Merge branch 'develop' into claude/fix-issue-2649-738aba

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

README.md

@@ -363,7 +363,7 @@ std::cout << j_string << " == " << serialized_string << std::endl;
 
 [`.dump()`](https://json.nlohmann.me/api/basic_json/dump/) returns the originally stored string value.
 
-Note the library only supports UTF-8. When you store strings with different encodings in the library, calling [`dump()`](https://json.nlohmann.me/api/basic_json/dump/) may throw an exception unless `json::error_handler_t::replace`, `json::error_handler_t::ignore`, or `json::error_handler_t::keep` are used as error handlers.
+Note the library only supports UTF-8. When you store strings with different encodings in the library, calling [`dump()`](https://json.nlohmann.me/api/basic_json/dump/) may throw an exception unless `json::error_handler_t::replace` or `json::error_handler_t::ignore` are used as error handlers.
 
 #### To/from streams (e.g., files, string streams)
 
@@ -1915,7 +1915,7 @@ The library supports **Unicode input** as follows:
 - [Unicode noncharacters](https://www.unicode.org/faq/private_use.html#nonchar1) will not be replaced by the library.
 - Invalid surrogates (e.g., incomplete pairs such as `\uDEAD`) will yield parse errors.
 - The strings stored in the library are UTF-8 encoded. When using the default string type (`std::string`), note that its length/size functions return the number of stored bytes rather than the number of characters or glyphs.
-- When you store strings with different encodings in the library, calling [`dump()`](https://json.nlohmann.me/api/basic_json/dump/) may throw an exception unless `json::error_handler_t::replace`, `json::error_handler_t::ignore`, or `json::error_handler_t::keep` are used as error handlers.
+- When you store strings with different encodings in the library, calling [`dump()`](https://json.nlohmann.me/api/basic_json/dump/) may throw an exception unless `json::error_handler_t::replace` or `json::error_handler_t::ignore` are used as error handlers.
 - To store wide strings (e.g., `std::wstring`), you need to convert them to a UTF-8 encoded `std::string` before, see [an example](https://json.nlohmann.me/home/faq/#wide-string-handling).
 
 ### Comments in JSON

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

@@ -272,6 +272,15 @@ 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"
@@ -420,7 +429,8 @@ 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.
+4. Since version 3.2.0. Explicit for different string types if `JSON_USE_IMPLICIT_CONVERSIONS` is `0` since
+   version 3.13.0.
 5. Since version 1.0.0.
 6. Since version 1.0.0.
 7. Since version 1.0.0.

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

@@ -25,15 +25,10 @@ and `ensure_ascii` parameters.
     result consists of ASCII characters only.
 
 `error_handler` (in)
-:   how to react on decoding errors; there are four possible values (see [`error_handler_t`](error_handler_t.md)):
-
-    - `strict`: throw a [`type_error`](../../home/exceptions.md#type-errors) exception in case a decoding error occurs
-      (default),
-    - `replace`: replace invalid UTF-8 sequences with U+FFFD (� REPLACEMENT CHARACTER),
-    - `ignore`: ignore invalid UTF-8 sequences during serialization; all valid bytes are copied to the output unchanged,
-      and invalid bytes are dropped, and
-    - `keep`: keep invalid UTF-8 sequences during serialization; all bytes are copied to the output unchanged, so the
-      result is not valid UTF-8.
+:   how to react on decoding errors; there are three possible values (see [`error_handler_t`](error_handler_t.md):
+    `strict` (throws an exception in case a decoding error occurs; default), `replace` (replace invalid UTF-8 sequences
+    with U+FFFD), and `ignore` (ignore invalid UTF-8 sequences during serialization; all valid bytes are copied to the
+    output unchanged, and invalid bytes are dropped)).
     
 ## Return value
 
@@ -99,4 +94,3 @@ Binary values are serialized as an object containing two keys:
 - Indentation character `indent_char`, option `ensure_ascii` and exceptions added in version 3.0.0.
 - Error handlers added in version 3.4.0.
 - Serialization of binary values added in version 3.8.0.
-- Error handler value `keep` added in version 3.13.0.

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

@@ -4,13 +4,12 @@
 enum class error_handler_t {
     strict,
     replace,
-    ignore,
-    keep
+    ignore
 };
 ```
 
 This enumeration is used in the [`dump`](dump.md) function to choose how to treat decoding errors while serializing a
-`basic_json` value. Four values are differentiated:
+`basic_json` value. Three values are differentiated:
 
 strict
 :   throw a `type_error` exception in case of invalid UTF-8
@@ -21,12 +20,6 @@ replace
 ignore
 :   ignore invalid UTF-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped
 
-keep
-:   keep invalid UTF-8 sequences; all bytes are copied to the output unchanged. Valid characters are still escaped as
-    usual (e.g., `"`, `\\`, and control characters), so the result has valid JSON syntax, but it is not valid UTF-8.
-    In particular, [`parse`](parse.md) rejects it, and with `ensure_ascii` set to `true`, the invalid bytes are the
-    only non-ASCII bytes of the output.
-
 ## Examples
 
 ??? example
@@ -47,4 +40,3 @@ keep
 ## Version history
 
 - Added in version 3.4.0.
-- Added value `keep` in version 3.13.0.

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

@@ -5,7 +5,9 @@
 ```
 
 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).
+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).
 
 ## Default definition
 
@@ -57,6 +59,25 @@ 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)
@@ -66,3 +87,4 @@ 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.

docs/mkdocs/docs/examples/error_handler_t.cpp

@@ -1,4 +1,3 @@
-#include <iomanip>
 #include <iostream>
 #include <nlohmann/json.hpp>
 
@@ -22,12 +21,4 @@ int main()
               << "\nstring with ignored invalid characters: "
               << j_invalid.dump(-1, ' ', false, json::error_handler_t::ignore)
               << '\n';
-
-    // the invalid byte is kept; print the result byte-wise to make it visible
-    std::cout << "string with kept invalid characters:";
-    for (const unsigned char c : j_invalid.dump(-1, ' ', false, json::error_handler_t::keep))
-    {
-        std::cout << ' ' << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(c);
-    }
-    std::cout << '\n';
 }

docs/mkdocs/docs/examples/error_handler_t.output

@@ -1,4 +1,3 @@
 [json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9
 string with replaced invalid characters: "ä�ü"
 string with ignored invalid characters: "äü"
-string with kept invalid characters: 22 c3 a4 a9 c3 bc 22

docs/mkdocs/docs/features/serialization.md

@@ -64,7 +64,6 @@ serialization fails by default. The fourth argument of `dump` selects an
 - `strict` (default) — throw a [`type_error.316`](../home/exceptions.md#jsonexceptiontype_error316) exception.
 - `replace` — replace invalid bytes with the Unicode replacement character U+FFFD (`�`).
 - `ignore` — silently drop invalid bytes.
-- `keep` — copy invalid bytes to the output unchanged; the result is not valid UTF-8.
 
 ??? example
 

docs/mkdocs/docs/home/exceptions.md

@@ -755,7 +755,6 @@ The `dump()` function only works with UTF-8 encoded strings; that is, if you ass
     - Pass an error handler as last parameter to the `dump()` function to avoid this exception:
         - `json::error_handler_t::replace` will replace invalid bytes sequences with `U+FFFD` 
         - `json::error_handler_t::ignore` will silently ignore invalid byte sequences
-        - `json::error_handler_t::keep` will copy invalid byte sequences to the output unchanged
 
 ### json.exception.type_error.317
 

docs/mkdocs/docs/home/faq.md

@@ -85,7 +85,7 @@ The library supports **Unicode input** as follows:
 - The library will not replace [Unicode noncharacters](http://www.unicode.org/faq/private_use.html#nonchar1).
 - Invalid surrogates (e.g., incomplete pairs such as `\uDEAD`) will yield parse errors.
 - The strings stored in the library are UTF-8 encoded. When using the default string type (`std::string`), note that its length/size functions return the number of stored bytes rather than the number of characters or glyphs.
-- When you store strings with different encodings in the library, calling [`dump()`](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a50ec80b02d0f3f51130d4abb5d1cfdc5.html#a50ec80b02d0f3f51130d4abb5d1cfdc5) may throw an exception unless `json::error_handler_t::replace`, `json::error_handler_t::ignore`, or `json::error_handler_t::keep` are used as error handlers.
+- When you store strings with different encodings in the library, calling [`dump()`](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a50ec80b02d0f3f51130d4abb5d1cfdc5.html#a50ec80b02d0f3f51130d4abb5d1cfdc5) may throw an exception unless `json::error_handler_t::replace` or `json::error_handler_t::ignore` are used as error handlers.
 
 In most cases, the parser is right to complain, because the input is not UTF-8 encoded. This is especially true for Microsoft Windows, where Latin-1 or ISO 8859-1 is often the standard encoding.
 

include/nlohmann/detail/conversions/to_json.hpp

@@ -291,7 +291,9 @@ void to_json(BasicJsonType& j, const std::optional<T>& opt) noexcept
 {
     if (opt.has_value())
     {
-        j = *opt;
+        // 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);
     }
     else
     {

include/nlohmann/detail/output/serializer.hpp

@@ -48,8 +48,7 @@ enum class error_handler_t
 {
     strict,  ///< throw a type_error exception in case of invalid UTF-8
     replace, ///< replace invalid UTF-8 sequences with U+FFFD
-    ignore,  ///< ignore invalid UTF-8 sequences
-    keep     ///< keep invalid UTF-8 sequences; their bytes are copied unchanged
+    ignore   ///< ignore invalid UTF-8 sequences
 };
 
 template<typename BasicJsonType>
@@ -1020,47 +1019,6 @@ class serializer
                             break;
                         }
 
-                        case error_handler_t::keep:
-                        {
-                            // drop whatever the incomplete sequence left in
-                            // the buffer (only copied if !EnsureAscii) and copy
-                            // the ill-formed bytes from the input instead
-                            bytes = bytes_after_last_accept;
-
-                            if (undumped_chars > 0)
-                            {
-                                // the pending bytes of the incomplete sequence
-                                // are ill-formed; the current byte may be OK for
-                                // itself, so we would like to read it again
-                                for (std::size_t j = i - undumped_chars; j < i; ++j)
-                                {
-                                    string_buffer[bytes++] = s[j];
-                                }
-                                --i;
-                            }
-                            else
-                            {
-                                // the current byte cannot start any sequence
-                                string_buffer[bytes++] = s[i];
-                            }
-
-                            // write buffer and reset index; there must be 13 bytes
-                            // left, as this is the maximal number of bytes to be
-                            // written ("\uxxxx\uxxxx\0") for one code point
-                            if (string_buffer.size() - bytes < 13)
-                            {
-                                put_buffer(string_buffer, bytes);
-                                bytes = 0;
-                            }
-
-                            bytes_after_last_accept = bytes;
-                            undumped_chars = 0;
-
-                            // continue processing the string
-                            state = UTF8_ACCEPT;
-                            break;
-                        }
-
                         default:            // LCOV_EXCL_LINE
                             JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
                     }
@@ -1106,15 +1064,6 @@ class serializer
                     break;
                 }
 
-                case error_handler_t::keep:
-                {
-                    // write all accepted bytes
-                    put_buffer(string_buffer, bytes_after_last_accept);
-                    // copy the bytes of the incomplete sequence unchanged
-                    put_string(s, s.size() - undumped_chars, s.size());
-                    break;
-                }
-
                 case error_handler_t::replace:
                 {
                     // write all accepted bytes

include/nlohmann/json.hpp

@@ -1605,12 +1605,42 @@ 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, int > = 0 >
+                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value
+                   && is_implicitly_convertible_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())
@@ -1666,6 +1696,7 @@ 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,
@@ -2432,7 +2463,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                    int > = 0 >
     BasicJsonType get_impl(detail::priority_tag<2> /*unused*/) const
     {
-        return *this;
+        return BasicJsonType(*this);
     }
 
     /*!
@@ -2571,7 +2602,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                  int> = 0>
     ValueType & get_to(ValueType& v) const
     {
-        v = *this;
+        v = ValueType(*this);
         return v;
     }
 

single_include/nlohmann/json.hpp

@@ -6820,7 +6820,9 @@ void to_json(BasicJsonType& j, const std::optional<T>& opt) noexcept
 {
     if (opt.has_value())
     {
-        j = *opt;
+        // 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);
     }
     else
     {
@@ -23931,8 +23933,7 @@ enum class error_handler_t
 {
     strict,  ///< throw a type_error exception in case of invalid UTF-8
     replace, ///< replace invalid UTF-8 sequences with U+FFFD
-    ignore,  ///< ignore invalid UTF-8 sequences
-    keep     ///< keep invalid UTF-8 sequences; their bytes are copied unchanged
+    ignore   ///< ignore invalid UTF-8 sequences
 };
 
 template<typename BasicJsonType>
@@ -24903,47 +24904,6 @@ class serializer
                             break;
                         }
 
-                        case error_handler_t::keep:
-                        {
-                            // drop whatever the incomplete sequence left in
-                            // the buffer (only copied if !EnsureAscii) and copy
-                            // the ill-formed bytes from the input instead
-                            bytes = bytes_after_last_accept;
-
-                            if (undumped_chars > 0)
-                            {
-                                // the pending bytes of the incomplete sequence
-                                // are ill-formed; the current byte may be OK for
-                                // itself, so we would like to read it again
-                                for (std::size_t j = i - undumped_chars; j < i; ++j)
-                                {
-                                    string_buffer[bytes++] = s[j];
-                                }
-                                --i;
-                            }
-                            else
-                            {
-                                // the current byte cannot start any sequence
-                                string_buffer[bytes++] = s[i];
-                            }
-
-                            // write buffer and reset index; there must be 13 bytes
-                            // left, as this is the maximal number of bytes to be
-                            // written ("\uxxxx\uxxxx\0") for one code point
-                            if (string_buffer.size() - bytes < 13)
-                            {
-                                put_buffer(string_buffer, bytes);
-                                bytes = 0;
-                            }
-
-                            bytes_after_last_accept = bytes;
-                            undumped_chars = 0;
-
-                            // continue processing the string
-                            state = UTF8_ACCEPT;
-                            break;
-                        }
-
                         default:            // LCOV_EXCL_LINE
                             JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
                     }
@@ -24989,15 +24949,6 @@ class serializer
                     break;
                 }
 
-                case error_handler_t::keep:
-                {
-                    // write all accepted bytes
-                    put_buffer(string_buffer, bytes_after_last_accept);
-                    // copy the bytes of the incomplete sequence unchanged
-                    put_string(s, s.size() - undumped_chars, s.size());
-                    break;
-                }
-
                 case error_handler_t::replace:
                 {
                     // write all accepted bytes
@@ -27539,12 +27490,42 @@ 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, int > = 0 >
+                   detail::is_basic_json<BasicJsonType>::value&& !std::is_same<basic_json, BasicJsonType>::value
+                   && is_implicitly_convertible_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())
@@ -27600,6 +27581,7 @@ 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,
@@ -28366,7 +28348,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                    int > = 0 >
     BasicJsonType get_impl(detail::priority_tag<2> /*unused*/) const
     {
-        return *this;
+        return BasicJsonType(*this);
     }
 
     /*!
@@ -28505,7 +28487,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                  int> = 0>
     ValueType & get_to(ValueType& v) const
     {
-        v = *this;
+        v = ValueType(*this);
         return v;
     }
 

tests/src/unit-alt-string.cpp

@@ -13,6 +13,7 @@
 
 #include <cstdint>
 #include <string>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -374,4 +375,39 @@ 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

@@ -766,15 +766,6 @@ TEST_CASE("regression tests 2")
         CHECK(j == k);
     }
 
-    SECTION("issue #4552 - UTF-8 invalid characters are not always ignored when dumping with error_handler_t::ignore")
-    {
-        json node;
-        node["test"] = "test\334\005";
-        CHECK(node.dump(-1, ' ', false, json::error_handler_t::ignore) == "{\"test\":\"test\\u0005\"}");
-        CHECK(node.dump(-1, ' ', false, json::error_handler_t::keep) == "{\"test\":\"test\334\\u0005\"}");
-        CHECK(node.dump(-1, ' ', true, json::error_handler_t::keep) == "{\"test\":\"test\334\\u0005\"}");
-    }
-
 }
 
 TEST_CASE("regression test - parser callback must not lose a duplicate key's prior value")

tests/src/unit-serialization.cpp

@@ -92,8 +92,6 @@ TEST_CASE("serialization")
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"äü\"");
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"ä\xEF\xBF\xBDü\"");
             CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"\\u00e4\\ufffd\\u00fc\"");
-            CHECK(j.dump(-1, ' ', false, json::error_handler_t::keep) == "\"ä\xA9ü\"");
-            CHECK(j.dump(-1, ' ', true, json::error_handler_t::keep) == "\"\\u00e4\xA9\\u00fc\"");
         }
 
         SECTION("invalid character (regression guard for shared UTF-8 decoder, see #5529)")
@@ -116,8 +114,6 @@ TEST_CASE("serialization")
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"123\"");
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"123\xEF\xBF\xBD\"");
             CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"123\\ufffd\"");
-            CHECK(j.dump(-1, ' ', false, json::error_handler_t::keep) == "\"123\xC2\"");
-            CHECK(j.dump(-1, ' ', true, json::error_handler_t::keep) == "\"123\xC2\"");
         }
 
         SECTION("unexpected character")
@@ -130,39 +126,6 @@ TEST_CASE("serialization")
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"123456\"");
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"123\xEF\xBF\xBD\x34\x35\x36\"");
             CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"123\\ufffd456\"");
-            CHECK(j.dump(-1, ' ', false, json::error_handler_t::keep) == "\"123\xF1\xB0\x34\x35\x36\"");
-            CHECK(j.dump(-1, ' ', true, json::error_handler_t::keep) == "\"123\xF1\xB0\x34\x35\x36\"");
-        }
-
-        SECTION("keep: valid characters are still escaped")
-        {
-            // an invalid byte followed by characters that must be escaped
-            const json j = "\xC2\"\\\n\xFF\x05";
-            CHECK(j.dump(-1, ' ', false, json::error_handler_t::keep) == "\"\xC2\\\"\\\\\\n\xFF\\u0005\"");
-            CHECK(j.dump(-1, ' ', true, json::error_handler_t::keep) == "\"\xC2\\\"\\\\\\n\xFF\\u0005\"");
-        }
-
-        SECTION("keep: truncated multibyte sequences")
-        {
-            CHECK(json("\xF0\x9F\x98").dump(-1, ' ', false, json::error_handler_t::keep) == "\"\xF0\x9F\x98\"");
-            CHECK(json("\xF0\x9F\x98").dump(-1, ' ', true, json::error_handler_t::keep) == "\"\xF0\x9F\x98\"");
-            CHECK(json("\xF0\x9F\x98" "a").dump(-1, ' ', false, json::error_handler_t::keep) == "\"\xF0\x9F\x98" "a\"");
-            CHECK(json("\xF0\x9F\x98" "a").dump(-1, ' ', true, json::error_handler_t::keep) == "\"\xF0\x9F\x98" "a\"");
-        }
-
-        SECTION("keep: long string with many invalid bytes")
-        {
-            // exceeds the internal string buffer several times
-            std::string input;
-            std::string expected = "\"";
-            for (int i = 0; i < 2000; ++i)
-            {
-                input += "\xFF\xE2\x82\n\xC3\xA4";
-                expected += "\xFF\xE2\x82\\n\xC3\xA4";
-            }
-            expected += "\"";
-            const json j = input;
-            CHECK(j.dump(-1, ' ', false, json::error_handler_t::keep) == expected);
         }
 
         SECTION("U+FFFD Substitution of Maximal Subparts")

tests/src/unit-unicode2.cpp

@@ -14,7 +14,6 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
-#include <algorithm>
 #include <fstream>
 #include <sstream>
 #include <iostream>
@@ -76,11 +75,8 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     static std::string s_replaced2;
     static std::string s_replaced_ascii;
     static std::string s_replaced2_ascii;
-    static std::string s_kept;
-    static std::string s_kept2;
-    static std::string s_kept_ascii;
 
-    // dumping with ignore/replace/keep must not throw in any case
+    // dumping with ignore/replace must not throw in any case
     s_ignored = j.dump(-1, ' ', false, json::error_handler_t::ignore);
     s_ignored2 = j2.dump(-1, ' ', false, json::error_handler_t::ignore);
     s_ignored_ascii = j.dump(-1, ' ', true, json::error_handler_t::ignore);
@@ -89,9 +85,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     s_replaced2 = j2.dump(-1, ' ', false, json::error_handler_t::replace);
     s_replaced_ascii = j.dump(-1, ' ', true, json::error_handler_t::replace);
     s_replaced2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::replace);
-    s_kept = j.dump(-1, ' ', false, json::error_handler_t::keep);
-    s_kept2 = j2.dump(-1, ' ', false, json::error_handler_t::keep);
-    s_kept_ascii = j.dump(-1, ' ', true, json::error_handler_t::keep);
 
     if (success_expected)
     {
@@ -101,7 +94,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
         // all dumps should agree on the string
         CHECK(s_strict == s_ignored);
         CHECK(s_strict == s_replaced);
-        CHECK(s_strict == s_kept);
     }
     else
     {
@@ -113,20 +105,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
 
         // check that replace string contains a replacement character
         CHECK(s_replaced.find("\xEF\xBF\xBD") != std::string::npos);
-
-        // ignore drops the invalid bytes, keep copies them
-        CHECK(s_ignored != s_kept);
-        CHECK(s_ignored_ascii != s_kept_ascii);
-
-        // unless a byte needs escaping, keep copies the input unchanged
-        const bool needs_escaping = std::any_of(json_string.begin(), json_string.end(), [](char c)
-        {
-            return static_cast<unsigned char>(c) < 0x20 || c == '"' || c == '\\';
-        });
-        if (!needs_escaping)
-        {
-            CHECK(s_kept == "\"" + json_string + "\"");
-        }
     }
 
     // check that prefix and suffix are preserved
@@ -138,8 +116,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     CHECK(s_replaced2.substr(s_replaced2.size() - 4, 3) == "xyz");
     CHECK(s_replaced2_ascii.substr(1, 3) == "abc");
     CHECK(s_replaced2_ascii.substr(s_replaced2_ascii.size() - 4, 3) == "xyz");
-    CHECK(s_kept2.substr(1, 3) == "abc");
-    CHECK(s_kept2.substr(s_kept2.size() - 4, 3) == "xyz");
 }
 
 void check_utf8string(bool success_expected, int byte1, int byte2, int byte3, int byte4);

tests/src/unit-unicode3.cpp

@@ -14,7 +14,6 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
-#include <algorithm>
 #include <fstream>
 #include <sstream>
 #include <iostream>
@@ -76,11 +75,8 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     static std::string s_replaced2;
     static std::string s_replaced_ascii;
     static std::string s_replaced2_ascii;
-    static std::string s_kept;
-    static std::string s_kept2;
-    static std::string s_kept_ascii;
 
-    // dumping with ignore/replace/keep must not throw in any case
+    // dumping with ignore/replace must not throw in any case
     s_ignored = j.dump(-1, ' ', false, json::error_handler_t::ignore);
     s_ignored2 = j2.dump(-1, ' ', false, json::error_handler_t::ignore);
     s_ignored_ascii = j.dump(-1, ' ', true, json::error_handler_t::ignore);
@@ -89,9 +85,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     s_replaced2 = j2.dump(-1, ' ', false, json::error_handler_t::replace);
     s_replaced_ascii = j.dump(-1, ' ', true, json::error_handler_t::replace);
     s_replaced2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::replace);
-    s_kept = j.dump(-1, ' ', false, json::error_handler_t::keep);
-    s_kept2 = j2.dump(-1, ' ', false, json::error_handler_t::keep);
-    s_kept_ascii = j.dump(-1, ' ', true, json::error_handler_t::keep);
 
     if (success_expected)
     {
@@ -101,7 +94,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
         // all dumps should agree on the string
         CHECK(s_strict == s_ignored);
         CHECK(s_strict == s_replaced);
-        CHECK(s_strict == s_kept);
     }
     else
     {
@@ -113,20 +105,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
 
         // check that replace string contains a replacement character
         CHECK(s_replaced.find("\xEF\xBF\xBD") != std::string::npos);
-
-        // ignore drops the invalid bytes, keep copies them
-        CHECK(s_ignored != s_kept);
-        CHECK(s_ignored_ascii != s_kept_ascii);
-
-        // unless a byte needs escaping, keep copies the input unchanged
-        const bool needs_escaping = std::any_of(json_string.begin(), json_string.end(), [](char c)
-        {
-            return static_cast<unsigned char>(c) < 0x20 || c == '"' || c == '\\';
-        });
-        if (!needs_escaping)
-        {
-            CHECK(s_kept == "\"" + json_string + "\"");
-        }
     }
 
     // check that prefix and suffix are preserved
@@ -138,8 +116,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     CHECK(s_replaced2.substr(s_replaced2.size() - 4, 3) == "xyz");
     CHECK(s_replaced2_ascii.substr(1, 3) == "abc");
     CHECK(s_replaced2_ascii.substr(s_replaced2_ascii.size() - 4, 3) == "xyz");
-    CHECK(s_kept2.substr(1, 3) == "abc");
-    CHECK(s_kept2.substr(s_kept2.size() - 4, 3) == "xyz");
 }
 
 void check_utf8string(bool success_expected, int byte1, int byte2, int byte3, int byte4);

tests/src/unit-unicode4.cpp

@@ -14,7 +14,6 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
-#include <algorithm>
 #include <fstream>
 #include <sstream>
 #include <iostream>
@@ -76,11 +75,8 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     static std::string s_replaced2;
     static std::string s_replaced_ascii;
     static std::string s_replaced2_ascii;
-    static std::string s_kept;
-    static std::string s_kept2;
-    static std::string s_kept_ascii;
 
-    // dumping with ignore/replace/keep must not throw in any case
+    // dumping with ignore/replace must not throw in any case
     s_ignored = j.dump(-1, ' ', false, json::error_handler_t::ignore);
     s_ignored2 = j2.dump(-1, ' ', false, json::error_handler_t::ignore);
     s_ignored_ascii = j.dump(-1, ' ', true, json::error_handler_t::ignore);
@@ -89,9 +85,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     s_replaced2 = j2.dump(-1, ' ', false, json::error_handler_t::replace);
     s_replaced_ascii = j.dump(-1, ' ', true, json::error_handler_t::replace);
     s_replaced2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::replace);
-    s_kept = j.dump(-1, ' ', false, json::error_handler_t::keep);
-    s_kept2 = j2.dump(-1, ' ', false, json::error_handler_t::keep);
-    s_kept_ascii = j.dump(-1, ' ', true, json::error_handler_t::keep);
 
     if (success_expected)
     {
@@ -101,7 +94,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
         // all dumps should agree on the string
         CHECK(s_strict == s_ignored);
         CHECK(s_strict == s_replaced);
-        CHECK(s_strict == s_kept);
     }
     else
     {
@@ -113,20 +105,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
 
         // check that replace string contains a replacement character
         CHECK(s_replaced.find("\xEF\xBF\xBD") != std::string::npos);
-
-        // ignore drops the invalid bytes, keep copies them
-        CHECK(s_ignored != s_kept);
-        CHECK(s_ignored_ascii != s_kept_ascii);
-
-        // unless a byte needs escaping, keep copies the input unchanged
-        const bool needs_escaping = std::any_of(json_string.begin(), json_string.end(), [](char c)
-        {
-            return static_cast<unsigned char>(c) < 0x20 || c == '"' || c == '\\';
-        });
-        if (!needs_escaping)
-        {
-            CHECK(s_kept == "\"" + json_string + "\"");
-        }
     }
 
     // check that prefix and suffix are preserved
@@ -138,8 +116,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     CHECK(s_replaced2.substr(s_replaced2.size() - 4, 3) == "xyz");
     CHECK(s_replaced2_ascii.substr(1, 3) == "abc");
     CHECK(s_replaced2_ascii.substr(s_replaced2_ascii.size() - 4, 3) == "xyz");
-    CHECK(s_kept2.substr(1, 3) == "abc");
-    CHECK(s_kept2.substr(s_kept2.size() - 4, 3) == "xyz");
 }
 
 void check_utf8string(bool success_expected, int byte1, int byte2, int byte3, int byte4);

tests/src/unit-unicode5.cpp

@@ -14,7 +14,6 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
-#include <algorithm>
 #include <fstream>
 #include <sstream>
 #include <iostream>
@@ -76,11 +75,8 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     static std::string s_replaced2;
     static std::string s_replaced_ascii;
     static std::string s_replaced2_ascii;
-    static std::string s_kept;
-    static std::string s_kept2;
-    static std::string s_kept_ascii;
 
-    // dumping with ignore/replace/keep must not throw in any case
+    // dumping with ignore/replace must not throw in any case
     s_ignored = j.dump(-1, ' ', false, json::error_handler_t::ignore);
     s_ignored2 = j2.dump(-1, ' ', false, json::error_handler_t::ignore);
     s_ignored_ascii = j.dump(-1, ' ', true, json::error_handler_t::ignore);
@@ -89,9 +85,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     s_replaced2 = j2.dump(-1, ' ', false, json::error_handler_t::replace);
     s_replaced_ascii = j.dump(-1, ' ', true, json::error_handler_t::replace);
     s_replaced2_ascii = j2.dump(-1, ' ', true, json::error_handler_t::replace);
-    s_kept = j.dump(-1, ' ', false, json::error_handler_t::keep);
-    s_kept2 = j2.dump(-1, ' ', false, json::error_handler_t::keep);
-    s_kept_ascii = j.dump(-1, ' ', true, json::error_handler_t::keep);
 
     if (success_expected)
     {
@@ -101,7 +94,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
         // all dumps should agree on the string
         CHECK(s_strict == s_ignored);
         CHECK(s_strict == s_replaced);
-        CHECK(s_strict == s_kept);
     }
     else
     {
@@ -113,20 +105,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
 
         // check that replace string contains a replacement character
         CHECK(s_replaced.find("\xEF\xBF\xBD") != std::string::npos);
-
-        // ignore drops the invalid bytes, keep copies them
-        CHECK(s_ignored != s_kept);
-        CHECK(s_ignored_ascii != s_kept_ascii);
-
-        // unless a byte needs escaping, keep copies the input unchanged
-        const bool needs_escaping = std::any_of(json_string.begin(), json_string.end(), [](char c)
-        {
-            return static_cast<unsigned char>(c) < 0x20 || c == '"' || c == '\\';
-        });
-        if (!needs_escaping)
-        {
-            CHECK(s_kept == "\"" + json_string + "\"");
-        }
     }
 
     // check that prefix and suffix are preserved
@@ -138,8 +116,6 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     CHECK(s_replaced2.substr(s_replaced2.size() - 4, 3) == "xyz");
     CHECK(s_replaced2_ascii.substr(1, 3) == "abc");
     CHECK(s_replaced2_ascii.substr(s_replaced2_ascii.size() - 4, 3) == "xyz");
-    CHECK(s_kept2.substr(1, 3) == "abc");
-    CHECK(s_kept2.substr(s_kept2.size() - 4, 3) == "xyz");
 }
 
 void check_utf8string(bool success_expected, int byte1, int byte2, int byte3, int byte4);