Handle placeholder types better

Author: cdce8p

mypy/expandtype.py

@@ -9,8 +9,10 @@
     ANY_STRATEGY,
     AnyType,
     BoolTypeQuery,
+    CallableArgument,
     CallableType,
     DeletedType,
+    EllipsisType,
     ErasedType,
     FunctionLike,
     Instance,
@@ -20,16 +22,20 @@
     Parameters,
     ParamSpecType,
     PartialType,
+    PlaceholderType,
     ProperType,
+    RawExpressionType,
+    StarType,
+    SyntheticTypeVisitor,
     TupleType,
     Type,
     TypeAliasType,
     TypedDictType,
+    TypeList,
     TypeType,
     TypeVarId,
     TypeVarTupleType,
     TypeVarType,
-    TypeVisitor,
     UnboundType,
     UninhabitedType,
     UnionType,
@@ -189,7 +195,7 @@ def visit_type_alias_type(self, t: TypeAliasType) -> Type:
         return t.copy_modified(args=[arg.accept(self) for arg in t.args])
 
 
-class ExpandTypeVisitor(TypeVisitor[Type]):
+class ExpandTypeVisitor(SyntheticTypeVisitor[Type]):
     """Visitor that substitutes type variables with values."""
 
     variables: Mapping[TypeVarId, Type]  # TypeVar id -> TypeVar value
@@ -486,6 +492,24 @@ def visit_type_alias_type(self, t: TypeAliasType) -> Type:
     def expand_types(self, types: Iterable[Type]) -> list[Type]:
         return [t.accept(self) for t in types]
 
+    def visit_star_type(self, t: StarType) -> Type:
+        return t
+
+    def visit_type_list(self, t: TypeList) -> Type:
+        return t
+
+    def visit_callable_argument(self, t: CallableArgument) -> Type:
+        return t
+
+    def visit_ellipsis_type(self, t: EllipsisType) -> Type:
+        return t
+
+    def visit_raw_expression_type(self, t: RawExpressionType) -> Type:
+        return t
+
+    def visit_placeholder_type(self, t: PlaceholderType) -> Type:
+        return t
+
 
 def expand_unpack_with_variables(
     t: UnpackType, variables: Mapping[TypeVarId, Type]

mypy/semanal.py

@@ -1565,11 +1565,17 @@ def analyze_class(self, defn: ClassDef) -> None:
 
         for tvd in tvar_defs:
             if isinstance(tvd, TypeVarType) and any(
-                has_placeholder(t) for t in [tvd.upper_bound, tvd.default] + tvd.values
+                has_placeholder(t) for t in [tvd.upper_bound] + tvd.values
             ):
                 # Some type variable bounds or values are not ready, we need
                 # to re-analyze this class.
                 self.defer()
+            if isinstance(tvd, TypeVarLikeType) and has_placeholder(tvd.default):
+                # Placeholder values in TypeVarLikeTypes may get substituted in.
+                # Defer current target until they are ready.
+                self.defer()
+                self.mark_incomplete(defn.name, defn)
+                return
 
         self.analyze_class_keywords(defn)
         bases_result = self.analyze_base_classes(bases)