[aoti] Add error msg if we can't find a proxy executor (pytorch#140308)

Fixes #ISSUE_NUMBER

Pull Request resolved: pytorch#140308
Approved by: https://github.com/desertfire

test/inductor/test_aot_inductor.py

@@ -2934,6 +2934,20 @@ def forward(self, x, y):
         )
         self.check_model(m, args)
 
+    def test_custom_op_add_output_path(self) -> None:
+        class M(torch.nn.Module):
+            def forward(self, x, y):
+                return torch.ops.aoti_custom_ops.custom_add(x, y)
+
+        m = M().to(device=self.device)
+        args = (
+            torch.randn(3, 3, device=self.device),
+            torch.randn(3, 3, device=self.device),
+        )
+        with config.patch("aot_inductor.output_path", "model.so"):
+            with self.assertRaises(Exception):
+                self.check_model(m, args)
+
     def test_custom_op_all_inputs(self) -> None:
         class MyModel(torch.nn.Module):
             # pyre-fixme[3]: Return type must be annotated.

torch/csrc/inductor/aoti_runner/model_container_runner.cpp

@@ -74,6 +74,8 @@ AOTIModelContainerRunner::AOTIModelContainerRunner(
         json_filename, device_str == "cpu");
     proxy_executor_handle_ =
         reinterpret_cast<AOTIProxyExecutorHandle>(proxy_executor_.get());
+  } else {
+    proxy_executor_handle_ = nullptr;
   }
 
   AOTI_RUNTIME_ERROR_CODE_CHECK(create_func_(

torch/csrc/inductor/aoti_torch/shim_common.cpp

@@ -1136,6 +1136,13 @@ AOTITorchError aoti_torch_proxy_executor_call_function(
     int num_tensors,
     AtenTensorHandle* flatten_tensor_args) {
   AOTI_TORCH_CONVERT_EXCEPTION_TO_ERROR_CODE({
+    if (!proxy_executor) {
+      throw std::runtime_error(
+          "Unable to find a proxy executor to run custom ops. Please check if "
+          "there is a json file generated in the same directory as the so, or use "
+          "torch._inductor.aoti_compile_and_package to package everything into a "
+          "PT2 artifact.");
+    }
     ProxyExecutor* executor = reinterpret_cast<ProxyExecutor*>(proxy_executor);
     executor->call_function(
         extern_node_index,