Treating NoneType as None and warning against using NoneType.

mypy/typeanal.py

@@ -508,6 +508,11 @@ def analyze_type_with_type_info(
             # Create a named TypedDictType
             return td.copy_modified(item_types=self.anal_array(list(td.items.values())),
                                     fallback=instance)
+
+        if info.fullname == 'types.NoneType':
+            self.fail("NoneType should not be used as a type, please use None instead", ctx)
+            return NoneType(ctx.line, ctx.column)
+
         return instance
 
     def analyze_unbound_type_without_type_info(self, t: UnboundType, sym: SymbolTableNode,

test-data/unit/check-python310.test

@@ -1591,3 +1591,12 @@ def test_func(test_str: str) -> str:
             return "special"
         case _:
             return "other"
+
+
+[case testNoneTypeWarning]
+from types import NoneType
+
+def foo(x: NoneType): # E: NoneType should not be used as a type, please use None instead
+    reveal_type(x) # N: Revealed type is "None"
+
+[builtins fixtures/tuple.pyi]

test-data/unit/lib-stub/types.pyi

@@ -11,3 +11,6 @@ class ModuleType:
 if sys.version_info >= (3, 10):
     class Union:
         def __or__(self, x) -> Union: ...
+
+    class NoneType:
+        ...