support function + method variants

Differential Revision: D75006941

Pull Request resolved: pytorch#10974

Author: JacobSzwejbka

codegen/gen.py

@@ -134,15 +134,14 @@ def __call__(self, f: NativeFunction) -> str | None:
         if not self.selector.is_root_operator(f"{f.namespace}::{f.func.name}"):
             return None
 
-        if Variant.function not in f.variants and Variant.method in f.variants:
-            is_method_variant = True
-
-        # only valid remaining case is only function is in f.variants
-        elif not (Variant.function in f.variants and Variant.method not in f.variants):
+        if Variant.function not in f.variants and Variant.method not in f.variants:
             raise Exception(  # noqa: TRY002
-                f"Can't handle native function {f.func} with the following variant specification {f.variants}."
+                f"Expected one of function or method to be in variants for {f.func.name}"
             )
 
+        if Variant.function not in f.variants and Variant.method in f.variants:
+            is_method_variant = True
+
         sig: CppSignature | ExecutorchCppSignature = (
             CppSignatureGroup.from_native_function(
                 f, method=False, fallback_binding=f.manual_cpp_binding