[cpyrt] Cache anonymous-enum constant values in CPPDataMember (#94)

dm_get computed the value of an anonymous-enum constant but did not
cache it. kIsEnumPrep is cleared on the first access and kIsEnumType was
never set, so later accesses skipped the enum branch and read the
instance memory at the member's offset instead. Cache the value in
fDescription and set kIsEnumType, as the named-enum path does.

Author: aaronj0

src/cpyrt/CPPDataMember.cxx

@@ -88,9 +88,17 @@ static PyObject* dm_get(CPPDataMember* dm, CPPInstance* pyobj,
     }
 
     if (interop::IsEnumConstant(dm->fScope)) {
-      // anonymous enum
-      return pyval_from_enum(interop::ResolveEnum(dm->fScope), nullptr, nullptr,
-                             dm->fScope);
+      // anonymous enum; cache the value in fDescription like the named case
+      // above: once kIsEnumPrep is cleared this block is not reached again
+      PyObject* pyval = pyval_from_enum(interop::ResolveEnum(dm->fScope),
+                                        nullptr, nullptr, dm->fScope);
+      if (pyval) {
+        Py_DECREF(dm->fDescription);
+        dm->fDescription = pyval;
+        dm->fFlags |= kIsEnumType;
+        Py_INCREF(pyval);
+        return pyval;
+      }
     }
   }
   // non-initialized or public data accesses through class (e.g. by help())

test/test_datatypes.py

@@ -2736,3 +2736,21 @@ def test55_qt_cache_alias_collision(self):
         ns.take_schar("e")
         ns.take_int8(101)
         raises(TypeError, ns.take_int8, "e")
+
+
+class TestANONENUM:
+    def test01_anonymous_enum_repeated_access(self):
+        """An anonymous-enum constant keeps its value across accesses"""
+
+        import cppjit
+
+        cppjit.cppdef("""\
+        namespace AnonEnum { struct Holder { enum { kAnon = 42 }; }; }""")
+
+        h = cppjit.gbl.AnonEnum.Holder()
+
+        # the value is computed on the first access and cached; without the
+        # cache later accesses fall through to the data-member converter
+        assert h.kAnon == 42
+        assert h.kAnon == 42
+        assert h.kAnon == 42