Re-implement union_items function

Since mypy v0.980 this function has been removed from `mypy.types`.
This this commit we re-implement the same version
present in v0.970.

Author: ivanovmg

classes/contrib/mypy/typeops/call_signatures.py

@@ -6,10 +6,11 @@
 from mypy.typeops import get_type_vars, make_simplified_union
 from mypy.types import CallableType, Instance, ProperType
 from mypy.types import Type as MypyType
-from mypy.types import TypeVarType, union_items
+from mypy.types import TypeVarType
 from typing_extensions import Final, final
 
 from classes.contrib.mypy.typeops import type_loader
+from classes.contrib.mypy.typeops.union_items import union_items
 
 _INCOMPATIBLE_TYPEVAR_MSG: Final = (
     'Argument 1 to {0} has incompatible type "{1}"; expected "{2}"'

classes/contrib/mypy/typeops/mro.py

@@ -4,10 +4,11 @@
 from mypy.subtypes import is_equivalent
 from mypy.types import Instance
 from mypy.types import Type as MypyType
-from mypy.types import UnionType, union_items
+from mypy.types import UnionType
 from typing_extensions import final
 
 from classes.contrib.mypy.typeops import type_loader
+from classes.contrib.mypy.typeops.union_items import union_items
 
 
 @final

classes/contrib/mypy/typeops/union_items.py

@@ -0,0 +1,21 @@
+from mypy.types import ProperType, Type, UnionType, get_proper_type
+
+
+def union_items(typ: Type) -> list[ProperType]:
+    """Return the flattened items of a union type.
+
+    For non-union types, return a list containing just the argument.
+
+    This is a re-implementation of the old `mypy.types.union_items`
+    function (v0.970):
+    Since mypy version 0.980 they removed this function from `mypy.types`.
+    """
+    # https://github.com/python/mypy/blob/1f08cf44c7ec3dc4111aaf817958f7a51018ba38/mypy/types.py#L2960
+    typ = get_proper_type(typ)
+    if isinstance(typ, UnionType):
+        union_types = []
+        for a_type in typ.items:
+            union_types.extend(union_items(a_type))
+        return union_types
+
+    return [typ]

classes/contrib/mypy/validation/validate_instance/validate_runtime.py

@@ -2,8 +2,7 @@
 
 from mypy.erasetype import erase_type
 from mypy.plugin import MethodContext
-from mypy.sametypes import is_same_type
-from mypy.subtypes import is_subtype
+from mypy.subtypes import is_same_type, is_subtype
 from mypy.types import Instance
 from mypy.types import Type as MypyType
 from mypy.types import TypedDictType