qapi: Tighten QAPISchemaFOO.check() assertions

When we introduced the QAPISchema intermediate representation (commit
ac88219a6c), we took a shortcut: we left check_exprs() & friends
alone instead of moving semantic checks into the
QAPISchemaFOO.check().  check_exprs() still checks and reports errors,
and the .check() assert check_exprs() did the job.  There are a few
gaps, though.

QAPISchemaArrayType.check() neglects to assert the element type is not
an array.  Add the assertion.

QAPISchemaObjectTypeVariants.check() neglects to assert the tag member
is not optional.  Add the assertion.

It neglects to assert the tag member is not conditional.  Add the
assertion.

It neglects to assert we actually have variants.  Add the assertion.

It asserts the variants are object types, but neglects to assert they
don't have variants.  Tighten the assertion.

QAPISchemaObjectTypeVariants.check_clash() has the same issue.
However, it can run only after .check().  Delete the assertion instead
of tightening it.

QAPISchemaAlternateType.check() neglects to assert the branch types
don't conflict.  Fixing that isn't trivial, so add just a TODO comment
for now.  It'll be resolved later in this series.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190927134639.4284-2-armbru@redhat.com>

scripts/qapi/common.py

@@ -1362,6 +1362,7 @@ class QAPISchemaArrayType(QAPISchemaType):
         QAPISchemaType.check(self, schema)
         self.element_type = schema.lookup_type(self._element_type_name)
         assert self.element_type
+        assert not isinstance(self.element_type, QAPISchemaArrayType)
 
     @property
     def ifcond(self):
@@ -1606,6 +1607,8 @@ class QAPISchemaObjectTypeVariants(object):
             self.tag_member = seen[c_name(self._tag_name)]
             assert self._tag_name == self.tag_member.name
         assert isinstance(self.tag_member.type, QAPISchemaEnumType)
+        assert not self.tag_member.optional
+        assert self.tag_member.ifcond == []
         if self._tag_name:    # flat union
             # branches that are not explicitly covered get an empty type
             cases = set([v.name for v in self.variants])
@@ -1615,20 +1618,21 @@ class QAPISchemaObjectTypeVariants(object):
                                                     m.ifcond)
                     v.set_owner(self.tag_member.owner)
                     self.variants.append(v)
+        assert self.variants
         for v in self.variants:
             v.check(schema)
             # Union names must match enum values; alternate names are
             # checked separately. Use 'seen' to tell the two apart.
             if seen:
                 assert v.name in self.tag_member.type.member_names()
-                assert isinstance(v.type, QAPISchemaObjectType)
+                assert (isinstance(v.type, QAPISchemaObjectType)
+                        and not v.type.variants)
                 v.type.check(schema)
 
     def check_clash(self, info, seen):
         for v in self.variants:
             # Reset seen map for each variant, since qapi names from one
             # branch do not affect another branch
-            assert isinstance(v.type, QAPISchemaObjectType)
             v.type.check_clash(info, dict(seen))
 
 
@@ -1659,6 +1663,7 @@ class QAPISchemaAlternateType(QAPISchemaType):
         seen = {}
         for v in self.variants.variants:
             v.check_clash(self.info, seen)
+            # TODO check conflicting qtypes
             if self.doc:
                 self.doc.connect_member(v)
         if self.doc: