[Dy2St]Raise TypeError when call to_static to convert a method of a common class (#44781)

* Fix to_static error when call to_static to convert a method of a common class

* raise typerror when class no inherits from layer

* Fix @to_static

python/paddle/fluid/dygraph/dygraph_to_static/program_translator.py

@@ -257,6 +257,10 @@ class StaticFunction(object):
             self._dygraph_function = getattr(function, '__func__')
             self._class_instance = getattr(function, '__self__')
 
+            if not hasattr(self._class_instance, '_original_funcs'):
+                raise TypeError(
+                    "When using 'to_static' to convert method of a class, "
+                    "please ensure the class inherits from nn.Layer")
             self._class_instance._original_funcs[
                 function.__name__] = self._dygraph_function
         else:
@@ -406,6 +410,10 @@ class StaticFunction(object):
 
     def _is_train_mode(self):
         if self._class_instance is not None:
+            if not hasattr(self._class_instance, 'training'):
+                raise TypeError(
+                    "When using 'to_static' to convert method of a class, "
+                    "please ensure the class inherits from nn.Layer")
             return self._class_instance.training
         else:
             return self._training

python/paddle/fluid/tests/unittests/dygraph_to_static/test_declarative.py

@@ -478,5 +478,21 @@ class TestSetBuffers(unittest.TestCase):
         paddle.enable_static()
 
 
+class ClassNoInheritLayer:
+
+    def func(self, x):
+        return x + 1
+
+
+class TestClassNoInheritLayer(unittest.TestCase):
+
+    def test_to_static(self):
+        paddle.disable_static()
+        net = ClassNoInheritLayer()
+        input_spec = [paddle.static.InputSpec(name='x', shape=[1])]
+        with self.assertRaises(TypeError):
+            static_func = paddle.jit.to_static(net.func, input_spec=input_spec)
+
+
 if __name__ == '__main__':
     unittest.main()