Update benchmark Python bindings for nanobind 2.0, and update to nano…

…bind 2.0. (#1817)

Incorporates the nanobind_bazel change from #1795.

nanobind 2.0 reworked the nanobind::enum_ class so it uses a real Python enum or intenum rather than its previous hand-rolled implementation.
https://nanobind.readthedocs.io/en/latest/changelog.html#version-2-0-0-may-23-2024

As a consequence of that change, nanobind now checks when casting an integer to a enum value that the integer corresponds to a valid enum. Counter::Flags is a bitmask, and many combinations are not valid enum members.

This change:
a) sets nb::is_arithmetic(), which means Counter::Flags becomes an IntEnum that can be freely cast to an integer.
b) defines the | operator for flags to return an integer, not an enum, avoiding the error.
c) changes Counter's constructor to accept an int, not a Counter::Flags enum. Since Counter::Flags is an IntEnum now, it can be freely coerced to an int.

If wjakob/nanobind#599 is merged into nanobind, then we can perhaps use a flag enum here instead.

MODULE.bazel

@@ -38,4 +38,4 @@ use_repo(pip, "tools_pip_deps")
 
 # -- bazel_dep definitions -- #
 
-bazel_dep(name = "nanobind_bazel", version = "1.0.0", dev_dependency = True)
+bazel_dep(name = "nanobind_bazel", version = "2.0.0", dev_dependency = True)

bindings/python/google_benchmark/benchmark.cc

@@ -118,7 +118,7 @@ NB_MODULE(_benchmark, m) {
   using benchmark::Counter;
   nb::class_<Counter> py_counter(m, "Counter");
 
-  nb::enum_<Counter::Flags>(py_counter, "Flags")
+  nb::enum_<Counter::Flags>(py_counter, "Flags", nb::is_arithmetic())
       .value("kDefaults", Counter::Flags::kDefaults)
       .value("kIsRate", Counter::Flags::kIsRate)
       .value("kAvgThreads", Counter::Flags::kAvgThreads)
@@ -130,18 +130,25 @@ NB_MODULE(_benchmark, m) {
       .value("kAvgIterationsRate", Counter::Flags::kAvgIterationsRate)
       .value("kInvert", Counter::Flags::kInvert)
       .export_values()
-      .def(nb::self | nb::self);
+      .def("__or__", [](Counter::Flags a, Counter::Flags b) {
+        return static_cast<int>(a) | static_cast<int>(b);
+      });
 
   nb::enum_<Counter::OneK>(py_counter, "OneK")
       .value("kIs1000", Counter::OneK::kIs1000)
       .value("kIs1024", Counter::OneK::kIs1024)
       .export_values();
 
   py_counter
-      .def(nb::init<double, Counter::Flags, Counter::OneK>(),
-           nb::arg("value") = 0., nb::arg("flags") = Counter::kDefaults,
-           nb::arg("k") = Counter::kIs1000)
-      .def("__init__", ([](Counter *c, double value) { new (c) Counter(value); }))
+      .def(
+          "__init__",
+          [](Counter* c, double value, int flags, Counter::OneK oneK) {
+            new (c) Counter(value, static_cast<Counter::Flags>(flags), oneK);
+          },
+          nb::arg("value") = 0., nb::arg("flags") = Counter::kDefaults,
+          nb::arg("k") = Counter::kIs1000)
+      .def("__init__",
+           ([](Counter* c, double value) { new (c) Counter(value); }))
       .def_rw("value", &Counter::value)
       .def_rw("flags", &Counter::flags)
       .def_rw("oneK", &Counter::oneK)