[jit] Allow instance overrides of ignored methods (pytorch#61076)

Summary:
Pull Request resolved: pytorch#61076

Previously we would always retrieve ignored methods from the
type, which doesn't work when the user has overriden the ignored method
for a specific instance.

This PR changes things up so we retrieve the ignored method as a bound
method from the object being scripted, unwrap it, then re-bind it to the
scriptmodule.

Test Plan: Imported from OSS

Differential Revision: D29504421

Pulled By: suo

fbshipit-source-id: 14649863ea69a8d2180dd2c4341ec9a826039de1

Author: suo

test/jit/test_recursive_script.py

@@ -1,5 +1,6 @@
 import os
 import sys
+import types
 import typing
 import typing_extensions
 from typing import List, Dict, Optional, Tuple
@@ -729,3 +730,23 @@ def forward(self, x):
         self.checkModule(mod, (torch.rand(2, 2),))
         mod.foo = None
         self.checkModule(mod, (torch.rand(2, 2),))
+
+    def test_override_instance_method_ignore(self):
+        class M(torch.nn.Module):
+            @torch.jit.ignore
+            def i_am_ignored(self):
+                return "old"
+
+        m = M()
+
+        # Override the ignored method by binding a new method to this instance.
+        @torch.jit.ignore
+        def i_am_ignored(self):
+            return "new"
+
+        m.i_am_ignored = types.MethodType(i_am_ignored, m)
+        self.assertEqual(m.i_am_ignored(), "new")
+
+        # ScriptModule should correctly reflect the override.
+        s = torch.jit.script(m)
+        self.assertEqual(s.i_am_ignored(), "new")

torch/jit/_recursive.py

@@ -499,7 +499,7 @@ def init_fn(script_module):
                 continue
             item = getattr(nn_module, name, None)
             if inspect.ismethod(item) and _jit_internal.is_ignored_fn(item):
-                unbound_function = getattr(type(nn_module), name)
+                unbound_function = getattr(nn_module, name).__func__
                 bound_method = unbound_function.__get__(script_module)
                 setattr(script_module, name, bound_method)
             elif concrete_type.is_ignored_attribute(name):