Guard the image part of the alt_string test against big-endian targets

The test for json_view documents over an alternative string type called alt_editable_document::load() and save(). Both exist only on little-endian targets, so the test suite did not compile on big-endian targets such as s390x. Guard the two image lines with the condition the other image tests use (unit-json_view_image.cpp, unit-json_view_positions.cpp).

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

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

@@ -67,11 +67,7 @@ basic_json(basic_json&& other) noexcept;
     - **objects**: [`object_t`](object_t.md) and all kinds of compatible associative containers such as `std::map`,
      `std::unordered_map`, `std::multimap`, and `std::unordered_multimap` with a `key_type` compatible to `string_t`
      and a `value_type` from which a `basic_json` value can be constructed.
-    - **strings**: `string_t`, string literals, and all compatible string containers can be used. Since version 3.13.0,
+    - **strings**: `string_t`, string literals, and all compatible string containers can be used.
-      this includes `#!cpp std::u8string` (C++20): its code units are stored as a JSON string and
-      [`get<std::u8string>()`](get.md) reads it back (in version 3.12.0, a `#!cpp std::u8string` was stored as an array
-      of numbers; `get<std::u8string>()` still accepts such an array). `#!cpp std::u8string_view` and `#!cpp char8_t`
-      arrays are not strings; they are stored as arrays of code units.
 
     !!! note "Rvalue containers are moved from"
 

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

@@ -130,12 +130,6 @@ overload (3).
     `#!cpp json(true).get<double>()` throw. This is the behavior of all 3.x versions;
     [`basic_json_view::get<T>()`](../basic_json_view/get.md) behaves the same.
 
-!!! note "`std::u8string` conversions"
-
-    Since version 3.13.0, `#!cpp get<std::u8string>()` (C++20) reads a JSON string; it also accepts an array of numbers,
-    the form in which version 3.12.0 stored a `#!cpp std::u8string`. Any other JSON type throws
-    [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) ("type must be string or array").
-
 !!! note "`std::optional` conversions"
 
     Prior to version 3.13.0, `#!cpp get<std::optional<T>>()` (and other conversions to `std::optional<T>`) failed to

docs/mkdocs/docs/features/types/template_parameters.md

@@ -425,7 +425,7 @@ using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;
 | Type                                                                 | Reason                                                                                                  |
 |----------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------|
 | `#!cpp std::wstring`, `#!cpp std::u16string`, `#!cpp std::u32string` | the character type is not one byte wide                                                                 |
-| `#!cpp std::u8string`                                                | one byte wide, but `#!cpp char8_t` is not `#!cpp char`-compatible (as a *value*, it converts to and from a JSON string) |
+| `#!cpp std::u8string`                                                | one byte wide, but `#!cpp char8_t` is not `#!cpp char`-compatible                                       |
 | `absl::Cord`                                                         | no `value_type`, and the storage is not contiguous                                                      |
 | `QString`                                                            | no `append(const char*, size_type)`; its `QChar` is also two bytes wide, though that is never diagnosed |
 

docs/mkdocs/docs/home/releases/unreleased.md

@@ -8,16 +8,6 @@ These changes are part of the `develop` branch, but not of a release yet.
   exception is thrown during the conversion, the source may be partially moved-from, so the strong exception guarantee
   no longer holds for the source of an rvalue conversion (the JSON value itself is unaffected). Lvalues and `const`
   objects are still copied. See [`basic_json`](../../api/basic_json/basic_json.md).
-- In C++20 (library support for `char8_t`, `__cpp_lib_char8_t`), a `#!cpp std::u8string` is a JSON **string**:
-  `json j = std::u8string(u8"abc");` stores `"abc"`, and `#!cpp j.get<std::u8string>()` reads it back. Version 3.12.0
-  stored a `#!cpp std::u8string` as an array of code units (`[97,98,99]`); on the 3.13.0 development branch it was
-  already stored as a string if `std::filesystem` is available, but could not be read back. Now the result no longer
-  depends on whether `std::filesystem::path` is supported, and `#!cpp get<std::u8string>()` accepts both a JSON string
-  and the array of numbers written by 3.12.0. **Consequence:** JSON documents produced from a `#!cpp std::u8string` by
-  3.12.0 (arrays) are still read, but code that checks `is_array()` on such a value, or that reads it as
-  `#!cpp std::vector<char8_t>` / `#!cpp std::vector<std::uint8_t>`, now sees a string; to keep the array form, convert
-  explicitly, e.g., `#!cpp json(std::vector<char8_t>(s.begin(), s.end()))`. `#!cpp std::u8string_view` and
-  `#!cpp char8_t` arrays are unchanged (arrays of code units). See [`basic_json`](../../api/basic_json/basic_json.md).
 
 ## API changes
 

include/nlohmann/detail/conversions/from_json.hpp

@@ -785,37 +785,6 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
     from_json_pair_array_to_map(j, m);
 }
 
-#if defined(__cpp_lib_char8_t)
-// a std::u8string is read from a JSON string; the array of code units written by
-// versions before 3.13.0 is still accepted
-template < typename BasicJsonType, typename Tr, typename Allocator,
-           enable_if_t < std::is_same<typename json_type_of_t<BasicJsonType>::string_t::value_type, char>::value, int > = 0 >
-inline void from_json(const BasicJsonType& j, std::basic_string<char8_t, Tr, Allocator>& s)
-{
-    if (j.is_string())
-    {
-        const auto& str = string_value(j);
-        const char* const data = str.data();
-        const std::size_t size = str.size();
-        std::basic_string<char8_t, Tr, Allocator> ret(s.get_allocator());
-        ret.reserve(size);
-        for (std::size_t i = 0; i < size; ++i)
-        {
-            ret.push_back(static_cast<char8_t>(static_cast<unsigned char>(data[i])));
-        }
-        s = std::move(ret);
-    }
-    else if (j.is_array())
-    {
-        from_json_array_impl(j, s, priority_tag<3> {});
-    }
-    else
-    {
-        throw_type_must_be("string or array", j);
-    }
-}
-#endif
-
 #if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 
 // Workaround for MSVC 19.51 (and possibly later): in large cpp files, the compiler may fail to resolve with generic has_from_json (issue #4996)

include/nlohmann/detail/conversions/to_json.hpp

@@ -625,20 +625,16 @@ inline void to_json(BasicJsonType& j, const T& t)
     to_json_tuple_impl(j, t, make_index_sequence<std::tuple_size<T>::value> {});
 }
 
-// a std::u8string is a JSON string (it was an array of code units before 3.13.0);
+#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
-// defined outside the std::filesystem guard so that the result does not depend
-// on whether std::filesystem::path is supported
 #if defined(__cpp_lib_char8_t)
 template<typename BasicJsonType, typename Tr, typename Allocator>
 inline void to_json(BasicJsonType& j, const std::basic_string<char8_t, Tr, Allocator>& s)
 {
-    using string_t = typename BasicJsonType::string_t;
+    using OtherAllocator = typename std::allocator_traits<Allocator>::template rebind_alloc<char>;
-    // char may alias any object; the code units are copied unchanged
+    j = std::basic_string<char, std::char_traits<char>, OtherAllocator>(s.begin(), s.end(), s.get_allocator());
-    j = string_t(reinterpret_cast<const char*>(s.data()), s.size());
 }
 #endif
 
-#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 // Workaround for MSVC 19.51 (and possibly later): in large cpp files, the compiler may fail to resolve with generic has_to_json (issue #4996)
 template<typename BasicJsonType>
 struct has_to_json<BasicJsonType, std_fs::path, void> : std::true_type {};

single_include/nlohmann/json.hpp

@@ -6928,37 +6928,6 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
     from_json_pair_array_to_map(j, m);
 }
 
-#if defined(__cpp_lib_char8_t)
-// a std::u8string is read from a JSON string; the array of code units written by
-// versions before 3.13.0 is still accepted
-template < typename BasicJsonType, typename Tr, typename Allocator,
-           enable_if_t < std::is_same<typename json_type_of_t<BasicJsonType>::string_t::value_type, char>::value, int > = 0 >
-inline void from_json(const BasicJsonType& j, std::basic_string<char8_t, Tr, Allocator>& s)
-{
-    if (j.is_string())
-    {
-        const auto& str = string_value(j);
-        const char* const data = str.data();
-        const std::size_t size = str.size();
-        std::basic_string<char8_t, Tr, Allocator> ret(s.get_allocator());
-        ret.reserve(size);
-        for (std::size_t i = 0; i < size; ++i)
-        {
-            ret.push_back(static_cast<char8_t>(static_cast<unsigned char>(data[i])));
-        }
-        s = std::move(ret);
-    }
-    else if (j.is_array())
-    {
-        from_json_array_impl(j, s, priority_tag<3> {});
-    }
-    else
-    {
-        throw_type_must_be("string or array", j);
-    }
-}
-#endif
-
 #if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 
 // Workaround for MSVC 19.51 (and possibly later): in large cpp files, the compiler may fail to resolve with generic has_from_json (issue #4996)
@@ -8360,20 +8329,16 @@ inline void to_json(BasicJsonType& j, const T& t)
     to_json_tuple_impl(j, t, make_index_sequence<std::tuple_size<T>::value> {});
 }
 
-// a std::u8string is a JSON string (it was an array of code units before 3.13.0);
+#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
-// defined outside the std::filesystem guard so that the result does not depend
-// on whether std::filesystem::path is supported
 #if defined(__cpp_lib_char8_t)
 template<typename BasicJsonType, typename Tr, typename Allocator>
 inline void to_json(BasicJsonType& j, const std::basic_string<char8_t, Tr, Allocator>& s)
 {
-    using string_t = typename BasicJsonType::string_t;
+    using OtherAllocator = typename std::allocator_traits<Allocator>::template rebind_alloc<char>;
-    // char may alias any object; the code units are copied unchanged
+    j = std::basic_string<char, std::char_traits<char>, OtherAllocator>(s.begin(), s.end(), s.get_allocator());
-    j = string_t(reinterpret_cast<const char*>(s.data()), s.size());
 }
 #endif
 
-#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 // Workaround for MSVC 19.51 (and possibly later): in large cpp files, the compiler may fail to resolve with generic has_to_json (issue #4996)
 template<typename BasicJsonType>
 struct has_to_json<BasicJsonType, std_fs::path, void> : std::true_type {};

tests/CMakeLists.txt

@@ -364,16 +364,6 @@ json_test_add_test_for(src/unit-class_parser.cpp
     MAIN test_main CXX_STANDARDS ${test_cxx_standards} ${test_force}
 )
 
-# test the conversions again without std::filesystem::path support: a
-# std::u8string must be a JSON string in this configuration, too
-json_test_set_test_options(test-conversions2_no_filesystem
-    COMPILE_DEFINITIONS JSON_HAS_FILESYSTEM=0 JSON_HAS_EXPERIMENTAL_FILESYSTEM=0
-)
-json_test_add_test_for(src/unit-conversions2.cpp
-    NAME test-conversions2_no_filesystem
-    MAIN test_main CXX_STANDARDS ${test_cxx_standards} ${test_force}
-)
-
 # test diagnostic positions again without regular diagnostics (JSON pointer paths)
 json_test_set_test_options(test-diagnostic-positions_only
     COMPILE_DEFINITIONS JSON_DIAGNOSTICS=0

tests/src/unit-alt-string.cpp

@@ -531,25 +531,12 @@ TEST_CASE("alternative string type with json_view")
         CHECK(d.root().materialize() == expected);
         CHECK(alt_json::parse(d.root().dump()) == expected);
 
+        // save() and load() do not exist on big-endian targets
+#if !(defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
         const alt_editable_document loaded = alt_editable_document::load(d.save());
         CHECK(loaded.root().materialize() == expected);
+#endif
     }
 }
 
-// a std::u8string is a JSON string, whatever the string type of the JSON value
-// JSON_HAS_CPP_20 JSON_HAS_CPP_23 (do not remove; see note at top of file)
-#if defined(__cpp_lib_char8_t)
-TEST_CASE("alternative string type and std::u8string")
-{
-    const std::u8string s = u8"abc";
-    const alt_json j = s;
-    CHECK(j.is_string());
-    CHECK(j.get<alt_string>() == alt_string("abc"));
-    CHECK(j.get<std::u8string>() == s);
-
-    // the array of code units written by versions before 3.13.0
-    CHECK(alt_json::array({0x61, 0x62, 0x63}).get<std::u8string>() == s);
-}
-#endif
-
 DOCTEST_CLANG_SUPPRESS_WARNING_POP

tests/src/unit-conversions2.cpp

@@ -27,12 +27,10 @@ using nlohmann::json;
 #include <deque>
 #include <forward_list>
 #include <list>
-#include <map>
 #include <set>
 #include <unordered_map>
 #include <unordered_set>
 #include <valarray>
-#include <vector>
 
 // NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
@@ -709,13 +707,24 @@ TEST_CASE("std::filesystem::path")
 }
 #endif
 
-// a std::u8string is a JSON string since 3.13.0 (it was an array of code units
+// the ADL to_json overload for std::u8string only exists under the same guard
-// before); independent of whether std::filesystem::path is supported, see the
+// as std::filesystem::path support (it is otherwise only reached indirectly,
-// test-conversions2_no_filesystem target
+// via std::filesystem::path::u8string()) -- mirror both #if conditions from
-// JSON_HAS_CPP_20 JSON_HAS_CPP_23 (do not remove; see note at top of file)
+// include/nlohmann/detail/conversions/to_json.hpp exactly
+#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 #if defined(__cpp_lib_char8_t)
 TEST_CASE("std::u8string")
 {
+    SECTION("ascii")
+    {
+        const std::u8string s = u8"Path";
+        json const j = s;
+
+        CHECK(j.template get<std::string>() == "Path");
+    }
+
+    SECTION("utf-8")
+    {
         // use \u universal-character-names (rather than raw \x byte escapes
         // or literal non-ASCII source bytes) to compose the multi-byte UTF-8
         // encoding -- MSVC treats \x escapes used that way inside a u8
@@ -723,101 +732,14 @@ TEST_CASE("std::u8string")
         // our CI configs promote to an error; \u is portable and produces
         // the exact same encoded bytes without depending on the source
         // file's encoding
-    const std::u8string utf8 = u8"P\u011B\u0161ina";
+        const std::u8string s = u8"P\u011B\u0161ina";
-
-    SECTION("ascii")
-    {
-        const std::u8string s = u8"Path";
         json const j = s;
 
-        CHECK(j.is_string());
-        CHECK(j.template get<std::string>() == "Path");
-    }
-
-    SECTION("utf-8")
-    {
-        json const j = utf8;
-
-        CHECK(j.is_string());
         CHECK(j.template get<std::string>() == "P\xc4\x9b\xc5\xa1ina");
     }
-
-    SECTION("round trip")
-    {
-        json const j = utf8;
-        CHECK(j.template get<std::u8string>() == utf8);
-
-        std::u8string back;
-        j.get_to(back);
-        CHECK(back == utf8);
-
-        // from a string
-        json const j_string = "P\xc4\x9b\xc5\xa1ina";
-        CHECK(j_string.template get<std::u8string>() == utf8);
-
-        // empty, and with an embedded NUL
-        CHECK(json(std::u8string()).template get<std::u8string>().empty());
-        const std::u8string with_nul(u8"a\0b", 3);
-        CHECK(json(with_nul).template get<std::u8string>() == with_nul);
-
-        // the lvalue and rvalue paths, and in containers
-        std::u8string lvalue = utf8;
-        CHECK(json(lvalue).template get<std::u8string>() == utf8);
-        CHECK(json(std::move(lvalue)).template get<std::u8string>() == utf8);
-        const std::vector<std::u8string> vec = {utf8, u8"x"};
-        json const j_vec = vec;
-        CHECK(j_vec.is_array());
-        CHECK(j_vec[0].is_string());
-        CHECK(j_vec.template get<std::vector<std::u8string>>() == vec);
-        const std::map<std::string, std::u8string> map = {{"k", utf8}};
-        CHECK(json(map).template get<std::map<std::string, std::u8string>>() == map);
-    }
-
-    SECTION("array of code units (written by versions before 3.13.0)")
-    {
-        json const j = json::array({0x50, 0xC4, 0x9B, 0xC5, 0xA1, 0x69, 0x6E, 0x61});
-        CHECK(j.template get<std::u8string>() == utf8);
-        CHECK(json::array().template get<std::u8string>().empty());
-        CHECK(json::parse("[97, 98]").template get<std::u8string>() == u8"ab");
-
-        std::u8string s = u8"overwritten";
-        j.get_to(s);
-        CHECK(s == utf8);
-    }
-
-    SECTION("other types")
-    {
-#if !defined(JSON_NOEXCEPTION)
-        CHECK_THROWS_WITH_AS(json(1).template get<std::u8string>(), "[json.exception.type_error.302] type must be string or array, but is number", json::type_error);
-        CHECK_THROWS_WITH_AS(json(nullptr).template get<std::u8string>(), "[json.exception.type_error.302] type must be string or array, but is null", json::type_error);
-        CHECK_THROWS_AS(json::object().template get<std::u8string>(), json::type_error);
-        // an element that is not a number
-        CHECK_THROWS_AS(json::array({"a"}).template get<std::u8string>(), json::type_error);
-#endif
-    }
-
-    SECTION("ordered_json")
-    {
-        nlohmann::ordered_json const j = utf8;
-        CHECK(j.is_string());
-        CHECK(j.template get<std::string>() == "P\xc4\x9b\xc5\xa1ina");
-        CHECK(j.template get<std::u8string>() == utf8);
-        CHECK(nlohmann::ordered_json::array({0x61, 0x62}).template get<std::u8string>() == u8"ab");
-    }
-
-    SECTION("std::u8string_view and char8_t arrays are unchanged (arrays of code units)")
-    {
-        const std::u8string_view view = utf8;
-        json const j_view = view;
-        CHECK(j_view.is_array());
-        CHECK(j_view.size() == 8);
-
-        const char8_t arr[] = u8"ab";
-        json const j_arr = arr;
-        CHECK(j_arr == json::array({0x61, 0x62, 0}));
-    }
 }
 #endif
+#endif
 
 #if !defined(JSON_NOEXCEPTION)
 namespace