sol2/include/sol/stack_check_unqualified.hpp

// sol2

// The MIT License (MIT)

// Copyright (c) 2013-2022 Rapptz, ThePhD and contributors

// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in
// the Software without restriction, including without limitation the rights to
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software is furnished to do so,
// subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
// COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
// IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
// CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

#ifndef SOL_STACK_CHECK_UNQUALIFIED_HPP
#define SOL_STACK_CHECK_UNQUALIFIED_HPP

#include <sol/stack_core.hpp>
#include <sol/usertype_traits.hpp>
#include <sol/inheritance.hpp>
#include <memory>
#include <functional>
#include <utility>
#include <cmath>
#include <optional>
#if SOL_IS_ON(SOL_STD_VARIANT)
#include <variant>
#endif // variant shenanigans

namespace sol { namespace stack {
	template <typename Handler>
	bool loose_table_check(lua_State* L_, int index, Handler&& handler, record& tracking) {
		tracking.use(1);
		type t = type_of(L_, index);
		if (t == type::table) {
			return true;
		}
		if (t != type::userdata) {
			handler(L_, index, type::table, t, "value is not a table or a userdata that can behave like one");
			return false;
		}
		return true;
	}

	namespace stack_detail {
		inline bool impl_check_metatable(lua_State* L_, int index, const std::string& metakey, bool poptable) {
			luaL_getmetatable(L_, &metakey[0]);
			const type expectedmetatabletype = static_cast<type>(lua_type(L_, -1));
			if (expectedmetatabletype != type::lua_nil) {
				if (lua_rawequal(L_, -1, index) == 1) {
					lua_pop(L_, 1 + static_cast<int>(poptable));
					return true;
				}
			}
			lua_pop(L_, 1);
			return false;
		}

		template <typename T, bool poptable = true>
		inline bool check_metatable(lua_State* L_, int index = -2) {
			return impl_check_metatable(L_, index, usertype_traits<T>::metatable(), poptable);
		}

		template <type expected, int (*check_func)(lua_State*, int)>
		struct basic_check {
			template <typename Handler>
			static bool check(lua_State* L_, int index, Handler&& handler, record& tracking) {
				tracking.use(1);
				bool success = check_func(L_, index) == 1;
				if (!success) {
					// expected type, actual type
					handler(L_, index, expected, type_of(L_, index), "");
				}
				return success;
			}
		};
	} // namespace stack_detail

	template <typename T, typename>
	struct unqualified_interop_checker {
		template <typename Handler>
		static bool check(lua_State*, int, type, Handler&&, record&) {
			return false;
		}
	};

	template <typename T, typename>
	struct qualified_interop_checker {
		template <typename Handler>
		static bool check(lua_State* L_, int index, type index_type, Handler&& handler, record& tracking) {
			return stack_detail::unqualified_interop_check<T>(L_, index, index_type, std::forward<Handler>(handler), tracking);
		}
	};

	template <typename T, type expected, typename>
	struct unqualified_checker {
		template <typename Handler>
		static bool check(lua_State* L_, int index, Handler&& handler, record& tracking) {
			if constexpr (std::is_same_v<T, bool>) {
				tracking.use(1);
				bool success = lua_isboolean(L_, index) == 1;
				if (!success) {
					// expected type, actual type
					handler(L_, index, expected, type_of(L_, index), "");
				}
				return success;
			}
			else if constexpr (meta::any_same_v<T,
				                   char
#if SOL_IS_ON(SOL_CHAR8_T)
				                   ,
				                   char8_t
#endif
				                   ,
				                   char16_t,
				                   char32_t>) {
				return stack::check<std::basic_string<T>>(L_, index, std::forward<Handler>(handler), tracking);
			}
			else if constexpr (std::is_integral_v<T> || std::is_same_v<T, lua_Integer>) {
				tracking.use(1);
#if SOL_LUA_VERSION_I_ >= 503
				// Lua 5.3 and greater checks for numeric precision
#if SOL_IS_ON(SOL_STRINGS_ARE_NUMBERS)
				// imprecise, sloppy conversions
				int isnum = 0;
				lua_tointegerx(L_, index, &isnum);
				const bool success = isnum != 0;
				if (!success) {
					// expected type, actual type
					handler(L_, index, type::number, type_of(L_, index), detail::not_a_number_or_number_string_integral);
				}
#elif SOL_IS_ON(SOL_NUMBER_PRECISION_CHECKS)
				// this check is precise, do not convert
				if (lua_isinteger(L_, index) == 1) {
					return true;
				}
				const bool success = false;
				if (!success) {
					// expected type, actual type
					handler(L_, index, type::number, type_of(L_, index), detail::not_a_number_integral);
				}
#else
				// Numerics are neither safe nor string-convertible
				type t = type_of(L_, index);
				const bool success = t == type::number;
#endif
				if (!success) {
					// expected type, actual type
					handler(L_, index, type::number, type_of(L_, index), detail::not_a_number);
				}
				return success;
#else
				// Lua 5.2 and below checks
#if SOL_IS_OFF(SOL_STRINGS_ARE_NUMBERS)
				// must pre-check, because it will convert
				type t = type_of(L_, index);
				if (t != type::number) {
					// expected type, actual type
					handler(L_, index, type::number, t, detail::not_a_number);
					return false;
				}
#endif // Do not allow strings to be numbers

#if SOL_IS_ON(SOL_NUMBER_PRECISION_CHECKS)
				int isnum = 0;
				const lua_Number v = lua_tonumberx(L_, index, &isnum);
				const bool success = isnum != 0 && static_cast<lua_Number>(llround(v)) == v;
#else
				const bool success = true;
#endif // Safe numerics and number precision checking
				if (!success) {
					// Use defines to provide a better error message!
#if SOL_IS_ON(SOL_STRINGS_ARE_NUMBERS)
					handler(L_, index, type::number, type_of(L_, index), detail::not_a_number_or_number_string);
#elif SOL_IS_ON(SOL_NUMBER_PRECISION_CHECKS)
					handler(L_, index, type::number, t, detail::not_a_number_or_number_string);
#else
					handler(L_, index, type::number, t, detail::not_a_number);
#endif
				}
				return success;
#endif
			}
			else if constexpr (std::is_floating_point_v<T> || std::is_same_v<T, lua_Number>) {
				tracking.use(1);
#if SOL_IS_ON(SOL_STRINGS_ARE_NUMBERS)
				bool success = lua_isnumber(L_, index) == 1;
				if (!success) {
					// expected type, actual type
					handler(L_, index, type::number, type_of(L_, index), detail::not_a_number_or_number_string);
				}
				return success;
#else
				type t = type_of(L_, index);
				bool success = t == type::number;
				if (!success) {
					// expected type, actual type
					handler(L_, index, type::number, t, detail::not_a_number);
				}
				return success;
#endif // Strings are Numbers
			}
			else if constexpr (meta::any_same_v<T, type, this_state, this_main_state, this_environment, variadic_args>) {
				(void)L_;
				(void)index;
				(void)handler;
				tracking.use(0);
				return true;
			}
			else if constexpr (is_unique_usertype_v<T>) {
				using element = unique_usertype_element_t<T>;
				using actual = unique_usertype_actual_t<T>;
				const type indextype = type_of(L_, index);
				tracking.use(1);
				if (indextype != type::userdata) {
					handler(L_, index, type::userdata, indextype, "value is not a userdata");
					return false;
				}
				if (lua_getmetatable(L_, index) == 0) {
					return true;
				}
				int metatableindex = lua_gettop(L_);
				if (stack_detail::check_metatable<d::u<element>>(L_, metatableindex)) {
					void* memory = lua_touserdata(L_, index);
					memory = detail::align_usertype_unique_destructor(memory);
					detail::unique_destructor& pdx = *static_cast<detail::unique_destructor*>(memory);
					bool success = &detail::usertype_unique_alloc_destroy<element, actual> == pdx;
					if (!success) {
						memory = detail::align_usertype_unique_tag<true>(memory);
#if 0
						// New version, one day
#else
						const char*& name_tag = *static_cast<const char**>(memory);
						success = usertype_traits<T>::qualified_name() == name_tag;
#endif
						if (!success) {
							handler(L_, index, type::userdata, indextype, "value is a userdata but is not the correct unique usertype");
						}
					}
					return success;
				}
				lua_pop(L_, 1);
				handler(L_, index, type::userdata, indextype, "unrecognized userdata (not pushed by sol?)");
				return false;
			}
			else if constexpr (meta::any_same_v<T, lua_nil_t, std::nullopt_t, nullopt_t>) {
				bool success = lua_isnil(L_, index);
				if (success) {
					tracking.use(1);
					return success;
				}
				tracking.use(0);
				success = lua_isnone(L_, index);
				if (!success) {
					// expected type, actual type
					handler(L_, index, expected, type_of(L_, index), "");
				}
				return success;
			}
			else if constexpr (std::is_same_v<T, env_key_t>) {
				tracking.use(1);
				type t = type_of(L_, index);
				if (t == type::table || t == type::none || t == type::lua_nil || t == type::userdata) {
					return true;
				}
				handler(L_, index, type::table, t, "value cannot not have a valid environment");
				return true;
			}
			else if constexpr (std::is_same_v<T, detail::non_lua_nil_t>) {
				return !stack::unqualified_check<lua_nil_t>(L_, index, std::forward<Handler>(handler), tracking);
			}
			else if constexpr (meta::is_specialization_of_v<T, basic_lua_table>) {
				tracking.use(1);
				type t = type_of(L_, index);
				if (t != type::table) {
					handler(L_, index, type::table, t, "value is not a table");
					return false;
				}
				return true;
			}
			else if constexpr (meta::is_specialization_of_v<T, basic_bytecode>) {
				tracking.use(1);
				type t = type_of(L_, index);
				if (t != type::function) {
					handler(L_, index, type::function, t, "value is not a function that can be dumped");
					return false;
				}
				return true;
			}
			else if constexpr (meta::is_specialization_of_v<T, basic_environment>) {
				tracking.use(1);
				if (lua_getmetatable(L_, index) == 0) {
					return true;
				}
				type t = type_of(L_, -1);
				if (t == type::table || t == type::none || t == type::lua_nil) {
					lua_pop(L_, 1);
					return true;
				}
				if (t != type::userdata) {
					lua_pop(L_, 1);
					handler(L_, index, type::table, t, "value does not have a valid metatable");
					return false;
				}
				return true;
			}
			else if constexpr (std::is_same_v<T, metatable_key_t>) {
				tracking.use(1);
				if (lua_getmetatable(L_, index) == 0) {
					return true;
				}
				type t = type_of(L_, -1);
				if (t == type::table || t == type::none || t == type::lua_nil) {
					lua_pop(L_, 1);
					return true;
				}
				if (t != type::userdata) {
					lua_pop(L_, 1);
					handler(L_, index, expected, t, "value does not have a valid metatable");
					return false;
				}
				return true;
			}
			else if constexpr (std::is_same_v<T, luaL_Stream*> || std::is_same_v<T, luaL_Stream>) {
				if (lua_getmetatable(L_, index) == 0) {
					type t = type_of(L_, index);
					handler(L_, index, expected, t, "value is not a valid luaL_Stream (has no metatable/is not a valid value)");
					return false;
				}
				luaL_getmetatable(L_, LUA_FILEHANDLE);
				if (type_of(L_, index) != type::table) {
					type t = type_of(L_, index);
					lua_pop(L_, 1);
					handler(L_,
						index,
						expected,
						t,
						"value is not a valid luaL_Stream (there is no metatable for luaL_Stream -- did you forget to "
						"my_lua_state.open_libraries(sol::lib::state) or equivalent?)");
					return false;
				}
				int is_stream_table = lua_compare(L_, -1, -2, LUA_OPEQ);
				lua_pop(L_, 2);
				if (is_stream_table == 0) {
					type t = type_of(L_, index);
					handler(L_, index, expected, t, "value is not a valid luaL_Stream (incorrect metatable)");
					return false;
				}
				return true;
			}
			else if constexpr (meta::is_optional_v<T>) {
				using ValueType = typename T::value_type;
				(void)handler;
				type t = type_of(L_, index);
				if (t == type::none) {
					tracking.use(0);
					return true;
				}
				if (t == type::lua_nil) {
					tracking.use(1);
					return true;
				}
				return stack::unqualified_check<ValueType>(L_, index, &no_panic, tracking);
			}
#if SOL_IS_ON(SOL_GET_FUNCTION_POINTER_UNSAFE)
			else if constexpr (std::is_function_v<T> || (std::is_pointer_v<T> && std::is_function_v<std::remove_pointer_t<T>>)) {
				return stack_detail::check_function_pointer<std::remove_pointer_t<T>>(L_, index, std::forward<Handler>(handler), tracking);
			}
#endif
			else if constexpr (expected == type::userdata) {
				if constexpr (meta::any_same_v<T, userdata_value> || meta::is_specialization_of_v<T, basic_userdata>) {
					tracking.use(1);
					type t = type_of(L_, index);
					bool success = t == type::userdata;
					if (!success) {
						// expected type, actual type
						handler(L_, index, type::userdata, t, "");
					}
					return success;
				}
				else if constexpr (meta::is_specialization_of_v<T, user>) {
					unqualified_checker<lightuserdata_value, type::userdata> c;
					(void)c;
					return c.check(L_, index, std::forward<Handler>(handler), tracking);
				}
				else {
					if constexpr (std::is_pointer_v<T>) {
						return check_usertype<T>(L_, index, std::forward<Handler>(handler), tracking);
					}
					else if constexpr (meta::is_specialization_of_v<T, std::reference_wrapper>) {
						using T_internal = typename T::type;
						return stack::check<T_internal>(L_, index, std::forward<Handler>(handler), tracking);
					}
					else {
						return check_usertype<T>(L_, index, std::forward<Handler>(handler), tracking);
					}
				}
			}
			else if constexpr (expected == type::poly) {
				tracking.use(1);
				bool success = is_lua_reference_v<T> || !lua_isnone(L_, index);
				if (!success) {
					// expected type, actual type
					handler(L_, index, type::poly, type_of(L_, index), "");
				}
				return success;
			}
			else if constexpr (expected == type::lightuserdata) {
				tracking.use(1);
				type t = type_of(L_, index);
				bool success = t == type::userdata || t == type::lightuserdata;
				if (!success) {
					// expected type, actual type
					handler(L_, index, type::lightuserdata, t, "");
				}
				return success;
			}
			else if constexpr (expected == type::function) {
				if constexpr (meta::any_same_v<T, lua_CFunction, std::remove_pointer_t<lua_CFunction>, c_closure>) {
					tracking.use(1);
					bool success = lua_iscfunction(L_, index) == 1;
					if (!success) {
						// expected type, actual type
						handler(L_, index, expected, type_of(L_, index), "");
					}
					return success;
				}
				else {
					tracking.use(1);
					type t = type_of(L_, index);
					if (t == type::lua_nil || t == type::none || t == type::function) {
						// allow for lua_nil to be returned
						return true;
					}
					if (t != type::userdata && t != type::table) {
						handler(L_, index, type::function, t, "must be a function or table or a userdata");
						return false;
					}
					// Do advanced check for call-style userdata?
					static const auto& callkey = to_string(meta_function::call);
					if (lua_getmetatable(L_, index) == 0) {
						// No metatable, no __call key possible
						handler(L_, index, type::function, t, "value is not a function and does not have overriden metatable");
						return false;
					}
					if (lua_isnoneornil(L_, -1)) {
						lua_pop(L_, 1);
						handler(L_, index, type::function, t, "value is not a function and does not have valid metatable");
						return false;
					}
					lua_getfield(L_, -1, &callkey[0]);
					if (lua_isnoneornil(L_, -1)) {
						lua_pop(L_, 2);
						handler(L_, index, type::function, t, "value's metatable does not have __call overridden in metatable, cannot call this type");
						return false;
					}
					// has call, is definitely a function
					lua_pop(L_, 2);
					return true;
				}
			}
			else if constexpr (expected == type::table) {
				return stack::loose_table_check(L_, index, std::forward<Handler>(handler), tracking);
			}
			else {
				tracking.use(1);
				const type indextype = type_of(L_, index);
				bool success = expected == indextype;
				if (!success) {
					// expected type, actual type, message
					handler(L_, index, expected, indextype, "");
				}
				return success;
			}
		}
	};

	template <typename T>
	struct unqualified_checker<non_null<T>, type::userdata> : unqualified_checker<T, lua_type_of_v<T>> { };

	template <typename T>
	struct unqualified_checker<detail::as_value_tag<T>, type::userdata> {
		template <typename Handler>
		static bool check(lua_State* L_, int index, Handler&& handler, record& tracking) {
			const type indextype = type_of(L_, index);
			return check(types<T>(), L_, index, indextype, std::forward<Handler>(handler), tracking);
		}

		template <typename U, typename Handler>
		static bool check(types<U>, lua_State* L_, int index, type indextype, Handler&& handler, record& tracking) {
			if constexpr (
				std::is_same_v<T,
				     lightuserdata_value> || std::is_same_v<T, userdata_value> || std::is_same_v<T, userdata> || std::is_same_v<T, lightuserdata>) {
				tracking.use(1);
				if (indextype != type::userdata) {
					handler(L_, index, type::userdata, indextype, "value is not a valid userdata");
					return false;
				}
				return true;
			}
			else {
#if SOL_IS_ON(SOL_USE_INTEROP)
				if (stack_detail::interop_check<U>(L_, index, indextype, handler, tracking)) {
					return true;
				}
#endif // interop extensibility
				tracking.use(1);
#if SOL_IS_ON(SOL_GET_FUNCTION_POINTER_UNSAFE)
				if (lua_iscfunction(L_, index) != 0) {
					// a potential match...
					return true;
				}
#endif
				if (indextype != type::userdata) {
					handler(L_, index, type::userdata, indextype, "value is not a valid userdata");
					return false;
				}
				if (lua_getmetatable(L_, index) == 0) {
					return true;
				}
				int metatableindex = lua_gettop(L_);
				if (stack_detail::check_metatable<U>(L_, metatableindex))
					return true;
				if (stack_detail::check_metatable<U*>(L_, metatableindex))
					return true;
				if (stack_detail::check_metatable<d::u<U>>(L_, metatableindex))
					return true;
				if (stack_detail::check_metatable<as_container_t<U>>(L_, metatableindex))
					return true;
				bool success = false;
				bool has_derived = derive<T>::value || weak_derive<T>::value;
				if (has_derived) {
#if SOL_IS_ON(SOL_SAFE_STACK_CHECK)
					luaL_checkstack(L_, 1, detail::not_enough_stack_space_string);
#endif // make sure stack doesn't overflow
					auto pn = stack::pop_n(L_, 1);
					lua_pushstring(L_, &detail::base_class_check_key()[0]);
					lua_rawget(L_, metatableindex);
					if (type_of(L_, -1) != type::lua_nil) {
						void* basecastdata = lua_touserdata(L_, -1);
						detail::inheritance_check_function ic = reinterpret_cast<detail::inheritance_check_function>(basecastdata);
						success = ic(usertype_traits<T>::qualified_name());
					}
				}
				lua_pop(L_, 1);
				if (!success) {
					handler(L_, index, type::userdata, indextype, "value at this index does not properly reflect the desired type");
					return false;
				}
				return true;
			}
		}
	};

	template <typename T>
	struct unqualified_checker<detail::as_pointer_tag<T>, type::userdata> {
		template <typename Handler>
		static bool check(lua_State* L_, int index, type indextype, Handler&& handler, record& tracking) {
			if (indextype == type::lua_nil) {
				tracking.use(1);
				return true;
			}
			return check_usertype<std::remove_pointer_t<T>>(L_, index, std::forward<Handler>(handler), tracking);
		}

		template <typename Handler>
		static bool check(lua_State* L_, int index, Handler&& handler, record& tracking) {
			const type indextype = type_of(L_, index);
			return check(L_, index, indextype, std::forward<Handler>(handler), tracking);
		}
	};

	template <typename T, std::size_t N, type expect>
	struct unqualified_checker<exhaustive_until<T, N>, expect> {
		template <typename K, typename V, typename Handler>
		static bool check_two(types<K, V>, lua_State* arg_L, int index, type indextype, Handler&& handler, record& tracking) {
			tracking.use(1);

#if SOL_IS_ON(SOL_SAFE_STACK_CHECK)
			luaL_checkstack(arg_L, 3, detail::not_enough_stack_space_generic);
#endif // make sure stack doesn't overflow

			int index = lua_absindex(arg_L, relindex);
			lua_pushnil(arg_L);
			while (lua_next(arg_L, index) != 0) {
				const bool is_key_okay = stack::check<K>(arg_L, -2, std::forward<Handler>(handler), tracking);
				if (!is_key_okay) {
					lua_pop(arg_L, 2);
					return false;
				}
				const bool is_value_okay = stack::check<V>(arg_L, -1, std::forward<Handler>(handler), tracking);
				if (!is_value_okay) {
					lua_pop(arg_L, 2);
					return false;
				}
				lua_pop(arg_L, 1);
			}
			return true;
		}

		template <typename V, typename Handler>
		static bool check_one(types<V>, lua_State* arg_L, int relindex, type indextype, Handler&& handler, record& tracking) {
			tracking.use(1);

			size_t index = lua_absindex(arg_L, relindex);
			// Zzzz slower but necessary thanks to the lower version API and missing functions qq
			std::size_t idx = 0;
			int vi = 0;
			for (lua_Integer i = 0;; (void)(i += lua_size<V>::value), lua_pop(arg_L, static_cast<int>(vi))) {
				vi = 0;
				if (idx >= N) {
					return true;
				}
#if SOL_IS_ON(SOL_SAFE_STACK_CHECK)
				luaL_checkstack(arg_L, 2, detail::not_enough_stack_space_generic);
#endif // make sure stack doesn't overflow
				bool isnil = false;
				for (; vi < static_cast<int>(lua_size<V>::value); ++vi) {
					lua_pushinteger(arg_L, i);
					lua_gettable(arg_L, static_cast<int>(index));
					type vt = type_of(arg_L, -1);
					isnil = vt == type::lua_nil;
					if (isnil) {
						if (i == 0) {
							vi += 1;
							goto loop_continue;
						}
						lua_pop(arg_L, static_cast<int>(vi + 1));
						return true;
					}
				}
				if (!stack::check<V>(arg_L, -lua_size<V>::value, std::forward<Handler>(handler), tracking)) {
					lua_pop(arg_L, lua_size<V>::value);
					return false;
				}
				++idx;
			loop_continue:;
			}
			return true;
		}

		template <typename Handler>
		static bool check(lua_State* arg_L, int index, Handler&& handler, record& tracking) {
			using Tu = meta::unqualified_t<T>;
			if constexpr (is_container_v<Tu>) {
				if constexpr (meta::is_associative<Tu>::value) {
					typedef typename Tu::value_type P;
					typedef typename P::first_type K;
					typedef typename P::second_type V;
					return check_two(types<K, V>(), arg_L, index, expect, std::forward<Handler>(handler), tracking);
				}
				else {
					typedef typename Tu::value_type V;
					return check_one(types<V>(), arg_L, index, expect, std::forward<Handler>(handler), tracking);
				}
			}
			else {
				unqualified_checker<Tu, expect> c {};
				return c.check(arg_L, index, std::forward<Handler>(handler), tracking);
			}
		}
	};

	template <typename T, type expect>
	struct unqualified_checker<non_exhaustive<T>, expect> {
		template <typename Handler>
		static bool check(lua_State* arg_L, int index, Handler&& handler, record& tracking) {
			return stack::check<T>(arg_L, index, std::forward<Handler>(handler), tracking);
		}
	};

	template <typename... Args>
	struct unqualified_checker<std::tuple<Args...>, type::poly> {
		template <typename Handler>
		static bool check(lua_State* L_, int index, Handler&& handler, record& tracking) {
			return stack::multi_check<Args...>(L_, index, std::forward<Handler>(handler), tracking);
		}
	};

	template <typename A, typename B>
	struct unqualified_checker<std::pair<A, B>, type::poly> {
		template <typename Handler>
		static bool check(lua_State* L_, int index, Handler&& handler, record& tracking) {
			return stack::multi_check<A, B>(L_, index, std::forward<Handler>(handler), tracking);
		}
	};

#if SOL_IS_ON(SOL_STD_VARIANT)

	template <typename... Tn>
	struct unqualified_checker<std::variant<Tn...>, type::poly> {
		typedef std::variant<Tn...> V;
		typedef std::variant_size<V> V_size;
		typedef std::integral_constant<bool, V_size::value == 0> V_is_empty;

		template <typename Handler>
		static bool is_one(std::integral_constant<std::size_t, 0>, lua_State* L_, int index, Handler&& handler, record& tracking) {
			if constexpr (V_is_empty::value) {
				if (lua_isnone(L_, index)) {
					return true;
				}
			}
			tracking.use(1);
			handler(L_, index, type::poly, type_of(L_, index), "value does not fit any type present in the variant");
			return false;
		}

		template <std::size_t I, typename Handler>
		static bool is_one(std::integral_constant<std::size_t, I>, lua_State* L_, int index, Handler&& handler, record& tracking) {
			typedef std::variant_alternative_t<I - 1, V> T;
			record temp_tracking = tracking;
			if (stack::check<T>(L_, index, &no_panic, temp_tracking)) {
				tracking = temp_tracking;
				return true;
			}
			return is_one(std::integral_constant<std::size_t, I - 1>(), L_, index, std::forward<Handler>(handler), tracking);
		}

		template <typename Handler>
		static bool check(lua_State* L_, int index, Handler&& handler, record& tracking) {
			return is_one(std::integral_constant<std::size_t, V_size::value>(), L_, index, std::forward<Handler>(handler), tracking);
		}
	};

#endif // variant shenanigans

}} // namespace sol::stack

#endif // SOL_STACK_CHECK_UNQUALIFIED_HPP