Constructing a SpecBuildInterface from another gives no inconsistent MRO (#7457)

fixes #7239

lib/spack/llnl/util/lang.py

@@ -458,5 +458,17 @@ class ObjectWrapper(object):
     def __init__(self, wrapped_object):
         wrapped_cls = type(wrapped_object)
         wrapped_name = wrapped_cls.__name__
-        self.__class__ = type(wrapped_name, (type(self), wrapped_cls), {})
+
+        # If the wrapped object is already an ObjectWrapper, or a derived class
+        # of it, adding type(self) in front of type(wrapped_object)
+        # results in an inconsistent MRO.
+        #
+        # TODO: the implementation below doesn't account for the case where we
+        # TODO: have different base classes of ObjectWrapper, say A and B, and
+        # TODO: we want to wrap an instance of A with B.
+        if type(self) not in wrapped_cls.__mro__:
+            self.__class__ = type(wrapped_name, (type(self), wrapped_cls), {})
+        else:
+            self.__class__ = type(wrapped_name, (wrapped_cls,), {})
+
         self.__dict__ = wrapped_object.__dict__

lib/spack/spack/test/concretize.py

@@ -23,8 +23,10 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 import pytest
+import llnl.util.lang
 import spack
 import spack.architecture
+
 from spack.concretize import find_spec
 from spack.spec import Spec, CompilerSpec
 from spack.spec import ConflictsInSpecError, SpecError
@@ -444,3 +446,22 @@ def test_regression_issue_4492(self):
         s._concrete = False
 
         assert not s.concrete
+
+    @pytest.mark.regression('7239')
+    def test_regression_issue_7239(self):
+        # Constructing a SpecBuildInterface from another SpecBuildInterface
+        # results in an inconsistent MRO
+
+        # Normal Spec
+        s = Spec('mpileaks')
+        s.concretize()
+
+        assert llnl.util.lang.ObjectWrapper not in type(s).__mro__
+
+        # Spec wrapped in a build interface
+        build_interface = s['mpileaks']
+        assert llnl.util.lang.ObjectWrapper in type(build_interface).__mro__
+
+        # Mimics asking the build interface from a build interface
+        build_interface = s['mpileaks']['mpileaks']
+        assert llnl.util.lang.ObjectWrapper in type(build_interface).__mro__