Ensure backward compatibility in MessagePassing via torch.load

CHANGELOG.md

@@ -34,6 +34,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
+- Ensure backward compatibility in `MessagePassing` via `torch.load` ([#9105](https://github.com/pyg-team/pytorch_geometric/pull/9105))
 - Prevent model compilation on custom `propagate` functions ([#9079](https://github.com/pyg-team/pytorch_geometric/pull/9079))
 - Ignore `self.propagate` appearances in comments when parsing `MessagePassing` implementation ([#9044](https://github.com/pyg-team/pytorch_geometric/pull/9044))
 - Fixed `OSError` on read-only file systems within `MessagePassing` ([#9032](https://github.com/pyg-team/pytorch_geometric/pull/9032))

test/nn/conv/test_message_passing.py

@@ -130,6 +130,22 @@ def test_my_conv_basic():
         assert torch_adj_t.grad is not None
 
 
+def test_my_conv_save(tmp_path):
+    conv = MyConv(8, 32)
+    assert conv._jinja_propagate is not None
+    assert conv.__class__._jinja_propagate is not None
+    assert conv._orig_propagate is not None
+    assert conv.__class__._orig_propagate is not None
+
+    path = osp.join(tmp_path, 'model.pt')
+    torch.save(conv, path)
+    conv = torch.load(path)
+    assert conv._jinja_propagate is not None
+    assert conv.__class__._jinja_propagate is not None
+    assert conv._orig_propagate is not None
+    assert conv.__class__._orig_propagate is not None
+
+
 def test_my_conv_edge_index():
     x = torch.randn(4, 8)
     edge_index = torch.tensor([[0, 1, 2, 3], [0, 0, 1, 1]])

torch_geometric/nn/conv/message_passing.py

@@ -731,13 +731,14 @@ def decomposed_layers(self, decomposed_layers: int) -> None:
         self._decomposed_layers = decomposed_layers
 
         if decomposed_layers != 1:
-            self.propagate = self.__class__._orig_propagate.__get__(
-                self, MessagePassing)
+            if hasattr(self.__class__, '_orig_propagate'):
+                self.propagate = self.__class__._orig_propagate.__get__(
+                    self, MessagePassing)
 
-        elif ((self.explain is None or self.explain is False)
-              and not self.propagate.__module__.endswith('_propagate')):
-            self.propagate = self.__class__._jinja_propagate.__get__(
-                self, MessagePassing)
+        elif self.explain is None or self.explain is False:
+            if hasattr(self.__class__, '_jinja_propagate'):
+                self.propagate = self.__class__._jinja_propagate.__get__(
+                    self, MessagePassing)
 
     # Explainability ##########################################################
 
@@ -761,16 +762,18 @@ def explain(self, explain: Optional[bool]) -> None:
                 funcs=['message', 'explain_message', 'aggregate', 'update'],
                 exclude=self.special_args,
             )
-            self.propagate = self.__class__._orig_propagate.__get__(
-                self, MessagePassing)
+            if hasattr(self.__class__, '_orig_propagate'):
+                self.propagate = self.__class__._orig_propagate.__get__(
+                    self, MessagePassing)
         else:
             self._user_args = self.inspector.get_flat_param_names(
                 funcs=['message', 'aggregate', 'update'],
                 exclude=self.special_args,
             )
             if self.decomposed_layers == 1:
-                self.propagate = self.__class__._jinja_propagate.__get__(
-                    self, MessagePassing)
+                if hasattr(self.__class__, '_jinja_propagate'):
+                    self.propagate = self.__class__._jinja_propagate.__get__(
+                        self, MessagePassing)
 
     def explain_message(
         self,