✨ Proper keep-alive semantics!

— Fixes #1247

include/sol/pairs_iterator.hpp

@@ -31,7 +31,7 @@
 #include <sol/table_iterator.hpp>
 #include <sol/protected_function.hpp>
 
-#include <sol/detail/pairs.hpp>
+#include <sol/stack/detail/pairs.hpp>
 
 namespace sol {
 
@@ -120,8 +120,7 @@ namespace sol {
 			}
 
 			{
-				stack::get_field<true, false>(m_L, "next");
+				auto maybe_next = stack::stack_detail::find_lua_next_function(m_L);
-				auto maybe_next = stack::pop<optional<protected_function>>(m_L);
 				if (maybe_next.has_value()) {
 					m_next_function_ref = std::move(*maybe_next);
 					m_table_ref = source_;

include/sol/stack/detail/pairs.hpp

@@ -28,10 +28,39 @@
 
 #include <sol/stack.hpp>
 #include <sol/stack_reference.hpp>
+#include <sol/protected_function.hpp>
 #include <sol/assert.hpp>
 
+#include <optional>
+
 namespace sol { namespace stack { namespace stack_detail {
 
+	inline bool maybe_push_lua_next_function(lua_State* L_) {
+		stack::get_field<true, false>(L_, "next");
+		bool is_next = stack::check<protected_function>(L_);
+		if (is_next) {
+			return true;
+		}
+		stack::get_field<true, false>(L_, "table");
+		if (!stack::check<table>(L_, -1)) {
+			return false;
+		}
+		lua_getfield(L_, -1, "next");
+		bool is_table_next_func = stack::check<protected_function>(L_, -1);
+		if (is_table_next_func) {
+			return true;
+		}
+		lua_pop(L_, 1);
+		return false;
+	}
+
+	inline std::optional<protected_function> find_lua_next_function(lua_State* L_) {
+		if (maybe_push_lua_next_function(L_)) {
+			return stack::pop<protected_function>(L_);
+		}
+		return std::nullopt;
+	}
+
 	inline int c_lua_next(lua_State* L_) noexcept {
 		stack_reference table_stack_ref(L_, raw_index(1));
 		stateless_stack_reference key_stack_ref(L_, raw_index(2));
@@ -45,8 +74,7 @@ namespace sol { namespace stack { namespace stack_detail {
 
 	inline int readonly_pairs(lua_State* L_) noexcept {
 		int pushed = 0;
-		stack::get_field<true, false>(L_, "next");
+		if (!maybe_push_lua_next_function(L_)) {
-		if (!stack::check<unsafe_function>(L_, -1)) {
 			// we do not have the "next" function in the global namespace
 			// from the "table" global entiry, use our own
 			pushed += stack::push(L_, &c_lua_next);

tests/inclusion/source/detail/build_version.cpp

@@ -0,0 +1,24 @@
+// sol2
+
+// The MIT License (MIT)
+
+// Copyright (c) 2013-2021 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.
+
+#include <sol/detail/build_version.hpp>

tests/inclusion/source/stack/detail/pairs.cpp

@@ -0,0 +1,24 @@
+// sol2
+
+// The MIT License (MIT)
+
+// Copyright (c) 2013-2021 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.
+
+#include <sol/stack/detail/pairs.hpp>