[Python] Switch CIRCT Python extension and dialects to nanobind.

This follows the general nanobind porting guide and the upstream MLIR
changes in the same vein. For the most part, this is a very direct
migration accomplished with sed.

There were a couple minor differences.

Nanobind is more strict about implicit casting, which popped up in a
couple places:

* In MSFTModule, getNearestFreeInColumn was expecting a
CIRCTMSFTPrimitiveType (int), but was actually being passed
PrimitiveType enums at the call sites. Nanobind refused to
automatically cast enum to int, so it was done manually.
* In SVModule, SVAttributeAttr.get was expecting a bool for
emitAsComment, even though it was declared as having a default of
None. Nanobind refused to automatically cast None to bool, so it was
done manually, with a default of false.

Nanobind also prints enums slightly differently, so one FileCheck test
had to be updated for ESI.

Otherwise, the changes were purely mechanical.

CMakeLists.txt

@@ -514,11 +514,11 @@ option(CIRCT_BINDINGS_PYTHON_ENABLED "Enables CIRCT Python bindings." OFF)
 if(CIRCT_BINDINGS_PYTHON_ENABLED)
   message(STATUS "CIRCT Python bindings are enabled.")
   set(MLIR_DISABLE_CONFIGURE_PYTHON_DEV_PACKAGES 0)
-  mlir_detect_pybind11_install()
+  mlir_detect_nanobind_install()
   # Prime the search like mlir_configure_python_dev_modules
   find_package(Python3 3.8 COMPONENTS Interpreter Development)
   find_package(Python3 3.8 COMPONENTS Interpreter Development.Module)
-  find_package(pybind11 2.10 CONFIG REQUIRED)
+  find_package(nanobind 2.4.0 CONFIG REQUIRED)
 else()
   message(STATUS "CIRCT Python bindings are disabled.")
   # Lookup python either way as some integration tests use python without the

integration_test/Bindings/Python/dialects/esi.py

@@ -31,7 +31,7 @@
   assert (not bundle_type.resettable)
   for bchan in bundle_type.channels:
     print(bchan)
-  # CHECK: ('i16chan', <ChannelDirection.TO: 1>, Type(!esi.channel<i16>))
+  # CHECK: ('i16chan', ChannelDirection.TO, Type(!esi.channel<i16>))
   print()
 
   bundle_type = esi.BundleType.get(

lib/Bindings/Python/CIRCTModule.cpp

@@ -1,4 +1,4 @@
-//===- CIRCTModule.cpp - Main pybind module -------------------------------===//
+//===- CIRCTModule.cpp - Main nanobind module -----------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -35,14 +35,14 @@
 #include "mlir-c/Bindings/Python/Interop.h"
 #include "mlir-c/IR.h"
 #include "mlir-c/Transforms.h"
-#include "mlir/Bindings/Python/PybindAdaptors.h"
+#include "mlir/Bindings/Python/NanobindAdaptors.h"
 
 #include "llvm-c/ErrorHandling.h"
 #include "llvm/Support/Signals.h"
 
-#include "PybindUtils.h"
-#include <pybind11/pybind11.h>
-namespace py = pybind11;
+#include "NanobindUtils.h"
+#include <nanobind/nanobind.h>
+namespace nb = nanobind;
 
 static void registerPasses() {
   registerArcPasses();
@@ -59,15 +59,15 @@ static void registerPasses() {
   mlirRegisterTransformsCSE();
 }
 
-PYBIND11_MODULE(_circt, m) {
+NB_MODULE(_circt, m) {
   m.doc() = "CIRCT Python Native Extension";
   registerPasses();
   llvm::sys::PrintStackTraceOnErrorSignal(/*argv=*/"");
   LLVMEnablePrettyStackTrace();
 
   m.def(
       "register_dialects",
-      [](py::object capsule) {
+      [](nb::object capsule) {
         // Get the MlirContext capsule from PyMlirContext capsule.
         auto wrappedCapsule = capsule.attr(MLIR_PYTHON_CAPI_PTR_ATTR);
         MlirContext context = mlirPythonCapsuleToContext(wrappedCapsule.ptr());
@@ -145,9 +145,9 @@ PYBIND11_MODULE(_circt, m) {
       },
       "Register CIRCT dialects on a PyMlirContext.");
 
-  m.def("export_verilog", [](MlirModule mod, py::object fileObject) {
+  m.def("export_verilog", [](MlirModule mod, nb::object fileObject) {
     circt::python::PyFileAccumulator accum(fileObject, false);
-    py::gil_scoped_release();
+    nb::gil_scoped_release();
     mlirExportVerilog(mod, accum.getCallback(), accum.getUserData());
   });
 
@@ -156,26 +156,26 @@ PYBIND11_MODULE(_circt, m) {
     mlirExportSplitVerilog(mod, cDirectory);
   });
 
-  py::module esi = m.def_submodule("_esi", "ESI API");
+  nb::module_ esi = m.def_submodule("_esi", "ESI API");
   circt::python::populateDialectESISubmodule(esi);
-  py::module msft = m.def_submodule("_msft", "MSFT API");
+  nb::module_ msft = m.def_submodule("_msft", "MSFT API");
   circt::python::populateDialectMSFTSubmodule(msft);
-  py::module hw = m.def_submodule("_hw", "HW API");
+  nb::module_ hw = m.def_submodule("_hw", "HW API");
   circt::python::populateDialectHWSubmodule(hw);
-  py::module seq = m.def_submodule("_seq", "Seq API");
+  nb::module_ seq = m.def_submodule("_seq", "Seq API");
   circt::python::populateDialectSeqSubmodule(seq);
-  py::module om = m.def_submodule("_om", "OM API");
+  nb::module_ om = m.def_submodule("_om", "OM API");
   circt::python::populateDialectOMSubmodule(om);
-  py::module rtg = m.def_submodule("_rtg", "RTG API");
+  nb::module_ rtg = m.def_submodule("_rtg", "RTG API");
   circt::python::populateDialectRTGSubmodule(rtg);
-  py::module rtgtool = m.def_submodule("_rtgtool", "RTGTool API");
+  nb::module_ rtgtool = m.def_submodule("_rtgtool", "RTGTool API");
   circt::python::populateDialectRTGToolSubmodule(rtgtool);
 #ifdef CIRCT_INCLUDE_TESTS
-  py::module rtgtest = m.def_submodule("_rtgtest", "RTGTest API");
+  nb::module_ rtgtest = m.def_submodule("_rtgtest", "RTGTest API");
   circt::python::populateDialectRTGTestSubmodule(rtgtest);
 #endif
-  py::module sv = m.def_submodule("_sv", "SV API");
+  nb::module_ sv = m.def_submodule("_sv", "SV API");
   circt::python::populateDialectSVSubmodule(sv);
-  py::module support = m.def_submodule("_support", "CIRCT support");
+  nb::module_ support = m.def_submodule("_support", "CIRCT support");
   circt::python::populateSupportSubmodule(support);
 }

lib/Bindings/Python/CIRCTModules.h

@@ -13,23 +13,23 @@
 #ifndef CIRCT_BINDINGS_PYTHON_CIRCTMODULES_H
 #define CIRCT_BINDINGS_PYTHON_CIRCTMODULES_H
 
-#include <pybind11/pybind11.h>
+#include <nanobind/nanobind.h>
 
 namespace circt {
 namespace python {
 
-void populateDialectESISubmodule(pybind11::module &m);
-void populateDialectHWSubmodule(pybind11::module &m);
-void populateDialectMSFTSubmodule(pybind11::module &m);
-void populateDialectOMSubmodule(pybind11::module &m);
-void populateDialectRTGSubmodule(pybind11::module &m);
-void populateDialectRTGToolSubmodule(pybind11::module &m);
+void populateDialectESISubmodule(nanobind::module_ &m);
+void populateDialectHWSubmodule(nanobind::module_ &m);
+void populateDialectMSFTSubmodule(nanobind::module_ &m);
+void populateDialectOMSubmodule(nanobind::module_ &m);
+void populateDialectRTGSubmodule(nanobind::module_ &m);
+void populateDialectRTGToolSubmodule(nanobind::module_ &m);
 #ifdef CIRCT_INCLUDE_TESTS
-void populateDialectRTGTestSubmodule(pybind11::module &m);
+void populateDialectRTGTestSubmodule(nanobind::module_ &m);
 #endif
-void populateDialectSeqSubmodule(pybind11::module &m);
-void populateDialectSVSubmodule(pybind11::module &m);
-void populateSupportSubmodule(pybind11::module &m);
+void populateDialectSeqSubmodule(nanobind::module_ &m);
+void populateDialectSVSubmodule(nanobind::module_ &m);
+void populateSupportSubmodule(nanobind::module_ &m);
 
 } // namespace python
 } // namespace circt

lib/Bindings/Python/CMakeLists.txt

@@ -26,7 +26,7 @@ set(PYTHON_BINDINGS_SOURCES
   SVModule.cpp
   # Headers must be included explicitly so they are installed.
   CIRCTModules.h
-  PybindUtils.h
+  NanobindUtils.h
 )
 
 set(PYTHON_BINDINGS_LINK_LIBS
@@ -70,6 +70,8 @@ declare_mlir_python_extension(CIRCTBindingsPythonExtension
     ${PYTHON_BINDINGS_LINK_LIBS}
   PRIVATE_LINK_LIBS
     LLVMSupport
+  PYTHON_BINDINGS_LIBRARY
+    nanobind
 )
 
 add_dependencies(CIRCTBindingsPythonExtension circt-headers)