver/concretize.lp

@@ -434,20 +434,12 @@ variant_not_default(Package, Variant, Actual, 1)
     not variant_value(Package, Variant, Value),
     variant_default_value(Package, Variant, Value),
     Actual != Value,
+    % variants set explicitly on the CLI don't count as non-default
     not variant_set(Package, Variant, Actual),
-    not external_with_variant_set(Package, Variant, Value),
+    % variants set on externals that we could use don't count as non-default
-    node(Package).
+    % this makes spack prefer to use an external over rebuilding with the
-
+    % default configuration
-% We are using the default value for a variant
+    not external_with_variant_set(Package, Variant, Actual),
-variant_not_default(Package, Variant, Value, 0)
- :- variant_value(Package, Variant, Value),
-    variant_default_value(Package, Variant, Value),
-    node(Package).
-
-% The variant is set in the spec
-variant_not_default(Package, Variant, Value, 0)
- :- variant_value(Package, Variant, Value),
-    variant_set(Package, Variant, Value),
     node(Package).
 
 % The variant is set in an external spec
@@ -458,11 +450,6 @@ external_with_variant_set(Package, Variant, Value)
     external(Package),
     node(Package).
 
-variant_not_default(Package, Variant, Value, 0)
- :- variant_value(Package, Variant, Value),
-    external_with_variant_set(Package, Variant, Value),
-    node(Package).
-
 % The default value for a variant in a package is what is prescribed:
 %
 % 1. On the command line
@@ -864,20 +851,6 @@ opt_criterion(11, "preferred providers for roots").
       build_priority(Provider, Priority)
 }.
 
-% If the value is a multivalued variant there could be multiple
-% values set as default. Since a default value has a weight of 0 we
-% need to maximize their number below to ensure they're all set
-opt_criterion(10, "number of values in multi-valued variants (root)").
-#minimize{ 0@210 : #true }.
-#minimize{ 0@10 : #true }.
-#maximize {
-    1@10+Priority,Package,Variant,Value
-    : variant_not_default(Package, Variant, Value, Weight),
-      not variant_single_value(Package, Variant),
-      root(Package),
-      build_priority(Package, Priority)
-}.
-
 % Try to use default variants or variants that have been set
 opt_criterion(9, "number of non-default variants (non-roots)").
 #minimize{ 0@209: #true }.