Fix "Could not find builtin symbol 'NoneType'" in the ctypes plugin (#6097)

The error was triggered by creating an array of pointers. Instead, `NoneTyp()` should be used.

Author: jstasiak

mypy/plugins/ctypes.py

@@ -6,7 +6,9 @@
 import mypy.plugin
 from mypy.maptype import map_instance_to_supertype
 from mypy.subtypes import is_subtype
-from mypy.types import AnyType, CallableType, Instance, Type, TypeOfAny, UnionType, union_items
+from mypy.types import (
+    AnyType, CallableType, Instance, NoneTyp, Type, TypeOfAny, UnionType, union_items
+)
 
 
 def _get_bytes_type(api: 'mypy.plugin.CheckerPluginInterface') -> Instance:
@@ -70,7 +72,7 @@ def _autoconvertible_to_cdata(tp: Type, api: 'mypy.plugin.CheckerPluginInterface
                     # Pointer-like _SimpleCData subclasses can also be converted from
                     # an int or None.
                     allowed_types.append(api.named_generic_type('builtins.int', []))
-                    allowed_types.append(api.named_generic_type('builtins.NoneType', []))
+                    allowed_types.append(NoneTyp())
 
     return UnionType.make_simplified_union(allowed_types)
 

test-data/unit/check-ctypes.test

@@ -80,6 +80,13 @@ reveal_type(ca.value)  # E: Revealed type is 'builtins.bytes'
 reveal_type(ca.raw)  # E: Revealed type is 'builtins.bytes'
 [builtins fixtures/floatdict.pyi]
 
+[case testCtypesCharPArrayDoesNotCrash]
+import ctypes
+
+# The following line used to crash with "Could not find builtin symbol 'NoneType'"
+ca = (ctypes.c_char_p * 0)()
+[builtins fixtures/floatdict.pyi]
+
 [case testCtypesCharArrayAttrsPy2]
 # flags: --py2
 import ctypes