From a87c1885cb784ea5b884ed6dd1c96e39b7b4ec64 Mon Sep 17 00:00:00 2001
From: Florian Albrechtskirchinger <falbrechtskirchinger@gmail.com>
Date: Thu, 28 Jul 2022 21:52:23 +0200
Subject: [PATCH] Re-add value_type detection to distinguish string types
 (#3604)

* Re-add value_type detection to is_constructible_string_type trait

* Add value_type detection to from_json for strings
---
 include/nlohmann/detail/conversions/from_json.hpp | 1 +
 include/nlohmann/detail/meta/type_traits.hpp      | 6 ++++--
 single_include/nlohmann/json.hpp                  | 7 +++++--
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/include/nlohmann/detail/conversions/from_json.hpp b/include/nlohmann/detail/conversions/from_json.hpp
index f1df783e5..af2abddbf 100644
--- a/include/nlohmann/detail/conversions/from_json.hpp
+++ b/include/nlohmann/detail/conversions/from_json.hpp
@@ -117,6 +117,7 @@ template <
     typename BasicJsonType, typename StringType,
     enable_if_t <
         std::is_assignable<StringType&, const typename BasicJsonType::string_t>::value
+        && is_detected_exact<typename BasicJsonType::string_t::value_type, value_type_t, StringType>::value
         && !std::is_same<typename BasicJsonType::string_t, StringType>::value
         && !is_json_ref<StringType>::value, int > = 0 >
 inline void from_json(const BasicJsonType& j, StringType& s)
diff --git a/include/nlohmann/detail/meta/type_traits.hpp b/include/nlohmann/detail/meta/type_traits.hpp
index 11bf3c12a..796d5b0cd 100644
--- a/include/nlohmann/detail/meta/type_traits.hpp
+++ b/include/nlohmann/detail/meta/type_traits.hpp
@@ -363,8 +363,10 @@ struct is_constructible_string_type
 #endif
 
     static constexpr auto value =
-        is_constructible<laundered_type,
-        typename BasicJsonType::string_t>::value;
+        conjunction <
+        is_constructible<laundered_type, typename BasicJsonType::string_t>,
+        is_detected_exact<typename BasicJsonType::string_t::value_type,
+        value_type_t, laundered_type >>::value;
 };
 
 template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 36481050e..78b41822e 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -3651,8 +3651,10 @@ struct is_constructible_string_type
 #endif
 
     static constexpr auto value =
-        is_constructible<laundered_type,
-        typename BasicJsonType::string_t>::value;
+        conjunction <
+        is_constructible<laundered_type, typename BasicJsonType::string_t>,
+        is_detected_exact<typename BasicJsonType::string_t::value_type,
+        value_type_t, laundered_type >>::value;
 };
 
 template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
@@ -4478,6 +4480,7 @@ template <
     typename BasicJsonType, typename StringType,
     enable_if_t <
         std::is_assignable<StringType&, const typename BasicJsonType::string_t>::value
+        && is_detected_exact<typename BasicJsonType::string_t::value_type, value_type_t, StringType>::value
         && !std::is_same<typename BasicJsonType::string_t, StringType>::value
         && !is_json_ref<StringType>::value, int > = 0 >
 inline void from_json(const BasicJsonType& j, StringType& s)