diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
index 67c7d89..4679b1b 100644
--- a/scripts/qapi/introspect.py
+++ b/scripts/qapi/introspect.py
@@ -227,10 +227,14 @@
 
         # Map the various integer types to plain int
         if typ.json_type() == 'int':
-            typ = self._schema.lookup_type('int')
+            type_int = self._schema.lookup_type('int')
+            assert type_int
+            typ = type_int
         elif (isinstance(typ, QAPISchemaArrayType) and
               typ.element_type.json_type() == 'int'):
-            typ = self._schema.lookup_type('intList')
+            type_intList = self._schema.lookup_type('intList')
+            assert type_intList
+            typ = type_intList
         # Add type to work queue if new
         if typ not in self._used_types:
             self._used_types.append(typ)
diff --git a/scripts/qapi/mypy.ini b/scripts/qapi/mypy.ini
index 56e0dfb..8109470 100644
--- a/scripts/qapi/mypy.ini
+++ b/scripts/qapi/mypy.ini
@@ -2,8 +2,3 @@
 strict = True
 disallow_untyped_calls = False
 python_version = 3.8
-
-[mypy-qapi.schema]
-disallow_untyped_defs = False
-disallow_incomplete_defs = False
-check_untyped_defs = False
diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
index d8f7606..7b13a58 100644
--- a/scripts/qapi/parser.py
+++ b/scripts/qapi/parser.py
@@ -19,6 +19,7 @@
 import re
 from typing import (
     TYPE_CHECKING,
+    Any,
     Dict,
     List,
     Mapping,
@@ -43,7 +44,7 @@
 _ExprValue = Union[List[object], Dict[str, object], str, bool]
 
 
-class QAPIExpression(Dict[str, object]):
+class QAPIExpression(Dict[str, Any]):
     # pylint: disable=too-few-public-methods
     def __init__(self,
                  data: Mapping[str, object],
@@ -607,6 +608,7 @@
     """
 
     class Section:
+        # pylint: disable=too-few-public-methods
         def __init__(self, info: QAPISourceInfo,
                      tag: Optional[str] = None):
             # section source info, i.e. where it begins
@@ -705,6 +707,7 @@
 
     def connect_member(self, member: 'QAPISchemaMember') -> None:
         if member.name not in self.args:
+            assert member.info
             if self.symbol not in member.info.pragma.documentation_exceptions:
                 raise QAPISemError(member.info,
                                    "%s '%s' lacks documentation"
@@ -733,7 +736,7 @@
                     "'Returns' section is only valid for commands")
             if self.errors:
                 raise QAPISemError(
-                    self.returns.info,
+                    self.errors.info,
                     "'Errors' section is only valid for commands")
 
     def check(self) -> None:
diff --git a/scripts/qapi/pylintrc b/scripts/qapi/pylintrc
index 90546df..c028a1f 100644
--- a/scripts/qapi/pylintrc
+++ b/scripts/qapi/pylintrc
@@ -1,10 +1,5 @@
 [MASTER]
 
-# Add files or directories matching the regex patterns to the ignore list.
-# The regex matches against base names, not paths.
-ignore-patterns=schema.py,
-
-
 [MESSAGES CONTROL]
 
 # Disable the message, report, category or checker with the given id(s). You
@@ -16,13 +11,13 @@
 # --enable=similarities". If you want to run only the classes checker, but have
 # no Warning level messages displayed, use "--disable=all --enable=classes
 # --disable=W".
-disable=fixme,
+disable=consider-using-f-string,
+        fixme,
         missing-docstring,
         too-many-arguments,
         too-many-branches,
-        too-many-statements,
         too-many-instance-attributes,
-        consider-using-f-string,
+        too-many-statements,
         useless-option-value,
 
 [REPORTS]
diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 8ba5665..5924947 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -12,12 +12,25 @@
 # This work is licensed under the terms of the GNU GPL, version 2.
 # See the COPYING file in the top-level directory.
 
+# pylint: disable=too-many-lines
+
 # TODO catching name collisions in generated code would be nice
 
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
 from collections import OrderedDict
 import os
 import re
-from typing import List, Optional
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    List,
+    Optional,
+    Union,
+    cast,
+)
 
 from .common import (
     POINTER_SUFFIX,
@@ -29,140 +42,230 @@
 )
 from .error import QAPIError, QAPISemError, QAPISourceError
 from .expr import check_exprs
-from .parser import QAPIExpression, QAPISchemaParser
+from .parser import QAPIDoc, QAPIExpression, QAPISchemaParser
+from .source import QAPISourceInfo
 
 
 class QAPISchemaIfCond:
-    def __init__(self, ifcond=None):
+    def __init__(
+        self,
+        ifcond: Optional[Union[str, Dict[str, object]]] = None,
+    ) -> None:
         self.ifcond = ifcond
 
-    def _cgen(self):
+    def _cgen(self) -> str:
         return cgen_ifcond(self.ifcond)
 
-    def gen_if(self):
+    def gen_if(self) -> str:
         return gen_if(self._cgen())
 
-    def gen_endif(self):
+    def gen_endif(self) -> str:
         return gen_endif(self._cgen())
 
-    def docgen(self):
+    def docgen(self) -> str:
         return docgen_ifcond(self.ifcond)
 
-    def is_present(self):
+    def is_present(self) -> bool:
         return bool(self.ifcond)
 
 
 class QAPISchemaEntity:
-    meta: Optional[str] = None
+    """
+    A schema entity.
 
-    def __init__(self, name: str, info, doc, ifcond=None, features=None):
-        assert name is None or isinstance(name, str)
-        for f in features or []:
-            assert isinstance(f, QAPISchemaFeature)
-            f.set_defined_in(name)
-        self.name = name
-        self._module = None
+    This is either a directive, such as include, or a definition.
+    The latter uses sub-class `QAPISchemaDefinition`.
+    """
+    def __init__(self, info: Optional[QAPISourceInfo]):
+        self._module: Optional[QAPISchemaModule] = None
         # For explicitly defined entities, info points to the (explicit)
         # definition.  For builtins (and their arrays), info is None.
         # For implicitly defined entities, info points to a place that
         # triggered the implicit definition (there may be more than one
         # such place).
         self.info = info
-        self.doc = doc
-        self._ifcond = ifcond or QAPISchemaIfCond()
-        self.features = features or []
         self._checked = False
 
-    def __repr__(self):
-        if self.name is None:
-            return "<%s at 0x%x>" % (type(self).__name__, id(self))
-        return "<%s:%s at 0x%x>" % (type(self).__name__, self.name,
-                                    id(self))
+    def __repr__(self) -> str:
+        return "<%s at 0x%x>" % (type(self).__name__, id(self))
 
-    def c_name(self):
-        return c_name(self.name)
-
-    def check(self, schema):
-        assert not self._checked
-        seen = {}
-        for f in self.features:
-            f.check_clash(self.info, seen)
+    def check(self, schema: QAPISchema) -> None:
+        # pylint: disable=unused-argument
         self._checked = True
 
-    def connect_doc(self, doc=None):
-        doc = doc or self.doc
-        if doc:
-            for f in self.features:
-                doc.connect_feature(f)
+    def connect_doc(self, doc: Optional[QAPIDoc] = None) -> None:
+        pass
 
-    def _set_module(self, schema, info):
+    def _set_module(
+        self, schema: QAPISchema, info: Optional[QAPISourceInfo]
+    ) -> None:
         assert self._checked
         fname = info.fname if info else QAPISchemaModule.BUILTIN_MODULE_NAME
         self._module = schema.module_by_fname(fname)
         self._module.add_entity(self)
 
-    def set_module(self, schema):
+    def set_module(self, schema: QAPISchema) -> None:
         self._set_module(schema, self.info)
 
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
+        # pylint: disable=unused-argument
+        assert self._checked
+
+
+class QAPISchemaDefinition(QAPISchemaEntity):
+    meta: str
+
+    def __init__(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        doc: Optional[QAPIDoc],
+        ifcond: Optional[QAPISchemaIfCond] = None,
+        features: Optional[List[QAPISchemaFeature]] = None,
+    ):
+        super().__init__(info)
+        for f in features or []:
+            f.set_defined_in(name)
+        self.name = name
+        self.doc = doc
+        self._ifcond = ifcond or QAPISchemaIfCond()
+        self.features = features or []
+
+    def __repr__(self) -> str:
+        return "<%s:%s at 0x%x>" % (type(self).__name__, self.name,
+                                    id(self))
+
+    def c_name(self) -> str:
+        return c_name(self.name)
+
+    def check(self, schema: QAPISchema) -> None:
+        assert not self._checked
+        super().check(schema)
+        seen: Dict[str, QAPISchemaMember] = {}
+        for f in self.features:
+            f.check_clash(self.info, seen)
+
+    def connect_doc(self, doc: Optional[QAPIDoc] = None) -> None:
+        super().connect_doc(doc)
+        doc = doc or self.doc
+        if doc:
+            for f in self.features:
+                doc.connect_feature(f)
+
     @property
-    def ifcond(self):
+    def ifcond(self) -> QAPISchemaIfCond:
         assert self._checked
         return self._ifcond
 
-    def is_implicit(self):
+    def is_implicit(self) -> bool:
         return not self.info
 
-    def visit(self, visitor):
-        assert self._checked
-
-    def describe(self):
-        assert self.meta
+    def describe(self) -> str:
         return "%s '%s'" % (self.meta, self.name)
 
 
 class QAPISchemaVisitor:
-    def visit_begin(self, schema):
+    def visit_begin(self, schema: QAPISchema) -> None:
         pass
 
-    def visit_end(self):
+    def visit_end(self) -> None:
         pass
 
-    def visit_module(self, name):
+    def visit_module(self, name: str) -> None:
         pass
 
-    def visit_needed(self, entity):
+    def visit_needed(self, entity: QAPISchemaEntity) -> bool:
+        # pylint: disable=unused-argument
         # Default to visiting everything
         return True
 
-    def visit_include(self, name, info):
+    def visit_include(self, name: str, info: Optional[QAPISourceInfo]) -> None:
         pass
 
-    def visit_builtin_type(self, name, info, json_type):
+    def visit_builtin_type(
+        self, name: str, info: Optional[QAPISourceInfo], json_type: str
+    ) -> None:
         pass
 
-    def visit_enum_type(self, name, info, ifcond, features, members, prefix):
+    def visit_enum_type(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: QAPISchemaIfCond,
+        features: List[QAPISchemaFeature],
+        members: List[QAPISchemaEnumMember],
+        prefix: Optional[str],
+    ) -> None:
         pass
 
-    def visit_array_type(self, name, info, ifcond, element_type):
+    def visit_array_type(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: QAPISchemaIfCond,
+        element_type: QAPISchemaType,
+    ) -> None:
         pass
 
-    def visit_object_type(self, name, info, ifcond, features,
-                          base, members, variants):
+    def visit_object_type(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: QAPISchemaIfCond,
+        features: List[QAPISchemaFeature],
+        base: Optional[QAPISchemaObjectType],
+        members: List[QAPISchemaObjectTypeMember],
+        variants: Optional[QAPISchemaVariants],
+    ) -> None:
         pass
 
-    def visit_object_type_flat(self, name, info, ifcond, features,
-                               members, variants):
+    def visit_object_type_flat(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: QAPISchemaIfCond,
+        features: List[QAPISchemaFeature],
+        members: List[QAPISchemaObjectTypeMember],
+        variants: Optional[QAPISchemaVariants],
+    ) -> None:
         pass
 
-    def visit_alternate_type(self, name, info, ifcond, features, variants):
+    def visit_alternate_type(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: QAPISchemaIfCond,
+        features: List[QAPISchemaFeature],
+        variants: QAPISchemaVariants,
+    ) -> None:
         pass
 
-    def visit_command(self, name, info, ifcond, features,
-                      arg_type, ret_type, gen, success_response, boxed,
-                      allow_oob, allow_preconfig, coroutine):
+    def visit_command(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: QAPISchemaIfCond,
+        features: List[QAPISchemaFeature],
+        arg_type: Optional[QAPISchemaObjectType],
+        ret_type: Optional[QAPISchemaType],
+        gen: bool,
+        success_response: bool,
+        boxed: bool,
+        allow_oob: bool,
+        allow_preconfig: bool,
+        coroutine: bool,
+    ) -> None:
         pass
 
-    def visit_event(self, name, info, ifcond, features, arg_type, boxed):
+    def visit_event(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: QAPISchemaIfCond,
+        features: List[QAPISchemaFeature],
+        arg_type: Optional[QAPISchemaObjectType],
+        boxed: bool,
+    ) -> None:
         pass
 
 
@@ -170,9 +273,9 @@
 
     BUILTIN_MODULE_NAME = './builtin'
 
-    def __init__(self, name):
+    def __init__(self, name: str):
         self.name = name
-        self._entity_list = []
+        self._entity_list: List[QAPISchemaEntity] = []
 
     @staticmethod
     def is_system_module(name: str) -> bool:
@@ -201,10 +304,10 @@
         """
         return name == cls.BUILTIN_MODULE_NAME
 
-    def add_entity(self, ent):
+    def add_entity(self, ent: QAPISchemaEntity) -> None:
         self._entity_list.append(ent)
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         visitor.visit_module(self.name)
         for entity in self._entity_list:
             if visitor.visit_needed(entity):
@@ -212,33 +315,35 @@
 
 
 class QAPISchemaInclude(QAPISchemaEntity):
-    def __init__(self, sub_module, info):
-        super().__init__(None, info, None)
+    def __init__(self, sub_module: QAPISchemaModule, info: QAPISourceInfo):
+        super().__init__(info)
         self._sub_module = sub_module
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_include(self._sub_module.name, self.info)
 
 
-class QAPISchemaType(QAPISchemaEntity):
+class QAPISchemaType(QAPISchemaDefinition, ABC):
     # Return the C type for common use.
     # For the types we commonly box, this is a pointer type.
-    def c_type(self):
+    @abstractmethod
+    def c_type(self) -> str:
         pass
 
     # Return the C type to be used in a parameter list.
-    def c_param_type(self):
+    def c_param_type(self) -> str:
         return self.c_type()
 
     # Return the C type to be used where we suppress boxing.
-    def c_unboxed_type(self):
+    def c_unboxed_type(self) -> str:
         return self.c_type()
 
-    def json_type(self):
+    @abstractmethod
+    def json_type(self) -> str:
         pass
 
-    def alternate_qtype(self):
+    def alternate_qtype(self) -> Optional[str]:
         json2qtype = {
             'null':    'QTYPE_QNULL',
             'string':  'QTYPE_QSTRING',
@@ -250,17 +355,17 @@
         }
         return json2qtype.get(self.json_type())
 
-    def doc_type(self):
+    def doc_type(self) -> Optional[str]:
         if self.is_implicit():
             return None
         return self.name
 
-    def need_has_if_optional(self):
+    def need_has_if_optional(self) -> bool:
         # When FOO is a pointer, has_FOO == !!FOO, i.e. has_FOO is redundant.
         # Except for arrays; see QAPISchemaArrayType.need_has_if_optional().
         return not self.c_type().endswith(POINTER_SUFFIX)
 
-    def check(self, schema):
+    def check(self, schema: QAPISchema) -> None:
         super().check(schema)
         for feat in self.features:
             if feat.is_special():
@@ -268,40 +373,38 @@
                     self.info,
                     f"feature '{feat.name}' is not supported for types")
 
-    def describe(self):
-        assert self.meta
+    def describe(self) -> str:
         return "%s type '%s'" % (self.meta, self.name)
 
 
 class QAPISchemaBuiltinType(QAPISchemaType):
     meta = 'built-in'
 
-    def __init__(self, name, json_type, c_type):
+    def __init__(self, name: str, json_type: str, c_type: str):
         super().__init__(name, None, None)
-        assert not c_type or isinstance(c_type, str)
         assert json_type in ('string', 'number', 'int', 'boolean', 'null',
                              'value')
         self._json_type_name = json_type
         self._c_type_name = c_type
 
-    def c_name(self):
+    def c_name(self) -> str:
         return self.name
 
-    def c_type(self):
+    def c_type(self) -> str:
         return self._c_type_name
 
-    def c_param_type(self):
+    def c_param_type(self) -> str:
         if self.name == 'str':
             return 'const ' + self._c_type_name
         return self._c_type_name
 
-    def json_type(self):
+    def json_type(self) -> str:
         return self._json_type_name
 
-    def doc_type(self):
+    def doc_type(self) -> str:
         return self.json_type()
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_builtin_type(self.name, self.info, self.json_type())
 
@@ -309,41 +412,48 @@
 class QAPISchemaEnumType(QAPISchemaType):
     meta = 'enum'
 
-    def __init__(self, name, info, doc, ifcond, features, members, prefix):
+    def __init__(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        doc: Optional[QAPIDoc],
+        ifcond: Optional[QAPISchemaIfCond],
+        features: Optional[List[QAPISchemaFeature]],
+        members: List[QAPISchemaEnumMember],
+        prefix: Optional[str],
+    ):
         super().__init__(name, info, doc, ifcond, features)
         for m in members:
-            assert isinstance(m, QAPISchemaEnumMember)
             m.set_defined_in(name)
-        assert prefix is None or isinstance(prefix, str)
         self.members = members
         self.prefix = prefix
 
-    def check(self, schema):
+    def check(self, schema: QAPISchema) -> None:
         super().check(schema)
-        seen = {}
+        seen: Dict[str, QAPISchemaMember] = {}
         for m in self.members:
             m.check_clash(self.info, seen)
 
-    def connect_doc(self, doc=None):
+    def connect_doc(self, doc: Optional[QAPIDoc] = None) -> None:
         super().connect_doc(doc)
         doc = doc or self.doc
         for m in self.members:
             m.connect_doc(doc)
 
-    def is_implicit(self):
+    def is_implicit(self) -> bool:
         # See QAPISchema._def_predefineds()
         return self.name == 'QType'
 
-    def c_type(self):
+    def c_type(self) -> str:
         return c_name(self.name)
 
-    def member_names(self):
+    def member_names(self) -> List[str]:
         return [m.name for m in self.members]
 
-    def json_type(self):
+    def json_type(self) -> str:
         return 'string'
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_enum_type(
             self.name, self.info, self.ifcond, self.features,
@@ -353,82 +463,89 @@
 class QAPISchemaArrayType(QAPISchemaType):
     meta = 'array'
 
-    def __init__(self, name, info, element_type):
+    def __init__(
+        self, name: str, info: Optional[QAPISourceInfo], element_type: str
+    ):
         super().__init__(name, info, None)
-        assert isinstance(element_type, str)
         self._element_type_name = element_type
-        self.element_type = None
+        self.element_type: QAPISchemaType
 
-    def need_has_if_optional(self):
+    def need_has_if_optional(self) -> bool:
         # When FOO is an array, we still need has_FOO to distinguish
         # absent (!has_FOO) from present and empty (has_FOO && !FOO).
         return True
 
-    def check(self, schema):
+    def check(self, schema: QAPISchema) -> None:
         super().check(schema)
         self.element_type = schema.resolve_type(
             self._element_type_name, self.info,
-            self.info and self.info.defn_meta)
+            self.info.defn_meta if self.info else None)
         assert not isinstance(self.element_type, QAPISchemaArrayType)
 
-    def set_module(self, schema):
+    def set_module(self, schema: QAPISchema) -> None:
         self._set_module(schema, self.element_type.info)
 
     @property
-    def ifcond(self):
+    def ifcond(self) -> QAPISchemaIfCond:
         assert self._checked
         return self.element_type.ifcond
 
-    def is_implicit(self):
+    def is_implicit(self) -> bool:
         return True
 
-    def c_type(self):
+    def c_type(self) -> str:
         return c_name(self.name) + POINTER_SUFFIX
 
-    def json_type(self):
+    def json_type(self) -> str:
         return 'array'
 
-    def doc_type(self):
+    def doc_type(self) -> Optional[str]:
         elt_doc_type = self.element_type.doc_type()
         if not elt_doc_type:
             return None
         return 'array of ' + elt_doc_type
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_array_type(self.name, self.info, self.ifcond,
                                  self.element_type)
 
-    def describe(self):
-        assert self.meta
+    def describe(self) -> str:
         return "%s type ['%s']" % (self.meta, self._element_type_name)
 
 
 class QAPISchemaObjectType(QAPISchemaType):
-    def __init__(self, name, info, doc, ifcond, features,
-                 base, local_members, variants):
+    def __init__(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        doc: Optional[QAPIDoc],
+        ifcond: Optional[QAPISchemaIfCond],
+        features: Optional[List[QAPISchemaFeature]],
+        base: Optional[str],
+        local_members: List[QAPISchemaObjectTypeMember],
+        variants: Optional[QAPISchemaVariants],
+    ):
         # struct has local_members, optional base, and no variants
         # union has base, variants, and no local_members
         super().__init__(name, info, doc, ifcond, features)
         self.meta = 'union' if variants else 'struct'
-        assert base is None or isinstance(base, str)
         for m in local_members:
-            assert isinstance(m, QAPISchemaObjectTypeMember)
             m.set_defined_in(name)
         if variants is not None:
-            assert isinstance(variants, QAPISchemaVariants)
             variants.set_defined_in(name)
         self._base_name = base
         self.base = None
         self.local_members = local_members
         self.variants = variants
-        self.members = None
+        self.members: List[QAPISchemaObjectTypeMember]
+        self._check_complete = False
 
-    def check(self, schema):
+    def check(self, schema: QAPISchema) -> None:
         # This calls another type T's .check() exactly when the C
         # struct emitted by gen_object() contains that T's C struct
         # (pointers don't count).
-        if self.members is not None:
+        if self._check_complete:
             # A previous .check() completed: nothing to do
             return
         if self._checked:
@@ -437,7 +554,7 @@
                                "object %s contains itself" % self.name)
 
         super().check(schema)
-        assert self._checked and self.members is None
+        assert self._checked and not self._check_complete
 
         seen = OrderedDict()
         if self._base_name:
@@ -454,25 +571,34 @@
         for m in self.local_members:
             m.check(schema)
             m.check_clash(self.info, seen)
-        members = seen.values()
+
+        # self.check_clash() works in terms of the supertype, but
+        # self.members is declared List[QAPISchemaObjectTypeMember].
+        # Cast down to the subtype.
+        members = cast(List[QAPISchemaObjectTypeMember], list(seen.values()))
 
         if self.variants:
             self.variants.check(schema, seen)
             self.variants.check_clash(self.info, seen)
 
-        self.members = members  # mark completed
+        self.members = members
+        self._check_complete = True  # mark completed
 
     # Check that the members of this type do not cause duplicate JSON members,
     # and update seen to track the members seen so far. Report any errors
     # on behalf of info, which is not necessarily self.info
-    def check_clash(self, info, seen):
+    def check_clash(
+        self,
+        info: Optional[QAPISourceInfo],
+        seen: Dict[str, QAPISchemaMember],
+    ) -> None:
         assert self._checked
         for m in self.members:
             m.check_clash(info, seen)
         if self.variants:
             self.variants.check_clash(info, seen)
 
-    def connect_doc(self, doc=None):
+    def connect_doc(self, doc: Optional[QAPIDoc] = None) -> None:
         super().connect_doc(doc)
         doc = doc or self.doc
         if self.base and self.base.is_implicit():
@@ -480,34 +606,32 @@
         for m in self.local_members:
             m.connect_doc(doc)
 
-    def is_implicit(self):
+    def is_implicit(self) -> bool:
         # See QAPISchema._make_implicit_object_type(), as well as
         # _def_predefineds()
         return self.name.startswith('q_')
 
-    def is_empty(self):
-        assert self.members is not None
+    def is_empty(self) -> bool:
         return not self.members and not self.variants
 
-    def has_conditional_members(self):
-        assert self.members is not None
+    def has_conditional_members(self) -> bool:
         return any(m.ifcond.is_present() for m in self.members)
 
-    def c_name(self):
+    def c_name(self) -> str:
         assert self.name != 'q_empty'
         return super().c_name()
 
-    def c_type(self):
+    def c_type(self) -> str:
         assert not self.is_implicit()
         return c_name(self.name) + POINTER_SUFFIX
 
-    def c_unboxed_type(self):
+    def c_unboxed_type(self) -> str:
         return c_name(self.name)
 
-    def json_type(self):
+    def json_type(self) -> str:
         return 'object'
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_object_type(
             self.name, self.info, self.ifcond, self.features,
@@ -520,15 +644,22 @@
 class QAPISchemaAlternateType(QAPISchemaType):
     meta = 'alternate'
 
-    def __init__(self, name, info, doc, ifcond, features, variants):
+    def __init__(
+        self,
+        name: str,
+        info: QAPISourceInfo,
+        doc: Optional[QAPIDoc],
+        ifcond: Optional[QAPISchemaIfCond],
+        features: List[QAPISchemaFeature],
+        variants: QAPISchemaVariants,
+    ):
         super().__init__(name, info, doc, ifcond, features)
-        assert isinstance(variants, QAPISchemaVariants)
         assert variants.tag_member
         variants.set_defined_in(name)
         variants.tag_member.set_defined_in(self.name)
         self.variants = variants
 
-    def check(self, schema):
+    def check(self, schema: QAPISchema) -> None:
         super().check(schema)
         self.variants.tag_member.check(schema)
         # Not calling self.variants.check_clash(), because there's nothing
@@ -536,8 +667,8 @@
         self.variants.check(schema, {})
         # Alternate branch names have no relation to the tag enum values;
         # so we have to check for potential name collisions ourselves.
-        seen = {}
-        types_seen = {}
+        seen: Dict[str, QAPISchemaMember] = {}
+        types_seen: Dict[str, str] = {}
         for v in self.variants.variants:
             v.check_clash(self.info, seen)
             qtype = v.type.alternate_qtype()
@@ -566,55 +697,75 @@
                         % (v.describe(self.info), types_seen[qt]))
                 types_seen[qt] = v.name
 
-    def connect_doc(self, doc=None):
+    def connect_doc(self, doc: Optional[QAPIDoc] = None) -> None:
         super().connect_doc(doc)
         doc = doc or self.doc
         for v in self.variants.variants:
             v.connect_doc(doc)
 
-    def c_type(self):
+    def c_type(self) -> str:
         return c_name(self.name) + POINTER_SUFFIX
 
-    def json_type(self):
+    def json_type(self) -> str:
         return 'value'
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_alternate_type(
             self.name, self.info, self.ifcond, self.features, self.variants)
 
 
 class QAPISchemaVariants:
-    def __init__(self, tag_name, info, tag_member, variants):
+    def __init__(
+        self,
+        tag_name: Optional[str],
+        info: QAPISourceInfo,
+        tag_member: Optional[QAPISchemaObjectTypeMember],
+        variants: List[QAPISchemaVariant],
+    ):
         # Unions pass tag_name but not tag_member.
         # Alternates pass tag_member but not tag_name.
         # After check(), tag_member is always set.
         assert bool(tag_member) != bool(tag_name)
         assert (isinstance(tag_name, str) or
                 isinstance(tag_member, QAPISchemaObjectTypeMember))
-        for v in variants:
-            assert isinstance(v, QAPISchemaVariant)
         self._tag_name = tag_name
         self.info = info
-        self.tag_member = tag_member
+        self._tag_member = tag_member
         self.variants = variants
 
-    def set_defined_in(self, name):
+    @property
+    def tag_member(self) -> QAPISchemaObjectTypeMember:
+        if self._tag_member is None:
+            raise RuntimeError(
+                "QAPISchemaVariants has no tag_member property until "
+                "after check() has been run."
+            )
+        return self._tag_member
+
+    def set_defined_in(self, name: str) -> None:
         for v in self.variants:
             v.set_defined_in(name)
 
-    def check(self, schema, seen):
+    def check(
+        self, schema: QAPISchema, seen: Dict[str, QAPISchemaMember]
+    ) -> None:
         if self._tag_name:      # union
-            self.tag_member = seen.get(c_name(self._tag_name))
+            # We need to narrow the member type:
+            tmp = seen.get(c_name(self._tag_name))
+            assert tmp is None or isinstance(tmp, QAPISchemaObjectTypeMember)
+            self._tag_member = tmp
+
             base = "'base'"
             # Pointing to the base type when not implicit would be
             # nice, but we don't know it here
-            if not self.tag_member or self._tag_name != self.tag_member.name:
+            if not self._tag_member or self._tag_name != self._tag_member.name:
                 raise QAPISemError(
                     self.info,
                     "discriminator '%s' is not a member of %s"
                     % (self._tag_name, base))
             # Here we do:
+            assert self.tag_member.defined_in
             base_type = schema.lookup_type(self.tag_member.defined_in)
             assert base_type
             if not base_type.is_implicit():
@@ -635,11 +786,13 @@
                     "discriminator member '%s' of %s must not be conditional"
                     % (self._tag_name, base))
         else:                   # alternate
+            assert self._tag_member
             assert isinstance(self.tag_member.type, QAPISchemaEnumType)
             assert not self.tag_member.optional
             assert not self.tag_member.ifcond.is_present()
         if self._tag_name:      # union
             # branches that are not explicitly covered get an empty type
+            assert self.tag_member.defined_in
             cases = {v.name for v in self.variants}
             for m in self.tag_member.type.members:
                 if m.name not in cases:
@@ -666,10 +819,17 @@
                         % (v.describe(self.info), v.type.describe()))
                 v.type.check(schema)
 
-    def check_clash(self, info, seen):
+    def check_clash(
+        self,
+        info: Optional[QAPISourceInfo],
+        seen: Dict[str, QAPISchemaMember],
+    ) -> None:
         for v in self.variants:
             # Reset seen map for each variant, since qapi names from one
-            # branch do not affect another branch
+            # branch do not affect another branch.
+            #
+            # v.type's typing is enforced in check() above.
+            assert isinstance(v.type, QAPISchemaObjectType)
             v.type.check_clash(info, dict(seen))
 
 
@@ -677,18 +837,26 @@
     """ Represents object members, enum members and features """
     role = 'member'
 
-    def __init__(self, name, info, ifcond=None):
-        assert isinstance(name, str)
+    def __init__(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: Optional[QAPISchemaIfCond] = None,
+    ):
         self.name = name
         self.info = info
         self.ifcond = ifcond or QAPISchemaIfCond()
-        self.defined_in = None
+        self.defined_in: Optional[str] = None
 
-    def set_defined_in(self, name):
+    def set_defined_in(self, name: str) -> None:
         assert not self.defined_in
         self.defined_in = name
 
-    def check_clash(self, info, seen):
+    def check_clash(
+        self,
+        info: Optional[QAPISourceInfo],
+        seen: Dict[str, QAPISchemaMember],
+    ) -> None:
         cname = c_name(self.name)
         if cname in seen:
             raise QAPISemError(
@@ -697,11 +865,11 @@
                 % (self.describe(info), seen[cname].describe(info)))
         seen[cname] = self
 
-    def connect_doc(self, doc):
+    def connect_doc(self, doc: Optional[QAPIDoc]) -> None:
         if doc:
             doc.connect_member(self)
 
-    def describe(self, info):
+    def describe(self, info: Optional[QAPISourceInfo]) -> str:
         role = self.role
         meta = 'type'
         defined_in = self.defined_in
@@ -724,6 +892,7 @@
             else:
                 assert False
 
+        assert info is not None
         if defined_in != info.defn_name:
             return "%s '%s' of %s '%s'" % (role, self.name, meta, defined_in)
         return "%s '%s'" % (role, self.name)
@@ -732,14 +901,19 @@
 class QAPISchemaEnumMember(QAPISchemaMember):
     role = 'value'
 
-    def __init__(self, name, info, ifcond=None, features=None):
+    def __init__(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        ifcond: Optional[QAPISchemaIfCond] = None,
+        features: Optional[List[QAPISchemaFeature]] = None,
+    ):
         super().__init__(name, info, ifcond)
         for f in features or []:
-            assert isinstance(f, QAPISchemaFeature)
             f.set_defined_in(name)
         self.features = features or []
 
-    def connect_doc(self, doc):
+    def connect_doc(self, doc: Optional[QAPIDoc]) -> None:
         super().connect_doc(doc)
         if doc:
             for f in self.features:
@@ -749,36 +923,40 @@
 class QAPISchemaFeature(QAPISchemaMember):
     role = 'feature'
 
-    def is_special(self):
+    def is_special(self) -> bool:
         return self.name in ('deprecated', 'unstable')
 
 
 class QAPISchemaObjectTypeMember(QAPISchemaMember):
-    def __init__(self, name, info, typ, optional, ifcond=None, features=None):
+    def __init__(
+        self,
+        name: str,
+        info: QAPISourceInfo,
+        typ: str,
+        optional: bool,
+        ifcond: Optional[QAPISchemaIfCond] = None,
+        features: Optional[List[QAPISchemaFeature]] = None,
+    ):
         super().__init__(name, info, ifcond)
-        assert isinstance(typ, str)
-        assert isinstance(optional, bool)
         for f in features or []:
-            assert isinstance(f, QAPISchemaFeature)
             f.set_defined_in(name)
         self._type_name = typ
-        self.type = None
+        self.type: QAPISchemaType  # set during check()
         self.optional = optional
         self.features = features or []
 
-    def need_has(self):
-        assert self.type
+    def need_has(self) -> bool:
         return self.optional and self.type.need_has_if_optional()
 
-    def check(self, schema):
+    def check(self, schema: QAPISchema) -> None:
         assert self.defined_in
         self.type = schema.resolve_type(self._type_name, self.info,
                                         self.describe)
-        seen = {}
+        seen: Dict[str, QAPISchemaMember] = {}
         for f in self.features:
             f.check_clash(self.info, seen)
 
-    def connect_doc(self, doc):
+    def connect_doc(self, doc: Optional[QAPIDoc]) -> None:
         super().connect_doc(doc)
         if doc:
             for f in self.features:
@@ -788,24 +966,40 @@
 class QAPISchemaVariant(QAPISchemaObjectTypeMember):
     role = 'branch'
 
-    def __init__(self, name, info, typ, ifcond=None):
+    def __init__(
+        self,
+        name: str,
+        info: QAPISourceInfo,
+        typ: str,
+        ifcond: QAPISchemaIfCond,
+    ):
         super().__init__(name, info, typ, False, ifcond)
 
 
-class QAPISchemaCommand(QAPISchemaEntity):
+class QAPISchemaCommand(QAPISchemaDefinition):
     meta = 'command'
 
-    def __init__(self, name, info, doc, ifcond, features,
-                 arg_type, ret_type,
-                 gen, success_response, boxed, allow_oob, allow_preconfig,
-                 coroutine):
+    def __init__(
+        self,
+        name: str,
+        info: QAPISourceInfo,
+        doc: Optional[QAPIDoc],
+        ifcond: QAPISchemaIfCond,
+        features: List[QAPISchemaFeature],
+        arg_type: Optional[str],
+        ret_type: Optional[str],
+        gen: bool,
+        success_response: bool,
+        boxed: bool,
+        allow_oob: bool,
+        allow_preconfig: bool,
+        coroutine: bool,
+    ):
         super().__init__(name, info, doc, ifcond, features)
-        assert not arg_type or isinstance(arg_type, str)
-        assert not ret_type or isinstance(ret_type, str)
         self._arg_type_name = arg_type
-        self.arg_type = None
+        self.arg_type: Optional[QAPISchemaObjectType] = None
         self._ret_type_name = ret_type
-        self.ret_type = None
+        self.ret_type: Optional[QAPISchemaType] = None
         self.gen = gen
         self.success_response = success_response
         self.boxed = boxed
@@ -813,16 +1007,18 @@
         self.allow_preconfig = allow_preconfig
         self.coroutine = coroutine
 
-    def check(self, schema):
+    def check(self, schema: QAPISchema) -> None:
+        assert self.info is not None
         super().check(schema)
         if self._arg_type_name:
-            self.arg_type = schema.resolve_type(
+            arg_type = schema.resolve_type(
                 self._arg_type_name, self.info, "command's 'data'")
-            if not isinstance(self.arg_type, QAPISchemaObjectType):
+            if not isinstance(arg_type, QAPISchemaObjectType):
                 raise QAPISemError(
                     self.info,
                     "command's 'data' cannot take %s"
-                    % self.arg_type.describe())
+                    % arg_type.describe())
+            self.arg_type = arg_type
             if self.arg_type.variants and not self.boxed:
                 raise QAPISemError(
                     self.info,
@@ -839,22 +1035,21 @@
             if self.name not in self.info.pragma.command_returns_exceptions:
                 typ = self.ret_type
                 if isinstance(typ, QAPISchemaArrayType):
-                    typ = self.ret_type.element_type
-                    assert typ
+                    typ = typ.element_type
                 if not isinstance(typ, QAPISchemaObjectType):
                     raise QAPISemError(
                         self.info,
                         "command's 'returns' cannot take %s"
                         % self.ret_type.describe())
 
-    def connect_doc(self, doc=None):
+    def connect_doc(self, doc: Optional[QAPIDoc] = None) -> None:
         super().connect_doc(doc)
         doc = doc or self.doc
         if doc:
             if self.arg_type and self.arg_type.is_implicit():
                 self.arg_type.connect_doc(doc)
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_command(
             self.name, self.info, self.ifcond, self.features,
@@ -863,26 +1058,35 @@
             self.coroutine)
 
 
-class QAPISchemaEvent(QAPISchemaEntity):
+class QAPISchemaEvent(QAPISchemaDefinition):
     meta = 'event'
 
-    def __init__(self, name, info, doc, ifcond, features, arg_type, boxed):
+    def __init__(
+        self,
+        name: str,
+        info: QAPISourceInfo,
+        doc: Optional[QAPIDoc],
+        ifcond: QAPISchemaIfCond,
+        features: List[QAPISchemaFeature],
+        arg_type: Optional[str],
+        boxed: bool,
+    ):
         super().__init__(name, info, doc, ifcond, features)
-        assert not arg_type or isinstance(arg_type, str)
         self._arg_type_name = arg_type
-        self.arg_type = None
+        self.arg_type: Optional[QAPISchemaObjectType] = None
         self.boxed = boxed
 
-    def check(self, schema):
+    def check(self, schema: QAPISchema) -> None:
         super().check(schema)
         if self._arg_type_name:
-            self.arg_type = schema.resolve_type(
+            typ = schema.resolve_type(
                 self._arg_type_name, self.info, "event's 'data'")
-            if not isinstance(self.arg_type, QAPISchemaObjectType):
+            if not isinstance(typ, QAPISchemaObjectType):
                 raise QAPISemError(
                     self.info,
                     "event's 'data' cannot take %s"
-                    % self.arg_type.describe())
+                    % typ.describe())
+            self.arg_type = typ
             if self.arg_type.variants and not self.boxed:
                 raise QAPISemError(
                     self.info,
@@ -894,14 +1098,14 @@
                     self.info,
                     "conditional event arguments require 'boxed': true")
 
-    def connect_doc(self, doc=None):
+    def connect_doc(self, doc: Optional[QAPIDoc] = None) -> None:
         super().connect_doc(doc)
         doc = doc or self.doc
         if doc:
             if self.arg_type and self.arg_type.is_implicit():
                 self.arg_type.connect_doc(doc)
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         super().visit(visitor)
         visitor.visit_event(
             self.name, self.info, self.ifcond, self.features,
@@ -909,7 +1113,7 @@
 
 
 class QAPISchema:
-    def __init__(self, fname):
+    def __init__(self, fname: str):
         self.fname = fname
 
         try:
@@ -921,9 +1125,9 @@
 
         exprs = check_exprs(parser.exprs)
         self.docs = parser.docs
-        self._entity_list = []
-        self._entity_dict = {}
-        self._module_dict = OrderedDict()
+        self._entity_list: List[QAPISchemaEntity] = []
+        self._entity_dict: Dict[str, QAPISchemaDefinition] = {}
+        self._module_dict: Dict[str, QAPISchemaModule] = OrderedDict()
         self._schema_dir = os.path.dirname(fname)
         self._make_module(QAPISchemaModule.BUILTIN_MODULE_NAME)
         self._make_module(fname)
@@ -933,37 +1137,44 @@
         self._def_exprs(exprs)
         self.check()
 
-    def _def_entity(self, ent):
-        # Only the predefined types are allowed to not have info
-        assert ent.info or self._predefining
+    def _def_entity(self, ent: QAPISchemaEntity) -> None:
         self._entity_list.append(ent)
-        if ent.name is None:
-            return
+
+    def _def_definition(self, defn: QAPISchemaDefinition) -> None:
+        # Only the predefined types are allowed to not have info
+        assert defn.info or self._predefining
+        self._def_entity(defn)
         # TODO reject names that differ only in '_' vs. '.'  vs. '-',
         # because they're liable to clash in generated C.
-        other_ent = self._entity_dict.get(ent.name)
-        if other_ent:
-            if other_ent.info:
-                where = QAPISourceError(other_ent.info, "previous definition")
+        other_defn = self._entity_dict.get(defn.name)
+        if other_defn:
+            if other_defn.info:
+                where = QAPISourceError(other_defn.info, "previous definition")
                 raise QAPISemError(
-                    ent.info,
-                    "'%s' is already defined\n%s" % (ent.name, where))
+                    defn.info,
+                    "'%s' is already defined\n%s" % (defn.name, where))
             raise QAPISemError(
-                ent.info, "%s is already defined" % other_ent.describe())
-        self._entity_dict[ent.name] = ent
+                defn.info, "%s is already defined" % other_defn.describe())
+        self._entity_dict[defn.name] = defn
 
-    def lookup_entity(self, name, typ=None):
-        ent = self._entity_dict.get(name)
-        if typ and not isinstance(ent, typ):
-            return None
-        return ent
+    def lookup_entity(self,name: str) -> Optional[QAPISchemaEntity]:
+        return self._entity_dict.get(name)
 
-    def lookup_type(self, name):
-        return self.lookup_entity(name, QAPISchemaType)
+    def lookup_type(self, name: str) -> Optional[QAPISchemaType]:
+        typ = self.lookup_entity(name)
+        if isinstance(typ, QAPISchemaType):
+            return typ
+        return None
 
-    def resolve_type(self, name, info, what):
+    def resolve_type(
+        self,
+        name: str,
+        info: Optional[QAPISourceInfo],
+        what: Union[None, str, Callable[[QAPISourceInfo], str]],
+    ) -> QAPISchemaType:
         typ = self.lookup_type(name)
         if not typ:
+            assert info and what  # built-in types must not fail lookup
             if callable(what):
                 what = what(info)
             raise QAPISemError(
@@ -975,31 +1186,33 @@
             return fname
         return os.path.relpath(fname, self._schema_dir)
 
-    def _make_module(self, fname):
+    def _make_module(self, fname: str) -> QAPISchemaModule:
         name = self._module_name(fname)
         if name not in self._module_dict:
             self._module_dict[name] = QAPISchemaModule(name)
         return self._module_dict[name]
 
-    def module_by_fname(self, fname):
+    def module_by_fname(self, fname: str) -> QAPISchemaModule:
         name = self._module_name(fname)
         return self._module_dict[name]
 
-    def _def_include(self, expr: QAPIExpression):
+    def _def_include(self, expr: QAPIExpression) -> None:
         include = expr['include']
         assert expr.doc is None
         self._def_entity(
             QAPISchemaInclude(self._make_module(include), expr.info))
 
-    def _def_builtin_type(self, name, json_type, c_type):
-        self._def_entity(QAPISchemaBuiltinType(name, json_type, c_type))
+    def _def_builtin_type(
+        self, name: str, json_type: str, c_type: str
+    ) -> None:
+        self._def_definition(QAPISchemaBuiltinType(name, json_type, c_type))
         # Instantiating only the arrays that are actually used would
         # be nice, but we can't as long as their generated code
         # (qapi-builtin-types.[ch]) may be shared by some other
         # schema.
         self._make_array_type(name, None)
 
-    def _def_predefineds(self):
+    def _def_predefineds(self) -> None:
         for t in [('str',    'string',  'char' + POINTER_SUFFIX),
                   ('number', 'number',  'double'),
                   ('int',    'int',     'int64_t'),
@@ -1018,67 +1231,97 @@
             self._def_builtin_type(*t)
         self.the_empty_object_type = QAPISchemaObjectType(
             'q_empty', None, None, None, None, None, [], None)
-        self._def_entity(self.the_empty_object_type)
+        self._def_definition(self.the_empty_object_type)
 
         qtypes = ['none', 'qnull', 'qnum', 'qstring', 'qdict', 'qlist',
                   'qbool']
         qtype_values = self._make_enum_members(
             [{'name': n} for n in qtypes], None)
 
-        self._def_entity(QAPISchemaEnumType('QType', None, None, None, None,
-                                            qtype_values, 'QTYPE'))
+        self._def_definition(QAPISchemaEnumType(
+            'QType', None, None, None, None, qtype_values, 'QTYPE'))
 
-    def _make_features(self, features, info):
+    def _make_features(
+        self,
+        features: Optional[List[Dict[str, Any]]],
+        info: Optional[QAPISourceInfo],
+    ) -> List[QAPISchemaFeature]:
         if features is None:
             return []
         return [QAPISchemaFeature(f['name'], info,
                                   QAPISchemaIfCond(f.get('if')))
                 for f in features]
 
-    def _make_enum_member(self, name, ifcond, features, info):
+    def _make_enum_member(
+        self,
+        name: str,
+        ifcond: Optional[Union[str, Dict[str, Any]]],
+        features: Optional[List[Dict[str, Any]]],
+        info: Optional[QAPISourceInfo],
+    ) -> QAPISchemaEnumMember:
         return QAPISchemaEnumMember(name, info,
                                     QAPISchemaIfCond(ifcond),
                                     self._make_features(features, info))
 
-    def _make_enum_members(self, values, info):
+    def _make_enum_members(
+        self, values: List[Dict[str, Any]], info: Optional[QAPISourceInfo]
+    ) -> List[QAPISchemaEnumMember]:
         return [self._make_enum_member(v['name'], v.get('if'),
                                        v.get('features'), info)
                 for v in values]
 
-    def _make_array_type(self, element_type, info):
+    def _make_array_type(
+        self, element_type: str, info: Optional[QAPISourceInfo]
+    ) -> str:
         name = element_type + 'List'    # reserved by check_defn_name_str()
         if not self.lookup_type(name):
-            self._def_entity(QAPISchemaArrayType(name, info, element_type))
+            self._def_definition(QAPISchemaArrayType(
+                name, info, element_type))
         return name
 
-    def _make_implicit_object_type(self, name, info, ifcond, role, members):
+    def _make_implicit_object_type(
+        self,
+        name: str,
+        info: QAPISourceInfo,
+        ifcond: QAPISchemaIfCond,
+        role: str,
+        members: List[QAPISchemaObjectTypeMember],
+    ) -> Optional[str]:
         if not members:
             return None
         # See also QAPISchemaObjectTypeMember.describe()
         name = 'q_obj_%s-%s' % (name, role)
-        typ = self.lookup_entity(name, QAPISchemaObjectType)
+        typ = self.lookup_entity(name)
         if typ:
+            assert(isinstance(typ, QAPISchemaObjectType))
             # The implicit object type has multiple users.  This can
             # only be a duplicate definition, which will be flagged
             # later.
             pass
         else:
-            self._def_entity(QAPISchemaObjectType(
+            self._def_definition(QAPISchemaObjectType(
                 name, info, None, ifcond, None, None, members, None))
         return name
 
-    def _def_enum_type(self, expr: QAPIExpression):
+    def _def_enum_type(self, expr: QAPIExpression) -> None:
         name = expr['enum']
         data = expr['data']
         prefix = expr.get('prefix')
         ifcond = QAPISchemaIfCond(expr.get('if'))
         info = expr.info
         features = self._make_features(expr.get('features'), info)
-        self._def_entity(QAPISchemaEnumType(
+        self._def_definition(QAPISchemaEnumType(
             name, info, expr.doc, ifcond, features,
             self._make_enum_members(data, info), prefix))
 
-    def _make_member(self, name, typ, ifcond, features, info):
+    def _make_member(
+        self,
+        name: str,
+        typ: Union[List[str], str],
+        ifcond: QAPISchemaIfCond,
+        features: Optional[List[Dict[str, Any]]],
+        info: QAPISourceInfo,
+    ) -> QAPISchemaObjectTypeMember:
         optional = False
         if name.startswith('*'):
             name = name[1:]
@@ -1089,31 +1332,41 @@
         return QAPISchemaObjectTypeMember(name, info, typ, optional, ifcond,
                                           self._make_features(features, info))
 
-    def _make_members(self, data, info):
+    def _make_members(
+        self,
+        data: Dict[str, Any],
+        info: QAPISourceInfo,
+    ) -> List[QAPISchemaObjectTypeMember]:
         return [self._make_member(key, value['type'],
                                   QAPISchemaIfCond(value.get('if')),
                                   value.get('features'), info)
                 for (key, value) in data.items()]
 
-    def _def_struct_type(self, expr: QAPIExpression):
+    def _def_struct_type(self, expr: QAPIExpression) -> None:
         name = expr['struct']
         base = expr.get('base')
         data = expr['data']
         info = expr.info
         ifcond = QAPISchemaIfCond(expr.get('if'))
         features = self._make_features(expr.get('features'), info)
-        self._def_entity(QAPISchemaObjectType(
+        self._def_definition(QAPISchemaObjectType(
             name, info, expr.doc, ifcond, features, base,
             self._make_members(data, info),
             None))
 
-    def _make_variant(self, case, typ, ifcond, info):
+    def _make_variant(
+        self,
+        case: str,
+        typ: str,
+        ifcond: QAPISchemaIfCond,
+        info: QAPISourceInfo,
+    ) -> QAPISchemaVariant:
         if isinstance(typ, list):
             assert len(typ) == 1
             typ = self._make_array_type(typ[0], info)
         return QAPISchemaVariant(case, info, typ, ifcond)
 
-    def _def_union_type(self, expr: QAPIExpression):
+    def _def_union_type(self, expr: QAPIExpression) -> None:
         name = expr['union']
         base = expr['base']
         tag_name = expr['discriminator']
@@ -1132,13 +1385,13 @@
                                info)
             for (key, value) in data.items()]
         members: List[QAPISchemaObjectTypeMember] = []
-        self._def_entity(
+        self._def_definition(
             QAPISchemaObjectType(name, info, expr.doc, ifcond, features,
                                  base, members,
                                  QAPISchemaVariants(
                                      tag_name, info, None, variants)))
 
-    def _def_alternate_type(self, expr: QAPIExpression):
+    def _def_alternate_type(self, expr: QAPIExpression) -> None:
         name = expr['alternate']
         data = expr['data']
         assert isinstance(data, dict)
@@ -1151,12 +1404,12 @@
                                info)
             for (key, value) in data.items()]
         tag_member = QAPISchemaObjectTypeMember('type', info, 'QType', False)
-        self._def_entity(
+        self._def_definition(
             QAPISchemaAlternateType(
                 name, info, expr.doc, ifcond, features,
                 QAPISchemaVariants(None, info, tag_member, variants)))
 
-    def _def_command(self, expr: QAPIExpression):
+    def _def_command(self, expr: QAPIExpression) -> None:
         name = expr['command']
         data = expr.get('data')
         rets = expr.get('returns')
@@ -1176,13 +1429,12 @@
         if isinstance(rets, list):
             assert len(rets) == 1
             rets = self._make_array_type(rets[0], info)
-        self._def_entity(QAPISchemaCommand(name, info, expr.doc, ifcond,
-                                           features, data, rets,
-                                           gen, success_response,
-                                           boxed, allow_oob, allow_preconfig,
-                                           coroutine))
+        self._def_definition(
+            QAPISchemaCommand(name, info, expr.doc, ifcond, features, data,
+                              rets, gen, success_response, boxed, allow_oob,
+                              allow_preconfig, coroutine))
 
-    def _def_event(self, expr: QAPIExpression):
+    def _def_event(self, expr: QAPIExpression) -> None:
         name = expr['event']
         data = expr.get('data')
         boxed = expr.get('boxed', False)
@@ -1193,10 +1445,10 @@
             data = self._make_implicit_object_type(
                 name, info, ifcond,
                 'arg', self._make_members(data, info))
-        self._def_entity(QAPISchemaEvent(name, info, expr.doc, ifcond,
-                                         features, data, boxed))
+        self._def_definition(QAPISchemaEvent(name, info, expr.doc, ifcond,
+                                             features, data, boxed))
 
-    def _def_exprs(self, exprs):
+    def _def_exprs(self, exprs: List[QAPIExpression]) -> None:
         for expr in exprs:
             if 'enum' in expr:
                 self._def_enum_type(expr)
@@ -1215,7 +1467,7 @@
             else:
                 assert False
 
-    def check(self):
+    def check(self) -> None:
         for ent in self._entity_list:
             ent.check(self)
             ent.connect_doc()
@@ -1224,7 +1476,7 @@
         for doc in self.docs:
             doc.check()
 
-    def visit(self, visitor):
+    def visit(self, visitor: QAPISchemaVisitor) -> None:
         visitor.visit_begin(self)
         for mod in self._module_dict.values():
             mod.visit(visitor)