Allow users to supply preferred variants via packages.yaml

lib/spack/spack/concretize.py

@@ -254,13 +254,18 @@ def concretize_architecture(self, spec):
 
     def concretize_variants(self, spec):
         """If the spec already has variants filled in, return.  Otherwise, add
-           the default variants from the package specification.
+           the user preferences from packages.yaml or the default variants from
+           the package specification.
         """
         changed = False
+        preferred_variants = spack.pkgsort.spec_preferred_variants(spec.package_class.name)
         for name, variant in spec.package_class.variants.items():
             if name not in spec.variants:
-                spec.variants[name] = spack.spec.VariantSpec(name, variant.default)
                 changed = True
+                if name in preferred_variants:
+                    spec.variants[name] = preferred_variants.get(name)
+                else:
+                    spec.variants[name] = spack.spec.VariantSpec(name, variant.default)
         return changed
 
 

lib/spack/spack/config.py

@@ -257,7 +257,13 @@
                             'paths': {
                                 'type' : 'object',
                                 'default' : {},
-                            }
+                             },
+                            'variants': {
+                                'oneOf' : [
+                                    { 'type' : 'string' },
+                                    { 'type' : 'array',
+                                      'items' : { 'type' : 'string' } },
+                                    ], },
                         },},},},},},
 
     'modules': {

lib/spack/spack/preferred_packages.py

@@ -158,6 +158,13 @@ def spec_has_preferred_provider(self, pkgname, provider_str):
         return bool(self._order_for_package(pkgname, 'providers',
                     provider_str, False))
 
+    def spec_preferred_variants(self, pkgname):
+        """Return a VariantMap of preferred variants and their values"""
+        variants = self.preferred.get(pkgname, {}).get('variants', '')
+        if not isinstance(variants, basestring):
+            variants = "".join(variants)
+        return spack.spec.Spec(pkgname + variants).variants
+
     def version_compare(self, pkgname, a, b):
         """Return less-than-0, 0, or greater than 0 if version a of pkgname is
            respectively less-than, equal-to, or greater-than version b of