[smart_holder] Auto select return value policy for clif_automatic (#4381)

* Auto select return value policy for clif_automatic

* Try fixing test failures

* Add more tests.

* remove comments

* Fix test failures

* Fix test failures

* Fix test failure for windows platform

* Fix clangtidy

include/pybind11/detail/smart_holder_type_casters.h

@@ -630,7 +630,8 @@ struct smart_holder_type_caster : smart_holder_type_caster_load<T>,
     static handle cast(T const &src, return_value_policy policy, handle parent) {
         // type_caster_base BEGIN
         if (policy == return_value_policy::automatic
-            || policy == return_value_policy::automatic_reference) {
+            || policy == return_value_policy::automatic_reference
+            || policy == return_value_policy::_clif_automatic) {
             policy = return_value_policy::copy;
         }
         return cast(&src, policy, parent);
@@ -638,11 +639,21 @@ struct smart_holder_type_caster : smart_holder_type_caster_load<T>,
     }
 
     static handle cast(T &src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::_clif_automatic) {
+            if (std::is_move_constructible<T>::value) {
+                policy = return_value_policy::move;
+            } else {
+                policy = return_value_policy::automatic;
+            }
+        }
         return cast(const_cast<T const &>(src), policy, parent); // Mutbl2Const
     }
 
     static handle cast(T const *src, return_value_policy policy, handle parent) {
         auto st = type_caster_base<T>::src_and_type(src);
+        if (policy == return_value_policy::_clif_automatic) {
+            policy = return_value_policy::copy;
+        }
         return cast_const_raw_ptr( // Originally type_caster_generic::cast.
             st.first,
             policy,
@@ -653,6 +664,9 @@ struct smart_holder_type_caster : smart_holder_type_caster_load<T>,
     }
 
     static handle cast(T *src, return_value_policy policy, handle parent) {
+        if (policy == return_value_policy::_clif_automatic) {
+            policy = return_value_policy::reference;
+        }
         return cast(const_cast<T const *>(src), policy, parent); // Mutbl2Const
     }
 
@@ -867,7 +881,8 @@ struct smart_holder_type_caster<std::unique_ptr<T, D>> : smart_holder_type_caste
     static handle cast(std::unique_ptr<T, D> &&src, return_value_policy policy, handle parent) {
         if (policy != return_value_policy::automatic
             && policy != return_value_policy::reference_internal
-            && policy != return_value_policy::move) {
+            && policy != return_value_policy::move
+            && policy != return_value_policy::_clif_automatic) {
             // SMART_HOLDER_WIP: IMPROVABLE: Error message.
             throw cast_error("Invalid return_value_policy for unique_ptr.");
         }

tests/test_return_value_policy_override.cpp

@@ -1,12 +1,166 @@
+#include <pybind11/smart_holder.h>
+
 #include "pybind11_tests.h"
 
 namespace test_return_value_policy_override {
 
 struct some_type {};
 
+// cp = copyable, mv = movable, 1 = yes, 0 = no
+struct type_cp1_mv1 {
+    std::string mtxt;
+    explicit type_cp1_mv1(const std::string &mtxt_) : mtxt(mtxt_) {}
+    type_cp1_mv1(const type_cp1_mv1 &other) { mtxt = other.mtxt + "_CpCtor"; }
+    type_cp1_mv1(type_cp1_mv1 &&other) noexcept { mtxt = other.mtxt + "_MvCtor"; }
+    type_cp1_mv1 &operator=(const type_cp1_mv1 &other) {
+        mtxt = other.mtxt + "_CpCtor";
+        return *this;
+    }
+    type_cp1_mv1 &operator=(type_cp1_mv1 &&other) noexcept {
+        mtxt = other.mtxt + "_MvCtor";
+        return *this;
+    }
+};
+
+// nocopy
+struct type_cp0_mv1 {
+    std::string mtxt;
+    explicit type_cp0_mv1(const std::string &mtxt_) : mtxt(mtxt_) {}
+    type_cp0_mv1(const type_cp0_mv1 &) = delete;
+    type_cp0_mv1(type_cp0_mv1 &&other) noexcept { mtxt = other.mtxt + "_MvCtor"; }
+    type_cp0_mv1 &operator=(const type_cp0_mv1 &) = delete;
+    type_cp0_mv1 &operator=(type_cp0_mv1 &&other) noexcept {
+        mtxt = other.mtxt + "_MvCtor";
+        return *this;
+    }
+};
+
+// nomove
+struct type_cp1_mv0 {
+    std::string mtxt;
+    explicit type_cp1_mv0(const std::string &mtxt_) : mtxt(mtxt_) {}
+    type_cp1_mv0(const type_cp1_mv0 &other) { mtxt = other.mtxt + "_CpCtor"; }
+    type_cp1_mv0(type_cp1_mv0 &&other) = delete;
+    type_cp1_mv0 &operator=(const type_cp1_mv0 &other) {
+        mtxt = other.mtxt + "_CpCtor";
+        return *this;
+    }
+    type_cp1_mv0 &operator=(type_cp1_mv0 &&other) = delete;
+};
+
+// nocopy_nomove
+struct type_cp0_mv0 {
+    std::string mtxt;
+    explicit type_cp0_mv0(const std::string &mtxt_) : mtxt(mtxt_) {}
+    type_cp0_mv0(const type_cp0_mv0 &) = delete;
+    type_cp0_mv0(type_cp0_mv0 &&other) = delete;
+    type_cp0_mv0 &operator=(const type_cp0_mv0 &other) = delete;
+    type_cp0_mv0 &operator=(type_cp0_mv0 &&other) = delete;
+};
+
+type_cp1_mv1 return_value() { return type_cp1_mv1{"value"}; }
+
+type_cp1_mv1 *return_pointer() {
+    static type_cp1_mv1 value("pointer");
+    return &value;
+}
+
+const type_cp1_mv1 *return_const_pointer() {
+    static type_cp1_mv1 value("const_pointer");
+    return &value;
+}
+
+type_cp1_mv1 &return_reference() {
+    static type_cp1_mv1 value("reference");
+    return value;
+}
+
+const type_cp1_mv1 &return_const_reference() {
+    static type_cp1_mv1 value("const_reference");
+    return value;
+}
+
+std::shared_ptr<type_cp1_mv1> return_shared_pointer() {
+    return std::make_shared<type_cp1_mv1>("shared_pointer");
+}
+
+std::unique_ptr<type_cp1_mv1> return_unique_pointer() {
+    return std::unique_ptr<type_cp1_mv1>(new type_cp1_mv1("unique_pointer"));
+}
+
+type_cp0_mv1 return_value_nocopy() { return type_cp0_mv1{"value_nocopy"}; }
+
+type_cp0_mv1 *return_pointer_nocopy() {
+    static type_cp0_mv1 value("pointer_nocopy");
+    return &value;
+}
+
+const type_cp0_mv1 *return_const_pointer_nocopy() {
+    static type_cp0_mv1 value("const_pointer_nocopy");
+    return &value;
+}
+
+type_cp0_mv1 &return_reference_nocopy() {
+    static type_cp0_mv1 value("reference_nocopy");
+    return value;
+}
+
+std::shared_ptr<type_cp0_mv1> return_shared_pointer_nocopy() {
+    return std::make_shared<type_cp0_mv1>("shared_pointer_nocopy");
+}
+
+std::unique_ptr<type_cp0_mv1> return_unique_pointer_nocopy() {
+    return std::unique_ptr<type_cp0_mv1>(new type_cp0_mv1("unique_pointer_nocopy"));
+}
+
+type_cp1_mv0 *return_pointer_nomove() {
+    static type_cp1_mv0 value("pointer_nomove");
+    return &value;
+}
+
+const type_cp1_mv0 *return_const_pointer_nomove() {
+    static type_cp1_mv0 value("const_pointer_nomove");
+    return &value;
+}
+
+type_cp1_mv0 &return_reference_nomove() {
+    static type_cp1_mv0 value("reference_nomove");
+    return value;
+}
+
+const type_cp1_mv0 &return_const_reference_nomove() {
+    static type_cp1_mv0 value("const_reference_nomove");
+    return value;
+}
+
+std::shared_ptr<type_cp1_mv0> return_shared_pointer_nomove() {
+    return std::make_shared<type_cp1_mv0>("shared_pointer_nomove");
+}
+
+std::unique_ptr<type_cp1_mv0> return_unique_pointer_nomove() {
+    return std::unique_ptr<type_cp1_mv0>(new type_cp1_mv0("unique_pointer_nomove"));
+}
+
+type_cp0_mv0 *return_pointer_nocopy_nomove() {
+    static type_cp0_mv0 value("pointer_nocopy_nomove");
+    return &value;
+}
+
+std::shared_ptr<type_cp0_mv0> return_shared_pointer_nocopy_nomove() {
+    return std::make_shared<type_cp0_mv0>("shared_pointer_nocopy_nomove");
+}
+
+std::unique_ptr<type_cp0_mv0> return_unique_pointer_nocopy_nomove() {
+    return std::unique_ptr<type_cp0_mv0>(new type_cp0_mv0("unique_pointer_nocopy_nomove"));
+}
+
 } // namespace test_return_value_policy_override
 
 using test_return_value_policy_override::some_type;
+using test_return_value_policy_override::type_cp0_mv0;
+using test_return_value_policy_override::type_cp0_mv1;
+using test_return_value_policy_override::type_cp1_mv0;
+using test_return_value_policy_override::type_cp1_mv1;
 
 namespace pybind11 {
 namespace detail {
@@ -51,6 +205,11 @@ struct type_caster<some_type> : type_caster_base<some_type> {
 } // namespace detail
 } // namespace pybind11
 
+PYBIND11_SMART_HOLDER_TYPE_CASTERS(type_cp1_mv1)
+PYBIND11_SMART_HOLDER_TYPE_CASTERS(type_cp0_mv1)
+PYBIND11_SMART_HOLDER_TYPE_CASTERS(type_cp1_mv0)
+PYBIND11_SMART_HOLDER_TYPE_CASTERS(type_cp0_mv0)
+
 TEST_SUBMODULE(return_value_policy_override, m) {
     m.def("return_value_with_default_policy", []() { return some_type(); });
     m.def(
@@ -79,4 +238,86 @@ TEST_SUBMODULE(return_value_policy_override, m) {
             return &value;
         },
         py::return_value_policy::_clif_automatic);
+
+    py::classh<type_cp1_mv1>(m, "type_cp1_mv1")
+        .def(py::init<std::string>())
+        .def_readonly("mtxt", &type_cp1_mv1::mtxt);
+    m.def("return_value",
+          &test_return_value_policy_override::return_value,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_pointer",
+          &test_return_value_policy_override::return_pointer,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_const_pointer",
+          &test_return_value_policy_override::return_const_pointer,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_reference",
+          &test_return_value_policy_override::return_reference,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_const_reference",
+          &test_return_value_policy_override::return_const_reference,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_unique_pointer",
+          &test_return_value_policy_override::return_unique_pointer,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_shared_pointer",
+          &test_return_value_policy_override::return_shared_pointer,
+          py::return_value_policy::_clif_automatic);
+
+    py::classh<type_cp0_mv1>(m, "type_cp0_mv1")
+        .def(py::init<std::string>())
+        .def_readonly("mtxt", &type_cp0_mv1::mtxt);
+    m.def("return_value_nocopy",
+          &test_return_value_policy_override::return_value_nocopy,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_pointer_nocopy",
+          &test_return_value_policy_override::return_pointer_nocopy,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_const_pointer_nocopy",
+          &test_return_value_policy_override::return_const_pointer_nocopy,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_reference_nocopy",
+          &test_return_value_policy_override::return_reference_nocopy,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_shared_pointer_nocopy",
+          &test_return_value_policy_override::return_shared_pointer_nocopy,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_unique_pointer_nocopy",
+          &test_return_value_policy_override::return_unique_pointer_nocopy,
+          py::return_value_policy::_clif_automatic);
+
+    py::classh<type_cp1_mv0>(m, "type_cp1_mv0")
+        .def(py::init<std::string>())
+        .def_readonly("mtxt", &type_cp1_mv0::mtxt);
+    m.def("return_pointer_nomove",
+          &test_return_value_policy_override::return_pointer_nomove,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_const_pointer_nomove",
+          &test_return_value_policy_override::return_const_pointer_nomove,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_reference_nomove",
+          &test_return_value_policy_override::return_reference_nomove,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_const_reference_nomove",
+          &test_return_value_policy_override::return_const_reference_nomove,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_shared_pointer_nomove",
+          &test_return_value_policy_override::return_shared_pointer_nomove,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_unique_pointer_nomove",
+          &test_return_value_policy_override::return_unique_pointer_nomove,
+          py::return_value_policy::_clif_automatic);
+
+    py::classh<type_cp0_mv0>(m, "type_cp0_mv0")
+        .def(py::init<std::string>())
+        .def_readonly("mtxt", &type_cp0_mv0::mtxt);
+    m.def("return_pointer_nocopy_nomove",
+          &test_return_value_policy_override::return_pointer_nocopy_nomove,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_shared_pointer_nocopy_nomove",
+          &test_return_value_policy_override::return_shared_pointer_nocopy_nomove,
+          py::return_value_policy::_clif_automatic);
+    m.def("return_unique_pointer_nocopy_nomove",
+          &test_return_value_policy_override::return_unique_pointer_nocopy_nomove,
+          py::return_value_policy::_clif_automatic);
 }

tests/test_return_value_policy_override.py

@@ -1,3 +1,7 @@
+import re
+
+import pytest
+
 from pybind11_tests import return_value_policy_override as m
 
 
@@ -11,3 +15,33 @@ def test_return_pointer():
     assert m.return_pointer_with_default_policy() == "automatic"
     assert m.return_pointer_with_policy_move() == "move"
     assert m.return_pointer_with_policy_clif_automatic() == "_clif_automatic"
+
+
+@pytest.mark.parametrize(
+    "func, expected",
+    [
+        (m.return_value, "value(_MvCtor)*_MvCtor"),
+        (m.return_pointer, "pointer"),
+        (m.return_const_pointer, "const_pointer_CpCtor"),
+        (m.return_reference, "reference_MvCtor"),
+        (m.return_const_reference, "const_reference_CpCtor"),
+        (m.return_unique_pointer, "unique_pointer"),
+        (m.return_shared_pointer, "shared_pointer"),
+        (m.return_value_nocopy, "value_nocopy(_MvCtor)*_MvCtor"),
+        (m.return_pointer_nocopy, "pointer_nocopy"),
+        (m.return_reference_nocopy, "reference_nocopy_MvCtor"),
+        (m.return_unique_pointer_nocopy, "unique_pointer_nocopy"),
+        (m.return_shared_pointer_nocopy, "shared_pointer_nocopy"),
+        (m.return_pointer_nomove, "pointer_nomove"),
+        (m.return_const_pointer_nomove, "const_pointer_nomove_CpCtor"),
+        (m.return_reference_nomove, "reference_nomove_CpCtor"),
+        (m.return_const_reference_nomove, "const_reference_nomove_CpCtor"),
+        (m.return_unique_pointer_nomove, "unique_pointer_nomove"),
+        (m.return_shared_pointer_nomove, "shared_pointer_nomove"),
+        (m.return_pointer_nocopy_nomove, "pointer_nocopy_nomove"),
+        (m.return_unique_pointer_nocopy_nomove, "unique_pointer_nocopy_nomove"),
+        (m.return_shared_pointer_nocopy_nomove, "shared_pointer_nocopy_nomove"),
+    ],
+)
+def test_clif_automatic_return_value_policy_override(func, expected):
+    assert re.match(expected, func().mtxt)