qapi: leave the ifcond attribute undefined until check()

We commonly initialize attributes to None in .init(), then set their
real value in .check().  Accessing the attribute before .check()
yields None.  If we're lucky, the code that accesses the attribute
prematurely chokes on None.

It won't for .ifcond, because None is a legitimate value.

Leave the ifcond attribute undefined until check().
Suggested-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20180703155648.11933-4-marcandre.lureau@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

scripts/qapi/common.py

@@ -1021,13 +1021,19 @@ class QAPISchemaEntity(object):
         # such place).
         self.info = info
         self.doc = doc
-        self.ifcond = listify_cond(ifcond)
+        self._ifcond = ifcond  # self.ifcond is set only after .check()
 
     def c_name(self):
         return c_name(self.name)
 
     def check(self, schema):
-        pass
+        if isinstance(self._ifcond, QAPISchemaType):
+            # inherit the condition from a type
+            typ = self._ifcond
+            typ.check(schema)
+            self.ifcond = typ.ifcond
+        else:
+            self.ifcond = listify_cond(self._ifcond)
 
     def is_implicit(self):
         return not self.info
@@ -1164,6 +1170,7 @@ class QAPISchemaEnumType(QAPISchemaType):
         self.prefix = prefix
 
     def check(self, schema):
+        QAPISchemaType.check(self, schema)
         seen = {}
         for v in self.values:
             v.check_clash(self.info, seen)
@@ -1196,8 +1203,10 @@ class QAPISchemaArrayType(QAPISchemaType):
         self.element_type = None
 
     def check(self, schema):
+        QAPISchemaType.check(self, schema)
         self.element_type = schema.lookup_type(self._element_type_name)
         assert self.element_type
+        self.element_type.check(schema)
         self.ifcond = self.element_type.ifcond
 
     def is_implicit(self):
@@ -1240,6 +1249,7 @@ class QAPISchemaObjectType(QAPISchemaType):
         self.members = None
 
     def check(self, schema):
+        QAPISchemaType.check(self, schema)
         if self.members is False:               # check for cycles
             raise QAPISemError(self.info,
                                "Object %s contains itself" % self.name)
@@ -1430,6 +1440,7 @@ class QAPISchemaAlternateType(QAPISchemaType):
         self.variants = variants
 
     def check(self, schema):
+        QAPISchemaType.check(self, schema)
         self.variants.tag_member.check(schema)
         # Not calling self.variants.check_clash(), because there's nothing
         # to clash with
@@ -1474,6 +1485,7 @@ class QAPISchemaCommand(QAPISchemaEntity):
         self.allow_preconfig = allow_preconfig
 
     def check(self, schema):
+        QAPISchemaEntity.check(self, schema)
         if self._arg_type_name:
             self.arg_type = schema.lookup_type(self._arg_type_name)
             assert (isinstance(self.arg_type, QAPISchemaObjectType) or
@@ -1509,6 +1521,7 @@ class QAPISchemaEvent(QAPISchemaEntity):
         self.boxed = boxed
 
     def check(self, schema):
+        QAPISchemaEntity.check(self, schema)
         if self._arg_type_name:
             self.arg_type = schema.lookup_type(self._arg_type_name)
             assert (isinstance(self.arg_type, QAPISchemaObjectType) or
@@ -1642,7 +1655,7 @@ class QAPISchema(object):
             # But it's not tight: the disjunction need not imply it.  We
             # may end up compiling useless wrapper types.
             # TODO kill simple unions or implement the disjunction
-            assert ifcond == typ.ifcond
+            assert ifcond == typ._ifcond # pylint: disable=protected-access
         else:
             self._def_entity(QAPISchemaObjectType(name, info, doc, ifcond,
                                                   None, members, None))
@@ -1688,7 +1701,7 @@ class QAPISchema(object):
             assert len(typ) == 1
             typ = self._make_array_type(typ[0], info)
         typ = self._make_implicit_object_type(
-            typ, info, None, self.lookup_type(typ).ifcond,
+            typ, info, None, self.lookup_type(typ),
             'wrapper', [self._make_member('data', typ, info)])
         return QAPISchemaObjectTypeVariant(case, typ)