LuaWrapper: Add support for std::variant

ext/luawrapper/include/LuaContext.hpp

@@ -38,7 +38,6 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <list>
 #include <map>
 #include <memory>
-#include <optional>
 #include <random>
 #include <set>
 #include <stdexcept>
@@ -56,6 +55,11 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <boost/type_traits.hpp>
 #include <lua.hpp>
 
+#if __cplusplus >= 201703L
+#include <variant>
+#include <optional>
+#endif /* C++17 */
+
 // Set the older gcc define for tsan if clang or modern gcc tell us we have tsan.
 #if defined(__has_feature)
 #if __has_feature(thread_sanitizer)
@@ -2001,8 +2005,10 @@ struct LuaContext::FunctionArgumentsCounter<> {
 // implementation of IsOptional
 template<typename T>
 struct LuaContext::IsOptional<boost::optional<T>> : public std::true_type {};
+#if __cplusplus >= 201703L
 template<typename T>
 struct LuaContext::IsOptional<std::optional<T>> : public std::true_type {};
+#endif /* C++ 17 */
 
 // implementation of LuaFunctionCaller
 template<typename TFunctionType>
@@ -2556,6 +2562,25 @@ struct LuaContext::Pusher<boost::variant<TTypes...>>
     };
 };
 
+#if __cplusplus >= 201703L
+// std::variant
+template<typename... TTypes>
+struct LuaContext::Pusher<std::variant<TTypes...>>
+{
+    static const int minSize = PusherMinSize<TTypes...>::size;
+    static const int maxSize = PusherMaxSize<TTypes...>::size;
+
+    static PushedObject push(lua_State* state, const std::variant<TTypes...>& value) noexcept {
+        PushedObject obj{state, 0};
+        std::visit([&](auto&& arg) {
+            using T = std::decay_t<decltype(arg)>;
+            obj = Pusher<T>::push(state, arg);
+        }, value);
+        return obj;
+    }
+};
+#endif /* C++17 */
+
 // boost::optional
 template<typename TType>
 struct LuaContext::Pusher<boost::optional<TType>> {
@@ -2575,6 +2600,7 @@ struct LuaContext::Pusher<boost::optional<TType>> {
     }
 };
 
+#if __cplusplus >= 201703L
 // std::optional
 template<typename TType>
 struct LuaContext::Pusher<std::optional<TType>> {
@@ -2593,6 +2619,7 @@ struct LuaContext::Pusher<std::optional<TType>> {
         }
     }
 };
+#endif /* C++17 */
 
 // tuple
 template<typename... TTypes>
@@ -2943,6 +2970,7 @@ struct LuaContext::Reader<boost::optional<TType>>
     }
 };
 
+#if __cplusplus >= 201703L
 // NOLINTBEGIN(clang-analyzer-cplusplus.NewDeleteLeaks)
 template<typename TType>
 struct LuaContext::Reader<std::optional<TType>>
@@ -2960,8 +2988,9 @@ struct LuaContext::Reader<std::optional<TType>>
     }
 };
 // NOLINTEND(clang-analyzer-cplusplus.NewDeleteLeaks)
+#endif /* C++ 17 */
 
-// variant
+// boost::variant
 template<typename... TTypes>
 struct LuaContext::Reader<boost::variant<TTypes...>>
 {
@@ -3008,6 +3037,42 @@ struct LuaContext::Reader<boost::variant<TTypes...>>
     }
 };
 
+#if __cplusplus >= 201703L
+// std::variant
+template<typename... TTypes>
+struct LuaContext::Reader<std::variant<TTypes...>>
+{
+    using ReturnType = std::variant<TTypes...>;
+
+private:
+    template<std::size_t I = 0> static boost::optional<ReturnType> variantRead(lua_State* state, int index)
+    {
+        constexpr auto nbTypes = std::variant_size_v<ReturnType>;
+        if constexpr (I >= nbTypes) {
+            return boost::none;
+        }
+        using InitialType = std::variant_alternative_t<I, ReturnType>;
+        using DecayedType = std::decay_t<InitialType>;
+        if (const auto val = Reader<DecayedType>::read(state, index)) {
+            // we are using the initial, non-decayed type so that a
+            // cv-qualifiers are not ignored
+            return ReturnType{std::in_place_type<InitialType>, *val};
+        }
+        if constexpr (I < (nbTypes - 1)) {
+            return variantRead<I + 1>(state, index);
+        }
+        return boost::none;
+    }
+
+public:
+    static auto read(lua_State* state, int index)
+        -> boost::optional<ReturnType>
+    {
+        return variantRead(state, index);
+    }
+};
+#endif /* C++ 17 */
+
 // reading a tuple
 // tuple have an additional argument for their functions, that is the maximum size to read
 // if maxSize is smaller than the tuple size, then the remaining parameters will be left to default value

pdns/test-luawrapper.cc

@@ -70,4 +70,64 @@ BOOST_AUTO_TEST_CASE(test_std_optional)
   }
 }
 
+BOOST_AUTO_TEST_CASE(test_boost_variant)
+{
+  using MyVariantType = boost::variant<int, const std::string, std::string, std::string*>;
+
+  LuaContext context;
+  context.writeFunction("testVariant", [](MyVariantType incoming) -> MyVariantType {
+    return incoming;
+  });
+
+  {
+    auto result = context.executeCode<MyVariantType>("return testVariant(1)");
+    const auto* content = boost::get<int>(&result);
+    BOOST_REQUIRE(content);
+    BOOST_CHECK_EQUAL(*content, 1);
+  }
+
+  {
+    auto result = context.executeCode<MyVariantType>("return testVariant('foo')");
+    const auto* content = boost::get<const std::string>(&result);
+    BOOST_REQUIRE(content);
+    BOOST_CHECK_EQUAL(*content, "foo");
+  }
+
+  {
+    auto func = [&]() {
+      context.executeCode<MyVariantType>("return testVariant(nil)");
+    };
+    BOOST_CHECK_THROW(func(), LuaContext::ExecutionErrorException);
+  }
+}
+
+BOOST_AUTO_TEST_CASE(test_std_variant)
+{
+  using MyVariantType = std::variant<int, const std::string, std::string, std::string*>;
+
+  LuaContext context;
+  context.writeFunction("testVariant", [](MyVariantType incoming) -> MyVariantType {
+    return incoming;
+  });
+
+  {
+    const auto result = context.executeCode<MyVariantType>("return testVariant(1)");
+    BOOST_REQUIRE(std::holds_alternative<int>(result));
+    BOOST_CHECK_EQUAL(std::get<int>(result), 1);
+  }
+
+  {
+    const auto result = context.executeCode<MyVariantType>("return testVariant('foo')");
+    BOOST_REQUIRE(std::holds_alternative<const std::string>(result));
+    BOOST_CHECK_EQUAL(std::get<const std::string>(result), "foo");
+  }
+
+  {
+    auto func = [&]() {
+      context.executeCode<MyVariantType>("return testVariant(nil)");
+    };
+    BOOST_CHECK_THROW(func(), LuaContext::ExecutionErrorException);
+  }
+}
+
 BOOST_AUTO_TEST_SUITE_END()