Fix type narrowing of == None and in (None,) conditions

mypy/checker.py

@@ -216,7 +216,7 @@
     is_literal_type,
     is_named_instance,
 )
-from mypy.types_utils import is_optional, remove_optional, store_argument_type, strip_type
+from mypy.types_utils import is_overlapping_none, remove_optional, store_argument_type, strip_type
 from mypy.typetraverser import TypeTraverserVisitor
 from mypy.typevars import fill_typevars, fill_typevars_with_any, has_no_typevars
 from mypy.util import is_dunder, is_sunder, is_typeshed_file
@@ -5657,13 +5657,13 @@ def has_no_custom_eq_checks(t: Type) -> bool:
 
                     if left_index in narrowable_operand_index_to_hash:
                         # We only try and narrow away 'None' for now
-                        if is_optional(item_type):
+                        if is_overlapping_none(item_type):
                             collection_item_type = get_proper_type(
                                 builtin_item_type(iterable_type)
                             )
                             if (
                                 collection_item_type is not None
-                                and not is_optional(collection_item_type)
+                                and not is_overlapping_none(collection_item_type)
                                 and not (
                                     isinstance(collection_item_type, Instance)
                                     and collection_item_type.type.fullname == "builtins.object"
@@ -6070,7 +6070,7 @@ def refine_away_none_in_comparison(
         non_optional_types = []
         for i in chain_indices:
             typ = operand_types[i]
-            if not is_optional(typ):
+            if not is_overlapping_none(typ):
                 non_optional_types.append(typ)
 
         # Make sure we have a mixture of optional and non-optional types.
@@ -6080,7 +6080,7 @@ def refine_away_none_in_comparison(
         if_map = {}
         for i in narrowable_operand_indices:
             expr_type = operand_types[i]
-            if not is_optional(expr_type):
+            if not is_overlapping_none(expr_type):
                 continue
             if any(is_overlapping_erased_types(expr_type, t) for t in non_optional_types):
                 if_map[operands[i]] = remove_optional(expr_type)

mypy/checkexpr.py

@@ -169,7 +169,12 @@
     is_named_instance,
     split_with_prefix_and_suffix,
 )
-from mypy.types_utils import is_generic_instance, is_optional, is_self_type_like, remove_optional
+from mypy.types_utils import (
+    is_generic_instance,
+    is_overlapping_none,
+    is_self_type_like,
+    remove_optional,
+)
 from mypy.typestate import type_state
 from mypy.typevars import fill_typevars
 from mypy.typevartuples import find_unpack_in_list
@@ -1809,7 +1814,7 @@ def infer_function_type_arguments_using_context(
         # valid results.
         erased_ctx = replace_meta_vars(ctx, ErasedType())
         ret_type = callable.ret_type
-        if is_optional(ret_type) and is_optional(ctx):
+        if is_overlapping_none(ret_type) and is_overlapping_none(ctx):
             # If both the context and the return type are optional, unwrap the optional,
             # since in 99% cases this is what a user expects. In other words, we replace
             #     Optional[T] <: Optional[int]

mypy/plugins/common.py

@@ -43,7 +43,7 @@
     deserialize_type,
     get_proper_type,
 )
-from mypy.types_utils import is_optional
+from mypy.types_utils import is_overlapping_none
 from mypy.typevars import fill_typevars
 from mypy.util import get_unique_redefinition_name
 
@@ -141,7 +141,7 @@ def find_shallow_matching_overload_item(overload: Overloaded, call: CallExpr) ->
                         break
                 elif (
                     arg_none
-                    and not is_optional(arg_type)
+                    and not is_overlapping_none(arg_type)
                     and not (
                         isinstance(arg_type, Instance)
                         and arg_type.type.fullname == "builtins.object"

mypy/suggestions.py

@@ -79,7 +79,7 @@
     UnionType,
     get_proper_type,
 )
-from mypy.types_utils import is_optional, remove_optional
+from mypy.types_utils import is_overlapping_none, remove_optional
 from mypy.util import split_target
 
 
@@ -752,7 +752,7 @@ def score_type(self, t: Type, arg_pos: bool) -> int:
                 return 20
             if any(has_any_type(x) for x in t.items):
                 return 15
-            if not is_optional(t):
+            if not is_overlapping_none(t):
                 return 10
         if isinstance(t, CallableType) and (has_any_type(t) or is_tricky_callable(t)):
             return 10
@@ -868,7 +868,7 @@ def visit_typeddict_type(self, t: TypedDictType) -> str:
         return t.fallback.accept(self)
 
     def visit_union_type(self, t: UnionType) -> str:
-        if len(t.items) == 2 and is_optional(t):
+        if len(t.items) == 2 and is_overlapping_none(t):
             return f"Optional[{remove_optional(t).accept(self)}]"
         else:
             return super().visit_union_type(t)

mypy/types_utils.py

@@ -101,10 +101,10 @@ def is_generic_instance(tp: Type) -> bool:
     return isinstance(tp, Instance) and bool(tp.args)
 
 
-def is_optional(t: Type) -> bool:
+def is_overlapping_none(t: Type) -> bool:
     t = get_proper_type(t)
-    return isinstance(t, UnionType) and any(
-        isinstance(get_proper_type(e), NoneType) for e in t.items
+    return isinstance(t, NoneType) or (
+        isinstance(t, UnionType) and any(isinstance(get_proper_type(e), NoneType) for e in t.items)
     )
 
 

test-data/unit/check-narrowing.test

@@ -1263,6 +1263,32 @@ def g() -> None:
 [builtins fixtures/dict.pyi]
 
 
+[case testNarrowingOptionalEqualsNone]
+from typing import Optional
+
+class A: ...
+
+val: Optional[A]
+
+if val == None:
+    reveal_type(val)  # N: Revealed type is "Union[__main__.A, None]"
+else:
+    reveal_type(val)  # N: Revealed type is "Union[__main__.A, None]"
+if val != None:
+    reveal_type(val)  # N: Revealed type is "Union[__main__.A, None]"
+else:
+    reveal_type(val)  # N: Revealed type is "Union[__main__.A, None]"
+
+if val in (None,):
+    reveal_type(val)  # N: Revealed type is "Union[__main__.A, None]"
+else:
+    reveal_type(val)  # N: Revealed type is "Union[__main__.A, None]"
+if val not in (None,):
+    reveal_type(val)  # N: Revealed type is "Union[__main__.A, None]"
+else:
+    reveal_type(val)  # N: Revealed type is "Union[__main__.A, None]"
+[builtins fixtures/primitives.pyi]
+
 [case testNarrowingWithTupleOfTypes]
 from typing import Tuple, Type
 

test-data/unit/fixtures/primitives.pyi

@@ -45,7 +45,8 @@ class memoryview(Sequence[int]):
     def __iter__(self) -> Iterator[int]: pass
     def __contains__(self, other: object) -> bool: pass
     def __getitem__(self, item: int) -> int: pass
-class tuple(Generic[T]): pass
+class tuple(Generic[T]):
+    def __contains__(self, other: object) -> bool: pass
 class list(Sequence[T]):
     def __iter__(self) -> Iterator[T]: pass
     def __contains__(self, other: object) -> bool: pass