Add minimal_real_caster (from PR pybind#3862) to test_async, test_buffers

Author: rwgk

tests/test_async.cpp

@@ -9,6 +9,48 @@
 
 #include "pybind11_tests.h"
 
+namespace mrc_ns { // minimal real caster
+
+struct minimal_real_caster;
+
+struct type_mrc {
+    int value = -9999;
+};
+
+struct minimal_real_caster {
+    static constexpr auto name = py::detail::const_name<type_mrc>();
+
+    static py::handle
+    cast(type_mrc const &src, py::return_value_policy /*policy*/, py::handle /*parent*/) {
+        return py::int_(src.value + 1010).release();
+    }
+
+    // Maximizing simplicity. This will go terribly wrong for other arg types.
+    template <typename>
+    using cast_op_type = const type_mrc &;
+
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator type_mrc const &() {
+        static type_mrc obj;
+        obj.value = 11;
+        return obj;
+    }
+
+    bool load(py::handle src, bool /*convert*/) {
+        // Only accepts str, but the value is ignored.
+        return py::isinstance<py::str>(src);
+    }
+};
+
+} // namespace mrc_ns
+
+namespace pybind11 {
+namespace detail {
+template <>
+struct type_caster<mrc_ns::type_mrc> : mrc_ns::minimal_real_caster {};
+} // namespace detail
+} // namespace pybind11
+
 TEST_SUBMODULE(async_module, m) {
     struct DoesNotSupportAsync {};
     py::class_<DoesNotSupportAsync>(m, "DoesNotSupportAsync").def(py::init<>());
@@ -22,4 +64,6 @@ TEST_SUBMODULE(async_module, m) {
             f.attr("set_result")(5);
             return f.attr("__await__")();
         });
+    m.def("type_mrc_to_python", []() { return mrc_ns::type_mrc{101}; });
+    m.def("type_mrc_from_python", [](const mrc_ns::type_mrc &obj) { return obj.value + 100; });
 }

tests/test_async.py

@@ -22,3 +22,8 @@ def test_await(event_loop):
 def test_await_missing(event_loop):
     with pytest.raises(TypeError):
         event_loop.run_until_complete(get_await_result(m.DoesNotSupportAsync()))
+
+
+def test_mrc():
+    assert m.type_mrc_to_python() == 1111
+    assert m.type_mrc_from_python("ignored") == 111

tests/test_buffers.cpp

@@ -12,6 +12,48 @@
 #include "constructor_stats.h"
 #include "pybind11_tests.h"
 
+namespace mrc_ns { // minimal real caster
+
+struct minimal_real_caster;
+
+struct type_mrc {
+    int value = -9999;
+};
+
+struct minimal_real_caster {
+    static constexpr auto name = py::detail::const_name<type_mrc>();
+
+    static py::handle
+    cast(type_mrc const &src, py::return_value_policy /*policy*/, py::handle /*parent*/) {
+        return py::int_(src.value + 2020).release();
+    }
+
+    // Maximizing simplicity. This will go terribly wrong for other arg types.
+    template <typename>
+    using cast_op_type = const type_mrc &;
+
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    operator type_mrc const &() {
+        static type_mrc obj;
+        obj.value = 22;
+        return obj;
+    }
+
+    bool load(py::handle src, bool /*convert*/) {
+        // Only accepts str, but the value is ignored.
+        return py::isinstance<py::str>(src);
+    }
+};
+
+} // namespace mrc_ns
+
+namespace pybind11 {
+namespace detail {
+template <>
+struct type_caster<mrc_ns::type_mrc> : mrc_ns::minimal_real_caster {};
+} // namespace detail
+} // namespace pybind11
+
 TEST_SUBMODULE(buffers, m) {
     // test_from_python / test_to_python:
     class Matrix {
@@ -221,4 +263,7 @@ TEST_SUBMODULE(buffers, m) {
         });
 
     m.def("get_buffer_info", [](const py::buffer &buffer) { return buffer.request(); });
+
+    m.def("type_mrc_to_python", []() { return mrc_ns::type_mrc{202}; });
+    m.def("type_mrc_from_python", [](const mrc_ns::type_mrc &obj) { return obj.value + 200; });
 }

tests/test_buffers.py

@@ -161,3 +161,8 @@ def test_ctypes_from_buffer():
         assert cinfo.shape == pyinfo.shape
         assert cinfo.strides == pyinfo.strides
         assert not cinfo.readonly
+
+
+def test_mrc():
+    assert m.type_mrc_to_python() == 1111
+    assert m.type_mrc_from_python("ignored") == 111