Merge branch 'develop' into claude/issue-5066-24ba30

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json/basic_json.md

@@ -272,15 +272,6 @@ basic_json(basic_json&& other) noexcept;
         When used without parentheses around an empty initializer list, `basic_json()` is called instead of this
         function, yielding the JSON `#!json null` value.
 
-- Overload 4:
-
-    !!! info "Implicit conversion"
-
-        The conversion is implicit unless [`JSON_USE_IMPLICIT_CONVERSIONS`](../macros/json_use_implicit_conversions.md)
-        is defined to `0` and `BasicJsonType::string_t` differs from `string_t`. In that case, the constructor is
-        `explicit`, so a JSON value with a different string type is no longer silently converted, for example when it is
-        passed to a function taking `#!cpp const json&`. Write `#!cpp json(other)` or `#!cpp other.get<json>()` instead.
-
 - Overload 7:
 
     !!! info "Preconditions"
@@ -429,8 +420,7 @@ basic_json(basic_json&& other) noexcept;
 1. Since version 1.0.0.
 2. Since version 1.0.0.
 3. Since version 2.1.0.
-4. Since version 3.2.0. Explicit for different string types if `JSON_USE_IMPLICIT_CONVERSIONS` is `0` since
-   version 3.13.0.
+4. Since version 3.2.0.
 5. Since version 1.0.0.
 6. Since version 1.0.0.
 7. Since version 1.0.0.

docs/mkdocs/docs/api/macros/json_use_implicit_conversions.md

@@ -5,9 +5,7 @@
 ```
 
 When defined to `0`, implicit conversions are switched off. By default, implicit conversions are switched on. The
-value directly affects [`operator ValueType`](../basic_json/operator_ValueType.md) and the
-[converting constructor](../basic_json/basic_json.md) from a `basic_json` specialization with a different string
-type (overload 4).
+value directly affects [`operator ValueType`](../basic_json/operator_ValueType.md).
 
 ## Default definition
 
@@ -59,25 +57,6 @@ By default, implicit conversions are enabled.
     auto s = j.get<std::string>();
     ```
 
-??? example "Conversion between `basic_json` specializations"
-
-    A `basic_json` specialization with a different string type is also no longer converted implicitly when
-    `JSON_USE_IMPLICIT_CONVERSIONS` is defined to `0`:
-
-    ```cpp
-    using wjson = nlohmann::basic_json<std::map, std::vector, std::wstring>;
-
-    void load(const nlohmann::json& j);
-
-    wjson wj = /* ... */;
-    load(wj);                            // error: no implicit conversion
-    load(nlohmann::json(wj));            // OK: explicit conversion
-    load(wj.get<nlohmann::json>());      // OK: explicit conversion
-    ```
-
-    Specializations that share the same string type, such as `json` and `ordered_json`, remain implicitly
-    convertible.
-
 ## See also
 
 - [**operator ValueType**](../basic_json/operator_ValueType.md) - get a value (implicit)
@@ -87,4 +66,3 @@ By default, implicit conversions are enabled.
 ## Version history
 
 - Added in version 3.9.0.
-- Also affects the conversion between `basic_json` specializations with different string types since version 3.13.0.

include/nlohmann/detail/conversions/to_json.hpp

@@ -291,9 +291,7 @@ void to_json(BasicJsonType& j, const std::optional<T>& opt) noexcept
 {
     if (opt.has_value())
     {
-        // explicit construction, as the conversion from a basic_json with a different
-        // string type is explicit if JSON_USE_IMPLICIT_CONVERSIONS is 0 (#2649)
-        j = BasicJsonType(*opt);
+        j = *opt;
     }
     else
     {

include/nlohmann/json.hpp

@@ -1605,42 +1605,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         assert_invariant();
     }
 
-  private:
-    /// whether a basic_json specialization can be converted implicitly into this one;
-    /// with JSON_USE_IMPLICIT_CONVERSIONS set to 0, this is only the case if both share
-    /// the same string type (see https://github.com/nlohmann/json/issues/2649)
-    template<typename BasicJsonType>
-    using is_implicitly_convertible_basic_json = std::integral_constant < bool,
-          (JSON_USE_IMPLICIT_CONVERSIONS != 0)
-          || std::is_same<typename BasicJsonType::string_t, string_t>::value >;
-
-    /// tag to select the constructor that performs the conversion from another basic_json specialization
-    struct convert_basic_json_tag {};
-
-  public:
     /// @brief create a JSON value from an existing one
     /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     template < typename BasicJsonType,
                detail::enable_if_t <
-                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value
-                   && is_implicitly_convertible_basic_json<BasicJsonType>::value, int > = 0 >
+                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value, int > = 0 >
     basic_json(const BasicJsonType& val)
-        : basic_json(val, convert_basic_json_tag{})
-    {}
-
-    /// @brief create a JSON value from an existing one
-    /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
-    template < typename BasicJsonType,
-               detail::enable_if_t <
-                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value
-                   && !is_implicitly_convertible_basic_json<BasicJsonType>::value, int > = 0 >
-    explicit basic_json(const BasicJsonType& val)
-        : basic_json(val, convert_basic_json_tag{})
-    {}
-
-  private:
-    template<typename BasicJsonType>
-    basic_json(const BasicJsonType& val, convert_basic_json_tag /*unused*/)
 #if JSON_DIAGNOSTIC_POSITIONS
         : start_position(val.start_pos()),
           end_position(val.end_pos())
@@ -1696,7 +1666,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         assert_invariant();
     }
 
-  public:
     /// @brief create a container (array or object) from an initializer list
     /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     basic_json(initializer_list_t init,
@@ -2463,7 +2432,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                    int > = 0 >
     BasicJsonType get_impl(detail::priority_tag<2> /*unused*/) const
     {
-        return BasicJsonType(*this);
+        return *this;
     }
 
     /*!
@@ -2602,7 +2571,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                  int> = 0>
     ValueType & get_to(ValueType& v) const
     {
-        v = ValueType(*this);
+        v = *this;
         return v;
     }
 

single_include/nlohmann/json.hpp

@@ -6820,9 +6820,7 @@ void to_json(BasicJsonType& j, const std::optional<T>& opt) noexcept
 {
     if (opt.has_value())
     {
-        // explicit construction, as the conversion from a basic_json with a different
-        // string type is explicit if JSON_USE_IMPLICIT_CONVERSIONS is 0 (#2649)
-        j = BasicJsonType(*opt);
+        j = *opt;
     }
     else
     {
@@ -27490,42 +27488,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         assert_invariant();
     }
 
-  private:
-    /// whether a basic_json specialization can be converted implicitly into this one;
-    /// with JSON_USE_IMPLICIT_CONVERSIONS set to 0, this is only the case if both share
-    /// the same string type (see https://github.com/nlohmann/json/issues/2649)
-    template<typename BasicJsonType>
-    using is_implicitly_convertible_basic_json = std::integral_constant < bool,
-        (JSON_USE_IMPLICIT_CONVERSIONS != 0)
-        || std::is_same<typename BasicJsonType::string_t, string_t>::value >;
-
-    /// tag to select the constructor that performs the conversion from another basic_json specialization
-    struct convert_basic_json_tag {};
-
-  public:
     /// @brief create a JSON value from an existing one
     /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     template < typename BasicJsonType,
                detail::enable_if_t <
-                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value
-                   && is_implicitly_convertible_basic_json<BasicJsonType>::value, int > = 0 >
+                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value, int > = 0 >
     basic_json(const BasicJsonType& val)
-        : basic_json(val, convert_basic_json_tag{})
-    {}
-
-    /// @brief create a JSON value from an existing one
-    /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
-    template < typename BasicJsonType,
-               detail::enable_if_t <
-                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value
-                   && !is_implicitly_convertible_basic_json<BasicJsonType>::value, int > = 0 >
-    explicit basic_json(const BasicJsonType& val)
-        : basic_json(val, convert_basic_json_tag{})
-    {}
-
-  private:
-    template<typename BasicJsonType>
-    basic_json(const BasicJsonType& val, convert_basic_json_tag /*unused*/)
 #if JSON_DIAGNOSTIC_POSITIONS
         : start_position(val.start_pos()),
           end_position(val.end_pos())
@@ -27581,7 +27549,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         assert_invariant();
     }
 
-  public:
     /// @brief create a container (array or object) from an initializer list
     /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     basic_json(initializer_list_t init,
@@ -28348,7 +28315,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                    int > = 0 >
     BasicJsonType get_impl(detail::priority_tag<2> /*unused*/) const
     {
-        return BasicJsonType(*this);
+        return *this;
     }
 
     /*!
@@ -28487,7 +28454,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                  int> = 0>
     ValueType & get_to(ValueType& v) const
     {
-        v = ValueType(*this);
+        v = *this;
         return v;
     }
 

tests/src/unit-alt-string.cpp

@@ -13,7 +13,6 @@
 
 #include <cstdint>
 #include <string>
-#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -375,39 +374,4 @@ TEST_CASE("alternative string type")
         const auto j2 = j.flatten();
         CHECK(j2.dump() == R"({"/foo/0":"bar","/foo/1":"baz"})");
     }
-
-    SECTION("conversion between basic_json specializations (#2649)")
-    {
-        // explicit conversions are always possible
-        CHECK(std::is_constructible<nlohmann::json, alt_json>::value);
-        CHECK(std::is_constructible<alt_json, nlohmann::json>::value);
-        CHECK(std::is_constructible<nlohmann::json, nlohmann::ordered_json>::value);
-        CHECK(std::is_constructible<nlohmann::ordered_json, nlohmann::json>::value);
-
-        // specializations with the same string type are implicitly convertible
-        CHECK(std::is_convertible<nlohmann::ordered_json, nlohmann::json>::value);
-        CHECK(std::is_convertible<nlohmann::json, nlohmann::ordered_json>::value);
-
-        // specializations with different string types are only implicitly convertible
-        // if implicit conversions are enabled
-#if JSON_USE_IMPLICIT_CONVERSIONS
-        CHECK(std::is_convertible<alt_json, nlohmann::json>::value);
-        CHECK(std::is_convertible<nlohmann::json, alt_json>::value);
-#else
-        CHECK_FALSE(std::is_convertible<alt_json, nlohmann::json>::value);
-        CHECK_FALSE(std::is_convertible<nlohmann::json, alt_json>::value);
-#endif
-
-        // get<BasicJsonType>() works in either case
-        const nlohmann::json j = {{"foo", 1}, {"bar", true}};
-        CHECK(j.get<nlohmann::ordered_json>() == nlohmann::ordered_json(j));
-        // (only a number is converted here, as objects and strings are affected by #3425)
-        CHECK(nlohmann::json(42).get<alt_json>() == 42);
-        CHECK(alt_json(nlohmann::json(42)) == 42);
-
-        // get_to() also works in either case
-        alt_json a;
-        nlohmann::json(42).get_to(a);
-        CHECK(a == 42);
-    }
 }

tests/src/unit-regression2.cpp

@@ -766,6 +766,20 @@ TEST_CASE("regression tests 2")
         CHECK(j == k);
     }
 
+#ifdef JSON_HAS_CPP_17
+    SECTION("issue #5066 - MSVC converts json to std::variant<json> via the conversion operator")
+    {
+        // std::variant<json> must not be retrievable via get<>(), because otherwise the
+        // implicit conversion operator becomes a candidate that MSVC picks over the variant's
+        // converting constructor, routing a number through the string from_json overload
+        static_assert(!nlohmann::detail::is_detected<nlohmann::detail::get_template_function, const json&, std::variant<json>>::value,
+                      "std::variant<json> must not be retrievable via get<>()");
+
+        std::vector<std::variant<json>> v;
+        v.push_back(json(1));
+        CHECK(std::get<0>(v[0]) == 1);
+    }
+#endif
 }
 
 TEST_CASE("regression test - parser callback must not lose a duplicate key's prior value")