[Python] Manually cast enums while we transition to nanobind.

As we transition from pybind11 to nanobind, the enums defined upstream
will be defined by nanobind. This no longer works with automatic
casting in the pybind11 APIs we define ourselves. To work around this
while we smooth the transition, this updates the APIs to work with
plain py::objects and manually cast to the appropriate C API enums in
a way that's compatible with both the pybind11 and nanobind versions
of enums.

lib/Bindings/Python/SupportModule.cpp

@@ -28,16 +28,32 @@ void circt::python::populateSupportSubmodule(py::module &m) {
   m.def(
       "_walk_with_filter",
       [](MlirOperation operation, const std::vector<std::string> &opNames,
-         std::function<MlirWalkResult(MlirOperation)> callback,
-         MlirWalkOrder walkOrder) {
+         std::function<py::object(MlirOperation)> callback,
+         py::object walkOrderRaw) {
         struct UserData {
-          std::function<MlirWalkResult(MlirOperation)> callback;
+          std::function<py::object(MlirOperation)> callback;
           bool gotException;
           std::string exceptionWhat;
           py::object exceptionType;
           std::vector<MlirIdentifier> opNames;
         };
 
+        // As we transition from pybind11 to nanobind, the WalkOrder enum and
+        // automatic casting will be defined as a nanobind enum upstream. Do a
+        // manual conversion that works with either pybind11 or nanobind for
+        // now. When we're on nanobind in CIRCT, we can go back to automatic
+        // casting.
+        MlirWalkOrder walkOrder;
+        auto walkOrderRawValue = py::cast<int>(walkOrderRaw.attr("value"));
+        switch (walkOrderRawValue) {
+        case 0:
+          walkOrder = MlirWalkOrder::MlirWalkPreOrder;
+          break;
+        case 1:
+          walkOrder = MlirWalkOrder::MlirWalkPostOrder;
+          break;
+        }
+
         std::vector<MlirIdentifier> opNamesIdentifiers;
         opNamesIdentifiers.reserve(opNames.size());
 
@@ -68,7 +84,27 @@ void circt::python::populateSupportSubmodule(py::module &m) {
             return MlirWalkResult::MlirWalkResultAdvance;
 
           try {
-            return (calleeUserData->callback)(op);
+            // As we transition from pybind11 to nanobind, the WalkResult enum
+            // and automatic casting will be defined as a nanobind enum
+            // upstream. Do a manual conversion that works with either pybind11
+            // or nanobind for now. When we're on nanobind in CIRCT, we can go
+            // back to automatic casting.
+            MlirWalkResult walkResult;
+            auto walkResultRaw = (calleeUserData->callback)(op);
+            auto walkResultRawValue =
+                py::cast<int>(walkResultRaw.attr("value"));
+            switch (walkResultRawValue) {
+            case 0:
+              walkResult = MlirWalkResult::MlirWalkResultAdvance;
+              break;
+            case 1:
+              walkResult = MlirWalkResult::MlirWalkResultInterrupt;
+              break;
+            case 2:
+              walkResult = MlirWalkResult::MlirWalkResultSkip;
+              break;
+            }
+            return walkResult;
           } catch (py::error_already_set &e) {
             calleeUserData->gotException = true;
             calleeUserData->exceptionWhat = e.what();