From 11fecc25af64529599e9a24675651115d6bae322 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Th=C3=A9o=20DELRIEU?= <theo.delrieu@tanker.io>
Date: Fri, 12 Oct 2018 10:54:58 +0200
Subject: [PATCH] add constraints for variadic json_ref constructors

Fixes #1292
---
 include/nlohmann/detail/json_ref.hpp | 12 ++++++++----
 single_include/nlohmann/json.hpp     | 13 +++++++++----
 test/src/unit-regression.cpp         | 16 ++++++++++++++++
 3 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/include/nlohmann/detail/json_ref.hpp b/include/nlohmann/detail/json_ref.hpp
index f9dba5de..c8dec733 100644
--- a/include/nlohmann/detail/json_ref.hpp
+++ b/include/nlohmann/detail/json_ref.hpp
@@ -3,6 +3,8 @@
 #include <initializer_list>
 #include <utility>
 
+#include <nlohmann/detail/meta/type_traits.hpp>
+
 namespace nlohmann
 {
 namespace detail
@@ -25,10 +27,12 @@ class json_ref
         : owned_value(init), value_ref(&owned_value), is_rvalue(true)
     {}
 
-    template<class... Args>
-    json_ref(Args&& ... args)
-        : owned_value(std::forward<Args>(args)...), value_ref(&owned_value), is_rvalue(true)
-    {}
+    template <
+        class... Args,
+        enable_if_t<std::is_constructible<value_type, Args...>::value, int> = 0 >
+    json_ref(Args && ... args)
+        : owned_value(std::forward<Args>(args)...), value_ref(&owned_value),
+          is_rvalue(true) {}
 
     // class should be movable only
     json_ref(json_ref&&) = default;
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index af1c8546..dc206d30 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -10591,6 +10591,9 @@ class serializer
 #include <initializer_list>
 #include <utility>
 
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
+
 namespace nlohmann
 {
 namespace detail
@@ -10613,10 +10616,12 @@ class json_ref
         : owned_value(init), value_ref(&owned_value), is_rvalue(true)
     {}
 
-    template<class... Args>
-    json_ref(Args&& ... args)
-        : owned_value(std::forward<Args>(args)...), value_ref(&owned_value), is_rvalue(true)
-    {}
+    template <
+        class... Args,
+        enable_if_t<std::is_constructible<value_type, Args...>::value, int> = 0 >
+    json_ref(Args && ... args)
+        : owned_value(std::forward<Args>(args)...), value_ref(&owned_value),
+          is_rvalue(true) {}
 
     // class should be movable only
     json_ref(json_ref&&) = default;
diff --git a/test/src/unit-regression.cpp b/test/src/unit-regression.cpp
index fe4913cb..98a53a50 100644
--- a/test/src/unit-regression.cpp
+++ b/test/src/unit-regression.cpp
@@ -33,6 +33,14 @@ SOFTWARE.
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
+#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
+    #define JSON_HAS_CPP_17
+#endif
+
+#ifdef JSON_HAS_CPP_17
+    #include <variant>
+#endif
+
 #include "fifo_map.hpp"
 
 #include <fstream>
@@ -1649,4 +1657,12 @@ TEST_CASE("regression tests")
 
         CHECK(diffs.size() == 1); // Note the change here, was 2
     }
+
+#ifdef JSON_HAS_CPP_17
+    SECTION("issue #1292 - Serializing std::variant causes stack overflow")
+    {
+        static_assert(
+            not std::is_constructible<json, std::variant<int, float>>::value, "");
+    }
+#endif
 }