Add compile-time option to enable table order preservation

Author: stackotter

include/toml++/impl/key.hpp

@@ -332,4 +332,10 @@ TOML_NAMESPACE_START
 }
 TOML_NAMESPACE_END;
 
+template<> struct std::hash<toml::key> {
+    std::size_t operator()(toml::key const& k) const noexcept {
+        return std::hash<std::string_view>{}(k.str());
+    }
+};
+
 #include "header_end.hpp"

include/toml++/impl/parser.inl

@@ -3186,10 +3186,18 @@ TOML_IMPL_NAMESPACE_START
 			for (size_t i = 0, e = key_buffer.size() - 1u; i < e; i++)
 			{
 				const std::string_view segment = key_buffer[i];
+#if TOML_ENABLE_ORDERED_TABLES
+				auto pit					   = parent->find(segment);
+#else
 				auto pit					   = parent->lower_bound(segment);
+#endif
 
 				// parent already existed
+#if TOML_ENABLE_ORDERED_TABLES
+				if (pit != parent->end())
+#else
 				if (pit != parent->end() && pit->first == segment)
+#endif
 				{
 					node& p = pit->second;
 
@@ -3240,13 +3248,21 @@ TOML_IMPL_NAMESPACE_START
 			}
 
 			const auto last_segment = key_buffer.back();
+#if TOML_ENABLE_ORDERED_TABLES
+			auto it					= parent->find(last_segment);
+#else
 			auto it					= parent->lower_bound(last_segment);
+#endif
 
 			// if there was already a matching node some sanity checking is necessary;
 			// this is ok if we're making an array and the existing element is already an array (new element)
 			// or if we're making a table and the existing element is an implicitly-created table (promote it),
 			// otherwise this is a redefinition error.
+#if TOML_ENABLE_ORDERED_TABLES
+			if (it != parent->end())
+#else
 			if (it != parent->end() && it->first == last_segment)
+#endif
 			{
 				node& matching_node = it->second;
 				if (auto arr = matching_node.as_array();
@@ -3376,10 +3392,18 @@ TOML_IMPL_NAMESPACE_START
 				for (size_t i = 0; i < key_buffer.size() - 1u; i++)
 				{
 					const std::string_view segment = key_buffer[i];
+#if TOML_ENABLE_ORDERED_TABLES
+					auto pit					   = tbl->find(segment);
+#else
 					auto pit					   = tbl->lower_bound(segment);
+#endif
 
 					// parent already existed
+#if TOML_ENABLE_ORDERED_TABLES
+					if (pit != tbl->end())
+#else
 					if (pit != tbl->end() && pit->first == segment)
+#endif
 					{
 						table* p = pit->second.as_table();
 
@@ -3413,8 +3437,13 @@ TOML_IMPL_NAMESPACE_START
 
 			// ensure this isn't a redefinition
 			const std::string_view last_segment = key_buffer.back();
+#if TOML_ENABLE_ORDERED_TABLES
+			auto it								= tbl->find(last_segment);
+			if (it != tbl->end())
+#else
 			auto it								= tbl->lower_bound(last_segment);
 			if (it != tbl->end() && it->first == last_segment)
+#endif
 			{
 				set_error("cannot redefine existing "sv,
 						  to_sv(it->second.type()),

include/toml++/impl/preprocessor.hpp

@@ -1211,6 +1211,42 @@ TOML_ENABLE_WARNINGS;
 /// \detail Defaults to `0`.
 //# }}
 
+#ifndef TOML_ENABLE_ORDERED_TABLES
+#define TOML_ENABLE_ORDERED_TABLES 0
+#endif
+//# {{
+/// \def TOML_ENABLE_ORDERED_TABLES
+/// \brief Make tables retain insertion order instead of lexicographic order.
+/// \detail Defaults to `0`.
+//# }}
+
+#ifndef TOML_DISABLE_CONDITIONAL_NOEXCEPT_LAMBDA
+#define TOML_DISABLE_CONDITIONAL_NOEXCEPT_LAMBDA 0
+#endif
+//# {{
+/// \def TOML_DISABLE_CONDITIONAL_NOEXCEPT_LAMBDA
+/// \brief Disable using noexcept(<condition>) in lambda definitions within the toml++ library implementation.
+/// \detail This macro offers a workaround to a bug in the old "legacy lambda processor" of Visual C++, which
+/// caused compile errors like "error C2057: expected constant expression", when it encountered such lambda's.
+/// These compile errors were reported by Kevin Dick, Jan 19, 2024, at https://github.com/marzer/tomlplusplus/issues/219
+//# }}
+
+#ifndef TOML_DISABLE_NOEXCEPT_NOEXCEPT
+#define TOML_DISABLE_NOEXCEPT_NOEXCEPT 0
+	#ifdef _MSC_VER
+		#if _MSC_VER <= 1943 // Up to Visual Studio 2022 Version 17.13.6
+		#undef TOML_DISABLE_NOEXCEPT_NOEXCEPT
+		#define TOML_DISABLE_NOEXCEPT_NOEXCEPT 1
+		#endif
+	#endif
+#endif
+//# {{
+/// \def TOML_DISABLE_NOEXCEPT_NOEXCEPT
+/// \brief Disable using noexcept(noexcept(<expression>)) within the toml++ library implementation.
+/// \detail This macro offers a workaround to a bug in Visual C++ (Visual Studio 2022), which caused
+/// compile errors, saying: "error C3878: syntax error: unexpected token ',' following 'simple-type-specifier'"
+//# }}
+
 /// @}
 //#====================================================================================================================
 //# CHARCONV SUPPORT

include/toml++/impl/std_list.hpp

@@ -0,0 +1,10 @@
+//# This file is a part of toml++ and is subject to the the terms of the MIT license.
+//# Copyright (c) Mark Gillard <[email protected]>
+//# See https://github.com/marzer/tomlplusplus/blob/master/LICENSE for the full license text.
+// SPDX-License-Identifier: MIT
+#pragma once
+
+#include "preprocessor.hpp"
+TOML_DISABLE_WARNINGS;
+#include <list>
+TOML_ENABLE_WARNINGS;