Revert "[smart_holder] Add a new return value policy `return_as_bytes` (#3838)"

This reverts commit 7064d43bc9.

Conflicts resolved in:
    include/pybind11/eigen.h
    tests/test_builtin_casters.cpp

include/pybind11/cast.h

@@ -476,15 +476,11 @@ struct string_caster {
         return true;
     }
 
-    static handle cast(const StringType &src, return_value_policy policy, handle /* parent */) {
+    static handle
+    cast(const StringType &src, return_value_policy /* policy */, handle /* parent */) {
         const char *buffer = reinterpret_cast<const char *>(src.data());
         auto nbytes = ssize_t(src.size() * sizeof(CharT));
-        handle s;
+        handle s = decode_utfN(buffer, nbytes);
-        if (policy == return_value_policy::_return_as_bytes) {
-            s = PyBytes_FromStringAndSize(buffer, nbytes);
-        } else {
-            s = decode_utfN(buffer, nbytes);
-        }
         if (!s) {
             throw error_already_set();
         }

include/pybind11/detail/common.h

@@ -542,19 +542,7 @@ enum class return_value_policy : uint8_t {
         collected while Python is still using the child. More advanced
         variations of this scheme are also possible using combinations of
         return_value_policy::reference and the keep_alive call policy */
-    reference_internal,
+    reference_internal
-
-    /** With this policy, C++ string types are converted to Python bytes,
-        instead of str. This is most useful when a C++ function returns a
-        container-like type with nested C++ string types, and `py::bytes` cannot
-        be applied easily. Dictionary like types might not work, for example,
-        `Dict[str, bytes]`, because this policy forces all string return values
-        to be converted to bytes. Note that this return_value_policy is not
-        concerned with lifetime/ownership semantics, like the other policies,
-        but the purpose of _return_as_bytes is certain to be orthogonal, because
-        C++ strings are always copied to Python `bytes` or `str`.
-        NOTE: This policy is NOT available on master. */
-    _return_as_bytes
 };
 
 #define PYBIND11_HAS_RETURN_VALUE_POLICY_RETURN_AS_BYTES

include/pybind11/detail/smart_holder_type_casters.h

@@ -909,15 +909,12 @@ struct smart_holder_type_caster<std::shared_ptr<T>> : smart_holder_type_caster_l
                 break;
             case return_value_policy::take_ownership:
                 throw cast_error("Invalid return_value_policy for shared_ptr (take_ownership).");
-                break;
             case return_value_policy::copy:
             case return_value_policy::move:
                 break;
             case return_value_policy::reference:
                 throw cast_error("Invalid return_value_policy for shared_ptr (reference).");
-                break;
             case return_value_policy::reference_internal:
-            case return_value_policy::_return_as_bytes:
                 break;
         }
         if (!src) {

include/pybind11/detail/type_caster_base.h

@@ -625,10 +625,6 @@ public:
                 keep_alive_impl(inst, parent);
                 break;
 
-            case return_value_policy::_return_as_bytes:
-                pybind11_fail("return_value_policy::_return_as_bytes does not apply.");
-                break;
-
             default:
                 throw cast_error("unhandled return_value_policy: should not happen!");
         }

tests/test_builtin_casters.cpp

@@ -11,17 +11,10 @@
 
 #include "pybind11_tests.h"
 
-#include <utility>
-
 struct ConstRefCasted {
     int tag;
 };
 
-struct StringAttr {
-    explicit StringAttr(std::string v) : value(std::move(v)) {}
-    std::string value;
-};
-
 PYBIND11_NAMESPACE_BEGIN(pybind11)
 PYBIND11_NAMESPACE_BEGIN(detail)
 template <>
@@ -390,29 +383,5 @@ TEST_SUBMODULE(builtin_casters, m) {
     m.def("takes_const_ref_wrap",
           [](std::reference_wrapper<const ConstRefCasted> x) { return x.get().tag; });
 
-    // test return_value_policy::_return_as_bytes
-    m.def(
-        "invalid_utf8_string_as_bytes",
-        []() { return std::string("\xba\xd0\xba\xd0"); },
-        py::return_value_policy::_return_as_bytes);
-    m.def("invalid_utf8_string_as_str", []() { return std::string("\xba\xd0\xba\xd0"); });
-    m.def(
-        "invalid_utf8_char_array_as_bytes",
-        []() { return "\xba\xd0\xba\xd0"; },
-        py::return_value_policy::_return_as_bytes);
-    py::class_<StringAttr>(m, "StringAttr")
-        .def(py::init<std::string>())
-        .def_property(
-            "value",
-            py::cpp_function([](StringAttr &self) { return self.value; },
-                             py::return_value_policy::_return_as_bytes),
-            py::cpp_function([](StringAttr &self, std::string v) { self.value = std::move(v); }));
-#ifdef PYBIND11_HAS_STRING_VIEW
-    m.def(
-        "invalid_utf8_string_view_as_bytes",
-        []() { return std::string_view("\xba\xd0\xba\xd0"); },
-        py::return_value_policy::_return_as_bytes);
-#endif
-
     PYBIND11_WARNING_POP
 }

tests/test_builtin_casters.py

@@ -526,17 +526,3 @@ def test_const_ref_caster():
     assert m.takes_const_ptr(x) == 5
     assert m.takes_const_ref(x) == 4
     assert m.takes_const_ref_wrap(x) == 4
-
-
-def test_return_as_bytes_policy():
-    expected_return_value = b"\xba\xd0\xba\xd0"
-    assert m.invalid_utf8_string_as_bytes() == expected_return_value
-    with pytest.raises(UnicodeDecodeError):
-        m.invalid_utf8_string_as_str()
-    assert m.invalid_utf8_char_array_as_bytes() == expected_return_value
-    obj = m.StringAttr(expected_return_value)
-    assert obj.value == expected_return_value
-    obj.value = "123"
-    assert obj.value == b"123"
-    if hasattr(m, "has_string_view"):
-        assert m.invalid_utf8_string_view_as_bytes() == expected_return_value

tests/test_stl.cpp

@@ -546,25 +546,4 @@ TEST_SUBMODULE(stl, m) {
         []() { return new std::vector<bool>(4513); },
         // Without explicitly specifying `take_ownership`, this function leaks.
         py::return_value_policy::take_ownership);
-
-    // test return_value_policy::_return_as_bytes
-    m.def(
-        "invalid_utf8_string_array_as_bytes",
-        []() { return std::array<std::string, 1>{{"\xba\xd0\xba\xd0"}}; },
-        py::return_value_policy::_return_as_bytes);
-    m.def("invalid_utf8_string_array_as_str",
-          []() { return std::array<std::string, 1>{{"\xba\xd0\xba\xd0"}}; });
-#ifdef PYBIND11_HAS_OPTIONAL
-    m.def(
-        "invalid_utf8_optional_string_as_bytes",
-        []() { return std::optional<std::string>{"\xba\xd0\xba\xd0"}; },
-        py::return_value_policy::_return_as_bytes);
-#endif
-
-#ifdef PYBIND11_TEST_VARIANT
-    m.def(
-        "invalid_utf8_variant_string_as_bytes",
-        []() { return variant<std::string, int>{"\xba\xd0\xba\xd0"}; },
-        py::return_value_policy::_return_as_bytes);
-#endif
 }

tests/test_stl.py

@@ -379,14 +379,3 @@ def test_return_vector_bool_raw_ptr():
     v = m.return_vector_bool_raw_ptr()
     assert isinstance(v, list)
     assert len(v) == 4513
-
-
-def test_return_as_bytes_policy():
-    expected_return_value = b"\xba\xd0\xba\xd0"
-    assert m.invalid_utf8_string_array_as_bytes() == [expected_return_value]
-    with pytest.raises(UnicodeDecodeError):
-        m.invalid_utf8_string_array_as_str()
-    if hasattr(m, "has_optional"):
-        assert m.invalid_utf8_optional_string_as_bytes() == expected_return_value
-    if hasattr(m, "load_variant"):
-        assert m.invalid_utf8_variant_string_as_bytes() == expected_return_value