1 files changed, 34 insertions, 0 deletions
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 46400859d3..88516470fb 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -2893,6 +2893,40 @@ class Spec(object):
         if not_existing:
             raise vt.UnknownVariantError(spec, not_existing)
 
+    def update_variant_validate(self, variant_name, values):
+        """If it is not already there, adds the variant named
+        `variant_name` to the spec `spec` based on the definition
+        contained in the package metadata. Validates the variant and
+        values before returning.
+
+        Used to add values to a variant without being sensitive to the
+        variant being single or multi-valued. If the variant already
+        exists on the spec it is assumed to be multi-valued and the
+        values are appended.
+
+        Args:
+           variant_name: the name of the variant to add or append to
+           values: the value or values (as a tuple) to add/append
+                   to the variant
+        """
+        if not isinstance(values, tuple):
+            values = (values,)
+
+        pkg_variant = self.package_class.variants[variant_name]
+
+        for value in values:
+            if self.variants.get(variant_name):
+                msg = ("Cannot append a value to a single-valued "
+                       "variant with an already set value")
+                assert pkg_variant.multi, msg
+                self.variants[variant_name].append(value)
+            else:
+                variant = pkg_variant.make_variant(value)
+                self.variants[variant_name] = variant
+
+        pkg_variant.validate_or_raise(
+            self.variants[variant_name], self.package)
+
     def constrain(self, other, deps=True):
         """Merge the constraints of other with self.