meta: rework is_compatible/is_constructible_string_type

These type traits performed an incorrect and insufficient check. Converting to a std::filesystem::path used to work by accident thanks to these brittle constraints, but the clean-up performed in nlohmann#3020 broke them.
theodelrieu · Oct 13, 2021 · a12ee7f · a12ee7f
1 parent 4b1cb9e
commit a12ee7f
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Showing 2 changed files with 4 additions and 50 deletions.
diff --git a/include/nlohmann/detail/meta/type_traits.hpp b/include/nlohmann/detail/meta/type_traits.hpp
@@ -309,44 +309,21 @@ struct is_constructible_object_type
     : is_constructible_object_type_impl<BasicJsonType,
       ConstructibleObjectType> {};
 
-template<typename BasicJsonType, typename CompatibleStringType,
-         typename = void>
-struct is_compatible_string_type_impl : std::false_type {};
-
 template<typename BasicJsonType, typename CompatibleStringType>
-struct is_compatible_string_type_impl <
-    BasicJsonType, CompatibleStringType,
-    enable_if_t<is_detected_convertible<typename BasicJsonType::string_t::value_type,
-    range_value_t,
-    CompatibleStringType>::value >>
+struct is_compatible_string_type
 {
     static constexpr auto value =
         is_constructible<typename BasicJsonType::string_t, CompatibleStringType>::value;
 };
 
 template<typename BasicJsonType, typename ConstructibleStringType>
-struct is_compatible_string_type
-    : is_compatible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
-
-template<typename BasicJsonType, typename ConstructibleStringType,
-         typename = void>
-struct is_constructible_string_type_impl : std::false_type {};
-
-template<typename BasicJsonType, typename ConstructibleStringType>
-struct is_constructible_string_type_impl <
-    BasicJsonType, ConstructibleStringType,
-    enable_if_t<is_detected_exact<typename BasicJsonType::string_t::value_type,
-    value_type_t, ConstructibleStringType>::value >>
+struct is_constructible_string_type
 {
     static constexpr auto value =
         is_constructible<ConstructibleStringType,
         typename BasicJsonType::string_t>::value;
 };
 
-template<typename BasicJsonType, typename ConstructibleStringType>
-struct is_constructible_string_type
-    : is_constructible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
-
 template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
 struct is_compatible_array_type_impl : std::false_type {};
 

diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
@@ -3783,44 +3783,21 @@ struct is_constructible_object_type
     : is_constructible_object_type_impl<BasicJsonType,
       ConstructibleObjectType> {};
 
-template<typename BasicJsonType, typename CompatibleStringType,
-         typename = void>
-struct is_compatible_string_type_impl : std::false_type {};
-
 template<typename BasicJsonType, typename CompatibleStringType>
-struct is_compatible_string_type_impl <
-    BasicJsonType, CompatibleStringType,
-    enable_if_t<is_detected_convertible<typename BasicJsonType::string_t::value_type,
-    range_value_t,
-    CompatibleStringType>::value >>
+struct is_compatible_string_type
 {
     static constexpr auto value =
         is_constructible<typename BasicJsonType::string_t, CompatibleStringType>::value;
 };
 
 template<typename BasicJsonType, typename ConstructibleStringType>
-struct is_compatible_string_type
-    : is_compatible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
-
-template<typename BasicJsonType, typename ConstructibleStringType,
-         typename = void>
-struct is_constructible_string_type_impl : std::false_type {};
-
-template<typename BasicJsonType, typename ConstructibleStringType>
-struct is_constructible_string_type_impl <
-    BasicJsonType, ConstructibleStringType,
-    enable_if_t<is_detected_exact<typename BasicJsonType::string_t::value_type,
-    value_type_t, ConstructibleStringType>::value >>
+struct is_constructible_string_type
 {
     static constexpr auto value =
         is_constructible<ConstructibleStringType,
         typename BasicJsonType::string_t>::value;
 };
 
-template<typename BasicJsonType, typename ConstructibleStringType>
-struct is_constructible_string_type
-    : is_constructible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
-
 template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
 struct is_compatible_array_type_impl : std::false_type {};