pybind11/include/pybind11/pybind11.h

/*
    pybind11/pybind11.h: Main header file of the C++11 python
    binding generator library

    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>

    All rights reserved. Use of this source code is governed by a
    BSD-style license that can be found in the LICENSE file.
*/

#pragma once
#include "detail/class.h"
#include "detail/dynamic_raw_ptr_cast_if_possible.h"
#include "detail/exception_translation.h"
#include "detail/function_record_pyobject.h"
#include "detail/init.h"
#include "detail/native_enum_data.h"
#include "detail/using_smart_holder.h"
#include "attr.h"
#include "gil.h"
#include "gil_safe_call_once.h"
#include "options.h"
#include "trampoline_self_life_support.h"
#include "typing.h"

#include <cassert>
#include <cstdlib>
#include <cstring>
#include <memory>
#include <new>
#include <stack>
#include <string>
#include <utility>
#include <vector>

// See PR #5448. This warning suppression is needed for the PYBIND11_OVERRIDE macro family.
// NOTE that this is NOT embedded in a push/pop pair because that is very difficult to achieve.
#if defined(__clang_major__) && __clang_major__ < 14
PYBIND11_WARNING_DISABLE_CLANG("-Wgnu-zero-variadic-macro-arguments")
#endif

#if defined(__GNUG__) && !defined(__clang__)
#    include <cxxabi.h>
#endif

PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)

/* https://stackoverflow.com/questions/46798456/handling-gccs-noexcept-type-warning
   This warning is about ABI compatibility, not code health.
   It is only actually needed in a couple places, but apparently GCC 7 "generates this warning if
   and only if the first template instantiation ... involves noexcept" [stackoverflow], therefore
   it could get triggered from seemingly random places, depending on user code.
   No other GCC version generates this warning.
 */
#if defined(__GNUC__) && __GNUC__ == 7
PYBIND11_WARNING_DISABLE_GCC("-Wnoexcept-type")
#endif

PYBIND11_WARNING_DISABLE_MSVC(4127)

PYBIND11_NAMESPACE_BEGIN(detail)

inline std::string replace_newlines_and_squash(const char *text) {
    const char *whitespaces = " \t\n\r\f\v";
    std::string result(text);
    bool previous_is_whitespace = false;

    if (result.size() >= 2) {
        // Do not modify string representations
        char first_char = result[0];
        char last_char = result[result.size() - 1];
        if (first_char == last_char && first_char == '\'') {
            return result;
        }
    }
    result.clear();

    // Replace characters in whitespaces array with spaces and squash consecutive spaces
    while (*text != '\0') {
        if (std::strchr(whitespaces, *text)) {
            if (!previous_is_whitespace) {
                result += ' ';
                previous_is_whitespace = true;
            }
        } else {
            result += *text;
            previous_is_whitespace = false;
        }
        ++text;
    }

    // Strip leading and trailing whitespaces
    const size_t str_begin = result.find_first_not_of(whitespaces);
    if (str_begin == std::string::npos) {
        return "";
    }

    const size_t str_end = result.find_last_not_of(whitespaces);
    const size_t str_range = str_end - str_begin + 1;

    return result.substr(str_begin, str_range);
}

/* Generate a proper function signature */
inline std::string generate_function_signature(const char *type_caster_name_field,
                                               detail::function_record *func_rec,
                                               const std::type_info *const *types,
                                               size_t &type_index,
                                               size_t &arg_index) {
    std::string signature;
    bool is_starred = false;
    // `is_return_value.top()` is true if we are currently inside the return type of the
    // signature. Using `@^`/`@$` we can force types to be arg/return types while `@!` pops
    // back to the previous state.
    std::stack<bool> is_return_value({false});
    // The following characters have special meaning in the signature parsing. Literals
    // containing these are escaped with `!`.
    std::string special_chars("!@%{}-");
    for (const auto *pc = type_caster_name_field; *pc != '\0'; ++pc) {
        const auto c = *pc;
        if (c == '{') {
            // Write arg name for everything except *args and **kwargs.
            is_starred = *(pc + 1) == '*';
            if (is_starred) {
                continue;
            }
            // Separator for keyword-only arguments, placed before the kw
            // arguments start (unless we are already putting an *args)
            if (!func_rec->has_args && arg_index == func_rec->nargs_pos) {
                signature += "*, ";
            }
            if (arg_index < func_rec->args.size() && func_rec->args[arg_index].name) {
                signature += func_rec->args[arg_index].name;
            } else if (arg_index == 0 && func_rec->is_method) {
                signature += "self";
            } else {
                signature += "arg" + std::to_string(arg_index - (func_rec->is_method ? 1 : 0));
            }
            signature += ": ";
        } else if (c == '}') {
            // Write default value if available.
            if (!is_starred && arg_index < func_rec->args.size()
                && func_rec->args[arg_index].descr) {
                signature += " = ";
                signature += detail::replace_newlines_and_squash(func_rec->args[arg_index].descr);
            }
            // Separator for positional-only arguments (placed after the
            // argument, rather than before like *
            if (func_rec->nargs_pos_only > 0 && (arg_index + 1) == func_rec->nargs_pos_only) {
                signature += ", /";
            }
            if (!is_starred) {
                arg_index++;
            }
        } else if (c == '%') {
            const std::type_info *t = types[type_index++];
            if (!t) {
                pybind11_fail("Internal error while parsing type signature (1)");
            }
            if (auto *tinfo = detail::get_type_info(*t)) {
                handle th((PyObject *) tinfo->type);
                signature += th.attr("__module__").cast<std::string>() + "."
                             + th.attr("__qualname__").cast<std::string>();
            } else if (auto th = detail::global_internals_native_enum_type_map_get_item(*t)) {
                signature += th.attr("__module__").cast<std::string>() + "."
                             + th.attr("__qualname__").cast<std::string>();
            } else if (func_rec->is_new_style_constructor && arg_index == 0) {
                // A new-style `__init__` takes `self` as `value_and_holder`.
                // Rewrite it to the proper class type.
                signature += func_rec->scope.attr("__module__").cast<std::string>() + "."
                             + func_rec->scope.attr("__qualname__").cast<std::string>();
            } else {
                signature += detail::quote_cpp_type_name(detail::clean_type_id(t->name()));
            }
        } else if (c == '!' && special_chars.find(*(pc + 1)) != std::string::npos) {
            // typing::Literal escapes special characters with !
            signature += *++pc;
        } else if (c == '@') {
            // `@^ ... @!` and `@$ ... @!` are used to force arg/return value type (see
            // typing::Callable/detail::arg_descr/detail::return_descr)
            if (*(pc + 1) == '^') {
                is_return_value.emplace(false);
                ++pc;
                continue;
            }
            if (*(pc + 1) == '$') {
                is_return_value.emplace(true);
                ++pc;
                continue;
            }
            if (*(pc + 1) == '!') {
                is_return_value.pop();
                ++pc;
                continue;
            }
            // Handle types that differ depending on whether they appear
            // in an argument or a return value position (see io_name<text1, text2>).
            // For named arguments (py::arg()) with noconvert set, return value type is used.
            ++pc;
            if (!is_return_value.top()
                && (!(arg_index < func_rec->args.size() && !func_rec->args[arg_index].convert))) {
                while (*pc != '\0' && *pc != '@') {
                    signature += *pc++;
                }
                if (*pc == '@') {
                    ++pc;
                }
                while (*pc != '\0' && *pc != '@') {
                    ++pc;
                }
            } else {
                while (*pc != '\0' && *pc != '@') {
                    ++pc;
                }
                if (*pc == '@') {
                    ++pc;
                }
                while (*pc != '\0' && *pc != '@') {
                    signature += *pc++;
                }
            }
        } else {
            if (c == '-' && *(pc + 1) == '>') {
                is_return_value.emplace(true);
            }
            signature += c;
        }
    }
    return signature;
}

template <typename T>
inline std::string generate_type_signature() {
    static constexpr auto caster_name_field = make_caster<T>::name;
    PYBIND11_DESCR_CONSTEXPR auto descr_types = decltype(caster_name_field)::types();
    // Create a default function_record to ensure the function signature has the proper
    // configuration e.g. no_convert.
    auto func_rec = function_record();
    size_t type_index = 0;
    size_t arg_index = 0;
    return generate_function_signature(
        caster_name_field.text, &func_rec, descr_types.data(), type_index, arg_index);
}

#if defined(_MSC_VER)
#    define PYBIND11_COMPAT_STRDUP _strdup
#else
#    define PYBIND11_COMPAT_STRDUP strdup
#endif

PYBIND11_NAMESPACE_END(detail)

/// Wraps an arbitrary C++ function/method/lambda function/.. into a callable Python object
class cpp_function : public function {
public:
    cpp_function() = default;
    // NOLINTNEXTLINE(google-explicit-constructor)
    cpp_function(std::nullptr_t) {}
    cpp_function(std::nullptr_t, const is_setter &) {}

    /// Construct a cpp_function from a vanilla function pointer
    template <typename Return, typename... Args, typename... Extra>
    // NOLINTNEXTLINE(google-explicit-constructor)
    cpp_function(Return (*f)(Args...), const Extra &...extra) {
        initialize(f, f, extra...);
    }

    /// Construct a cpp_function from a lambda function (possibly with internal state)
    template <typename Func,
              typename... Extra,
              typename = detail::enable_if_t<detail::is_lambda<Func>::value>>
    // NOLINTNEXTLINE(google-explicit-constructor)
    cpp_function(Func &&f, const Extra &...extra) {
        initialize(
            std::forward<Func>(f), (detail::function_signature_t<Func> *) nullptr, extra...);
    }

    /// Construct a cpp_function from a class method (non-const, no ref-qualifier)
    template <typename Return, typename Class, typename... Arg, typename... Extra>
    // NOLINTNEXTLINE(google-explicit-constructor)
    cpp_function(Return (Class::*f)(Arg...), const Extra &...extra) {
        initialize(
            [f](Class *c, Arg... args) -> Return { return (c->*f)(std::forward<Arg>(args)...); },
            (Return (*)(Class *, Arg...)) nullptr,
            extra...);
    }

    /// Construct a cpp_function from a class method (non-const, lvalue ref-qualifier)
    /// A copy of the overload for non-const functions without explicit ref-qualifier
    /// but with an added `&`.
    template <typename Return, typename Class, typename... Arg, typename... Extra>
    // NOLINTNEXTLINE(google-explicit-constructor)
    cpp_function(Return (Class::*f)(Arg...) &, const Extra &...extra) {
        initialize(
            [f](Class *c, Arg... args) -> Return { return (c->*f)(std::forward<Arg>(args)...); },
            (Return (*)(Class *, Arg...)) nullptr,
            extra...);
    }

    /// Construct a cpp_function from a class method (const, no ref-qualifier)
    template <typename Return, typename Class, typename... Arg, typename... Extra>
    // NOLINTNEXTLINE(google-explicit-constructor)
    cpp_function(Return (Class::*f)(Arg...) const, const Extra &...extra) {
        initialize([f](const Class *c,
                       Arg... args) -> Return { return (c->*f)(std::forward<Arg>(args)...); },
                   (Return (*)(const Class *, Arg...)) nullptr,
                   extra...);
    }

    /// Construct a cpp_function from a class method (const, lvalue ref-qualifier)
    /// A copy of the overload for const functions without explicit ref-qualifier
    /// but with an added `&`.
    template <typename Return, typename Class, typename... Arg, typename... Extra>
    // NOLINTNEXTLINE(google-explicit-constructor)
    cpp_function(Return (Class::*f)(Arg...) const &, const Extra &...extra) {
        initialize([f](const Class *c,
                       Arg... args) -> Return { return (c->*f)(std::forward<Arg>(args)...); },
                   (Return (*)(const Class *, Arg...)) nullptr,
                   extra...);
    }

    /// Return the function name
    object name() const { return attr("__name__"); }

protected:
    struct InitializingFunctionRecordDeleter {
        // `destruct(function_record, false)`: `initialize_generic` copies strings and
        // takes care of cleaning up in case of exceptions. So pass `false` to `free_strings`.
        void operator()(detail::function_record *rec) { destruct(rec, false); }
    };
    using unique_function_record
        = std::unique_ptr<detail::function_record, InitializingFunctionRecordDeleter>;

    /// Space optimization: don't inline this frequently instantiated fragment
    PYBIND11_NOINLINE unique_function_record make_function_record() {
        return unique_function_record(new detail::function_record());
    }

    /// Special internal constructor for functors, lambda functions, etc.
    template <typename Func, typename Return, typename... Args, typename... Extra>
    void initialize(Func &&f, Return (*)(Args...), const Extra &...extra) {
        using namespace detail;
        struct capture {
            remove_reference_t<Func> f;

            static capture *from_data(void **data) {
                return PYBIND11_STD_LAUNDER(reinterpret_cast<capture *>(data));
            }
        };

        /* Store the function including any extra state it might have (e.g. a lambda capture
         * object) */
        // The unique_ptr makes sure nothing is leaked in case of an exception.
        auto unique_rec = make_function_record();
        auto *rec = unique_rec.get();

        /* Store the capture object directly in the function record if there is enough space */
        if (sizeof(capture) <= sizeof(rec->data)) {
            /* Without these pragmas, GCC warns that there might not be
               enough space to use the placement new operator. However, the
               'if' statement above ensures that this is the case. */
            PYBIND11_WARNING_PUSH

#if defined(__GNUG__) && __GNUC__ >= 6
            PYBIND11_WARNING_DISABLE_GCC("-Wplacement-new")
#endif

            new (capture::from_data(rec->data)) capture{std::forward<Func>(f)};

#if !PYBIND11_HAS_STD_LAUNDER
            PYBIND11_WARNING_DISABLE_GCC("-Wstrict-aliasing")
#endif

            // UB without std::launder, but without breaking ABI and/or
            // a significant refactoring it's "impossible" to solve.
            if (!std::is_trivially_destructible<capture>::value) {
                rec->free_data = [](function_record *r) {
                    auto data = capture::from_data(r->data);
                    (void) data; // suppress "unused variable" warnings
                    data->~capture();
                };
            }
            PYBIND11_WARNING_POP
        } else {
            rec->data[0] = new capture{std::forward<Func>(f)};
            rec->free_data = [](function_record *r) { delete ((capture *) r->data[0]); };
        }

        /* Type casters for the function arguments and return value */
        using cast_in = argument_loader<Args...>;
        using cast_out
            = make_caster<conditional_t<std::is_void<Return>::value, void_type, Return>>;

        static_assert(
            expected_num_args<Extra...>(
                sizeof...(Args), cast_in::args_pos >= 0, cast_in::has_kwargs),
            "The number of argument annotations does not match the number of function arguments");

        /* Dispatch code which converts function arguments and performs the actual function call */
        rec->impl = [](function_call &call) -> handle {
            cast_in args_converter;

            /* Try to cast the function arguments into the C++ domain */
            if (!args_converter.load_args(call)) {
                return PYBIND11_TRY_NEXT_OVERLOAD;
            }

            /* Invoke call policy pre-call hook */
            process_attributes<Extra...>::precall(call);

            /* Get a pointer to the capture object */
            const auto *data = (sizeof(capture) <= sizeof(call.func.data) ? &call.func.data
                                                                          : call.func.data[0]);
            auto *cap = const_cast<capture *>(reinterpret_cast<const capture *>(data));

            /* Override policy for rvalues -- usually to enforce rvp::move on an rvalue */
            return_value_policy policy
                = return_value_policy_override<Return>::policy(call.func.policy);

            /* Function scope guard -- defaults to the compile-to-nothing `void_type` */
            using Guard = extract_guard_t<Extra...>;

            /* Perform the function call */
            handle result;
            if (call.func.is_setter) {
                (void) std::move(args_converter).template call<Return, Guard>(cap->f);
                result = none().release();
            } else {
                result = cast_out::cast(
                    std::move(args_converter).template call<Return, Guard>(cap->f),
                    policy,
                    call.parent);
            }

            /* Invoke call policy post-call hook */
            process_attributes<Extra...>::postcall(call, result);

            return result;
        };

        rec->nargs_pos = cast_in::args_pos >= 0
                             ? static_cast<std::uint16_t>(cast_in::args_pos)
                             : sizeof...(Args) - cast_in::has_kwargs; // Will get reduced more if
                                                                      // we have a kw_only
        rec->has_args = cast_in::args_pos >= 0;
        rec->has_kwargs = cast_in::has_kwargs;

        /* Process any user-provided function attributes */
        process_attributes<Extra...>::init(extra..., rec);

        {
            constexpr bool has_kw_only_args = any_of<std::is_same<kw_only, Extra>...>::value,
                           has_pos_only_args = any_of<std::is_same<pos_only, Extra>...>::value,
                           has_arg_annotations = any_of<is_keyword<Extra>...>::value;
            constexpr bool has_is_method = any_of<std::is_same<is_method, Extra>...>::value;
            // The implicit `self` argument is not present and not counted in method definitions.
            constexpr bool has_args = cast_in::args_pos >= 0;
            constexpr bool is_method_with_self_arg_only = has_is_method && !has_args;
            static_assert(has_arg_annotations || !has_kw_only_args,
                          "py::kw_only requires the use of argument annotations");
            static_assert(((/* Need `py::arg("arg_name")` annotation in function/method. */
                            has_arg_annotations)
                           || (/* Allow methods with no arguments `def method(self, /): ...`.
                                * A method has at least one argument `self`. There can be no
                                * `py::arg` annotation. E.g. `class.def("method", py::pos_only())`.
                                */
                               is_method_with_self_arg_only))
                              || !has_pos_only_args,
                          "py::pos_only requires the use of argument annotations (for docstrings "
                          "and aligning the annotations to the argument)");

            static_assert(constexpr_sum(is_kw_only<Extra>::value...) <= 1,
                          "py::kw_only may be specified only once");
            static_assert(constexpr_sum(is_pos_only<Extra>::value...) <= 1,
                          "py::pos_only may be specified only once");
            constexpr auto kw_only_pos = constexpr_first<is_kw_only, Extra...>();
            constexpr auto pos_only_pos = constexpr_first<is_pos_only, Extra...>();
            static_assert(!(has_kw_only_args && has_pos_only_args) || pos_only_pos < kw_only_pos,
                          "py::pos_only must come before py::kw_only");
        }

        /* Generate a readable signature describing the function's arguments and return
           value types */
        static constexpr auto signature
            = const_name("(") + cast_in::arg_names + const_name(") -> ") + cast_out::name;
        PYBIND11_DESCR_CONSTEXPR auto types = decltype(signature)::types();

        /* Register the function with Python from generic (non-templated) code */
        // Pass on the ownership over the `unique_rec` to `initialize_generic`. `rec` stays valid.
        initialize_generic(std::move(unique_rec), signature.text, types.data(), sizeof...(Args));

        /* Stash some additional information used by an important optimization in 'functional.h' */
        using FunctionType = Return (*)(Args...);
        constexpr bool is_function_ptr
            = std::is_convertible<Func, FunctionType>::value && sizeof(capture) == sizeof(void *);
        PYBIND11_ENSURE_PRECONDITION_FOR_FUNCTIONAL_H_PERFORMANCE_OPTIMIZATIONS(
            !is_function_ptr || std::is_standard_layout<capture>::value);
        if (is_function_ptr) {
            rec->is_stateless = true;
            rec->data[1]
                = const_cast<void *>(reinterpret_cast<const void *>(&typeid(FunctionType)));
        }
    }

    // Utility class that keeps track of all duplicated strings, and cleans them up in its
    // destructor, unless they are released. Basically a RAII-solution to deal with exceptions
    // along the way.
    class strdup_guard {
    public:
        strdup_guard() = default;
        strdup_guard(const strdup_guard &) = delete;
        strdup_guard &operator=(const strdup_guard &) = delete;

        ~strdup_guard() {
            for (auto *s : strings) {
                std::free(s);
            }
        }
        char *operator()(const char *s) {
            auto *t = PYBIND11_COMPAT_STRDUP(s);
            strings.push_back(t);
            return t;
        }
        void release() { strings.clear(); }

    private:
        std::vector<char *> strings;
    };

    /// Register a function call with Python (generic non-templated code goes here)
    void initialize_generic(unique_function_record &&unique_rec,
                            const char *text,
                            const std::type_info *const *types,
                            size_t args) {
        // Do NOT receive `unique_rec` by value. If this function fails to move out the unique_ptr,
        // we do not want this to destruct the pointer. `initialize` (the caller) still relies on
        // the pointee being alive after this call. Only move out if a `capsule` is going to keep
        // it alive.
        auto *rec = unique_rec.get();

        // Keep track of strdup'ed strings, and clean them up as long as the function's capsule
        // has not taken ownership yet (when `unique_rec.release()` is called).
        // Note: This cannot easily be fixed by a `unique_ptr` with custom deleter, because the
        // strings are only referenced before strdup'ing. So only *after* the following block could
        // `destruct` safely be called, but even then, `repr` could still throw in the middle of
        // copying all strings.
        strdup_guard guarded_strdup;

        /* Create copies of all referenced C-style strings */
        rec->name = guarded_strdup(rec->name ? rec->name : "");
        if (rec->doc) {
            rec->doc = guarded_strdup(rec->doc);
        }
        for (auto &a : rec->args) {
            if (a.name) {
                a.name = guarded_strdup(a.name);
            }
            if (a.descr) {
                a.descr = guarded_strdup(a.descr);
            } else if (a.value) {
                a.descr = guarded_strdup(repr(a.value).cast<std::string>().c_str());
            }
        }

        rec->is_constructor = (std::strcmp(rec->name, "__init__") == 0)
                              || (std::strcmp(rec->name, "__setstate__") == 0);

#if defined(PYBIND11_DETAILED_ERROR_MESSAGES) && !defined(PYBIND11_DISABLE_NEW_STYLE_INIT_WARNING)
        if (rec->is_constructor && !rec->is_new_style_constructor) {
            const auto class_name
                = detail::get_fully_qualified_tp_name((PyTypeObject *) rec->scope.ptr());
            const auto func_name = std::string(rec->name);
            PyErr_WarnEx(PyExc_FutureWarning,
                         ("pybind11-bound class '" + class_name
                          + "' is using an old-style "
                            "placement-new '"
                          + func_name
                          + "' which has been deprecated. See "
                            "the upgrade guide in pybind11's docs. This message is only visible "
                            "when compiled in debug mode.")
                             .c_str(),
                         0);
        }
#endif

        size_t type_index = 0, arg_index = 0;
        std::string signature
            = detail::generate_function_signature(text, rec, types, type_index, arg_index);

        if (arg_index != args - rec->has_args - rec->has_kwargs || types[type_index] != nullptr) {
            pybind11_fail("Internal error while parsing type signature (2)");
        }

        rec->signature = guarded_strdup(signature.c_str());
        rec->args.shrink_to_fit();
        rec->nargs = (std::uint16_t) args;

        if (rec->sibling && PYBIND11_INSTANCE_METHOD_CHECK(rec->sibling.ptr())) {
            rec->sibling = PYBIND11_INSTANCE_METHOD_GET_FUNCTION(rec->sibling.ptr());
        }

        detail::function_record *chain = nullptr, *chain_start = rec;
        if (rec->sibling) {
            if (PyCFunction_Check(rec->sibling.ptr())) {
                auto *self = PyCFunction_GET_SELF(rec->sibling.ptr());
                chain = detail::function_record_ptr_from_PyObject(self);
                if (chain && !chain->scope.is(rec->scope)) {
                    /* Never append a method to an overload chain of a parent class;
                       instead, hide the parent's overloads in this case */
                    chain = nullptr;
                }
            }
            // Don't trigger for things like the default __init__, which are wrapper_descriptors
            // that we are intentionally replacing
            else if (!rec->sibling.is_none() && rec->name[0] != '_') {
                pybind11_fail("Cannot overload existing non-function object \""
                              + std::string(rec->name) + "\" with a function of the same name");
            }
        }

        if (!chain) {
            /* No existing overload was found, create a new function object */
            rec->def = new PyMethodDef();
            std::memset(rec->def, 0, sizeof(PyMethodDef));
            rec->def->ml_name = rec->name;
            rec->def->ml_meth
                = reinterpret_cast<PyCFunction>(reinterpret_cast<void (*)()>(dispatcher));
            rec->def->ml_flags = METH_VARARGS | METH_KEYWORDS;

            detail::function_record_PyTypeObject_PyType_Ready(); // Call-once initialization.
            object py_func_rec = detail::function_record_PyObject_New();
            ((detail::function_record_PyObject *) py_func_rec.ptr())->cpp_func_rec
                = unique_rec.release();
            guarded_strdup.release();

            object scope_module = detail::get_scope_module(rec->scope);
            m_ptr = PyCFunction_NewEx(rec->def, py_func_rec.ptr(), scope_module.ptr());
            if (!m_ptr) {
                pybind11_fail("cpp_function::cpp_function(): Could not allocate function object");
            }
        } else {
            /* Append at the beginning or end of the overload chain */
            m_ptr = rec->sibling.ptr();
            inc_ref();
            if (chain->is_method != rec->is_method) {
                pybind11_fail(
                    "overloading a method with both static and instance methods is not supported; "
#if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
                    "#define PYBIND11_DETAILED_ERROR_MESSAGES or compile in debug mode for more "
                    "details"
#else
                    "error while attempting to bind "
                    + std::string(rec->is_method ? "instance" : "static") + " method "
                    + std::string(pybind11::str(rec->scope.attr("__name__"))) + "."
                    + std::string(rec->name) + signature
#endif
                );
            }

            if (rec->prepend) {
                // Beginning of chain; we need to replace the capsule's current head-of-the-chain
                // pointer with this one, then make this one point to the previous head of the
                // chain.
                chain_start = rec;
                rec->next = chain;
                auto *py_func_rec
                    = (detail::function_record_PyObject *) PyCFunction_GET_SELF(m_ptr);
                py_func_rec->cpp_func_rec = unique_rec.release();
                guarded_strdup.release();
            } else {
                // Or end of chain (normal behavior)
                chain_start = chain;
                while (chain->next) {
                    chain = chain->next;
                }
                chain->next = unique_rec.release();
                guarded_strdup.release();
            }
        }

        std::string signatures;
        int index = 0;
        /* Create a nice pydoc rec including all signatures and
           docstrings of the functions in the overload chain */
        if (chain && options::show_function_signatures()
            && std::strcmp(rec->name, "_pybind11_conduit_v1_") != 0) {
            // First a generic signature
            signatures += rec->name;
            signatures += "(*args, **kwargs)\n";
            signatures += "Overloaded function.\n\n";
        }
        // Then specific overload signatures
        bool first_user_def = true;
        for (auto *it = chain_start; it != nullptr; it = it->next) {
            if (options::show_function_signatures()
                && std::strcmp(rec->name, "_pybind11_conduit_v1_") != 0) {
                if (index > 0) {
                    signatures += '\n';
                }
                if (chain) {
                    signatures += std::to_string(++index) + ". ";
                }
                signatures += rec->name;
                signatures += it->signature;
                signatures += '\n';
            }
            if (it->doc && it->doc[0] != '\0' && options::show_user_defined_docstrings()) {
                // If we're appending another docstring, and aren't printing function signatures,
                // we need to append a newline first:
                if (!options::show_function_signatures()) {
                    if (first_user_def) {
                        first_user_def = false;
                    } else {
                        signatures += '\n';
                    }
                }
                if (options::show_function_signatures()) {
                    signatures += '\n';
                }
                signatures += it->doc;
                if (options::show_function_signatures()) {
                    signatures += '\n';
                }
            }
        }

        auto *func = (PyCFunctionObject *) m_ptr;
        // Install docstring if it's non-empty (when at least one option is enabled)
        auto *doc = signatures.empty() ? nullptr : PYBIND11_COMPAT_STRDUP(signatures.c_str());
        std::free(const_cast<char *>(PYBIND11_PYCFUNCTION_GET_DOC(func)));
        PYBIND11_PYCFUNCTION_SET_DOC(func, doc);

        if (rec->is_method) {
            m_ptr = PYBIND11_INSTANCE_METHOD_NEW(m_ptr, rec->scope.ptr());
            if (!m_ptr) {
                pybind11_fail(
                    "cpp_function::cpp_function(): Could not allocate instance method object");
            }
            Py_DECREF(func);
        }
    }

    friend void detail::function_record_PyTypeObject_methods::tp_dealloc_impl(PyObject *);

    /// When a cpp_function is GCed, release any memory allocated by pybind11
    static void destruct(detail::function_record *rec, bool free_strings = true) {
// If on Python 3.9, check the interpreter "MICRO" (patch) version.
// If this is running on 3.9.0, we have to work around a bug.
#if !defined(PYPY_VERSION) && PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION == 9
        static bool is_zero = Py_GetVersion()[4] == '0';
#endif

        while (rec) {
            detail::function_record *next = rec->next;
            if (rec->free_data) {
                rec->free_data(rec);
            }
            // During initialization, these strings might not have been copied yet,
            // so they cannot be freed. Once the function has been created, they can.
            // Check `make_function_record` for more details.
            if (free_strings) {
                std::free((char *) rec->name);
                std::free((char *) rec->doc);
                std::free((char *) rec->signature);
                for (auto &arg : rec->args) {
                    std::free(const_cast<char *>(arg.name));
                    std::free(const_cast<char *>(arg.descr));
                }
            }
            for (auto &arg : rec->args) {
                arg.value.dec_ref();
            }
            if (rec->def) {
                std::free(const_cast<char *>(rec->def->ml_doc));
// Python 3.9.0 decref's these in the wrong order; rec->def
// If loaded on 3.9.0, let these leak (use Python 3.9.1 at runtime to fix)
// See https://github.com/python/cpython/pull/22670
#if !defined(PYPY_VERSION) && PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION == 9
                if (!is_zero) {
                    delete rec->def;
                }
#else
                delete rec->def;
#endif
            }
            delete rec;
            rec = next;
        }
    }

    /// Main dispatch logic for calls to functions bound using pybind11
    static PyObject *dispatcher(PyObject *self, PyObject *args_in, PyObject *kwargs_in) {
        using namespace detail;
        const function_record *overloads = function_record_ptr_from_PyObject(self);
        assert(overloads != nullptr);

        /* Iterator over the list of potentially admissible overloads */
        const function_record *current_overload = overloads;

        /* Need to know how many arguments + keyword arguments there are to pick the right
           overload */
        const auto n_args_in = (size_t) PyTuple_GET_SIZE(args_in);

        handle parent = n_args_in > 0 ? PyTuple_GET_ITEM(args_in, 0) : nullptr,
               result = PYBIND11_TRY_NEXT_OVERLOAD;

        auto self_value_and_holder = value_and_holder();
        if (overloads->is_constructor) {
            if (!parent
                || !PyObject_TypeCheck(parent.ptr(), (PyTypeObject *) overloads->scope.ptr())) {
                set_error(PyExc_TypeError,
                          "__init__(self, ...) called with invalid or missing `self` argument");
                return nullptr;
            }

            auto *const tinfo = get_type_info((PyTypeObject *) overloads->scope.ptr());
            auto *const pi = reinterpret_cast<instance *>(parent.ptr());
            self_value_and_holder = pi->get_value_and_holder(tinfo, true);

            // If this value is already registered it must mean __init__ is invoked multiple times;
            // we really can't support that in C++, so just ignore the second __init__.
            if (self_value_and_holder.instance_registered()) {
                return none().release().ptr();
            }
        }

        try {
            // We do this in two passes: in the first pass, we load arguments with `convert=false`;
            // in the second, we allow conversion (except for arguments with an explicit
            // py::arg().noconvert()).  This lets us prefer calls without conversion, with
            // conversion as a fallback.
            std::vector<function_call> second_pass;

            // However, if there are no overloads, we can just skip the no-convert pass entirely
            const bool overloaded
                = current_overload != nullptr && current_overload->next != nullptr;

            for (; current_overload != nullptr; current_overload = current_overload->next) {

                /* For each overload:
                   1. Copy all positional arguments we were given, also checking to make sure that
                      named positional arguments weren't *also* specified via kwarg.
                   2. If we weren't given enough, try to make up the omitted ones by checking
                      whether they were provided by a kwarg matching the `py::arg("name")` name. If
                      so, use it (and remove it from kwargs); if not, see if the function binding
                      provided a default that we can use.
                   3. Ensure that either all keyword arguments were "consumed", or that the
                   function takes a kwargs argument to accept unconsumed kwargs.
                   4. Any positional arguments still left get put into a tuple (for args), and any
                      leftover kwargs get put into a dict.
                   5. Pack everything into a vector; if we have py::args or py::kwargs, they are an
                      extra tuple or dict at the end of the positional arguments.
                   6. Call the function call dispatcher (function_record::impl)

                   If one of these fail, move on to the next overload and keep trying until we get
                   a result other than PYBIND11_TRY_NEXT_OVERLOAD.
                 */

                const function_record &func = *current_overload;
                size_t num_args = func.nargs; // Number of positional arguments that we need
                if (func.has_args) {
                    --num_args; // (but don't count py::args
                }
                if (func.has_kwargs) {
                    --num_args; //  or py::kwargs)
                }
                size_t pos_args = func.nargs_pos;

                if (!func.has_args && n_args_in > pos_args) {
                    continue; // Too many positional arguments for this overload
                }

                if (n_args_in < pos_args && func.args.size() < pos_args) {
                    continue; // Not enough positional arguments given, and not enough defaults to
                              // fill in the blanks
                }

                function_call call(func, parent);

                // Protect std::min with parentheses
                size_t args_to_copy = (std::min) (pos_args, n_args_in);
                size_t args_copied = 0;

                // 0. Inject new-style `self` argument
                if (func.is_new_style_constructor) {
                    // The `value` may have been preallocated by an old-style `__init__`
                    // if it was a preceding candidate for overload resolution.
                    if (self_value_and_holder) {
                        self_value_and_holder.type->dealloc(self_value_and_holder);
                    }

                    call.init_self = PyTuple_GET_ITEM(args_in, 0);
                    call.args.emplace_back(reinterpret_cast<PyObject *>(&self_value_and_holder));
                    call.args_convert.push_back(false);
                    ++args_copied;
                }

                // 1. Copy any position arguments given.
                bool bad_arg = false;
                for (; args_copied < args_to_copy; ++args_copied) {
                    const argument_record *arg_rec
                        = args_copied < func.args.size() ? &func.args[args_copied] : nullptr;
                    if (kwargs_in && arg_rec && arg_rec->name
                        && dict_getitemstring(kwargs_in, arg_rec->name)) {
                        bad_arg = true;
                        break;
                    }

                    handle arg(PyTuple_GET_ITEM(args_in, args_copied));
                    if (arg_rec && !arg_rec->none && arg.is_none()) {
                        bad_arg = true;
                        break;
                    }
                    call.args.push_back(arg);
                    call.args_convert.push_back(arg_rec ? arg_rec->convert : true);
                }
                if (bad_arg) {
                    continue; // Maybe it was meant for another overload (issue #688)
                }

                // Keep track of how many position args we copied out in case we need to come back
                // to copy the rest into a py::args argument.
                size_t positional_args_copied = args_copied;

                // We'll need to copy this if we steal some kwargs for defaults
                dict kwargs = reinterpret_borrow<dict>(kwargs_in);

                // 1.5. Fill in any missing pos_only args from defaults if they exist
                if (args_copied < func.nargs_pos_only) {
                    for (; args_copied < func.nargs_pos_only; ++args_copied) {
                        const auto &arg_rec = func.args[args_copied];
                        handle value;

                        if (arg_rec.value) {
                            value = arg_rec.value;
                        }
                        if (value) {
                            call.args.push_back(value);
                            call.args_convert.push_back(arg_rec.convert);
                        } else {
                            break;
                        }
                    }

                    if (args_copied < func.nargs_pos_only) {
                        continue; // Not enough defaults to fill the positional arguments
                    }
                }

                // 2. Check kwargs and, failing that, defaults that may help complete the list
                if (args_copied < num_args) {
                    bool copied_kwargs = false;

                    for (; args_copied < num_args; ++args_copied) {
                        const auto &arg_rec = func.args[args_copied];

                        handle value;
                        if (kwargs_in && arg_rec.name) {
                            value = dict_getitemstring(kwargs.ptr(), arg_rec.name);
                        }

                        if (value) {
                            // Consume a kwargs value
                            if (!copied_kwargs) {
                                kwargs = reinterpret_steal<dict>(PyDict_Copy(kwargs.ptr()));
                                copied_kwargs = true;
                            }
                            if (PyDict_DelItemString(kwargs.ptr(), arg_rec.name) == -1) {
                                throw error_already_set();
                            }
                        } else if (arg_rec.value) {
                            value = arg_rec.value;
                        }

                        if (!arg_rec.none && value.is_none()) {
                            break;
                        }

                        if (value) {
                            // If we're at the py::args index then first insert a stub for it to be
                            // replaced later
                            if (func.has_args && call.args.size() == func.nargs_pos) {
                                call.args.push_back(none());
                            }

                            call.args.push_back(value);
                            call.args_convert.push_back(arg_rec.convert);
                        } else {
                            break;
                        }
                    }

                    if (args_copied < num_args) {
                        continue; // Not enough arguments, defaults, or kwargs to fill the
                                  // positional arguments
                    }
                }

                // 3. Check everything was consumed (unless we have a kwargs arg)
                if (kwargs && !kwargs.empty() && !func.has_kwargs) {
                    continue; // Unconsumed kwargs, but no py::kwargs argument to accept them
                }

                // 4a. If we have a py::args argument, create a new tuple with leftovers
                if (func.has_args) {
                    tuple extra_args;
                    if (args_to_copy == 0) {
                        // We didn't copy out any position arguments from the args_in tuple, so we
                        // can reuse it directly without copying:
                        extra_args = reinterpret_borrow<tuple>(args_in);
                    } else if (positional_args_copied >= n_args_in) {
                        extra_args = tuple(0);
                    } else {
                        size_t args_size = n_args_in - positional_args_copied;
                        extra_args = tuple(args_size);
                        for (size_t i = 0; i < args_size; ++i) {
                            extra_args[i] = PyTuple_GET_ITEM(args_in, positional_args_copied + i);
                        }
                    }
                    if (call.args.size() <= func.nargs_pos) {
                        call.args.push_back(extra_args);
                    } else {
                        call.args[func.nargs_pos] = extra_args;
                    }
                    call.args_convert.push_back(false);
                    call.args_ref = std::move(extra_args);
                }

                // 4b. If we have a py::kwargs, pass on any remaining kwargs
                if (func.has_kwargs) {
                    if (!kwargs.ptr()) {
                        kwargs = dict(); // If we didn't get one, send an empty one
                    }
                    call.args.push_back(kwargs);
                    call.args_convert.push_back(false);
                    call.kwargs_ref = std::move(kwargs);
                }

// 5. Put everything in a vector.  Not technically step 5, we've been building it
// in `call.args` all along.
#if defined(PYBIND11_DETAILED_ERROR_MESSAGES)
                if (call.args.size() != func.nargs || call.args_convert.size() != func.nargs) {
                    pybind11_fail("Internal error: function call dispatcher inserted wrong number "
                                  "of arguments!");
                }
#endif

                std::vector<bool> second_pass_convert;
                if (overloaded) {
                    // We're in the first no-convert pass, so swap out the conversion flags for a
                    // set of all-false flags.  If the call fails, we'll swap the flags back in for
                    // the conversion-allowed call below.
                    second_pass_convert.resize(func.nargs, false);
                    call.args_convert.swap(second_pass_convert);
                }

                // 6. Call the function.
                try {
                    loader_life_support guard{};
                    result = func.impl(call);
                } catch (reference_cast_error &) {
                    result = PYBIND11_TRY_NEXT_OVERLOAD;
                }

                if (result.ptr() != PYBIND11_TRY_NEXT_OVERLOAD) {
                    break;
                }

                if (overloaded) {
                    // The (overloaded) call failed; if the call has at least one argument that
                    // permits conversion (i.e. it hasn't been explicitly specified `.noconvert()`)
                    // then add this call to the list of second pass overloads to try.
                    for (size_t i = func.is_method ? 1 : 0; i < pos_args; i++) {
                        if (second_pass_convert[i]) {
                            // Found one: swap the converting flags back in and store the call for
                            // the second pass.
                            call.args_convert.swap(second_pass_convert);
                            second_pass.push_back(std::move(call));
                            break;
                        }
                    }
                }
            }

            if (overloaded && !second_pass.empty() && result.ptr() == PYBIND11_TRY_NEXT_OVERLOAD) {
                // The no-conversion pass finished without success, try again with conversion
                // allowed
                for (auto &call : second_pass) {
                    try {
                        loader_life_support guard{};
                        result = call.func.impl(call);
                    } catch (reference_cast_error &) {
                        result = PYBIND11_TRY_NEXT_OVERLOAD;
                    }

                    if (result.ptr() != PYBIND11_TRY_NEXT_OVERLOAD) {
                        // The error reporting logic below expects 'current_overload' to be valid,
                        // as it would be if we'd encountered this failure in the first-pass loop.
                        if (!result) {
                            current_overload = &call.func;
                        }
                        break;
                    }
                }
            }
        } catch (error_already_set &e) {
            e.restore();
            return nullptr;
#ifdef __GLIBCXX__
        } catch (abi::__forced_unwind &) {
            throw;
#endif
        } catch (...) {
            try_translate_exceptions();
            return nullptr;
        }

        auto append_note_if_missing_header_is_suspected = [](std::string &msg) {
            if (msg.find("std::") != std::string::npos) {
                msg += "\n\n"
                       "Did you forget to `#include <pybind11/stl.h>`? Or <pybind11/complex.h>,\n"
                       "<pybind11/functional.h>, <pybind11/chrono.h>, etc. Some automatic\n"
                       "conversions are optional and require extra headers to be included\n"
                       "when compiling your pybind11 module.";
            }
        };

        if (result.ptr() == PYBIND11_TRY_NEXT_OVERLOAD) {
            if (overloads->is_operator) {
                return handle(Py_NotImplemented).inc_ref().ptr();
            }

            std::string msg = std::string(overloads->name) + "(): incompatible "
                              + std::string(overloads->is_constructor ? "constructor" : "function")
                              + " arguments. The following argument types are supported:\n";

            int ctr = 0;
            for (const function_record *it2 = overloads; it2 != nullptr; it2 = it2->next) {
                msg += "    " + std::to_string(++ctr) + ". ";

                bool wrote_sig = false;
                if (overloads->is_constructor) {
                    // For a constructor, rewrite `(self: Object, arg0, ...) -> NoneType` as
                    // `Object(arg0, ...)`
                    std::string sig = it2->signature;
                    size_t start = sig.find('(') + 7; // skip "(self: "
                    if (start < sig.size()) {
                        // End at the , for the next argument
                        size_t end = sig.find(", "), next = end + 2;
                        size_t ret = sig.rfind(" -> ");
                        // Or the ), if there is no comma:
                        if (end >= sig.size()) {
                            next = end = sig.find(')');
                        }
                        if (start < end && next < sig.size()) {
                            msg.append(sig, start, end - start);
                            msg += '(';
                            msg.append(sig, next, ret - next);
                            wrote_sig = true;
                        }
                    }
                }
                if (!wrote_sig) {
                    msg += it2->signature;
                }

                msg += '\n';
            }
            msg += "\nInvoked with: ";
            auto args_ = reinterpret_borrow<tuple>(args_in);
            bool some_args = false;
            for (size_t ti = overloads->is_constructor ? 1 : 0; ti < args_.size(); ++ti) {
                if (!some_args) {
                    some_args = true;
                } else {
                    msg += ", ";
                }
                try {
                    msg += pybind11::repr(args_[ti]);
                } catch (const error_already_set &) {
                    msg += "<repr raised Error>";
                }
            }
            if (kwargs_in) {
                auto kwargs = reinterpret_borrow<dict>(kwargs_in);
                if (!kwargs.empty()) {
                    if (some_args) {
                        msg += "; ";
                    }
                    msg += "kwargs: ";
                    bool first = true;
                    for (const auto &kwarg : kwargs) {
                        if (first) {
                            first = false;
                        } else {
                            msg += ", ";
                        }
                        msg += pybind11::str("{}=").format(kwarg.first);
                        try {
                            msg += pybind11::repr(kwarg.second);
                        } catch (const error_already_set &) {
                            msg += "<repr raised Error>";
                        }
                    }
                }
            }

            append_note_if_missing_header_is_suspected(msg);
            // Attach additional error info to the exception if supported
            if (PyErr_Occurred()) {
                // #HelpAppreciated: unit test coverage for this branch.
                raise_from(PyExc_TypeError, msg.c_str());
                return nullptr;
            }
            set_error(PyExc_TypeError, msg.c_str());
            return nullptr;
        }
        if (!result) {
            std::string msg = "Unable to convert function return value to a "
                              "Python type! The signature was\n\t";
            assert(current_overload != nullptr);
            msg += current_overload->signature;
            append_note_if_missing_header_is_suspected(msg);
            // Attach additional error info to the exception if supported
            if (PyErr_Occurred()) {
                raise_from(PyExc_TypeError, msg.c_str());
                return nullptr;
            }
            set_error(PyExc_TypeError, msg.c_str());
            return nullptr;
        }
        if (overloads->is_constructor && !self_value_and_holder.holder_constructed()) {
            auto *pi = reinterpret_cast<instance *>(parent.ptr());
            self_value_and_holder.type->init_instance(pi, nullptr);
        }
        return result.ptr();
    }
};

PYBIND11_NAMESPACE_BEGIN(detail)

PYBIND11_NAMESPACE_BEGIN(function_record_PyTypeObject_methods)

// This implementation needs the definition of `class cpp_function`.
inline void tp_dealloc_impl(PyObject *self) {
    auto *py_func_rec = (function_record_PyObject *) self;
    cpp_function::destruct(py_func_rec->cpp_func_rec);
    py_func_rec->cpp_func_rec = nullptr;
}

PYBIND11_NAMESPACE_END(function_record_PyTypeObject_methods)

template <>
struct handle_type_name<cpp_function> {
    static constexpr auto name = const_name("collections.abc.Callable");
};

PYBIND11_NAMESPACE_END(detail)

// Use to activate Py_MOD_GIL_NOT_USED.
class mod_gil_not_used {
public:
    explicit mod_gil_not_used(bool flag = true) : flag_(flag) {}
    bool flag() const { return flag_; }

private:
    bool flag_;
};

class multiple_interpreters {
public:
    enum class level {
        not_supported,      /// Use to activate Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED
        shared_gil,         /// Use to activate Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED
        per_interpreter_gil /// Use to activate Py_MOD_PER_INTERPRETER_GIL_SUPPORTED
    };

    static multiple_interpreters not_supported() {
        return multiple_interpreters(level::not_supported);
    }
    static multiple_interpreters shared_gil() { return multiple_interpreters(level::shared_gil); }
    static multiple_interpreters per_interpreter_gil() {
        return multiple_interpreters(level::per_interpreter_gil);
    }

    explicit constexpr multiple_interpreters(level l) : level_(l) {}
    level value() const { return level_; }

private:
    level level_;
};

PYBIND11_NAMESPACE_BEGIN(detail)

inline bool gil_not_used_option() { return false; }
template <typename F, typename... O>
bool gil_not_used_option(F &&, O &&...o);
template <typename... O>
inline bool gil_not_used_option(mod_gil_not_used f, O &&...o) {
    return f.flag() || gil_not_used_option(o...);
}
template <typename F, typename... O>
inline bool gil_not_used_option(F &&, O &&...o) {
    return gil_not_used_option(o...);
}

#ifdef Py_mod_multiple_interpreters
inline void *multi_interp_slot() { return Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED; }
template <typename... O>
inline void *multi_interp_slot(multiple_interpreters mi, O &&...o) {
    switch (mi.value()) {
        case multiple_interpreters::level::per_interpreter_gil:
            return Py_MOD_PER_INTERPRETER_GIL_SUPPORTED;
        case multiple_interpreters::level::shared_gil:
            return Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED;
        case multiple_interpreters::level::not_supported:
            return Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED;
    }
    // silence warnings with this unreachable line:
    return multi_interp_slot(o...);
}
template <typename F, typename... O>
inline void *multi_interp_slot(F &&, O &&...o) {
    return multi_interp_slot(o...);
}
#endif

PYBIND11_NAMESPACE_END(detail)

/// Wrapper for Python extension modules
class module_ : public object {
public:
    PYBIND11_OBJECT_DEFAULT(module_, object, PyModule_Check)

    /// Create a new top-level Python module with the given name and docstring
    PYBIND11_DEPRECATED("Use PYBIND11_MODULE or module_::create_extension_module instead")
    explicit module_(const char *name, const char *doc = nullptr) {
        *this = create_extension_module(name, doc, new PyModuleDef());
    }

    /** \rst
        Create Python binding for a new function within the module scope. ``Func``
        can be a plain C++ function, a function pointer, or a lambda function. For
        details on the ``Extra&& ... extra`` argument, see section :ref:`extras`.
    \endrst */
    template <typename Func, typename... Extra>
    module_ &def(const char *name_, Func &&f, const Extra &...extra) {
        cpp_function func(std::forward<Func>(f),
                          name(name_),
                          scope(*this),
                          sibling(getattr(*this, name_, none())),
                          extra...);
        // NB: allow overwriting here because cpp_function sets up a chain with the intention of
        // overwriting (and has already checked internally that it isn't overwriting
        // non-functions).
        add_object(name_, func, true /* overwrite */);
        return *this;
    }

    /** \rst
        Create and return a new Python submodule with the given name and docstring.
        This also works recursively, i.e.

        .. code-block:: cpp

            py::module_ m("example", "pybind11 example plugin");
            py::module_ m2 = m.def_submodule("sub", "A submodule of 'example'");
            py::module_ m3 = m2.def_submodule("subsub", "A submodule of 'example.sub'");
    \endrst */
    module_ def_submodule(const char *name, const char *doc = nullptr) {
        const char *this_name = PyModule_GetName(m_ptr);
        if (this_name == nullptr) {
            throw error_already_set();
        }
        std::string full_name = std::string(this_name) + '.' + name;
        handle submodule = PyImport_AddModule(full_name.c_str());
        if (!submodule) {
            throw error_already_set();
        }
        auto result = reinterpret_borrow<module_>(submodule);
        if (doc && options::show_user_defined_docstrings()) {
            result.attr("__doc__") = pybind11::str(doc);
        }

#if defined(GRAALVM_PYTHON) && (!defined(GRAALPY_VERSION_NUM) || GRAALPY_VERSION_NUM < 0x190000)
        // GraalPy doesn't support PyModule_GetFilenameObject,
        // so getting by attribute (see PR #5584)
        handle this_module = m_ptr;
        if (object this_file = getattr(this_module, "__file__", none())) {
            result.attr("__file__") = this_file;
        }
#else
        handle this_file = PyModule_GetFilenameObject(m_ptr);
        if (this_file) {
            result.attr("__file__") = this_file;
        } else if (PyErr_ExceptionMatches(PyExc_SystemError) != 0) {
            PyErr_Clear();
        } else {
            throw error_already_set();
        }
#endif
        attr(name) = result;
        return result;
    }

    /// Import and return a module or throws `error_already_set`.
    static module_ import(const char *name) {
        PyObject *obj = PyImport_ImportModule(name);
        if (!obj) {
            throw error_already_set();
        }
        return reinterpret_steal<module_>(obj);
    }

    /// Reload the module or throws `error_already_set`.
    void reload() {
        PyObject *obj = PyImport_ReloadModule(ptr());
        if (!obj) {
            throw error_already_set();
        }
        *this = reinterpret_steal<module_>(obj);
    }

    /** \rst
        Adds an object to the module using the given name.  Throws if an object with the given name
        already exists.

        ``overwrite`` should almost always be false: attempting to overwrite objects that pybind11
        has established will, in most cases, break things.
    \endrst */
    PYBIND11_NOINLINE void add_object(const char *name, handle obj, bool overwrite = false) {
        if (!overwrite && hasattr(*this, name)) {
            pybind11_fail(
                "Error during initialization: multiple incompatible definitions with name \""
                + std::string(name) + "\"");
        }

        PyModule_AddObject(ptr(), name, obj.inc_ref().ptr() /* steals a reference */);
    }

    using module_def = PyModuleDef; // TODO: Can this be removed (it was needed only for Python 2)?

    /** \rst
        Create a new top-level module that can be used as the main module of a C extension.

        ``def`` should point to a statically allocated module_def.
    \endrst */
    static module_ create_extension_module(const char *name,
                                           const char *doc,
                                           module_def *def,
                                           mod_gil_not_used gil_not_used
                                           = mod_gil_not_used(false)) {
        // module_def is PyModuleDef
        // Placement new (not an allocation).
        new (def) PyModuleDef{/* m_base */ PyModuleDef_HEAD_INIT,
                              /* m_name */ name,
                              /* m_doc */ options::show_user_defined_docstrings() ? doc : nullptr,
                              /* m_size */ -1,
                              /* m_methods */ nullptr,
                              /* m_slots */ nullptr,
                              /* m_traverse */ nullptr,
                              /* m_clear */ nullptr,
                              /* m_free */ nullptr};
        auto *m = PyModule_Create(def);
        if (m == nullptr) {
            if (PyErr_Occurred()) {
                throw error_already_set();
            }
            pybind11_fail("Internal error in module_::create_extension_module()");
        }
        if (gil_not_used.flag()) {
#ifdef Py_GIL_DISABLED
            PyUnstable_Module_SetGIL(m, Py_MOD_GIL_NOT_USED);
#endif
        }
        // TODO: Should be reinterpret_steal for Python 3, but Python also steals it again when
        //       returned from PyInit_...
        //       For Python 2, reinterpret_borrow was correct.
        return reinterpret_borrow<module_>(m);
    }

    /// Must be a POD type, and must hold enough entries for all of the possible slots PLUS ONE for
    /// the sentinel (0) end slot.
    using slots_array = std::array<PyModuleDef_Slot, 4>;

    /** \rst
        Initialize a module def for use with multi-phase module initialization.

        ``def`` should point to a statically allocated module_def.
        ``slots`` must already contain a Py_mod_exec or Py_mod_create slot and will be filled with
            additional slots from the supplied options (and the empty sentinel slot).
    \endrst */
    template <typename... Options>
    static object initialize_multiphase_module_def(const char *name,
                                                   const char *doc,
                                                   module_def *def,
                                                   slots_array &slots,
                                                   Options &&...options) {
        size_t next_slot = 0;
        size_t term_slot = slots.size() - 1;

        // find the end of the supplied slots
        while (next_slot < term_slot && slots[next_slot].slot != 0) {
            ++next_slot;
        }

#ifdef Py_mod_multiple_interpreters
        if (next_slot >= term_slot) {
            pybind11_fail("initialize_multiphase_module_def: not enough space in slots");
        }
        slots[next_slot++] = {Py_mod_multiple_interpreters, detail::multi_interp_slot(options...)};
#endif

        if (detail::gil_not_used_option(options...)) {
#if defined(Py_mod_gil) && defined(Py_GIL_DISABLED)
            if (next_slot >= term_slot) {
                pybind11_fail("initialize_multiphase_module_def: not enough space in slots");
            }
            slots[next_slot++] = {Py_mod_gil, Py_MOD_GIL_NOT_USED};
#endif
        }

        // slots must have a zero end sentinel
        if (next_slot > term_slot) {
            pybind11_fail("initialize_multiphase_module_def: not enough space in slots");
        }
        slots[next_slot++] = {0, nullptr};

        // module_def is PyModuleDef
        // Placement new (not an allocation).
        new (def) PyModuleDef{/* m_base */ PyModuleDef_HEAD_INIT,
                              /* m_name */ name,
                              /* m_doc */ options::show_user_defined_docstrings() ? doc : nullptr,
                              /* m_size */ 0,
                              /* m_methods */ nullptr,
                              /* m_slots */ &slots[0],
                              /* m_traverse */ nullptr,
                              /* m_clear */ nullptr,
                              /* m_free */ nullptr};
        auto *m = PyModuleDef_Init(def);
        if (m == nullptr) {
            if (PyErr_Occurred()) {
                throw error_already_set();
            }
            pybind11_fail("Internal error in module_::initialize_multiphase_module_def()");
        }
        return reinterpret_borrow<object>(m);
    }
};

PYBIND11_NAMESPACE_BEGIN(detail)

template <>
struct handle_type_name<module_> {
    static constexpr auto name = const_name("types.ModuleType");
};

PYBIND11_NAMESPACE_END(detail)

// When inside a namespace (or anywhere as long as it's not the first item on a line),
// C++20 allows "module" to be used. This is provided for backward compatibility, and for
// simplicity, if someone wants to use py::module for example, that is perfectly safe.
using module = module_;

/// \ingroup python_builtins
/// Return a dictionary representing the global variables in the current execution frame,
/// or ``__main__.__dict__`` if there is no frame (usually when the interpreter is embedded).
inline dict globals() {
#if PY_VERSION_HEX >= 0x030d0000
    PyObject *p = PyEval_GetFrameGlobals();
    return p ? reinterpret_steal<dict>(p)
             : reinterpret_borrow<dict>(module_::import("__main__").attr("__dict__").ptr());
#else
    PyObject *p = PyEval_GetGlobals();
    return reinterpret_borrow<dict>(p ? p : module_::import("__main__").attr("__dict__").ptr());
#endif
}

PYBIND11_NAMESPACE_BEGIN(detail)
/// Generic support for creating new Python heap types
class generic_type : public object {
public:
    PYBIND11_OBJECT_DEFAULT(generic_type, object, PyType_Check)
protected:
    void initialize(const type_record &rec) {
        if (rec.scope && hasattr(rec.scope, "__dict__")
            && rec.scope.attr("__dict__").contains(rec.name)) {
            pybind11_fail("generic_type: cannot initialize type \"" + std::string(rec.name)
                          + "\": an object with that name is already defined");
        }

        if ((rec.module_local ? get_local_type_info(*rec.type) : get_global_type_info(*rec.type))
            != nullptr) {
            pybind11_fail("generic_type: type \"" + std::string(rec.name)
                          + "\" is already registered!");
        }

        m_ptr = make_new_python_type(rec);

        /* Register supplemental type information in C++ dict */
        auto *tinfo = new detail::type_info();
        tinfo->type = (PyTypeObject *) m_ptr;
        tinfo->cpptype = rec.type;
        tinfo->type_size = rec.type_size;
        tinfo->type_align = rec.type_align;
        tinfo->operator_new = rec.operator_new;
        tinfo->holder_size_in_ptrs = size_in_ptrs(rec.holder_size);
        tinfo->init_instance = rec.init_instance;
        tinfo->dealloc = rec.dealloc;
        tinfo->simple_type = true;
        tinfo->simple_ancestors = true;
        tinfo->module_local = rec.module_local;
        tinfo->holder_enum_v = rec.holder_enum_v;

        with_internals([&](internals &internals) {
            auto tindex = std::type_index(*rec.type);
            tinfo->direct_conversions = &internals.direct_conversions[tindex];
            if (rec.module_local) {
                get_local_internals().registered_types_cpp[tindex] = tinfo;
            } else {
                internals.registered_types_cpp[tindex] = tinfo;
            }

            PYBIND11_WARNING_PUSH
#if defined(__GNUC__) && __GNUC__ == 12
            // When using GCC 12 these warnings are disabled as they trigger
            // false positive warnings.  Discussed here:
            // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115824.
            PYBIND11_WARNING_DISABLE_GCC("-Warray-bounds")
            PYBIND11_WARNING_DISABLE_GCC("-Wstringop-overread")
#endif
            internals.registered_types_py[(PyTypeObject *) m_ptr] = {tinfo};
            PYBIND11_WARNING_POP
        });

        if (rec.bases.size() > 1 || rec.multiple_inheritance) {
            mark_parents_nonsimple(tinfo->type);
            tinfo->simple_ancestors = false;
        } else if (rec.bases.size() == 1) {
            auto *parent_tinfo = get_type_info((PyTypeObject *) rec.bases[0].ptr());
            assert(parent_tinfo != nullptr);
            bool parent_simple_ancestors = parent_tinfo->simple_ancestors;
            tinfo->simple_ancestors = parent_simple_ancestors;
            // The parent can no longer be a simple type if it has MI and has a child
            parent_tinfo->simple_type = parent_tinfo->simple_type && parent_simple_ancestors;
        }

        if (rec.module_local) {
            // Stash the local typeinfo and loader so that external modules can access it.
            tinfo->module_local_load = &type_caster_generic::local_load;
            setattr(m_ptr, PYBIND11_MODULE_LOCAL_ID, capsule(tinfo));
        }
    }

    /// Helper function which tags all parents of a type using mult. inheritance
    void mark_parents_nonsimple(PyTypeObject *value) {
        auto t = reinterpret_borrow<tuple>(value->tp_bases);
        for (handle h : t) {
            auto *tinfo2 = get_type_info((PyTypeObject *) h.ptr());
            if (tinfo2) {
                tinfo2->simple_type = false;
            }
            mark_parents_nonsimple((PyTypeObject *) h.ptr());
        }
    }

    void install_buffer_funcs(buffer_info *(*get_buffer)(PyObject *, void *),
                              void *get_buffer_data) {
        auto *type = (PyHeapTypeObject *) m_ptr;
        auto *tinfo = detail::get_type_info(&type->ht_type);

        if (!type->ht_type.tp_as_buffer) {
            pybind11_fail("To be able to register buffer protocol support for the type '"
                          + get_fully_qualified_tp_name(tinfo->type)
                          + "' the associated class<>(..) invocation must "
                            "include the pybind11::buffer_protocol() annotation!");
        }

        tinfo->get_buffer = get_buffer;
        tinfo->get_buffer_data = get_buffer_data;
    }

    // rec_func must be set for either fget or fset.
    void def_property_static_impl(const char *name,
                                  handle fget,
                                  handle fset,
                                  detail::function_record *rec_func) {
        const auto is_static = (rec_func != nullptr) && !(rec_func->is_method && rec_func->scope);
        const auto has_doc = (rec_func != nullptr) && (rec_func->doc != nullptr)
                             && pybind11::options::show_user_defined_docstrings();
        auto property = handle(
            (PyObject *) (is_static ? get_internals().static_property_type : &PyProperty_Type));
        attr(name) = property(fget.ptr() ? fget : none(),
                              fset.ptr() ? fset : none(),
                              /*deleter*/ none(),
                              pybind11::str(has_doc ? rec_func->doc : ""));
    }
};

/// Set the pointer to operator new if it exists. The cast is needed because it can be overloaded.
template <typename T,
          typename = void_t<decltype(static_cast<void *(*) (size_t)>(T::operator new))>>
void set_operator_new(type_record *r) {
    r->operator_new = &T::operator new;
}

template <typename>
void set_operator_new(...) {}

template <typename T, typename SFINAE = void>
struct has_operator_delete : std::false_type {};
template <typename T>
struct has_operator_delete<T, void_t<decltype(static_cast<void (*)(void *)>(T::operator delete))>>
    : std::true_type {};
template <typename T, typename SFINAE = void>
struct has_operator_delete_size : std::false_type {};
template <typename T>
struct has_operator_delete_size<
    T,
    void_t<decltype(static_cast<void (*)(void *, size_t)>(T::operator delete))>> : std::true_type {
};
/// Call class-specific delete if it exists or global otherwise. Can also be an overload set.
template <typename T, enable_if_t<has_operator_delete<T>::value, int> = 0>
void call_operator_delete(T *p, size_t, size_t) {
    T::operator delete(p);
}
template <typename T,
          enable_if_t<!has_operator_delete<T>::value && has_operator_delete_size<T>::value, int>
          = 0>
void call_operator_delete(T *p, size_t s, size_t) {
    T::operator delete(p, s);
}

inline void call_operator_delete(void *p, size_t s, size_t a) {
    (void) s;
    (void) a;
#if defined(__cpp_aligned_new) && (!defined(_MSC_VER) || _MSC_VER >= 1912)
    if (a > __STDCPP_DEFAULT_NEW_ALIGNMENT__) {
#    ifdef __cpp_sized_deallocation
        ::operator delete(p, s, std::align_val_t(a));
#    else
        ::operator delete(p, std::align_val_t(a));
#    endif
        return;
    }
#endif
#ifdef __cpp_sized_deallocation
    ::operator delete(p, s);
#else
    ::operator delete(p);
#endif
}

inline void add_class_method(object &cls, const char *name_, const cpp_function &cf) {
    cls.attr(cf.name()) = cf;
    if (std::strcmp(name_, "__eq__") == 0 && !cls.attr("__dict__").contains("__hash__")) {
        cls.attr("__hash__") = none();
    }
}

PYBIND11_NAMESPACE_END(detail)

/// Given a pointer to a member function, cast it to its `Derived` version.
/// Forward everything else unchanged.
template <typename /*Derived*/, typename F>
auto method_adaptor(F &&f) -> decltype(std::forward<F>(f)) {
    return std::forward<F>(f);
}

template <typename Derived, typename Return, typename Class, typename... Args>
auto method_adaptor(Return (Class::*pmf)(Args...)) -> Return (Derived::*)(Args...) {
    static_assert(
        detail::is_accessible_base_of<Class, Derived>::value,
        "Cannot bind an inaccessible base class method; use a lambda definition instead");
    return pmf;
}

template <typename Derived, typename Return, typename Class, typename... Args>
auto method_adaptor(Return (Class::*pmf)(Args...) const) -> Return (Derived::*)(Args...) const {
    static_assert(
        detail::is_accessible_base_of<Class, Derived>::value,
        "Cannot bind an inaccessible base class method; use a lambda definition instead");
    return pmf;
}

PYBIND11_NAMESPACE_BEGIN(detail)

// Helper for the property_cpp_function static member functions below.
// The only purpose of these functions is to support .def_readonly & .def_readwrite.
// In this context, the PM template parameter is certain to be a Pointer to a Member.
// The main purpose of must_be_member_function_pointer is to make this obvious, and to guard
// against accidents. As a side-effect, it also explains why the syntactical overhead for
// perfect forwarding is not needed.
template <typename PM>
using must_be_member_function_pointer = enable_if_t<std::is_member_pointer<PM>::value, int>;

// Note that property_cpp_function is intentionally in the main pybind11 namespace,
// because user-defined specializations could be useful.

// Classic (non-smart_holder) implementations for .def_readonly and .def_readwrite
// getter and setter functions.
// WARNING: This classic implementation can lead to dangling pointers for raw pointer members.
// See test_ptr() in tests/test_class_sh_property.py
// However, this implementation works as-is (and safely) for smart_holder std::shared_ptr members.
template <typename T, typename D>
struct property_cpp_function_classic {
    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function readonly(PM pm, const handle &hdl) {
        return cpp_function([pm](const T &c) -> const D & { return c.*pm; }, is_method(hdl));
    }

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function read(PM pm, const handle &hdl) {
        return readonly(pm, hdl);
    }

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function write(PM pm, const handle &hdl) {
        return cpp_function([pm](T &c, const D &value) { c.*pm = value; }, is_method(hdl));
    }
};

PYBIND11_NAMESPACE_END(detail)

template <typename T, typename D, typename SFINAE = void>
struct property_cpp_function : detail::property_cpp_function_classic<T, D> {};

PYBIND11_NAMESPACE_BEGIN(detail)

template <typename T, typename D, typename SFINAE = void>
struct both_t_and_d_use_type_caster_base : std::false_type {};

// `T` is assumed to be equivalent to `intrinsic_t<T>`.
// `D` is may or may not be equivalent to `intrinsic_t<D>`.
template <typename T, typename D>
struct both_t_and_d_use_type_caster_base<
    T,
    D,
    enable_if_t<all_of<std::is_base_of<type_caster_base<T>, type_caster<T>>,
                       std::is_base_of<type_caster_base<intrinsic_t<D>>, make_caster<D>>>::value>>
    : std::true_type {};

// Specialization for raw pointer members, using smart_holder if that is the class_ holder,
// or falling back to the classic implementation if not.
// WARNING: Like the classic implementation, this implementation can lead to dangling pointers.
// See test_ptr() in tests/test_class_sh_property.py
// However, the read functions return a shared_ptr to the member, emulating the PyCLIF approach:
// https://github.com/google/clif/blob/c371a6d4b28d25d53a16e6d2a6d97305fb1be25a/clif/python/instance.h#L233
// This prevents disowning of the Python object owning the raw pointer member.
template <typename T, typename D>
struct property_cpp_function_sh_raw_ptr_member {
    using drp = typename std::remove_pointer<D>::type;

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function readonly(PM pm, const handle &hdl) {
        type_info *tinfo = get_type_info(typeid(T), /*throw_if_missing=*/true);
        if (tinfo->holder_enum_v == holder_enum_t::smart_holder) {
            return cpp_function(
                [pm](handle c_hdl) -> std::shared_ptr<drp> {
                    std::shared_ptr<T> c_sp
                        = type_caster<std::shared_ptr<T>>::shared_ptr_with_responsible_parent(
                            c_hdl);
                    D ptr = (*c_sp).*pm;
                    return std::shared_ptr<drp>(c_sp, ptr);
                },
                is_method(hdl));
        }
        return property_cpp_function_classic<T, D>::readonly(pm, hdl);
    }

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function read(PM pm, const handle &hdl) {
        return readonly(pm, hdl);
    }

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function write(PM pm, const handle &hdl) {
        type_info *tinfo = get_type_info(typeid(T), /*throw_if_missing=*/true);
        if (tinfo->holder_enum_v == holder_enum_t::smart_holder) {
            return cpp_function([pm](T &c, D value) { c.*pm = std::forward<D>(std::move(value)); },
                                is_method(hdl));
        }
        return property_cpp_function_classic<T, D>::write(pm, hdl);
    }
};

// Specialization for members held by-value, using smart_holder if that is the class_ holder,
// or falling back to the classic implementation if not.
// The read functions return a shared_ptr to the member, emulating the PyCLIF approach:
// https://github.com/google/clif/blob/c371a6d4b28d25d53a16e6d2a6d97305fb1be25a/clif/python/instance.h#L233
// This prevents disowning of the Python object owning the member.
template <typename T, typename D>
struct property_cpp_function_sh_member_held_by_value {
    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function readonly(PM pm, const handle &hdl) {
        type_info *tinfo = get_type_info(typeid(T), /*throw_if_missing=*/true);
        if (tinfo->holder_enum_v == holder_enum_t::smart_holder) {
            return cpp_function(
                [pm](handle c_hdl) -> std::shared_ptr<typename std::add_const<D>::type> {
                    std::shared_ptr<T> c_sp
                        = type_caster<std::shared_ptr<T>>::shared_ptr_with_responsible_parent(
                            c_hdl);
                    return std::shared_ptr<typename std::add_const<D>::type>(c_sp,
                                                                             &(c_sp.get()->*pm));
                },
                is_method(hdl));
        }
        return property_cpp_function_classic<T, D>::readonly(pm, hdl);
    }

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function read(PM pm, const handle &hdl) {
        type_info *tinfo = get_type_info(typeid(T), /*throw_if_missing=*/true);
        if (tinfo->holder_enum_v == holder_enum_t::smart_holder) {
            return cpp_function(
                [pm](handle c_hdl) -> std::shared_ptr<D> {
                    std::shared_ptr<T> c_sp
                        = type_caster<std::shared_ptr<T>>::shared_ptr_with_responsible_parent(
                            c_hdl);
                    return std::shared_ptr<D>(c_sp, &(c_sp.get()->*pm));
                },
                is_method(hdl));
        }
        return property_cpp_function_classic<T, D>::read(pm, hdl);
    }

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function write(PM pm, const handle &hdl) {
        type_info *tinfo = get_type_info(typeid(T), /*throw_if_missing=*/true);
        if (tinfo->holder_enum_v == holder_enum_t::smart_holder) {
            return cpp_function([pm](T &c, const D &value) { c.*pm = value; }, is_method(hdl));
        }
        return property_cpp_function_classic<T, D>::write(pm, hdl);
    }
};

// Specialization for std::unique_ptr members, using smart_holder if that is the class_ holder,
// or falling back to the classic implementation if not.
// read disowns the member unique_ptr.
// write disowns the passed Python object.
// readonly is disabled (static_assert) because there is no safe & intuitive way to make the member
// accessible as a Python object without disowning the member unique_ptr. A .def_readonly disowning
// the unique_ptr member is deemed highly prone to misunderstandings.
template <typename T, typename D>
struct property_cpp_function_sh_unique_ptr_member {
    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function readonly(PM, const handle &) {
        static_assert(!is_instantiation<std::unique_ptr, D>::value,
                      "def_readonly cannot be used for std::unique_ptr members.");
        return cpp_function{}; // Unreachable.
    }

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function read(PM pm, const handle &hdl) {
        type_info *tinfo = get_type_info(typeid(T), /*throw_if_missing=*/true);
        if (tinfo->holder_enum_v == holder_enum_t::smart_holder) {
            return cpp_function(
                [pm](handle c_hdl) -> D {
                    std::shared_ptr<T> c_sp
                        = type_caster<std::shared_ptr<T>>::shared_ptr_with_responsible_parent(
                            c_hdl);
                    return D{std::move(c_sp.get()->*pm)};
                },
                is_method(hdl));
        }
        return property_cpp_function_classic<T, D>::read(pm, hdl);
    }

    template <typename PM, must_be_member_function_pointer<PM> = 0>
    static cpp_function write(PM pm, const handle &hdl) {
        return cpp_function([pm](T &c, D &&value) { c.*pm = std::move(value); }, is_method(hdl));
    }
};

PYBIND11_NAMESPACE_END(detail)

template <typename T, typename D>
struct property_cpp_function<
    T,
    D,
    detail::enable_if_t<detail::all_of<std::is_pointer<D>,
                                       detail::both_t_and_d_use_type_caster_base<T, D>>::value>>
    : detail::property_cpp_function_sh_raw_ptr_member<T, D> {};

template <typename T, typename D>
struct property_cpp_function<T,
                             D,
                             detail::enable_if_t<detail::all_of<
                                 detail::none_of<std::is_pointer<D>,
                                                 std::is_array<D>,
                                                 detail::is_instantiation<std::unique_ptr, D>,
                                                 detail::is_instantiation<std::shared_ptr, D>>,
                                 detail::both_t_and_d_use_type_caster_base<T, D>>::value>>
    : detail::property_cpp_function_sh_member_held_by_value<T, D> {};

template <typename T, typename D>
struct property_cpp_function<
    T,
    D,
    detail::enable_if_t<detail::all_of<
        detail::is_instantiation<std::unique_ptr, D>,
        detail::both_t_and_d_use_type_caster_base<T, typename D::element_type>>::value>>
    : detail::property_cpp_function_sh_unique_ptr_member<T, D> {};

#ifdef PYBIND11_RUN_TESTING_WITH_SMART_HOLDER_AS_DEFAULT_BUT_NEVER_USE_IN_PRODUCTION_PLEASE
// NOTE: THIS IS MEANT FOR STRESS-TESTING OR TRIAGING ONLY!
//       Running the pybind11 unit tests with smart_holder as the default holder is to ensure
//       that `py::smart_holder` / `py::classh` is backward-compatible with all pre-existing
//       functionality.
//       Be careful not to link translation units compiled with different default holders, because
//       this will cause ODR violations (https://en.wikipedia.org/wiki/One_Definition_Rule).
template <typename>
using default_holder_type = smart_holder;
#else
template <typename T>
using default_holder_type = std::unique_ptr<T>;
#endif

template <typename type_, typename... options>
class class_ : public detail::generic_type {
    template <typename T>
    using is_holder = detail::is_holder_type<type_, T>;
    template <typename T>
    using is_subtype = detail::is_strict_base_of<type_, T>;
    template <typename T>
    using is_base = detail::is_strict_base_of<T, type_>;
    // struct instead of using here to help MSVC:
    template <typename T>
    struct is_valid_class_option : detail::any_of<is_holder<T>, is_subtype<T>, is_base<T>> {};

public:
    using type = type_;
    using type_alias = detail::exactly_one_t<is_subtype, void, options...>;
    constexpr static bool has_alias = !std::is_void<type_alias>::value;
    using holder_type = detail::exactly_one_t<is_holder, default_holder_type<type>, options...>;

    static_assert(detail::all_of<is_valid_class_option<options>...>::value,
                  "Unknown/invalid class_ template parameters provided");

    static_assert(!has_alias || std::is_polymorphic<type>::value,
                  "Cannot use an alias class (aka trampoline) with a non-polymorphic type");

#ifndef PYBIND11_RUN_TESTING_WITH_SMART_HOLDER_AS_DEFAULT_BUT_NEVER_USE_IN_PRODUCTION_PLEASE
    static_assert(!has_alias || !detail::is_smart_holder<holder_type>::value
                      || std::is_base_of<trampoline_self_life_support, type_alias>::value,
                  "Alias class (aka trampoline) must inherit from"
                  " pybind11::trampoline_self_life_support if used in combination with"
                  " pybind11::smart_holder");
#endif
    static_assert(!has_alias || detail::is_smart_holder<holder_type>::value
                      || !std::is_base_of<trampoline_self_life_support, type_alias>::value,
                  "pybind11::trampoline_self_life_support is a smart_holder feature, therefore"
                  " an alias class (aka trampoline) should inherit from"
                  " pybind11::trampoline_self_life_support only if used in combination with"
                  " pybind11::smart_holder");

    PYBIND11_OBJECT(class_, generic_type, PyType_Check)

    template <typename... Extra>
    class_(handle scope, const char *name, const Extra &...extra) {
        using namespace detail;

        // MI can only be specified via class_ template options, not constructor parameters
        static_assert(
            none_of<is_pyobject<Extra>...>::value || // no base class arguments, or:
                (constexpr_sum(is_pyobject<Extra>::value...) == 1 && // Exactly one base
                 constexpr_sum(is_base<options>::value...) == 0 &&   // no template option bases
                 // no multiple_inheritance attr
                 none_of<std::is_same<multiple_inheritance, Extra>...>::value),
            "Error: multiple inheritance bases must be specified via class_ template options");

        type_record record;
        record.scope = scope;
        record.name = name;
        record.type = &typeid(type);
        record.type_size = sizeof(conditional_t<has_alias, type_alias, type>);
        record.type_align = alignof(conditional_t<has_alias, type_alias, type> &);
        record.holder_size = sizeof(holder_type);
        record.init_instance = init_instance;

        if (detail::is_instantiation<std::unique_ptr, holder_type>::value) {
            record.holder_enum_v = detail::holder_enum_t::std_unique_ptr;
        } else if (detail::is_instantiation<std::shared_ptr, holder_type>::value) {
            record.holder_enum_v = detail::holder_enum_t::std_shared_ptr;
        } else if (std::is_same<holder_type, smart_holder>::value) {
            record.holder_enum_v = detail::holder_enum_t::smart_holder;
        } else {
            record.holder_enum_v = detail::holder_enum_t::custom_holder;
        }

        set_operator_new<type>(&record);

        /* Register base classes specified via template arguments to class_, if any */
        PYBIND11_EXPAND_SIDE_EFFECTS(add_base<options>(record));

        /* Process optional arguments, if any */
        process_attributes<Extra...>::init(extra..., &record);

        if (record.release_gil_before_calling_cpp_dtor) {
            record.dealloc = dealloc_release_gil_before_calling_cpp_dtor;
        } else {
            record.dealloc = dealloc_without_manipulating_gil;
        }

        generic_type::initialize(record);

        if (has_alias) {
            with_internals([&](internals &internals) {
                auto &instances = record.module_local ? get_local_internals().registered_types_cpp
                                                      : internals.registered_types_cpp;
                instances[std::type_index(typeid(type_alias))]
                    = instances[std::type_index(typeid(type))];
            });
        }
        def("_pybind11_conduit_v1_", cpp_conduit_method);
    }

    template <typename Base, detail::enable_if_t<is_base<Base>::value, int> = 0>
    static void add_base(detail::type_record &rec) {
        rec.add_base(typeid(Base), [](void *src) -> void * {
            return static_cast<Base *>(reinterpret_cast<type *>(src));
        });
    }

    template <typename Base, detail::enable_if_t<!is_base<Base>::value, int> = 0>
    static void add_base(detail::type_record &) {}

    template <typename Func, typename... Extra>
    class_ &def(const char *name_, Func &&f, const Extra &...extra) {
        cpp_function cf(method_adaptor<type>(std::forward<Func>(f)),
                        name(name_),
                        is_method(*this),
                        sibling(getattr(*this, name_, none())),
                        extra...);
        add_class_method(*this, name_, cf);
        return *this;
    }

    template <typename Func, typename... Extra>
    class_ &def_static(const char *name_, Func &&f, const Extra &...extra) {
        static_assert(!std::is_member_function_pointer<Func>::value,
                      "def_static(...) called with a non-static member function pointer");
        cpp_function cf(std::forward<Func>(f),
                        name(name_),
                        scope(*this),
                        sibling(getattr(*this, name_, none())),
                        extra...);
        auto cf_name = cf.name();
        attr(std::move(cf_name)) = staticmethod(std::move(cf));
        return *this;
    }

    template <typename T, typename... Extra, detail::enable_if_t<T::op_enable_if_hook, int> = 0>
    class_ &def(const T &op, const Extra &...extra) {
        op.execute(*this, extra...);
        return *this;
    }

    template <typename T, typename... Extra, detail::enable_if_t<T::op_enable_if_hook, int> = 0>
    class_ &def_cast(const T &op, const Extra &...extra) {
        op.execute_cast(*this, extra...);
        return *this;
    }

    template <typename... Args, typename... Extra>
    class_ &def(const detail::initimpl::constructor<Args...> &init, const Extra &...extra) {
        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(init);
        init.execute(*this, extra...);
        return *this;
    }

    template <typename... Args, typename... Extra>
    class_ &def(const detail::initimpl::alias_constructor<Args...> &init, const Extra &...extra) {
        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(init);
        init.execute(*this, extra...);
        return *this;
    }

    template <typename... Args, typename... Extra>
    class_ &def(detail::initimpl::factory<Args...> &&init, const Extra &...extra) {
        std::move(init).execute(*this, extra...);
        return *this;
    }

    template <typename... Args, typename... Extra>
    class_ &def(detail::initimpl::pickle_factory<Args...> &&pf, const Extra &...extra) {
        std::move(pf).execute(*this, extra...);
        return *this;
    }

    template <typename Func>
    class_ &def_buffer(Func &&func) {
        struct capture {
            Func func;
        };
        auto *ptr = new capture{std::forward<Func>(func)};
        install_buffer_funcs(
            [](PyObject *obj, void *ptr) -> buffer_info * {
                detail::make_caster<type> caster;
                if (!caster.load(obj, false)) {
                    return nullptr;
                }
                return new buffer_info(((capture *) ptr)->func(std::move(caster)));
            },
            ptr);
        weakref(m_ptr, cpp_function([ptr](handle wr) {
                    delete ptr;
                    wr.dec_ref();
                }))
            .release();
        return *this;
    }

    template <typename Return, typename Class, typename... Args>
    class_ &def_buffer(Return (Class::*func)(Args...)) {
        return def_buffer([func](type &obj) { return (obj.*func)(); });
    }

    template <typename Return, typename Class, typename... Args>
    class_ &def_buffer(Return (Class::*func)(Args...) const) {
        return def_buffer([func](const type &obj) { return (obj.*func)(); });
    }

    template <typename C, typename D, typename... Extra>
    class_ &def_readwrite(const char *name, D C::*pm, const Extra &...extra) {
        static_assert(std::is_same<C, type>::value || std::is_base_of<C, type>::value,
                      "def_readwrite() requires a class member (or base class member)");
        def_property(name,
                     property_cpp_function<type, D>::read(pm, *this),
                     property_cpp_function<type, D>::write(pm, *this),
                     return_value_policy::reference_internal,
                     extra...);
        return *this;
    }

    template <typename C, typename D, typename... Extra>
    class_ &def_readonly(const char *name, const D C::*pm, const Extra &...extra) {
        static_assert(std::is_same<C, type>::value || std::is_base_of<C, type>::value,
                      "def_readonly() requires a class member (or base class member)");
        def_property_readonly(name,
                              property_cpp_function<type, D>::readonly(pm, *this),
                              return_value_policy::reference_internal,
                              extra...);
        return *this;
    }

    template <typename D, typename... Extra>
    class_ &def_readwrite_static(const char *name, D *pm, const Extra &...extra) {
        cpp_function fget([pm](const object &) -> const D & { return *pm; }, scope(*this)),
            fset([pm](const object &, const D &value) { *pm = value; }, scope(*this));
        def_property_static(name, fget, fset, return_value_policy::reference, extra...);
        return *this;
    }

    template <typename D, typename... Extra>
    class_ &def_readonly_static(const char *name, const D *pm, const Extra &...extra) {
        cpp_function fget([pm](const object &) -> const D & { return *pm; }, scope(*this));
        def_property_readonly_static(name, fget, return_value_policy::reference, extra...);
        return *this;
    }

    /// Uses return_value_policy::reference_internal by default
    template <typename Getter, typename... Extra>
    class_ &def_property_readonly(const char *name, const Getter &fget, const Extra &...extra) {
        return def_property_readonly(name,
                                     cpp_function(method_adaptor<type>(fget)),
                                     return_value_policy::reference_internal,
                                     extra...);
    }

    /// Uses cpp_function's return_value_policy by default
    template <typename... Extra>
    class_ &
    def_property_readonly(const char *name, const cpp_function &fget, const Extra &...extra) {
        return def_property(name, fget, nullptr, extra...);
    }

    /// Uses return_value_policy::reference by default
    template <typename Getter, typename... Extra>
    class_ &
    def_property_readonly_static(const char *name, const Getter &fget, const Extra &...extra) {
        return def_property_readonly_static(
            name, cpp_function(fget), return_value_policy::reference, extra...);
    }

    /// Uses cpp_function's return_value_policy by default
    template <typename... Extra>
    class_ &def_property_readonly_static(const char *name,
                                         const cpp_function &fget,
                                         const Extra &...extra) {
        return def_property_static(name, fget, nullptr, extra...);
    }

    /// Uses return_value_policy::reference_internal by default
    template <typename Getter, typename Setter, typename... Extra>
    class_ &
    def_property(const char *name, const Getter &fget, const Setter &fset, const Extra &...extra) {
        return def_property(
            name, fget, cpp_function(method_adaptor<type>(fset), is_setter()), extra...);
    }
    template <typename Getter, typename... Extra>
    class_ &def_property(const char *name,
                         const Getter &fget,
                         const cpp_function &fset,
                         const Extra &...extra) {
        return def_property(name,
                            cpp_function(method_adaptor<type>(fget)),
                            fset,
                            return_value_policy::reference_internal,
                            extra...);
    }

    /// Uses cpp_function's return_value_policy by default
    template <typename... Extra>
    class_ &def_property(const char *name,
                         const cpp_function &fget,
                         const cpp_function &fset,
                         const Extra &...extra) {
        return def_property_static(name, fget, fset, is_method(*this), extra...);
    }

    /// Uses return_value_policy::reference by default
    template <typename Getter, typename... Extra>
    class_ &def_property_static(const char *name,
                                const Getter &fget,
                                const cpp_function &fset,
                                const Extra &...extra) {
        return def_property_static(
            name, cpp_function(fget), fset, return_value_policy::reference, extra...);
    }

    /// Uses cpp_function's return_value_policy by default
    template <typename... Extra>
    class_ &def_property_static(const char *name,
                                const cpp_function &fget,
                                const cpp_function &fset,
                                const Extra &...extra) {
        static_assert(0 == detail::constexpr_sum(std::is_base_of<arg, Extra>::value...),
                      "Argument annotations are not allowed for properties");
        auto rec_fget = get_function_record(fget), rec_fset = get_function_record(fset);
        auto *rec_active = rec_fget;
        if (rec_fget) {
            char *doc_prev = rec_fget->doc; /* 'extra' field may include a property-specific
                                               documentation string */
            detail::process_attributes<Extra...>::init(extra..., rec_fget);
            if (rec_fget->doc && rec_fget->doc != doc_prev) {
                std::free(doc_prev);
                rec_fget->doc = PYBIND11_COMPAT_STRDUP(rec_fget->doc);
            }
        }
        if (rec_fset) {
            char *doc_prev = rec_fset->doc;
            detail::process_attributes<Extra...>::init(extra..., rec_fset);
            if (rec_fset->doc && rec_fset->doc != doc_prev) {
                std::free(doc_prev);
                rec_fset->doc = PYBIND11_COMPAT_STRDUP(rec_fset->doc);
            }
            if (!rec_active) {
                rec_active = rec_fset;
            }
        }
        def_property_static_impl(name, fget, fset, rec_active);
        return *this;
    }

private:
    /// Initialize holder object, variant 1: object derives from enable_shared_from_this
    template <typename T>
    static void init_holder(detail::instance *inst,
                            detail::value_and_holder &v_h,
                            const holder_type * /* unused */,
                            const std::enable_shared_from_this<T> * /* dummy */) {

        auto sh = std::dynamic_pointer_cast<typename holder_type::element_type>(
            detail::try_get_shared_from_this(v_h.value_ptr<type>()));
        if (sh) {
            new (std::addressof(v_h.holder<holder_type>())) holder_type(std::move(sh));
            v_h.set_holder_constructed();
        }

        if (!v_h.holder_constructed() && inst->owned) {
            new (std::addressof(v_h.holder<holder_type>())) holder_type(v_h.value_ptr<type>());
            v_h.set_holder_constructed();
        }
    }

    static void init_holder_from_existing(const detail::value_and_holder &v_h,
                                          const holder_type *holder_ptr,
                                          std::true_type /*is_copy_constructible*/) {
        new (std::addressof(v_h.holder<holder_type>()))
            holder_type(*reinterpret_cast<const holder_type *>(holder_ptr));
    }

    static void init_holder_from_existing(const detail::value_and_holder &v_h,
                                          const holder_type *holder_ptr,
                                          std::false_type /*is_copy_constructible*/) {
        new (std::addressof(v_h.holder<holder_type>()))
            holder_type(std::move(*const_cast<holder_type *>(holder_ptr)));
    }

    /// Initialize holder object, variant 2: try to construct from existing holder object, if
    /// possible
    static void init_holder(detail::instance *inst,
                            detail::value_and_holder &v_h,
                            const holder_type *holder_ptr,
                            const void * /* dummy -- not enable_shared_from_this<T>) */) {
        if (holder_ptr) {
            init_holder_from_existing(v_h, holder_ptr, std::is_copy_constructible<holder_type>());
            v_h.set_holder_constructed();
        } else if (detail::always_construct_holder<holder_type>::value || inst->owned) {
            new (std::addressof(v_h.holder<holder_type>())) holder_type(v_h.value_ptr<type>());
            v_h.set_holder_constructed();
        }
    }

    /// Performs instance initialization including constructing a holder and registering the known
    /// instance.  Should be called as soon as the `type` value_ptr is set for an instance.  Takes
    /// an optional pointer to an existing holder to use; if not specified and the instance is
    /// `.owned`, a new holder will be constructed to manage the value pointer.
    template <typename H = holder_type,
              detail::enable_if_t<!detail::is_smart_holder<H>::value, int> = 0>
    static void init_instance(detail::instance *inst, const void *holder_ptr) {
        auto v_h = inst->get_value_and_holder(detail::get_type_info(typeid(type)));
        if (!v_h.instance_registered()) {
            register_instance(inst, v_h.value_ptr(), v_h.type);
            v_h.set_instance_registered();
        }
        init_holder(inst, v_h, (const holder_type *) holder_ptr, v_h.value_ptr<type>());
    }

    template <typename WrappedType>
    static bool try_initialization_using_shared_from_this(holder_type *, WrappedType *, ...) {
        return false;
    }

    // Adopting existing approach used by type_caster_base, although it leads to somewhat fuzzy
    // ownership semantics: if we detected via shared_from_this that a shared_ptr exists already,
    // it is reused, irrespective of the return_value_policy in effect.
    // "SomeBaseOfWrappedType" is needed because std::enable_shared_from_this is not necessarily a
    // direct base of WrappedType.
    template <typename WrappedType, typename SomeBaseOfWrappedType>
    static bool try_initialization_using_shared_from_this(
        holder_type *uninitialized_location,
        WrappedType *value_ptr_w_t,
        const std::enable_shared_from_this<SomeBaseOfWrappedType> *) {
        auto shd_ptr = std::dynamic_pointer_cast<WrappedType>(
            detail::try_get_shared_from_this(value_ptr_w_t));
        if (!shd_ptr) {
            return false;
        }
        // Note: inst->owned ignored.
        new (uninitialized_location) holder_type(holder_type::from_shared_ptr(shd_ptr));
        return true;
    }

    template <typename H = holder_type,
              detail::enable_if_t<detail::is_smart_holder<H>::value, int> = 0>
    static void init_instance(detail::instance *inst, const void *holder_const_void_ptr) {
        // Need for const_cast is a consequence of the type_info::init_instance type:
        // void (*init_instance)(instance *, const void *);
        auto *holder_void_ptr = const_cast<void *>(holder_const_void_ptr);

        auto v_h = inst->get_value_and_holder(detail::get_type_info(typeid(type)));
        if (!v_h.instance_registered()) {
            register_instance(inst, v_h.value_ptr(), v_h.type);
            v_h.set_instance_registered();
        }
        auto *uninitialized_location = std::addressof(v_h.holder<holder_type>());
        auto *value_ptr_w_t = v_h.value_ptr<type>();
        // Try downcast from `type` to `type_alias`:
        inst->is_alias
            = detail::dynamic_raw_ptr_cast_if_possible<type_alias>(value_ptr_w_t) != nullptr;
        if (holder_void_ptr) {
            // Note: inst->owned ignored.
            auto *holder_ptr = static_cast<holder_type *>(holder_void_ptr);
            new (uninitialized_location) holder_type(std::move(*holder_ptr));
        } else if (!try_initialization_using_shared_from_this(
                       uninitialized_location, value_ptr_w_t, value_ptr_w_t)) {
            if (inst->owned) {
                new (uninitialized_location) holder_type(holder_type::from_raw_ptr_take_ownership(
                    value_ptr_w_t, /*void_cast_raw_ptr*/ inst->is_alias));
            } else {
                new (uninitialized_location)
                    holder_type(holder_type::from_raw_ptr_unowned(value_ptr_w_t));
            }
        }
        v_h.set_holder_constructed();
    }

    // Deallocates an instance; via holder, if constructed; otherwise via operator delete.
    // NOTE: The Python error indicator needs to cleared BEFORE this function is called.
    // This is because we could be deallocating while cleaning up after a Python exception.
    // If the error indicator is not cleared but the C++ destructor code makes Python C API
    // calls, those calls are likely to generate a new exception, and pybind11 will then
    // throw `error_already_set` from the C++ destructor. This is forbidden and will
    // trigger std::terminate().
    static void dealloc_impl(detail::value_and_holder &v_h) {
        if (v_h.holder_constructed()) {
            v_h.holder<holder_type>().~holder_type();
            v_h.set_holder_constructed(false);
        } else {
            detail::call_operator_delete(
                v_h.value_ptr<type>(), v_h.type->type_size, v_h.type->type_align);
        }
        v_h.value_ptr() = nullptr;
    }

    static void dealloc_without_manipulating_gil(detail::value_and_holder &v_h) {
        error_scope scope;
        dealloc_impl(v_h);
    }

    static void dealloc_release_gil_before_calling_cpp_dtor(detail::value_and_holder &v_h) {
        error_scope scope;
        // Intentionally not using `gil_scoped_release` because the non-simple
        // version unconditionally calls `get_internals()`.
        // `Py_BEGIN_ALLOW_THREADS`, `Py_END_ALLOW_THREADS` cannot be used
        // because those macros include `{` and `}`.
        PyThreadState *py_ts = PyEval_SaveThread();
        try {
            dealloc_impl(v_h);
        } catch (...) {
            // This code path is expected to be unreachable unless there is a
            // bug in pybind11 itself.
            // An alternative would be to mark this function, or
            // `dealloc_impl()`, with `nothrow`, but that would be a subtle
            // behavior change and could make debugging more difficult.
            PyEval_RestoreThread(py_ts);
            throw;
        }
        PyEval_RestoreThread(py_ts);
    }

    static detail::function_record *get_function_record(handle h) {
        h = detail::get_function(h);
        if (!h) {
            return nullptr;
        }

        handle func_self = PyCFunction_GET_SELF(h.ptr());
        if (!func_self) {
            throw error_already_set();
        }
        return detail::function_record_ptr_from_PyObject(func_self.ptr());
    }
};

// Supports easier switching between py::class_<T> and py::class_<T, py::smart_holder>:
// users can simply replace the `_` in `class_` with `h` or vice versa.
template <typename type_, typename... options>
using classh = class_<type_, smart_holder, options...>;

/// Binds an existing constructor taking arguments Args...
template <typename... Args>
detail::initimpl::constructor<Args...> init() {
    return {};
}
/// Like `init<Args...>()`, but the instance is always constructed through the alias class (even
/// when not inheriting on the Python side).
template <typename... Args>
detail::initimpl::alias_constructor<Args...> init_alias() {
    return {};
}

/// Binds a factory function as a constructor
template <typename Func, typename Ret = detail::initimpl::factory<Func>>
Ret init(Func &&f) {
    return {std::forward<Func>(f)};
}

/// Dual-argument factory function: the first function is called when no alias is needed, the
/// second when an alias is needed (i.e. due to python-side inheritance).  Arguments must be
/// identical.
template <typename CFunc, typename AFunc, typename Ret = detail::initimpl::factory<CFunc, AFunc>>
Ret init(CFunc &&c, AFunc &&a) {
    return {std::forward<CFunc>(c), std::forward<AFunc>(a)};
}

/// Binds pickling functions `__getstate__` and `__setstate__` and ensures that the type
/// returned by `__getstate__` is the same as the argument accepted by `__setstate__`.
template <typename GetState, typename SetState>
detail::initimpl::pickle_factory<GetState, SetState> pickle(GetState &&g, SetState &&s) {
    return {std::forward<GetState>(g), std::forward<SetState>(s)};
}

PYBIND11_NAMESPACE_BEGIN(detail)

inline str enum_name(handle arg) {
    dict entries = type::handle_of(arg).attr("__entries");
    for (auto kv : entries) {
        if (handle(kv.second[int_(0)]).equal(arg)) {
            return pybind11::str(kv.first);
        }
    }
    return "???";
}

struct enum_base {
    enum_base(const handle &base, const handle &parent) : m_base(base), m_parent(parent) {}

    PYBIND11_NOINLINE void init(bool is_arithmetic, bool is_convertible) {
        m_base.attr("__entries") = dict();
        auto property = handle((PyObject *) &PyProperty_Type);
        auto static_property = handle((PyObject *) get_internals().static_property_type);

        m_base.attr("__repr__") = cpp_function(
            [](const object &arg) -> str {
                handle type = type::handle_of(arg);
                object type_name = type.attr("__name__");
                return pybind11::str("<{}.{}: {}>")
                    .format(std::move(type_name), enum_name(arg), int_(arg));
            },
            name("__repr__"),
            is_method(m_base),
            pos_only());

        m_base.attr("name")
            = property(cpp_function(&enum_name, name("name"), is_method(m_base), pos_only()));

        m_base.attr("__str__") = cpp_function(
            [](handle arg) -> str {
                object type_name = type::handle_of(arg).attr("__name__");
                return pybind11::str("{}.{}").format(std::move(type_name), enum_name(arg));
            },
            name("__str__"),
            is_method(m_base),
            pos_only());

        if (options::show_enum_members_docstring()) {
            m_base.attr("__doc__") = static_property(
                cpp_function(
                    [](handle arg) -> std::string {
                        std::string docstring;
                        dict entries = arg.attr("__entries");
                        if (((PyTypeObject *) arg.ptr())->tp_doc) {
                            docstring += std::string(
                                reinterpret_cast<PyTypeObject *>(arg.ptr())->tp_doc);
                            docstring += "\n\n";
                        }
                        docstring += "Members:";
                        for (auto kv : entries) {
                            auto key = std::string(pybind11::str(kv.first));
                            auto comment = kv.second[int_(1)];
                            docstring += "\n\n  ";
                            docstring += key;
                            if (!comment.is_none()) {
                                docstring += " : ";
                                docstring += pybind11::str(comment).cast<std::string>();
                            }
                        }
                        return docstring;
                    },
                    name("__doc__")),
                none(),
                none(),
                "");
        }

        m_base.attr("__members__") = static_property(cpp_function(
                                                         [](handle arg) -> dict {
                                                             dict entries = arg.attr("__entries"),
                                                                  m;
                                                             for (auto kv : entries) {
                                                                 m[kv.first] = kv.second[int_(0)];
                                                             }
                                                             return m;
                                                         },
                                                         name("__members__")),
                                                     none(),
                                                     none(),
                                                     "");

#define PYBIND11_ENUM_OP_STRICT(op, expr, strict_behavior)                                        \
    m_base.attr(op) = cpp_function(                                                               \
        [](const object &a, const object &b) {                                                    \
            if (!type::handle_of(a).is(type::handle_of(b)))                                       \
                strict_behavior; /* NOLINT(bugprone-macro-parentheses) */                         \
            return expr;                                                                          \
        },                                                                                        \
        name(op),                                                                                 \
        is_method(m_base),                                                                        \
        arg("other"),                                                                             \
        pos_only())

#define PYBIND11_ENUM_OP_CONV(op, expr)                                                           \
    m_base.attr(op) = cpp_function(                                                               \
        [](const object &a_, const object &b_) {                                                  \
            int_ a(a_), b(b_);                                                                    \
            return expr;                                                                          \
        },                                                                                        \
        name(op),                                                                                 \
        is_method(m_base),                                                                        \
        arg("other"),                                                                             \
        pos_only())

#define PYBIND11_ENUM_OP_CONV_LHS(op, expr)                                                       \
    m_base.attr(op) = cpp_function(                                                               \
        [](const object &a_, const object &b) {                                                   \
            int_ a(a_);                                                                           \
            return expr;                                                                          \
        },                                                                                        \
        name(op),                                                                                 \
        is_method(m_base),                                                                        \
        arg("other"),                                                                             \
        pos_only())

        if (is_convertible) {
            PYBIND11_ENUM_OP_CONV_LHS("__eq__", !b.is_none() && a.equal(b));
            PYBIND11_ENUM_OP_CONV_LHS("__ne__", b.is_none() || !a.equal(b));

            if (is_arithmetic) {
                PYBIND11_ENUM_OP_CONV("__lt__", a < b);
                PYBIND11_ENUM_OP_CONV("__gt__", a > b);
                PYBIND11_ENUM_OP_CONV("__le__", a <= b);
                PYBIND11_ENUM_OP_CONV("__ge__", a >= b);
                PYBIND11_ENUM_OP_CONV("__and__", a & b);
                PYBIND11_ENUM_OP_CONV("__rand__", a & b);
                PYBIND11_ENUM_OP_CONV("__or__", a | b);
                PYBIND11_ENUM_OP_CONV("__ror__", a | b);
                PYBIND11_ENUM_OP_CONV("__xor__", a ^ b);
                PYBIND11_ENUM_OP_CONV("__rxor__", a ^ b);
                m_base.attr("__invert__")
                    = cpp_function([](const object &arg) { return ~(int_(arg)); },
                                   name("__invert__"),
                                   is_method(m_base),
                                   pos_only());
            }
        } else {
            PYBIND11_ENUM_OP_STRICT("__eq__", int_(a).equal(int_(b)), return false);
            PYBIND11_ENUM_OP_STRICT("__ne__", !int_(a).equal(int_(b)), return true);

            if (is_arithmetic) {
#define PYBIND11_THROW throw type_error("Expected an enumeration of matching type!");
                PYBIND11_ENUM_OP_STRICT("__lt__", int_(a) < int_(b), PYBIND11_THROW);
                PYBIND11_ENUM_OP_STRICT("__gt__", int_(a) > int_(b), PYBIND11_THROW);
                PYBIND11_ENUM_OP_STRICT("__le__", int_(a) <= int_(b), PYBIND11_THROW);
                PYBIND11_ENUM_OP_STRICT("__ge__", int_(a) >= int_(b), PYBIND11_THROW);
#undef PYBIND11_THROW
            }
        }

#undef PYBIND11_ENUM_OP_CONV_LHS
#undef PYBIND11_ENUM_OP_CONV
#undef PYBIND11_ENUM_OP_STRICT

        m_base.attr("__getstate__") = cpp_function([](const object &arg) { return int_(arg); },
                                                   name("__getstate__"),
                                                   is_method(m_base),
                                                   pos_only());

        m_base.attr("__hash__") = cpp_function([](const object &arg) { return int_(arg); },
                                               name("__hash__"),
                                               is_method(m_base),
                                               pos_only());
    }

    PYBIND11_NOINLINE void value(char const *name_, object value, const char *doc = nullptr) {
        dict entries = m_base.attr("__entries");
        str name(name_);
        if (entries.contains(name)) {
            std::string type_name = (std::string) str(m_base.attr("__name__"));
            throw value_error(std::move(type_name) + ": element \"" + std::string(name_)
                              + "\" already exists!");
        }

        entries[name] = pybind11::make_tuple(value, doc);
        m_base.attr(std::move(name)) = std::move(value);
    }

    PYBIND11_NOINLINE void export_values() {
        dict entries = m_base.attr("__entries");
        for (auto kv : entries) {
            m_parent.attr(kv.first) = kv.second[int_(0)];
        }
    }

    handle m_base;
    handle m_parent;
};

template <bool is_signed, size_t length>
struct equivalent_integer {};
template <>
struct equivalent_integer<true, 1> {
    using type = int8_t;
};
template <>
struct equivalent_integer<false, 1> {
    using type = uint8_t;
};
template <>
struct equivalent_integer<true, 2> {
    using type = int16_t;
};
template <>
struct equivalent_integer<false, 2> {
    using type = uint16_t;
};
template <>
struct equivalent_integer<true, 4> {
    using type = int32_t;
};
template <>
struct equivalent_integer<false, 4> {
    using type = uint32_t;
};
template <>
struct equivalent_integer<true, 8> {
    using type = int64_t;
};
template <>
struct equivalent_integer<false, 8> {
    using type = uint64_t;
};

template <typename IntLike>
using equivalent_integer_t =
    typename equivalent_integer<std::is_signed<IntLike>::value, sizeof(IntLike)>::type;

PYBIND11_NAMESPACE_END(detail)

/// Binds C++ enumerations and enumeration classes to Python
template <typename Type>
class enum_ : public class_<Type> {
public:
    using Base = class_<Type>;
    using Base::attr;
    using Base::def;
    using Base::def_property_readonly;
    using Base::def_property_readonly_static;
    using Underlying = typename std::underlying_type<Type>::type;
    // Scalar is the integer representation of underlying type
    using Scalar = detail::conditional_t<detail::any_of<detail::is_std_char_type<Underlying>,
                                                        std::is_same<Underlying, bool>>::value,
                                         detail::equivalent_integer_t<Underlying>,
                                         Underlying>;

    template <typename... Extra>
    enum_(const handle &scope, const char *name, const Extra &...extra)
        : class_<Type>(scope, name, extra...), m_base(*this, scope) {
        {
            if (detail::global_internals_native_enum_type_map_contains(
                    std::type_index(typeid(Type)))) {
                pybind11_fail("pybind11::enum_ \"" + std::string(name)
                              + "\" is already registered as a pybind11::native_enum!");
            }
        }

        constexpr bool is_arithmetic = detail::any_of<std::is_same<arithmetic, Extra>...>::value;
        constexpr bool is_convertible = std::is_convertible<Type, Underlying>::value;
        m_base.init(is_arithmetic, is_convertible);

        def(init([](Scalar i) { return static_cast<Type>(i); }), arg("value"));
        def_property_readonly("value", [](Type value) { return (Scalar) value; }, pos_only());
        def("__int__", [](Type value) { return (Scalar) value; }, pos_only());
        def("__index__", [](Type value) { return (Scalar) value; }, pos_only());
        attr("__setstate__") = cpp_function(
            [](detail::value_and_holder &v_h, Scalar arg) {
                detail::initimpl::setstate<Base>(
                    v_h, static_cast<Type>(arg), Py_TYPE(v_h.inst) != v_h.type->type);
            },
            detail::is_new_style_constructor(),
            pybind11::name("__setstate__"),
            is_method(*this),
            arg("state"),
            pos_only());
    }

    /// Export enumeration entries into the parent scope
    enum_ &export_values() {
        m_base.export_values();
        return *this;
    }

    /// Add an enumeration entry
    enum_ &value(char const *name, Type value, const char *doc = nullptr) {
        m_base.value(name, pybind11::cast(value, return_value_policy::copy), doc);
        return *this;
    }

private:
    detail::enum_base m_base;
};

PYBIND11_NAMESPACE_BEGIN(detail)

PYBIND11_NOINLINE void keep_alive_impl(handle nurse, handle patient) {
    if (!nurse || !patient) {
        pybind11_fail("Could not activate keep_alive!");
    }

    if (patient.is_none() || nurse.is_none()) {
        return; /* Nothing to keep alive or nothing to be kept alive by */
    }

    auto tinfo = all_type_info(Py_TYPE(nurse.ptr()));
    if (!tinfo.empty()) {
        /* It's a pybind-registered type, so we can store the patient in the
         * internal list. */
        add_patient(nurse.ptr(), patient.ptr());
    } else {
        /* Fall back to clever approach based on weak references taken from
         * Boost.Python. This is not used for pybind-registered types because
         * the objects can be destroyed out-of-order in a GC pass. */
        cpp_function disable_lifesupport([patient](handle weakref) {
            patient.dec_ref();
            weakref.dec_ref();
        });

        weakref wr(nurse, disable_lifesupport);

        patient.inc_ref(); /* reference patient and leak the weak reference */
        (void) wr.release();
    }
}

PYBIND11_NOINLINE void
keep_alive_impl(size_t Nurse, size_t Patient, function_call &call, handle ret) {
    auto get_arg = [&](size_t n) {
        if (n == 0) {
            return ret;
        }
        if (n == 1 && call.init_self) {
            return call.init_self;
        }
        if (n <= call.args.size()) {
            return call.args[n - 1];
        }
        return handle();
    };

    keep_alive_impl(get_arg(Nurse), get_arg(Patient));
}

inline std::pair<decltype(internals::registered_types_py)::iterator, bool>
all_type_info_get_cache(PyTypeObject *type) {
    auto res = with_internals([type](internals &internals) {
        auto ins = internals
                       .registered_types_py
#ifdef __cpp_lib_unordered_map_try_emplace
                       .try_emplace(type);
#else
                       .emplace(type, std::vector<detail::type_info *>());
#endif
        if (ins.second) {
            // For free-threading mode, this call must be under
            // the with_internals() mutex lock, to avoid that other threads
            // continue running with the empty ins.first->second.
            all_type_info_populate(type, ins.first->second);
        }
        return ins;
    });
    if (res.second) {
        // New cache entry created; set up a weak reference to automatically remove it if the type
        // gets destroyed:
        weakref((PyObject *) type, cpp_function([type](handle wr) {
                    with_internals([type](internals &internals) {
                        internals.registered_types_py.erase(type);

                        // TODO consolidate the erasure code in pybind11_meta_dealloc() in class.h
                        auto &cache = internals.inactive_override_cache;
                        for (auto it = cache.begin(), last = cache.end(); it != last;) {
                            if (it->first == reinterpret_cast<PyObject *>(type)) {
                                it = cache.erase(it);
                            } else {
                                ++it;
                            }
                        }
                    });

                    wr.dec_ref();
                }))
            .release();
    }

    return res;
}

/* There are a large number of apparently unused template arguments because
 * each combination requires a separate py::class_ registration.
 */
template <typename Access,
          return_value_policy Policy,
          typename Iterator,
          typename Sentinel,
          typename ValueType,
          typename... Extra>
struct iterator_state {
    Iterator it;
    Sentinel end;
    bool first_or_done;
};

// Note: these helpers take the iterator by non-const reference because some
// iterators in the wild can't be dereferenced when const. The & after Iterator
// is required for MSVC < 16.9. SFINAE cannot be reused for result_type due to
// bugs in ICC, NVCC, and PGI compilers. See PR #3293.
template <typename Iterator, typename SFINAE = decltype(*std::declval<Iterator &>())>
struct iterator_access {
    using result_type = decltype(*std::declval<Iterator &>());
    // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
    result_type operator()(Iterator &it) const { return *it; }
};

template <typename Iterator, typename SFINAE = decltype((*std::declval<Iterator &>()).first)>
class iterator_key_access {
private:
    using pair_type = decltype(*std::declval<Iterator &>());

public:
    /* If either the pair itself or the element of the pair is a reference, we
     * want to return a reference, otherwise a value. When the decltype
     * expression is parenthesized it is based on the value category of the
     * expression; otherwise it is the declared type of the pair member.
     * The use of declval<pair_type> in the second branch rather than directly
     * using *std::declval<Iterator &>() is a workaround for nvcc
     * (it's not used in the first branch because going via decltype and back
     * through declval does not perfectly preserve references).
     */
    using result_type
        = conditional_t<std::is_reference<decltype(*std::declval<Iterator &>())>::value,
                        decltype(((*std::declval<Iterator &>()).first)),
                        decltype(std::declval<pair_type>().first)>;
    result_type operator()(Iterator &it) const { return (*it).first; }
};

template <typename Iterator, typename SFINAE = decltype((*std::declval<Iterator &>()).second)>
class iterator_value_access {
private:
    using pair_type = decltype(*std::declval<Iterator &>());

public:
    using result_type
        = conditional_t<std::is_reference<decltype(*std::declval<Iterator &>())>::value,
                        decltype(((*std::declval<Iterator &>()).second)),
                        decltype(std::declval<pair_type>().second)>;
    result_type operator()(Iterator &it) const { return (*it).second; }
};

template <typename Access,
          return_value_policy Policy,
          typename Iterator,
          typename Sentinel,
          typename ValueType,
          typename... Extra>
// NOLINTNEXTLINE(performance-unnecessary-value-param)
iterator make_iterator_impl(Iterator first, Sentinel last, Extra &&...extra) {
    using state = detail::iterator_state<Access, Policy, Iterator, Sentinel, ValueType, Extra...>;
    // TODO: state captures only the types of Extra, not the values

    if (!detail::get_type_info(typeid(state), false)) {
        class_<state>(handle(), "iterator", pybind11::module_local())
            .def(
                "__iter__", [](state &s) -> state & { return s; }, pos_only())
            .def(
                "__next__",
                [](state &s) -> ValueType {
                    if (!s.first_or_done) {
                        ++s.it;
                    } else {
                        s.first_or_done = false;
                    }
                    if (s.it == s.end) {
                        s.first_or_done = true;
                        throw stop_iteration();
                    }
                    return Access()(s.it);
                    // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
                },
                std::forward<Extra>(extra)...,
                pos_only(),
                Policy);
    }

    return cast(state{std::forward<Iterator>(first), std::forward<Sentinel>(last), true});
}

PYBIND11_NAMESPACE_END(detail)

/// Makes a python iterator from a first and past-the-end C++ InputIterator.
template <return_value_policy Policy = return_value_policy::reference_internal,
          typename Iterator,
          typename Sentinel,
          typename ValueType = typename detail::iterator_access<Iterator>::result_type,
          typename... Extra>
// NOLINTNEXTLINE(performance-unnecessary-value-param)
typing::Iterator<ValueType> make_iterator(Iterator first, Sentinel last, Extra &&...extra) {
    return detail::make_iterator_impl<detail::iterator_access<Iterator>,
                                      Policy,
                                      Iterator,
                                      Sentinel,
                                      ValueType,
                                      Extra...>(std::forward<Iterator>(first),
                                                std::forward<Sentinel>(last),
                                                std::forward<Extra>(extra)...);
}

/// Makes a python iterator over the keys (`.first`) of a iterator over pairs from a
/// first and past-the-end InputIterator.
template <return_value_policy Policy = return_value_policy::reference_internal,
          typename Iterator,
          typename Sentinel,
          typename KeyType = typename detail::iterator_key_access<Iterator>::result_type,
          typename... Extra>
typing::Iterator<KeyType> make_key_iterator(Iterator first, Sentinel last, Extra &&...extra) {
    return detail::make_iterator_impl<detail::iterator_key_access<Iterator>,
                                      Policy,
                                      Iterator,
                                      Sentinel,
                                      KeyType,
                                      Extra...>(std::forward<Iterator>(first),
                                                std::forward<Sentinel>(last),
                                                std::forward<Extra>(extra)...);
}

/// Makes a python iterator over the values (`.second`) of a iterator over pairs from a
/// first and past-the-end InputIterator.
template <return_value_policy Policy = return_value_policy::reference_internal,
          typename Iterator,
          typename Sentinel,
          typename ValueType = typename detail::iterator_value_access<Iterator>::result_type,
          typename... Extra>
typing::Iterator<ValueType> make_value_iterator(Iterator first, Sentinel last, Extra &&...extra) {
    return detail::make_iterator_impl<detail::iterator_value_access<Iterator>,
                                      Policy,
                                      Iterator,
                                      Sentinel,
                                      ValueType,
                                      Extra...>(std::forward<Iterator>(first),
                                                std::forward<Sentinel>(last),
                                                std::forward<Extra>(extra)...);
}

/// Makes an iterator over values of an stl container or other container supporting
/// `std::begin()`/`std::end()`
template <return_value_policy Policy = return_value_policy::reference_internal,
          typename Type,
          typename ValueType = typename detail::iterator_access<
              decltype(std::begin(std::declval<Type &>()))>::result_type,
          typename... Extra>
typing::Iterator<ValueType> make_iterator(Type &value, Extra &&...extra) {
    return make_iterator<Policy>(
        std::begin(value), std::end(value), std::forward<Extra>(extra)...);
}

/// Makes an iterator over the keys (`.first`) of a stl map-like container supporting
/// `std::begin()`/`std::end()`
template <return_value_policy Policy = return_value_policy::reference_internal,
          typename Type,
          typename KeyType = typename detail::iterator_key_access<
              decltype(std::begin(std::declval<Type &>()))>::result_type,
          typename... Extra>
typing::Iterator<KeyType> make_key_iterator(Type &value, Extra &&...extra) {
    return make_key_iterator<Policy>(
        std::begin(value), std::end(value), std::forward<Extra>(extra)...);
}

/// Makes an iterator over the values (`.second`) of a stl map-like container supporting
/// `std::begin()`/`std::end()`
template <return_value_policy Policy = return_value_policy::reference_internal,
          typename Type,
          typename ValueType = typename detail::iterator_value_access<
              decltype(std::begin(std::declval<Type &>()))>::result_type,
          typename... Extra>
typing::Iterator<ValueType> make_value_iterator(Type &value, Extra &&...extra) {
    return make_value_iterator<Policy>(
        std::begin(value), std::end(value), std::forward<Extra>(extra)...);
}

template <typename InputType, typename OutputType>
void implicitly_convertible() {
    struct set_flag {
        bool &flag;
        explicit set_flag(bool &flag_) : flag(flag_) { flag_ = true; }
        ~set_flag() { flag = false; }
    };
    auto implicit_caster = [](PyObject *obj, PyTypeObject *type) -> PyObject * {
#ifdef Py_GIL_DISABLED
        thread_local bool currently_used = false;
#else
        static bool currently_used = false;
#endif
        if (currently_used) { // implicit conversions are non-reentrant
            return nullptr;
        }
        set_flag flag_helper(currently_used);
        if (!detail::make_caster<InputType>().load(obj, false)) {
            return nullptr;
        }
        tuple args(1);
        args[0] = obj;
        PyObject *result = PyObject_Call((PyObject *) type, args.ptr(), nullptr);
        if (result == nullptr) {
            PyErr_Clear();
        }
        return result;
    };

    if (auto *tinfo = detail::get_type_info(typeid(OutputType))) {
        tinfo->implicit_conversions.emplace_back(std::move(implicit_caster));
    } else {
        pybind11_fail("implicitly_convertible: Unable to find type " + type_id<OutputType>());
    }
}

inline void register_exception_translator(ExceptionTranslator &&translator) {
    detail::with_exception_translators(
        [&](std::forward_list<ExceptionTranslator> &exception_translators,
            std::forward_list<ExceptionTranslator> &local_exception_translators) {
            (void) local_exception_translators;
            exception_translators.push_front(std::forward<ExceptionTranslator>(translator));
        });
}

/**
 * Add a new module-local exception translator. Locally registered functions
 * will be tried before any globally registered exception translators, which
 * will only be invoked if the module-local handlers do not deal with
 * the exception.
 */
inline void register_local_exception_translator(ExceptionTranslator &&translator) {
    detail::with_exception_translators(
        [&](std::forward_list<ExceptionTranslator> &exception_translators,
            std::forward_list<ExceptionTranslator> &local_exception_translators) {
            (void) exception_translators;
            local_exception_translators.push_front(std::forward<ExceptionTranslator>(translator));
        });
}

/**
 * Wrapper to generate a new Python exception type.
 *
 * This should only be used with py::set_error() for now.
 * It is not (yet) possible to use as a py::base.
 * Template type argument is reserved for future use.
 */
template <typename type>
class exception : public object {
public:
    exception() = default;
    exception(handle scope, const char *name, handle base = PyExc_Exception) {
        std::string full_name
            = scope.attr("__name__").cast<std::string>() + std::string(".") + name;
        m_ptr = PyErr_NewException(const_cast<char *>(full_name.c_str()), base.ptr(), nullptr);
        if (hasattr(scope, "__dict__") && scope.attr("__dict__").contains(name)) {
            pybind11_fail("Error during initialization: multiple incompatible "
                          "definitions with name \""
                          + std::string(name) + "\"");
        }
        scope.attr(name) = *this;
    }

    // Sets the current python exception to this exception object with the given message
    PYBIND11_DEPRECATED("Please use py::set_error() instead "
                        "(https://github.com/pybind/pybind11/pull/4772)")
    void operator()(const char *message) const { set_error(*this, message); }
};

PYBIND11_NAMESPACE_BEGIN(detail)

template <>
struct handle_type_name<exception<void>> {
    static constexpr auto name = const_name("Exception");
};

// Helper function for register_exception and register_local_exception
template <typename CppException>
exception<CppException> &
register_exception_impl(handle scope, const char *name, handle base, bool isLocal) {
    PYBIND11_CONSTINIT static gil_safe_call_once_and_store<exception<CppException>> exc_storage;
    exc_storage.call_once_and_store_result(
        [&]() { return exception<CppException>(scope, name, base); });

    auto register_func
        = isLocal ? &register_local_exception_translator : &register_exception_translator;

    register_func([](std::exception_ptr p) {
        if (!p) {
            return;
        }
        try {
            std::rethrow_exception(p);
        } catch (const CppException &e) {
            set_error(exc_storage.get_stored(), e.what());
        }
    });
    return exc_storage.get_stored();
}

PYBIND11_NAMESPACE_END(detail)

/**
 * Registers a Python exception in `m` of the given `name` and installs a translator to
 * translate the C++ exception to the created Python exception using the what() method.
 * This is intended for simple exception translations; for more complex translation, register the
 * exception object and translator directly.
 */
template <typename CppException>
exception<CppException> &
register_exception(handle scope, const char *name, handle base = PyExc_Exception) {
    return detail::register_exception_impl<CppException>(scope, name, base, false /* isLocal */);
}

/**
 * Registers a Python exception in `m` of the given `name` and installs a translator to
 * translate the C++ exception to the created Python exception using the what() method.
 * This translator will only be used for exceptions that are thrown in this module and will be
 * tried before global exception translators, including those registered with register_exception.
 * This is intended for simple exception translations; for more complex translation, register the
 * exception object and translator directly.
 */
template <typename CppException>
exception<CppException> &
register_local_exception(handle scope, const char *name, handle base = PyExc_Exception) {
    return detail::register_exception_impl<CppException>(scope, name, base, true /* isLocal */);
}

PYBIND11_NAMESPACE_BEGIN(detail)
PYBIND11_NOINLINE void print(const tuple &args, const dict &kwargs) {
    auto strings = tuple(args.size());
    for (size_t i = 0; i < args.size(); ++i) {
        strings[i] = str(args[i]);
    }
    auto sep = kwargs.contains("sep") ? kwargs["sep"] : str(" ");
    auto line = sep.attr("join")(std::move(strings));

    object file;
    if (kwargs.contains("file")) {
        file = kwargs["file"].cast<object>();
    } else {
        try {
            file = module_::import("sys").attr("stdout");
        } catch (const error_already_set &) {
            /* If print() is called from code that is executed as
               part of garbage collection during interpreter shutdown,
               importing 'sys' can fail. Give up rather than crashing the
               interpreter in this case. */
            return;
        }
    }

    auto write = file.attr("write");
    write(std::move(line));
    write(kwargs.contains("end") ? kwargs["end"] : str("\n"));

    if (kwargs.contains("flush") && kwargs["flush"].cast<bool>()) {
        file.attr("flush")();
    }
}
PYBIND11_NAMESPACE_END(detail)

template <return_value_policy policy = return_value_policy::automatic_reference, typename... Args>
void print(Args &&...args) {
    auto c = detail::collect_arguments<policy>(std::forward<Args>(args)...);
    detail::print(c.args(), c.kwargs());
}

inline void
error_already_set::m_fetched_error_deleter(detail::error_fetch_and_normalize *raw_ptr) {
    gil_scoped_acquire gil;
    error_scope scope;
    delete raw_ptr;
}

inline const char *error_already_set::what() const noexcept {
    gil_scoped_acquire gil;
    error_scope scope;
    return m_fetched_error->error_string().c_str();
}

PYBIND11_NAMESPACE_BEGIN(detail)

inline function
get_type_override(const void *this_ptr, const type_info *this_type, const char *name) {
    handle self = get_object_handle(this_ptr, this_type);
    if (!self) {
        return function();
    }
    handle type = type::handle_of(self);
    auto key = std::make_pair(type.ptr(), name);

    /* Cache functions that aren't overridden in Python to avoid
       many costly Python dictionary lookups below */
    bool not_overridden = with_internals([&key](internals &internals) {
        auto &cache = internals.inactive_override_cache;
        return cache.find(key) != cache.end();
    });
    if (not_overridden) {
        return function();
    }

    function override = getattr(self, name, function());
    if (override.is_cpp_function()) {
        with_internals([&](internals &internals) {
            internals.inactive_override_cache.insert(std::move(key));
        });
        return function();
    }

    /* Don't call dispatch code if invoked from overridden function.
       Unfortunately this doesn't work on PyPy and GraalPy. */
#if !defined(PYPY_VERSION) && !defined(GRAALVM_PYTHON)
#    if PY_VERSION_HEX >= 0x03090000
    PyFrameObject *frame = PyThreadState_GetFrame(PyThreadState_Get());
    if (frame != nullptr) {
        PyCodeObject *f_code = PyFrame_GetCode(frame);
        // f_code is guaranteed to not be NULL
        if ((std::string) str(f_code->co_name) == name && f_code->co_argcount > 0) {
#        if PY_VERSION_HEX >= 0x030d0000
            PyObject *locals = PyEval_GetFrameLocals();
#        else
            PyObject *locals = PyEval_GetLocals();
            Py_XINCREF(locals);
#        endif
            if (locals != nullptr) {
#        if PY_VERSION_HEX >= 0x030b0000
                PyObject *co_varnames = PyCode_GetVarnames(f_code);
#        else
                PyObject *co_varnames = PyObject_GetAttrString((PyObject *) f_code, "co_varnames");
#        endif
                PyObject *self_arg = PyTuple_GET_ITEM(co_varnames, 0);
                Py_DECREF(co_varnames);
                PyObject *self_caller = dict_getitem(locals, self_arg);
                Py_DECREF(locals);
                if (self_caller == self.ptr()) {
                    Py_DECREF(f_code);
                    Py_DECREF(frame);
                    return function();
                }
            }
        }
        Py_DECREF(f_code);
        Py_DECREF(frame);
    }
#    else
    PyFrameObject *frame = PyThreadState_Get()->frame;
    if (frame != nullptr && (std::string) str(frame->f_code->co_name) == name
        && frame->f_code->co_argcount > 0) {
        PyFrame_FastToLocals(frame);
        PyObject *self_caller
            = dict_getitem(frame->f_locals, PyTuple_GET_ITEM(frame->f_code->co_varnames, 0));
        if (self_caller == self.ptr()) {
            return function();
        }
    }
#    endif

#else
    /* PyPy currently doesn't provide a detailed cpyext emulation of
       frame objects, so we have to emulate this using Python. This
       is going to be slow..*/
    dict d;
    d["self"] = self;
    d["name"] = pybind11::str(name);
    PyObject *result
        = PyRun_String("import inspect\n"
                       "frame = inspect.currentframe()\n"
                       "if frame is not None:\n"
                       "    frame = frame.f_back\n"
                       "    if frame is not None and str(frame.f_code.co_name) == name and "
                       "frame.f_code.co_argcount > 0:\n"
                       "        self_caller = frame.f_locals[frame.f_code.co_varnames[0]]\n"
                       "        if self_caller == self:\n"
                       "            self = None\n",
                       Py_file_input,
                       d.ptr(),
                       d.ptr());
    if (result == nullptr)
        throw error_already_set();
    Py_DECREF(result);
    if (d["self"].is_none())
        return function();
#endif

    return override;
}
PYBIND11_NAMESPACE_END(detail)

/** \rst
  Try to retrieve a python method by the provided name from the instance pointed to by the
  this_ptr.

  :this_ptr: The pointer to the object the overridden method should be retrieved for. This should
             be the first non-trampoline class encountered in the inheritance chain.
  :name: The name of the overridden Python method to retrieve.
  :return: The Python method by this name from the object or an empty function wrapper.
 \endrst */
template <class T>
function get_override(const T *this_ptr, const char *name) {
    auto *tinfo = detail::get_type_info(typeid(T));
    return tinfo ? detail::get_type_override(this_ptr, tinfo, name) : function();
}

#define PYBIND11_OVERRIDE_IMPL(ret_type, cname, name, ...)                                        \
    do {                                                                                          \
        pybind11::gil_scoped_acquire gil;                                                         \
        pybind11::function override                                                               \
            = pybind11::get_override(static_cast<const cname *>(this), name);                     \
        if (override) {                                                                           \
            auto o = override(__VA_ARGS__);                                                       \
            PYBIND11_WARNING_PUSH                                                                 \
            PYBIND11_WARNING_DISABLE_MSVC(4127)                                                   \
            if (pybind11::detail::cast_is_temporary_value_reference<ret_type>::value              \
                && !pybind11::detail::is_same_ignoring_cvref<ret_type, PyObject *>::value) {      \
                static pybind11::detail::override_caster_t<ret_type> caster;                      \
                return pybind11::detail::cast_ref<ret_type>(std::move(o), caster);                \
            }                                                                                     \
            PYBIND11_WARNING_POP                                                                  \
            return pybind11::detail::cast_safe<ret_type>(std::move(o));                           \
        }                                                                                         \
    } while (false)

/** \rst
    Macro to populate the virtual method in the trampoline class. This macro tries to look up a
    method named 'fn' from the Python side, deals with the :ref:`gil` and necessary argument
    conversions to call this method and return the appropriate type.
    See :ref:`overriding_virtuals` for more information. This macro should be used when the method
    name in C is not the same as the method name in Python. For example with `__str__`.

    .. code-block:: cpp

      std::string toString() override {
        PYBIND11_OVERRIDE_NAME(
            std::string, // Return type (ret_type)
            Animal,      // Parent class (cname)
            "__str__",   // Name of method in Python (name)
            toString,    // Name of function in C++ (fn)
        );
      }
\endrst */
#define PYBIND11_OVERRIDE_NAME(ret_type, cname, name, fn, ...)                                    \
    do {                                                                                          \
        PYBIND11_OVERRIDE_IMPL(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), name, __VA_ARGS__); \
        return cname::fn(__VA_ARGS__);                                                            \
    } while (false)

/** \rst
    Macro for pure virtual functions, this function is identical to
    :c:macro:`PYBIND11_OVERRIDE_NAME`, except that it throws if no override can be found.
\endrst */
#define PYBIND11_OVERRIDE_PURE_NAME(ret_type, cname, name, fn, ...)                               \
    do {                                                                                          \
        PYBIND11_OVERRIDE_IMPL(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), name, __VA_ARGS__); \
        pybind11::pybind11_fail(                                                                  \
            "Tried to call pure virtual function \"" PYBIND11_STRINGIFY(cname) "::" name "\"");   \
    } while (false)

/** \rst
    Macro to populate the virtual method in the trampoline class. This macro tries to look up the
    method from the Python side, deals with the :ref:`gil` and necessary argument conversions to
    call this method and return the appropriate type. This macro should be used if the method name
    in C and in Python are identical.
    See :ref:`overriding_virtuals` for more information.

    .. code-block:: cpp

      class PyAnimal : public Animal {
      public:
          // Inherit the constructors
          using Animal::Animal;

          // Trampoline (need one for each virtual function)
          std::string go(int n_times) override {
              PYBIND11_OVERRIDE_PURE(
                  std::string, // Return type (ret_type)
                  Animal,      // Parent class (cname)
                  go,          // Name of function in C++ (must match Python name) (fn)
                  n_times      // Argument(s) (...)
              );
          }
      };
\endrst */
#define PYBIND11_OVERRIDE(ret_type, cname, fn, ...)                                               \
    PYBIND11_OVERRIDE_NAME(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), #fn, fn, __VA_ARGS__)

/** \rst
    Macro for pure virtual functions, this function is identical to :c:macro:`PYBIND11_OVERRIDE`,
    except that it throws if no override can be found.
\endrst */
#define PYBIND11_OVERRIDE_PURE(ret_type, cname, fn, ...)                                          \
    PYBIND11_OVERRIDE_PURE_NAME(                                                                  \
        PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), #fn, fn, __VA_ARGS__)

// Deprecated versions

PYBIND11_DEPRECATED("get_type_overload has been deprecated")
inline function
get_type_overload(const void *this_ptr, const detail::type_info *this_type, const char *name) {
    return detail::get_type_override(this_ptr, this_type, name);
}

template <class T>
inline function get_overload(const T *this_ptr, const char *name) {
    return get_override(this_ptr, name);
}

#define PYBIND11_OVERLOAD_INT(ret_type, cname, name, ...)                                         \
    PYBIND11_OVERRIDE_IMPL(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), name, __VA_ARGS__)
#define PYBIND11_OVERLOAD_NAME(ret_type, cname, name, fn, ...)                                    \
    PYBIND11_OVERRIDE_NAME(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), name, fn, __VA_ARGS__)
#define PYBIND11_OVERLOAD_PURE_NAME(ret_type, cname, name, fn, ...)                               \
    PYBIND11_OVERRIDE_PURE_NAME(                                                                  \
        PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), name, fn, __VA_ARGS__);
#define PYBIND11_OVERLOAD(ret_type, cname, fn, ...)                                               \
    PYBIND11_OVERRIDE(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), fn, __VA_ARGS__)
#define PYBIND11_OVERLOAD_PURE(ret_type, cname, fn, ...)                                          \
    PYBIND11_OVERRIDE_PURE(PYBIND11_TYPE(ret_type), PYBIND11_TYPE(cname), fn, __VA_ARGS__);

PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)