Fix deferral logic for special types (#20678)

Fixes #20671

The crash was caused by extending a TypedDict that was itself not ready
(contained placeholders). While looking for a fix I noticed that for
some reason we check for placeholders in _previous_ version of a
TypedDict etc. Not sure why, this mat have been a remainder of an old
hack. Replacing it with a check for placeholders in current version
looks more correct (although there is probably no difference for other
special types) and turns out to be a fix for this issue.

Author: ilevkivskyi

mypy/semanal.py

@@ -2688,7 +2688,7 @@ def configure_tuple_base_class(self, defn: ClassDef, base: TupleType) -> Instanc
         if info.tuple_type and info.tuple_type != base and not has_placeholder(info.tuple_type):
             self.fail("Class has two incompatible bases derived from tuple", defn)
             defn.has_incompatible_baseclass = True
-        if info.special_alias and has_placeholder(info.special_alias.target):
+        if has_placeholder(base):
             self.process_placeholder(
                 None, "tuple base", defn, force_progress=base != info.tuple_type
             )

mypy/semanal_namedtuple.py

@@ -527,7 +527,7 @@ def build_namedtuple_typeinfo(
         info = existing_info or self.api.basic_new_typeinfo(name, fallback, line)
         info.is_named_tuple = True
         tuple_base = TupleType(types, fallback)
-        if info.special_alias and has_placeholder(info.special_alias.target):
+        if has_placeholder(tuple_base):
             self.api.process_placeholder(
                 None, "NamedTuple item", info, force_progress=tuple_base != info.tuple_type
             )

mypy/semanal_typeddict.py

@@ -607,7 +607,7 @@ def build_typeddict_typeinfo(
         assert fallback is not None
         info = existing_info or self.api.basic_new_typeinfo(name, fallback, line)
         typeddict_type = TypedDictType(item_types, required_keys, readonly_keys, fallback)
-        if info.special_alias and has_placeholder(info.special_alias.target):
+        if has_placeholder(typeddict_type):
             self.api.process_placeholder(
                 None, "TypedDict item", info, force_progress=typeddict_type != info.typeddict_type
             )

test-data/unit/check-typeddict.test

@@ -4581,3 +4581,31 @@ bad({"x": "foo"})  # E: Dict entry 0 has incompatible type "str": "str"; expecte
 
 [builtins fixtures/dict.pyi]
 [typing fixtures/typing-typeddict.pyi]
+
+[case testTypedDictUnpackImportCycle]
+import mre
+
+[file mre.py]
+from mre_pkg.model import Callback
+Callback(callback=1)  # E: Argument "callback" to "Callback" has incompatible type "int"; expected "Callback"
+
+[file mre_pkg/model.pyi]
+from typing_extensions import Unpack, TYPE_CHECKING, TypedDict
+from .callbacks import Callback as Callback
+
+class _ModelInit(TypedDict, total=False):
+    callback: Callback
+
+class Model:
+    def __init__(self, **kwargs: Unpack[_ModelInit]) -> None: ...
+
+[file mre_pkg/callbacks.pyi]
+from typing_extensions import Unpack, TYPE_CHECKING, TypedDict
+from .model import Model, _ModelInit
+
+class _CallbackInit(_ModelInit, total=False): ...
+
+class Callback(Model):
+    def __init__(self, **kwargs: Unpack[_CallbackInit]) -> None: ...
+[builtins fixtures/dict.pyi]
+[typing fixtures/typing-typeddict.pyi]