Reject calling NotImplemented() (fix #2918)

NotImplemented is a singleton; stubs model NotImplementedType with an Any base,
which made has_base_any treat it as implicitly callable. Skip that path for
types.NotImplementedType and builtins._NotImplementedType.

Adds regression test in pyrefly/lib/test/callable.rs.

Made-with: Cursor

Author: Louisvranderick

pyrefly/lib/alt/call.rs

@@ -366,9 +366,15 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                     // If the class has an unknown base (e.g. inherits from an
                     // unresolved name), it might have inherited `__call__` from
                     // that base, so treat it as callable with implicit Any.
+                    //
+                    // `NotImplemented` is a singleton instance of `NotImplementedType`; it must
+                    // never be treated as callable even when stubs use `NotImplementedType(Any)`,
+                    // which would otherwise set `has_base_any` and hit this branch.
                     None if self
                         .get_metadata_for_class(cls.class_object())
-                        .has_base_any() =>
+                        .has_base_any()
+                        && !cls.has_qname("types", "NotImplementedType")
+                        && !cls.has_qname("builtins", "_NotImplementedType") =>
                     {
                         CallTargetLookup::Ok(Box::new(CallTarget::Any(AnyStyle::Implicit)))
                     }

pyrefly/lib/test/callable.rs

@@ -1449,3 +1449,13 @@ def after_func() -> None: ...
 schedule(1000, after_func)
 "#,
 );
+
+// Regression test for https://github.com/facebook/pyrefly/issues/2918
+testcase!(
+    test_notimplemented_not_callable,
+    r#"
+NotImplemented()  # E: Expected a callable
+NotImplemented("not yet done")  # E: Expected a callable
+raise NotImplementedError()
+"#,
+);