Ensure that non-total TypedDicts can be falsy (#7745)

Fixes #7743

Author: henribru

mypy/types.py

@@ -1376,7 +1376,7 @@ def __init__(self, items: 'OrderedDict[str, Type]', required_keys: Set[str],
         self.required_keys = required_keys
         self.fallback = fallback
         self.can_be_true = len(self.items) > 0
-        self.can_be_false = len(self.items) == 0
+        self.can_be_false = len(self.required_keys) == 0
 
     def accept(self, visitor: 'TypeVisitor[T]') -> T:
         return visitor.visit_typeddict_type(self)

test-data/unit/check-typeddict.test

@@ -1126,6 +1126,25 @@ ll = [b, c]
 f(ll) # E: Argument 1 to "f" has incompatible type "List[TypedDict({'x'?: int, 'z'?: str})]"; expected "A"
 [builtins fixtures/dict.pyi]
 
+[case testNonTotalTypedDictCanBeEmpty]
+# flags: --warn-unreachable
+from mypy_extensions import TypedDict
+
+class A(TypedDict):
+    ...
+
+class B(TypedDict, total=False):
+    x: int
+
+a: A = {}
+b: B = {}
+
+if not a:
+    reveal_type(a) # N: Revealed type is 'TypedDict('__main__.A', {})'
+
+if not b:
+    reveal_type(b) # N: Revealed type is 'TypedDict('__main__.B', {'x'?: builtins.int})'
+[builtins fixtures/dict.pyi]
 
 -- Create Type (Errors)