Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2021-02-18' into staging

QAPI patches patches for 2021-02-18

# gpg: Signature made Thu 18 Feb 2021 18:51:35 GMT
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qapi-2021-02-18:
  qapi/introspect.py: set _gen_tree's default ifcond argument to ()
  qapi/introspect.py: Type _gen_tree variants as Sequence[str]
  qapi/introspect.py: Update copyright and authors list
  qapi/introspect.py: Add docstrings to _gen_tree and _tree_to_qlit
  qapi/introspect.py: add type hint annotations
  qapi/introspect.py: remove _gen_variants helper
  qapi/introspect.py: improve readability of _tree_to_qlit
  qapi/introspect.py: improve _tree_to_qlit error message
  qapi/introspect.py: create a typed 'Annotated' data strutcure
  qapi/introspect.py: Introduce preliminary tree typing
  qapi/introspect.py: Always define all 'extra' dict keys
  qapi/introspect.py: replace 'extra' dict with 'comment' argument
  qapi/introspect.py: Unify return type of _make_tree()
  qapi/introspect.py: guard against ifcond/comment misuse
  qapi/introspect.py: add _gen_features helper
  qapi/introspect.py: use _make_tree for features nodes
  qapi/introspect.py: assert schema is not None
  qapi: Replace List[str] with Sequence[str] for ifcond

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

8 files changed, 266 insertions, 131 deletions

diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
index 54af519..0a75a93 100644
--- a/scripts/qapi/commands.py
+++ b/scripts/qapi/commands.py
@@ -17,6 +17,7 @@ from typing import (
     Dict,
     List,
     Optional,
+    Sequence,
     Set,
 )
 
@@ -297,7 +298,7 @@ void %(c_prefix)sqmp_init_marshal(QmpCommandList *cmds)
     def visit_command(self,
                       name: str,
                       info: Optional[QAPISourceInfo],
-                      ifcond: List[str],
+                      ifcond: Sequence[str],
                       features: List[QAPISchemaFeature],
                       arg_type: Optional[QAPISchemaObjectType],
                       ret_type: Optional[QAPISchemaType],
diff --git a/scripts/qapi/events.py b/scripts/qapi/events.py
index 8c57deb..90d2f61 100644
--- a/scripts/qapi/events.py
+++ b/scripts/qapi/events.py
@@ -12,7 +12,7 @@ This work is licensed under the terms of the GNU GPL, version 2.
 See the COPYING file in the top-level directory.
 """
 
-from typing import List, Optional
+from typing import List, Optional, Sequence
 
 from .common import c_enum_const, c_name, mcgen
 from .gen import QAPISchemaModularCVisitor, build_params, ifcontext
@@ -214,7 +214,7 @@ void %(event_emit)s(%(event_enum)s event, QDict *qdict);
     def visit_event(self,
                     name: str,
                     info: Optional[QAPISourceInfo],
-                    ifcond: List[str],
+                    ifcond: Sequence[str],
                     features: List[QAPISchemaFeature],
                     arg_type: Optional[QAPISchemaObjectType],
                     boxed: bool) -> None:
diff --git a/scripts/qapi/gen.py b/scripts/qapi/gen.py
index 63549cc..1fa503b 100644
--- a/scripts/qapi/gen.py
+++ b/scripts/qapi/gen.py
@@ -17,8 +17,8 @@ import re
 from typing import (
     Dict,
     Iterator,
-    List,
     Optional,
+    Sequence,
     Tuple,
 )
 
@@ -85,7 +85,7 @@ class QAPIGen:
                 fp.write(text)
 
 
-def _wrap_ifcond(ifcond: List[str], before: str, after: str) -> str:
+def _wrap_ifcond(ifcond: Sequence[str], before: str, after: str) -> str:
     if before == after:
         return after   # suppress empty #if ... #endif
 
@@ -127,9 +127,9 @@ def build_params(arg_type: Optional[QAPISchemaObjectType],
 class QAPIGenCCode(QAPIGen):
     def __init__(self, fname: str):
         super().__init__(fname)
-        self._start_if: Optional[Tuple[List[str], str, str]] = None
+        self._start_if: Optional[Tuple[Sequence[str], str, str]] = None
 
-    def start_if(self, ifcond: List[str]) -> None:
+    def start_if(self, ifcond: Sequence[str]) -> None:
         assert self._start_if is None
         self._start_if = (ifcond, self._body, self._preamble)
 
@@ -187,11 +187,11 @@ class QAPIGenH(QAPIGenC):
 
 
 @contextmanager
-def ifcontext(ifcond: List[str], *args: QAPIGenCCode) -> Iterator[None]:
+def ifcontext(ifcond: Sequence[str], *args: QAPIGenCCode) -> Iterator[None]:
     """
     A with-statement context manager that wraps with `start_if()` / `end_if()`.
 
-    :param ifcond: A list of conditionals, passed to `start_if()`.
+    :param ifcond: A sequence of conditionals, passed to `start_if()`.
     :param args: any number of `QAPIGenCCode`.
 
     Example::
diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
index fafec94..9a348ca 100644
--- a/scripts/qapi/introspect.py
+++ b/scripts/qapi/introspect.py
@@ -1,15 +1,29 @@
 """
 QAPI introspection generator
 
-Copyright (C) 2015-2018 Red Hat, Inc.
+Copyright (C) 2015-2021 Red Hat, Inc.
 
 Authors:
  Markus Armbruster <armbru@redhat.com>
+ John Snow <jsnow@redhat.com>
 
 This work is licensed under the terms of the GNU GPL, version 2.
 See the COPYING file in the top-level directory.
 """
 
+from typing import (
+    Any,
+    Dict,
+    Generic,
+    Iterable,
+    List,
+    Optional,
+    Sequence,
+    Tuple,
+    TypeVar,
+    Union,
+)
+
 from .common import (
     c_name,
     gen_endif,
@@ -18,91 +32,158 @@ from .common import (
 )
 from .gen import QAPISchemaMonolithicCVisitor
 from .schema import (
+    QAPISchema,
     QAPISchemaArrayType,
     QAPISchemaBuiltinType,
+    QAPISchemaEntity,
+    QAPISchemaEnumMember,
+    QAPISchemaFeature,
+    QAPISchemaObjectType,
+    QAPISchemaObjectTypeMember,
     QAPISchemaType,
+    QAPISchemaVariant,
+    QAPISchemaVariants,
 )
-
-
-def _make_tree(obj, ifcond, features, extra=None):
-    if extra is None:
-        extra = {}
-    if ifcond:
-        extra['if'] = ifcond
-    if features:
-        obj['features'] = [(f.name, {'if': f.ifcond}) for f in features]
-    if extra:
-        return (obj, extra)
-    return obj
-
-
-def _tree_to_qlit(obj, level=0, suppress_first_indent=False):
-
-    def indent(level):
+from .source import QAPISourceInfo
+
+
+# This module constructs a tree data structure that is used to
+# generate the introspection information for QEMU. It is shaped
+# like a JSON value.
+#
+# A complexity over JSON is that our values may or may not be annotated.
+#
+# Un-annotated values may be:
+#     Scalar: str, bool, None.
+#     Non-scalar: List, Dict
+# _value = Union[str, bool, None, Dict[str, JSONValue], List[JSONValue]]
+#
+# With optional annotations, the type of all values is:
+# JSONValue = Union[_Value, Annotated[_Value]]
+#
+# Sadly, mypy does not support recursive types; so the _Stub alias is used to
+# mark the imprecision in the type model where we'd otherwise use JSONValue.
+_Stub = Any
+_Scalar = Union[str, bool, None]
+_NonScalar = Union[Dict[str, _Stub], List[_Stub]]
+_Value = Union[_Scalar, _NonScalar]
+JSONValue = Union[_Value, 'Annotated[_Value]']
+
+# These types are based on structures defined in QEMU's schema, so we
+# lack precise types for them here. Python 3.6 does not offer
+# TypedDict constructs, so they are broadly typed here as simple
+# Python Dicts.
+SchemaInfo = Dict[str, object]
+SchemaInfoObject = Dict[str, object]
+SchemaInfoObjectVariant = Dict[str, object]
+SchemaInfoObjectMember = Dict[str, object]
+SchemaInfoCommand = Dict[str, object]
+
+
+_ValueT = TypeVar('_ValueT', bound=_Value)
+
+
+class Annotated(Generic[_ValueT]):
+    """
+    Annotated generally contains a SchemaInfo-like type (as a dict),
+    But it also used to wrap comments/ifconds around scalar leaf values,
+    for the benefit of features and enums.
+    """
+    # TODO: Remove after Python 3.7 adds @dataclass:
+    # pylint: disable=too-few-public-methods
+    def __init__(self, value: _ValueT, ifcond: Iterable[str],
+                 comment: Optional[str] = None):
+        self.value = value
+        self.comment: Optional[str] = comment
+        self.ifcond: Tuple[str, ...] = tuple(ifcond)
+
+
+def _tree_to_qlit(obj: JSONValue,
+                  level: int = 0,
+                  dict_value: bool = False) -> str:
+    """
+    Convert the type tree into a QLIT C string, recursively.
+
+    :param obj: The value to convert.
+                This value may not be Annotated when dict_value is True.
+    :param level: The indentation level for this particular value.
+    :param dict_value: True when the value being processed belongs to a
+                       dict key; which suppresses the output indent.
+    """
+
+    def indent(level: int) -> str:
         return level * 4 * ' '
 
-    if isinstance(obj, tuple):
-        ifobj, extra = obj
-        ifcond = extra.get('if')
-        comment = extra.get('comment')
+    if isinstance(obj, Annotated):
+        # NB: _tree_to_qlit is called recursively on the values of a
+        # key:value pair; those values can't be decorated with
+        # comments or conditionals.
+        msg = "dict values cannot have attached comments or if-conditionals."
+        assert not dict_value, msg
+
         ret = ''
-        if comment:
-            ret += indent(level) + '/* %s */\n' % comment
-        if ifcond:
-            ret += gen_if(ifcond)
-        ret += _tree_to_qlit(ifobj, level)
-        if ifcond:
-            ret += '\n' + gen_endif(ifcond)
+        if obj.comment:
+            ret += indent(level) + f"/* {obj.comment} */\n"
+        if obj.ifcond:
+            ret += gen_if(obj.ifcond)
+        ret += _tree_to_qlit(obj.value, level)
+        if obj.ifcond:
+            ret += '\n' + gen_endif(obj.ifcond)
         return ret
 
     ret = ''
-    if not suppress_first_indent:
+    if not dict_value:
         ret += indent(level)
+
+    # Scalars:
     if obj is None:
         ret += 'QLIT_QNULL'
     elif isinstance(obj, str):
-        ret += 'QLIT_QSTR(' + to_c_string(obj) + ')'
+        ret += f"QLIT_QSTR({to_c_string(obj)})"
+    elif isinstance(obj, bool):
+        ret += f"QLIT_QBOOL({str(obj).lower()})"
+
+    # Non-scalars:
     elif isinstance(obj, list):
-        elts = [_tree_to_qlit(elt, level + 1).strip('\n')
-                for elt in obj]
-        elts.append(indent(level + 1) + "{}")
         ret += 'QLIT_QLIST(((QLitObject[]) {\n'
-        ret += '\n'.join(elts) + '\n'
+        for value in obj:
+            ret += _tree_to_qlit(value, level + 1).strip('\n') + '\n'
+        ret += indent(level + 1) + '{}\n'
         ret += indent(level) + '}))'
     elif isinstance(obj, dict):
-        elts = []
-        for key, value in sorted(obj.items()):
-            elts.append(indent(level + 1) + '{ %s, %s }' %
-                        (to_c_string(key),
-                         _tree_to_qlit(value, level + 1, True)))
-        elts.append(indent(level + 1) + '{}')
         ret += 'QLIT_QDICT(((QLitDictEntry[]) {\n'
-        ret += ',\n'.join(elts) + '\n'
+        for key, value in sorted(obj.items()):
+            ret += indent(level + 1) + "{{ {:s}, {:s} }},\n".format(
+                to_c_string(key),
+                _tree_to_qlit(value, level + 1, dict_value=True)
+            )
+        ret += indent(level + 1) + '{}\n'
         ret += indent(level) + '}))'
-    elif isinstance(obj, bool):
-        ret += 'QLIT_QBOOL(%s)' % ('true' if obj else 'false')
     else:
-        assert False                # not implemented
+        raise NotImplementedError(
+            f"type '{type(obj).__name__}' not implemented"
+        )
+
     if level > 0:
         ret += ','
     return ret
 
 
-def to_c_string(string):
+def to_c_string(string: str) -> str:
     return '"' + string.replace('\\', r'\\').replace('"', r'\"') + '"'
 
 
 class QAPISchemaGenIntrospectVisitor(QAPISchemaMonolithicCVisitor):
 
-    def __init__(self, prefix, unmask):
+    def __init__(self, prefix: str, unmask: bool):
         super().__init__(
             prefix, 'qapi-introspect',
             ' * QAPI/QMP schema introspection', __doc__)
         self._unmask = unmask
-        self._schema = None
-        self._trees = []
-        self._used_types = []
-        self._name_map = {}
+        self._schema: Optional[QAPISchema] = None
+        self._trees: List[Annotated[SchemaInfo]] = []
+        self._used_types: List[QAPISchemaType] = []
+        self._name_map: Dict[str, str] = {}
         self._genc.add(mcgen('''
 #include "qemu/osdep.h"
 #include "%(prefix)sqapi-introspect.h"
@@ -110,10 +191,10 @@ class QAPISchemaGenIntrospectVisitor(QAPISchemaMonolithicCVisitor):
 ''',
                              prefix=prefix))
 
-    def visit_begin(self, schema):
+    def visit_begin(self, schema: QAPISchema) -> None:
         self._schema = schema
 
-    def visit_end(self):
+    def visit_end(self) -> None:
         # visit the types that are actually used
         for typ in self._used_types:
             typ.visit(self)
@@ -135,18 +216,20 @@ const QLitObject %(c_name)s = %(c_string)s;
         self._used_types = []
         self._name_map = {}
 
-    def visit_needed(self, entity):
+    def visit_needed(self, entity: QAPISchemaEntity) -> bool:
         # Ignore types on first pass; visit_end() will pick up used types
         return not isinstance(entity, QAPISchemaType)
 
-    def _name(self, name):
+    def _name(self, name: str) -> str:
         if self._unmask:
             return name
         if name not in self._name_map:
             self._name_map[name] = '%d' % len(self._name_map)
         return self._name_map[name]
 
-    def _use_type(self, typ):
+    def _use_type(self, typ: QAPISchemaType) -> str:
+        assert self._schema is not None
+
         # Map the various integer types to plain int
         if typ.json_type() == 'int':
             typ = self._schema.lookup_type('int')
@@ -165,81 +248,137 @@ const QLitObject %(c_name)s = %(c_string)s;
             return '[' + self._use_type(typ.element_type) + ']'
         return self._name(typ.name)
 
-    def _gen_tree(self, name, mtype, obj, ifcond, features):
-        extra = None
+    @staticmethod
+    def _gen_features(features: Sequence[QAPISchemaFeature]
+                      ) -> List[Annotated[str]]:
+        return [Annotated(f.name, f.ifcond) for f in features]
+
+    def _gen_tree(self, name: str, mtype: str, obj: Dict[str, object],
+                  ifcond: Sequence[str] = (),
+                  features: Sequence[QAPISchemaFeature] = ()) -> None:
+        """
+        Build and append a SchemaInfo object to self._trees.
+
+        :param name: The SchemaInfo's name.
+        :param mtype: The SchemaInfo's meta-type.
+        :param obj: Additional SchemaInfo members, as appropriate for
+                    the meta-type.
+        :param ifcond: Conditionals to apply to the SchemaInfo.
+        :param features: The SchemaInfo's features.
+                         Will be omitted from the output if empty.
+        """
+        comment: Optional[str] = None
         if mtype not in ('command', 'event', 'builtin', 'array'):
             if not self._unmask:
                 # Output a comment to make it easy to map masked names
                 # back to the source when reading the generated output.
-                extra = {'comment': '"%s" = %s' % (self._name(name), name)}
+                comment = f'"{self._name(name)}" = {name}'
             name = self._name(name)
         obj['name'] = name
         obj['meta-type'] = mtype
-        self._trees.append(_make_tree(obj, ifcond, features, extra))
-
-    def _gen_member(self, member):
-        obj = {'name': member.name, 'type': self._use_type(member.type)}
+        if features:
+            obj['features'] = self._gen_features(features)
+        self._trees.append(Annotated(obj, ifcond, comment))
+
+    def _gen_member(self, member: QAPISchemaObjectTypeMember
+                    ) -> Annotated[SchemaInfoObjectMember]:
+        obj: SchemaInfoObjectMember = {
+            'name': member.name,
+            'type': self._use_type(member.type)
+        }
         if member.optional:
             obj['default'] = None
-        return _make_tree(obj, member.ifcond, member.features)
-
-    def _gen_variants(self, tag_name, variants):
-        return {'tag': tag_name,
-                'variants': [self._gen_variant(v) for v in variants]}
-
-    def _gen_variant(self, variant):
-        obj = {'case': variant.name, 'type': self._use_type(variant.type)}
-        return _make_tree(obj, variant.ifcond, None)
-
-    def visit_builtin_type(self, name, info, json_type):
-        self._gen_tree(name, 'builtin', {'json-type': json_type}, [], None)
-
-    def visit_enum_type(self, name, info, ifcond, features, members, prefix):
-        self._gen_tree(name, 'enum',
-                       {'values': [_make_tree(m.name, m.ifcond, None)
-                                   for m in members]},
-                       ifcond, features)
-
-    def visit_array_type(self, name, info, ifcond, element_type):
+        if member.features:
+            obj['features'] = self._gen_features(member.features)
+        return Annotated(obj, member.ifcond)
+
+    def _gen_variant(self, variant: QAPISchemaVariant
+                     ) -> Annotated[SchemaInfoObjectVariant]:
+        obj: SchemaInfoObjectVariant = {
+            'case': variant.name,
+            'type': self._use_type(variant.type)
+        }
+        return Annotated(obj, variant.ifcond)
+
+    def visit_builtin_type(self, name: str, info: Optional[QAPISourceInfo],
+                           json_type: str) -> None:
+        self._gen_tree(name, 'builtin', {'json-type': json_type})
+
+    def visit_enum_type(self, name: str, info: Optional[QAPISourceInfo],
+                        ifcond: Sequence[str],
+                        features: List[QAPISchemaFeature],
+                        members: List[QAPISchemaEnumMember],
+                        prefix: Optional[str]) -> None:
+        self._gen_tree(
+            name, 'enum',
+            {'values': [Annotated(m.name, m.ifcond) for m in members]},
+            ifcond, features
+        )
+
+    def visit_array_type(self, name: str, info: Optional[QAPISourceInfo],
+                         ifcond: Sequence[str],
+                         element_type: QAPISchemaType) -> None:
         element = self._use_type(element_type)
         self._gen_tree('[' + element + ']', 'array', {'element-type': element},
-                       ifcond, None)
-
-    def visit_object_type_flat(self, name, info, ifcond, features,
-                               members, variants):
-        obj = {'members': [self._gen_member(m) for m in members]}
+                       ifcond)
+
+    def visit_object_type_flat(self, name: str, info: Optional[QAPISourceInfo],
+                               ifcond: Sequence[str],
+                               features: List[QAPISchemaFeature],
+                               members: List[QAPISchemaObjectTypeMember],
+                               variants: Optional[QAPISchemaVariants]) -> None:
+        obj: SchemaInfoObject = {
+            'members': [self._gen_member(m) for m in members]
+        }
         if variants:
-            obj.update(self._gen_variants(variants.tag_member.name,
-                                          variants.variants))
-
+            obj['tag'] = variants.tag_member.name
+            obj['variants'] = [self._gen_variant(v) for v in variants.variants]
         self._gen_tree(name, 'object', obj, ifcond, features)
 
-    def visit_alternate_type(self, name, info, ifcond, features, variants):
-        self._gen_tree(name, 'alternate',
-                       {'members': [
-                           _make_tree({'type': self._use_type(m.type)},
-                                      m.ifcond, None)
-                           for m in variants.variants]},
-                       ifcond, features)
+    def visit_alternate_type(self, name: str, info: Optional[QAPISourceInfo],
+                             ifcond: Sequence[str],
+                             features: List[QAPISchemaFeature],
+                             variants: QAPISchemaVariants) -> None:
+        self._gen_tree(
+            name, 'alternate',
+            {'members': [Annotated({'type': self._use_type(m.type)},
+                                   m.ifcond)
+                         for m in variants.variants]},
+            ifcond, features
+        )
+
+    def visit_command(self, name: str, info: Optional[QAPISourceInfo],
+                      ifcond: Sequence[str],
+                      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:
+        assert self._schema is not None
 
-    def visit_command(self, name, info, ifcond, features,
-                      arg_type, ret_type, gen, success_response, boxed,
-                      allow_oob, allow_preconfig, coroutine):
         arg_type = arg_type or self._schema.the_empty_object_type
         ret_type = ret_type or self._schema.the_empty_object_type
-        obj = {'arg-type': self._use_type(arg_type),
-               'ret-type': self._use_type(ret_type)}
+        obj: SchemaInfoCommand = {
+            'arg-type': self._use_type(arg_type),
+            'ret-type': self._use_type(ret_type)
+        }
         if allow_oob:
             obj['allow-oob'] = allow_oob
         self._gen_tree(name, 'command', obj, ifcond, features)
 
-    def visit_event(self, name, info, ifcond, features, arg_type, boxed):
+    def visit_event(self, name: str, info: Optional[QAPISourceInfo],
+                    ifcond: Sequence[str], features: List[QAPISchemaFeature],
+                    arg_type: Optional[QAPISchemaObjectType],
+                    boxed: bool) -> None:
+        assert self._schema is not None
+
         arg_type = arg_type or self._schema.the_empty_object_type
         self._gen_tree(name, 'event', {'arg-type': self._use_type(arg_type)},
                        ifcond, features)
 
 
-def gen_introspect(schema, output_dir, prefix, opt_unmask):
+def gen_introspect(schema: QAPISchema, output_dir: str, prefix: str,
+                   opt_unmask: bool) -> None:
     vis = QAPISchemaGenIntrospectVisitor(prefix, opt_unmask)
     schema.visit(vis)
     vis.write(output_dir)
diff --git a/scripts/qapi/mypy.ini b/scripts/qapi/mypy.ini
index 04bd5db..0a000d5 100644
--- a/scripts/qapi/mypy.ini
+++ b/scripts/qapi/mypy.ini
@@ -13,11 +13,6 @@ disallow_untyped_defs = False
 disallow_incomplete_defs = False
 check_untyped_defs = False
 
-[mypy-qapi.introspect]
-disallow_untyped_defs = False
-disallow_incomplete_defs = False
-check_untyped_defs = False
-
 [mypy-qapi.parser]
 disallow_untyped_defs = False
 disallow_incomplete_defs = False
diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 353e802..ff16578 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -28,7 +28,7 @@ from .parser import QAPISchemaParser
 class QAPISchemaEntity:
     meta: Optional[str] = None
 
-    def __init__(self, name, info, doc, ifcond=None, features=None):
+    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)
diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py
index 2bdd626..20d572a 100644
--- a/scripts/qapi/types.py
+++ b/scripts/qapi/types.py
@@ -13,7 +13,7 @@ This work is licensed under the terms of the GNU GPL, version 2.
 # See the COPYING file in the top-level directory.
 """
 
-from typing import List, Optional
+from typing import List, Optional, Sequence
 
 from .common import (
     c_enum_const,
@@ -139,7 +139,7 @@ def gen_struct_members(members: List[QAPISchemaObjectTypeMember]) -> str:
     return ret
 
 
-def gen_object(name: str, ifcond: List[str],
+def gen_object(name: str, ifcond: Sequence[str],
                base: Optional[QAPISchemaObjectType],
                members: List[QAPISchemaObjectTypeMember],
                variants: Optional[QAPISchemaVariants]) -> str:
@@ -307,7 +307,7 @@ class QAPISchemaGenTypeVisitor(QAPISchemaModularCVisitor):
     def visit_enum_type(self,
                         name: str,
                         info: Optional[QAPISourceInfo],
-                        ifcond: List[str],
+                        ifcond: Sequence[str],
                         features: List[QAPISchemaFeature],
                         members: List[QAPISchemaEnumMember],
                         prefix: Optional[str]) -> None:
@@ -318,7 +318,7 @@ class QAPISchemaGenTypeVisitor(QAPISchemaModularCVisitor):
     def visit_array_type(self,
                          name: str,
                          info: Optional[QAPISourceInfo],
-                         ifcond: List[str],
+                         ifcond: Sequence[str],
                          element_type: QAPISchemaType) -> None:
         with ifcontext(ifcond, self._genh, self._genc):
             self._genh.preamble_add(gen_fwd_object_or_array(name))
@@ -328,7 +328,7 @@ class QAPISchemaGenTypeVisitor(QAPISchemaModularCVisitor):
     def visit_object_type(self,
                           name: str,
                           info: Optional[QAPISourceInfo],
-                          ifcond: List[str],
+                          ifcond: Sequence[str],
                           features: List[QAPISchemaFeature],
                           base: Optional[QAPISchemaObjectType],
                           members: List[QAPISchemaObjectTypeMember],
@@ -351,7 +351,7 @@ class QAPISchemaGenTypeVisitor(QAPISchemaModularCVisitor):
     def visit_alternate_type(self,
                              name: str,
                              info: Optional[QAPISourceInfo],
-                             ifcond: List[str],
+                             ifcond: Sequence[str],
                              features: List[QAPISchemaFeature],
                              variants: QAPISchemaVariants) -> None:
         with ifcontext(ifcond, self._genh):
diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
index 22e62df..9aa0b1e 100644
--- a/scripts/qapi/visit.py
+++ b/scripts/qapi/visit.py
@@ -13,7 +13,7 @@ This work is licensed under the terms of the GNU GPL, version 2.
 See the COPYING file in the top-level directory.
 """
 
-from typing import List, Optional
+from typing import List, Optional, Sequence
 
 from .common import (
     c_enum_const,
@@ -337,7 +337,7 @@ class QAPISchemaGenVisitVisitor(QAPISchemaModularCVisitor):
     def visit_enum_type(self,
                         name: str,
                         info: Optional[QAPISourceInfo],
-                        ifcond: List[str],
+                        ifcond: Sequence[str],
                         features: List[QAPISchemaFeature],
                         members: List[QAPISchemaEnumMember],
                         prefix: Optional[str]) -> None:
@@ -348,7 +348,7 @@ class QAPISchemaGenVisitVisitor(QAPISchemaModularCVisitor):
     def visit_array_type(self,
                          name: str,
                          info: Optional[QAPISourceInfo],
-                         ifcond: List[str],
+                         ifcond: Sequence[str],
                          element_type: QAPISchemaType) -> None:
         with ifcontext(ifcond, self._genh, self._genc):
             self._genh.add(gen_visit_decl(name))
@@ -357,7 +357,7 @@ class QAPISchemaGenVisitVisitor(QAPISchemaModularCVisitor):
     def visit_object_type(self,
                           name: str,
                           info: Optional[QAPISourceInfo],
-                          ifcond: List[str],
+                          ifcond: Sequence[str],
                           features: List[QAPISchemaFeature],
                           base: Optional[QAPISchemaObjectType],
                           members: List[QAPISchemaObjectTypeMember],
@@ -379,7 +379,7 @@ class QAPISchemaGenVisitVisitor(QAPISchemaModularCVisitor):
     def visit_alternate_type(self,
                              name: str,
                              info: Optional[QAPISourceInfo],
-                             ifcond: List[str],
+                             ifcond: Sequence[str],
                              features: List[QAPISchemaFeature],
                              variants: QAPISchemaVariants) -> None:
         with ifcontext(ifcond, self._genh, self._genc):