Make None compatible with SupportsBool protocol

mypy/subtypes.py

@@ -406,7 +406,9 @@ def visit_none_type(self, left: NoneType) -> bool:
                 # None is compatible with Hashable (and other similar protocols). This is
                 # slightly sloppy since we don't check the signature of "__hash__".
                 # None is also compatible with `SupportsStr` protocol.
-                return not members or all(member in ("__hash__", "__str__") for member in members)
+                return not members or all(
+                    member in ("__hash__", "__str__", "__bool__") for member in members
+                )
             return False
         else:
             return True

test-data/unit/check-protocols.test

@@ -2857,7 +2857,7 @@ c1: SupportsClassGetItem = C()
 
 [case testNoneVsProtocol]
 # mypy: strict-optional
-from typing_extensions import Protocol
+from typing_extensions import Literal, Protocol
 
 class MyHashable(Protocol):
     def __hash__(self) -> int: ...
@@ -2890,6 +2890,22 @@ class SupportsStr(Protocol):
 def ss(s: SupportsStr) -> None: pass
 ss(None)
 
+class SupportsBool(Protocol):
+    def __bool__(self) -> bool: ...
+
+class SupportsBoolLiteralTrue(Protocol):
+    def __bool__(self) -> Literal[True]: ...
+
+class SupportsBoolLiteralFalse(Protocol):
+    def __bool__(self) -> Literal[False]: ...
+
+def sb(s: SupportsBool) -> None: pass
+sb(None)
+def sblt(s: SupportsBoolLiteralTrue) -> None: pass
+sblt(None)
+def sblf(s: SupportsBoolLiteralFalse) -> None: pass
+sblf(None)
+
 class HashableStr(Protocol):
     def __str__(self) -> str: ...
     def __hash__(self) -> int: ...