Merge develop into #5901 and fix clang-tidy else-after-return

Resolve the json_sax.hpp conflicts (keep the shared error state next to the
object key index; the binary parser uses the shared error state as well) and
drop the else after return in the diff stack-frame code.

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

tests/src/unit-class_parser.cpp

@@ -2952,3 +2952,81 @@ TEST_CASE("diagnostic positions: value lifetime, input adapters, and SAX")
     }
 }
 #endif
+
+TEST_CASE("accept() agrees with parse() on floats around the overflow limit")
+{
+    // accept() does not convert a float that cannot overflow; the tokens
+    // around the limit (and beyond it) must still be rejected exactly as
+    // parse() rejects them
+    const std::vector<const char*> numbers =
+    {
+        "1e0", "123.456e-5", "1e-400", "-1e-400", "1e307", "1e308", "1e309", "-1e309",
+        "10e307", "100e307", "0.1e309", "0.1e310", "1E+308", "1E+309",
+        "1.7976931348623157e308", "1.7976931348623159e308", "1.8e308", "-1.7976931348623157e308",
+        "12345678901234567e291", "12345678901234567e292", "123456789012345678e290", "123456789012345678e291",
+        "1234567890123456789e289", "1234567890123456789e290", "9999999999999999999e289", "9999999999999999999e290",
+        "0.00000000000000000001e328", "0.00000000000000000001e329"
+    };
+
+    for (const char* number : numbers)
+    {
+        for (const std::string& text :
+                {
+                    std::string(number), "[" + std::string(number) + "]", "{\"a\":" + std::string(number) + "}"
+                })
+        {
+            INFO(text);
+            const bool parses = !json::parse(text, nullptr, false).is_discarded();
+            CHECK(json::accept(text) == parses);
+        }
+    }
+}
+
+namespace
+{
+// a DOM parser that reports parse errors without throwing, as in the sax_no_exception example
+template<typename BasicJsonType>
+class quiet_dom_parser : public nlohmann::detail::json_sax_dom_parser<BasicJsonType, nlohmann::detail::string_input_adapter_type>
+{
+  public:
+    explicit quiet_dom_parser(BasicJsonType& j)
+        : nlohmann::detail::json_sax_dom_parser<BasicJsonType, nlohmann::detail::string_input_adapter_type>(j, false)
+    {}
+
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const nlohmann::detail::exception& /*unused*/)
+    {
+        return false;
+    }
+};
+
+template<typename BasicJsonType>
+std::string read_before_error(const std::string& text)
+{
+    BasicJsonType j;
+    quiet_dom_parser<BasicJsonType> sax(j);
+    CHECK(!BasicJsonType::sax_parse(text, &sax));
+    return j.dump();
+}
+} // namespace
+
+TEST_CASE("a json_sax_dom_parser keeps the values read before a parse error")
+{
+    // a json_sax_dom_parser that a user constructs stores every value in place, so a
+    // handler that does not throw on a parse error sees what was read before it
+    const std::vector<std::pair<std::string, std::string>> cases =
+    {
+        {"[1,2,3,]", "[1,2,3]"},
+        {"[[1,[2,3],4],[5,", "[[1,[2,3],4],[5]]"},
+        {R"({"a":1,"b":[1,2,{"c":)", R"({"a":1,"b":[1,2,{"c":null}]})"},
+        {R"({"a":1,"a":)", R"({"a":1})"},
+        {"[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,]", "[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]"},
+        {R"({"k0":0,"k1":1,"k2":{"x":[true,)", R"({"k0":0,"k1":1,"k2":{"x":[true]}})"},
+        {R"([{},[],{"a":[]},x)", R"([{},[],{"a":[]}])"},
+    };
+    for (const auto& c : cases)
+    {
+        CAPTURE(c.first)
+        CHECK(read_before_error<json>(c.first) == c.second);
+        CHECK(read_before_error<nlohmann::ordered_json>(c.first) == c.second);
+    }
+}

tests/src/unit-json_view.cpp

@@ -185,6 +185,33 @@ TEST_CASE("json_view")
         // duplicate keys: the last value, at the position of the first key
         CHECK(materialized<json_document>(R"({"a":1,"b":2,"a":3})") == json::parse(R"({"a":1,"b":2,"a":3})"));
         CHECK(materialized<ordered_json_document>(R"({"a":1,"b":2,"a":3})").dump() == R"({"a":3,"b":2})");
+        // scalars (made without the handler), and nesting around the depth up to which the stack of open containers is local
+        for (const char* scalar :
+                {"null", "true", "false", "0", "-7", "18446744073709551615", "1.5e300", "-0.0", "\"\"", "\"short\"", "\"a string that is longer than fifteen bytes\"", R"("\u00e4\n")"
+                })
+        {
+            CAPTURE(scalar)
+            CHECK(materialized<json_document>(scalar) == json::parse(scalar));
+            const std::string in_array = std::string("[1,") + scalar + "]";
+            const json_document d = json_document::parse(in_array);
+            CHECK(d.root()[1].materialize() == json::parse(scalar));
+            CHECK(d.root()[1].get<json>() == json::parse(scalar));
+        }
+        for (const std::size_t levels :
+                {
+                    std::size_t{1}, std::size_t{15}, std::size_t{16}, std::size_t{17}, std::size_t{32}, std::size_t{33}
+                })
+        {
+            CAPTURE(levels)
+            const std::string nested = std::string(levels, '[') + R"({"k":[1,{"j":2}]})" + std::string(levels, ']');
+            CHECK(materialized<json_document>(nested) == json::parse(nested));
+            std::string wide = R"({"a":)";
+            wide += nested;
+            wide += R"(,"b":)";
+            wide += nested;
+            wide += "}";
+            CHECK(materialized<json_document>(wide) == json::parse(wide));
+        }
         // very deep nesting (iterative, as parse())
         const std::string deep = std::string(100000, '[') + std::string(100000, ']');
         // (one check per step, so that a failure shows which step it is)
@@ -410,6 +437,31 @@ TEST_CASE("json_view")
         std::istringstream rvalue_source("[1]");
         CHECK(json_document::parse_copy(std::move(rvalue_source)).owns_source());
 
+        // a C stream is read in blocks as well (more than one block, and a
+        // text whose length is a multiple of the block size)
+        for (const std::size_t extra :
+                {
+                    std::size_t{0}, std::size_t{1}
+                })
+        {
+            std::FILE* long_file = std::tmpfile(); // NOLINT(cppcoreguidelines-owning-memory)
+            if (long_file != nullptr)
+            {
+                std::string padded = text;
+                padded.append(((4096 - (padded.size() % 4096)) % 4096) + extra, ' ');
+                CHECK(std::fwrite(padded.data(), 1, padded.size(), long_file) == padded.size());
+                CHECK(std::fseek(long_file, 0, SEEK_SET) == 0);
+                const json_document from_long_file = json_document::parse(long_file);
+                CHECK(from_long_file.source() == padded);
+                CHECK(from_long_file.root().materialize() == json::parse(text));
+                CHECK(std::fclose(long_file) == 0); // NOLINT(cppcoreguidelines-owning-memory)
+            }
+        }
+        {
+            json_document from_null;
+            CHECK_THROWS_AS(from_null = json_document::parse(static_cast<std::FILE*>(nullptr)), json::parse_error&);
+        }
+
         // a stream without a buffer is an empty input
         std::istream no_buffer(nullptr);
         CHECK(json_document::parse(no_buffer, false).is_discarded());
@@ -1006,6 +1058,49 @@ TEST_CASE("json_view element access and iteration")
 #endif
     }
 
+    SECTION("arrays whose elements have no subtrees: index and back()")
+    {
+        // (the elements are adjacent in the index; an array, an object, or an
+        // empty container anywhere makes the lookup skip element by element)
+        const std::vector<std::string> texts =
+        {
+            "[]", "[1]", "[1,2,3]", "[1,\"two\",3.5,true,null,-7,18446744073709551615]", "[[]]", "[{}]", "[1,[2],3]",
+            "[1,2,{\"a\":3}]", "[[1,2],3,4]", "[1,2,3,[4,5,6,7,8],9,10,11,12]", "[{\"a\":[1]},2]", R"(["a\u00e4","b"])"
+        };
+        for (const std::string& text : texts)
+        {
+            CAPTURE(text)
+            const json_document d = json_document::parse(text);
+            const json_view v = d.root();
+            const json expected = json::parse(text);
+            for (std::size_t i = 0; i < expected.size(); ++i)
+            {
+                CHECK(v[i].materialize() == expected[i]);
+                CHECK(v.at(i).materialize() == expected[i]);
+            }
+            CHECK(v[expected.size()].is_discarded());
+            if (!expected.empty())
+            {
+                CHECK(v.back().materialize() == expected.back());
+            }
+        }
+        // a long array (the direct lookup is not limited to short ones), also with a container at its end
+        std::string text = "[0";
+        for (int i = 1; i < 1000; ++i)
+        {
+            text += "," + std::to_string(i);
+        }
+        const json_document scalars = json_document::parse(text + "]");
+        CHECK(scalars.root()[999].get<int>() == 999);
+        CHECK(scalars.root()[500].get<int>() == 500);
+        CHECK(scalars.root().at(1).get<int>() == 1);
+        CHECK(scalars.root().back().get<int>() == 999);
+        const json_document container_last = json_document::parse(text + ",[1000]]");
+        CHECK(container_last.root()[999].get<int>() == 999);
+        CHECK(container_last.root()[1000][0].get<int>() == 1000);
+        CHECK(container_last.root().back()[0].get<int>() == 1000);
+    }
+
     SECTION("iterators")
     {
         const json_document d = json_document::parse(R"({"x":[1,{"y":2}],"z":null})");
@@ -1045,6 +1140,28 @@ TEST_CASE("json_view element access and iteration")
         CHECK((*first++).key() == "0");
         CHECK((*first).key() == "1");
         CHECK(++first == items.end());
+
+        // the keys of array elements are their indexes, whether or not they are asked for
+        std::string numbers = "[0";
+        for (int i = 1; i < 1234; ++i)
+        {
+            numbers += "," + std::to_string(i);
+        }
+        const json_document array = json_document::parse(numbers + "]");
+        std::size_t position = 0;
+        for (const auto& item : array.root().items())
+        {
+            CHECK(item.value().get<std::size_t>() == position);
+            if (position % 3 != 0) // (not for every item: values alone do not make the key)
+            {
+                CHECK(item.key() == std::to_string(position));
+                CHECK(item.key().data() == item.key().data()); // (the same text every time)
+                const json_view::item copy = item;
+                CHECK(copy.key() == std::to_string(position));
+            }
+            ++position;
+        }
+        CHECK(position == 1234);
 #ifdef JSON_HAS_CPP_17
         std::string pairs;
         for (const auto [key, value] : d.root().items())
@@ -1383,7 +1500,17 @@ TEST_CASE("json_view values")
         CHECK(exception_of([&] { static_cast<void>(v.value("s", 0)); }) == without_path(exception_of([&] { static_cast<void>(j.value("s", 0)); })));
         CHECK(exception_of([&] { static_cast<void>(v["n"].value("x", 0)); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value("x", 0)); })));
         CHECK(exception_of([&] { static_cast<void>(v["n"].value(json::json_pointer("/x"), 0)); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value(json::json_pointer("/x"), 0)); })));
+        // string defaults: the member is not a string, or the value is neither an object nor an array
+        CHECK(exception_of([&] { static_cast<void>(v.value("n", "default")); }) == without_path(exception_of([&] { static_cast<void>(j.value("n", "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v["n"].value("x", "default")); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value("x", "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v.value(json::json_pointer("/n"), "default")); }) == without_path(exception_of([&] { static_cast<void>(j.value(json::json_pointer("/n"), "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v["s"].value(json::json_pointer("/x"), "default")); }) == without_path(exception_of([&] { static_cast<void>(j["s"].value(json::json_pointer("/x"), "default")); })));
 #endif
+        // (defaults and members longer than the short string optimization)
+        CHECK(v.value("s", "a default longer than fifteen characters") == "text");
+        CHECK(v.value("missing", "a default longer than fifteen characters") == "a default longer than fifteen characters");
+        CHECK(v.value(json::json_pointer("/s"), "a default longer than fifteen characters") == "text");
+        CHECK(v.value(json::json_pointer("/zz"), "a default longer than fifteen characters") == "a default longer than fifteen characters");
     }
 }
 

tests/src/unit-json_view_builder.cpp

@@ -523,6 +523,58 @@ TEST_CASE("json_view builder: strings across vector blocks")
     }
 }
 
+TEST_CASE("json_view builder: escapes between runs of text")
+{
+    // The text between escapes is copied 16 bytes at a time where there are
+    // that many bytes left, and with the UTF-8 check where there is
+    // non-ASCII text. Runs of every length from 0 to 40 between valid and
+    // invalid escapes, UTF-8 sequences, and control characters, in strings
+    // that are cut at all places near the end of the text.
+    const std::array<const char*, 9> valid = {{"\\n", "\\\"", "\\\\", "\\/", "\\t", "\\u00e4", "\\u20ac", "\\ud83d\\ude00", "\\u0000"}};
+    const std::array<const char*, 9> invalid = {{"\\x", "\\ud800", "\\udc00", "\\u12G4", "\\u12", "\\ud83dx", "\\ud83d\\u0041", "\\", "\x01"}};
+    const std::array<const char*, 6> utf8 = {{"\xc3\xa4", "\xe2\x82\xac", "\xf0\x9f\x98\x80", "\xc3", "\xff", "\x80"}};
+    std::mt19937 rng(2026); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
+    for (std::size_t run = 0; run <= 40; ++run)
+    {
+        for (int i = 0; i < 60; ++i)
+        {
+            std::string content = std::string(rng() % 20, 'a');
+            const auto pieces = 1 + (rng() % 6);
+            for (unsigned k = 0; k < pieces; ++k)
+            {
+                content += valid[rng() % valid.size()];
+                content += std::string(k == 0 ? run : rng() % 41, static_cast<char>('b' + (rng() % 20)));
+                switch (rng() % 8)
+                {
+                    case 0:
+                        content += utf8[rng() % 3];
+                        break;
+                    case 1:
+                        content += utf8[rng() % utf8.size()];
+                        break;
+                    case 2:
+                        content += invalid[rng() % invalid.size()];
+                        break;
+                    default:
+                        break;
+                }
+            }
+            check_string(content);
+            check_string(content.substr(0, content.size() - (rng() % 4)));
+        }
+    }
+    // the text before the first escape, and runs and escapes at the end of the text
+    for (std::size_t before = 0; before <= 40; ++before)
+    {
+        for (const char* escape : valid)
+        {
+            check_string(std::string(before, 'a') + escape);
+            check_string(std::string(before, 'a') + escape + std::string(before % 19, 'z'));
+            check_string(std::string(before, 'a') + escape + escape + std::string(before % 19, 'z'));
+        }
+    }
+}
+
 TEST_CASE("json_view node integer bits")
 {
     using nlohmann::detail::view::integer_bits;

tests/src/unit-json_view_dump.cpp

@@ -21,6 +21,7 @@ using nlohmann::ordered_json_view;
 using json_view_test::generator;
 using json_view_test::has_duplicate_keys;
 
+#include <algorithm>
 #include <array>
 #include <cmath>
 #include <cstddef>
@@ -29,6 +30,7 @@ using json_view_test::has_duplicate_keys;
 #include <iomanip>
 #include <map>
 #include <random>
+#include <set>
 #include <sstream>
 #include <string>
 #include <vector>
@@ -186,6 +188,133 @@ TEST_CASE("json_view dump")
         CHECK(deep_document.root().dump() == deep);
     }
 
+    SECTION("ensure_ascii: a character that needs an escape at each position of a string")
+    {
+        // string lengths around the width of the vector steps, in a string value, a key, and a value near the end of the text
+        for (const char* const special :
+                {
+                    "\xC3\xA9", "\xE4\xB8\xAD", "\xF0\x9F\x98\x80", "\x7F", "\\n", "\\u0001", "\\\"", "\\\\"
+                })
+        {
+            for (std::size_t length = 0; length <= 40; ++length)
+            {
+                for (std::size_t position = 0; position <= length; ++position)
+                {
+                    std::string content(length, 'a');
+                    content.insert(position, special);
+                    const std::array<std::string, 3> texts =
+                    {
+                        {
+                            "\"" + content + "\"",
+                            "[\"" + content + "\"]",
+                            "{\"" + content + "\":1}",
+                        }
+                    };
+                    for (const std::string& text : texts)
+                    {
+                        CAPTURE(text)
+                        const ordered_json_document d = ordered_json_document::parse(text);
+                        const ordered_json j = ordered_json::parse(text);
+                        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+                        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
+                        CHECK(d.root().dump() == j.dump());
+                    }
+                }
+            }
+        }
+    }
+
+    SECTION("ensure_ascii: every character of the Basic Multilingual Plane and some beyond")
+    {
+        // (the two- and three-byte sequences, including the ranges that need a check: E0, ED, EF BF BF)
+        std::string text = "[";
+        std::size_t in_chunk = 0;
+        const auto append = [&](std::uint32_t cp)
+        {
+            if (cp < 0x80)
+            {
+                if (cp < 0x20 || cp == '"' || cp == '\\')
+                {
+                    return;
+                }
+                text += static_cast<char>(cp);
+            }
+            else if (cp < 0x800)
+            {
+                text += static_cast<char>(0xC0 | (cp >> 6));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+            else if (cp < 0x10000)
+            {
+                text += static_cast<char>(0xE0 | (cp >> 12));
+                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+            else
+            {
+                text += static_cast<char>(0xF0 | (cp >> 18));
+                text += static_cast<char>(0x80 | ((cp >> 12) & 0x3F));
+                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+        };
+        for (std::uint32_t cp = 0x20; cp < 0x10400; ++cp)
+        {
+            if (cp >= 0xD800 && cp < 0xE000)
+            {
+                continue;
+            }
+            if (in_chunk == 0)
+            {
+                text += text.size() > 1 ? ",\"" : "\"";
+            }
+            append(cp);
+            if (++in_chunk == 37)
+            {
+                text += "\"";
+                in_chunk = 0;
+            }
+        }
+        text += in_chunk != 0 ? "\"]" : "]";
+        const ordered_json_document d = ordered_json_document::parse(text);
+        const ordered_json j = ordered_json::parse(text);
+        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
+        CHECK(d.root().dump() == j.dump());
+        CHECK(d.root().dump(2) == j.dump(2));
+    }
+
+    SECTION("deep nesting, indented")
+    {
+        // indentations of up to and beyond the width of the writer's fixed-size copy
+        for (const int depth :
+                {
+                    1, 5, 20, 70, 300
+                })
+        {
+            std::string text;
+            for (int i = 0; i < depth; ++i)
+            {
+                text += i % 2 == 0 ? "[1," : R"({"k":2,"\u00e9":)";
+            }
+            text += "[]";
+            for (int i = depth - 1; i >= 0; --i)
+            {
+                text += i % 2 == 0 ? "]" : "}";
+            }
+            const ordered_json_document d = ordered_json_document::parse(text);
+            const ordered_json j = ordered_json::parse(text);
+            for (const int indent :
+                    {
+                        0, 1, 2, 3, 8
+                    })
+            {
+                CHECK(d.root().dump(indent) == j.dump(indent));
+                CHECK(d.root().dump(indent, '\t') == j.dump(indent, '\t'));
+            }
+        }
+    }
+
     SECTION("the output buffer of a small value is small")
     {
         // an escaped key after the value: its node lies in the arena, so the
@@ -598,6 +727,152 @@ TEST_CASE("json_view large objects")
         CHECK(without_collisions.memory_usage() >= with_collisions.memory_usage() + (table_size * sizeof(std::uint32_t)));
     }
 
+    SECTION("keys that differ in their last bytes are spread over the table")
+    {
+        // The hash must spread the usual families of keys (numbered names, hex
+        // strings, dates, short names): a key farther than index_max_displacement
+        // from its home slot would leave the object without a table. The keys
+        // are placed with linear probing, as the table does.
+        const auto max_displacement = [](const std::vector<std::string>& keys)
+        {
+            std::size_t slots = 16;
+            while (slots < 2 * keys.size())
+            {
+                slots *= 2;
+            }
+            std::vector<bool> used(slots, false);
+            std::size_t farthest = 0;
+            for (const std::string& key : keys)
+            {
+                std::size_t i = nlohmann::detail::conditional_static_cast<std::size_t>(nlohmann::detail::view::key_hash(key.data(), key.size())) & (slots - 1);
+                std::size_t distance = 0;
+                while (used[i])
+                {
+                    i = (i + 1) & (slots - 1);
+                    ++distance;
+                }
+                used[i] = true;
+                farthest = (std::max)(farthest, distance);
+            }
+            return farthest;
+        };
+        // the keys of a printf-like pattern with one %d, %0Nd or %0Nx, formatted with a stream
+        // (a format string that is not a literal is a Flawfinder error)
+        const auto numbered = [](const char* format, int count, int step)
+        {
+            const std::string pattern(format);
+            const std::size_t percent = pattern.find('%');
+            std::size_t conversion = percent + 1;
+            std::size_t width = 0;
+            while (pattern[conversion] >= '0' && pattern[conversion] <= '9')
+            {
+                width = (width * 10) + static_cast<std::size_t>(pattern[conversion] - '0');
+                ++conversion;
+            }
+            const bool hex = pattern[conversion] == 'x';
+            std::vector<std::string> keys;
+            for (int i = 0; i < count; ++i)
+            {
+                std::ostringstream key;
+                key << pattern.substr(0, percent) << std::setfill('0') << std::setw(static_cast<int>(width))
+                    << (hex ? std::hex : std::dec) << (i * step) << pattern.substr(conversion + 1);
+                keys.push_back(key.str());
+            }
+            return keys;
+        };
+        for (const char* format :
+                {"key%d", "%d", "item_%04d", "a%05d", "%03dxyz", "id%d", "user_%d", "%d_suffix", "0x%04x", "A%07d", "12345678%d", "1234567%d", "123456789%d",
+                 "configuration_parameter_value_%04d_extra", "2026-01-%02dT00:00:00Z"
+                })
+        {
+            CAPTURE(format)
+            CHECK(max_displacement(numbered(format, std::string(format).find("%02d") != std::string::npos ? 60 : 1000, 1)) < nlohmann::detail::view::index_max_displacement); // NOLINT(abseil-string-find-str-contains)
+            CHECK(max_displacement(numbered(format, 600, 7)) < nlohmann::detail::view::index_max_displacement);
+        }
+        std::mt19937_64 rng(7); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        for (const std::size_t length :
+                {
+                    std::size_t{1}, std::size_t{2}, std::size_t{3}, std::size_t{5}, std::size_t{7}, std::size_t{8}, std::size_t{9}, std::size_t{12}, std::size_t{16}, std::size_t{17}, std::size_t{33}
+                })
+        {
+            CAPTURE(length)
+            std::set<std::string> distinct;
+            // (there are 26 and 676 keys of one and two letters)
+            std::size_t wanted = 700;
+            if (length == 1)
+            {
+                wanted = 26;
+            }
+            else if (length == 2)
+            {
+                wanted = 500;
+            }
+            while (distinct.size() < wanted)
+            {
+                std::string key(length, 'a');
+                for (char& c : key)
+                {
+                    c = static_cast<char>('a' + (rng() % 26));
+                }
+                distinct.insert(key);
+            }
+            CHECK(max_displacement(std::vector<std::string>(distinct.begin(), distinct.end())) < nlohmann::detail::view::index_max_displacement);
+        }
+    }
+
+    SECTION("keys of every length that differ in one byte")
+    {
+        // In a large object, a key is found by comparing its bytes with those of the member the
+        // table points to: up to 16 bytes as two overlapping words, longer ones with memcmp.
+        // Keys of every length from 0 to 40, and keys that differ from them in one byte.
+        std::mt19937_64 rng(2026); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        std::vector<std::string> keys;
+        std::set<std::string> distinct;
+        for (std::size_t length = 0; length <= 40; ++length)
+        {
+            for (int copy = 0; copy < 5; ++copy)
+            {
+                std::string key(length, 'a');
+                for (char& c : key)
+                {
+                    c = static_cast<char>('a' + (rng() % 26));
+                }
+                if (distinct.insert(key).second)
+                {
+                    keys.push_back(key);
+                }
+            }
+        }
+        std::string text = "{";
+        for (std::size_t i = 0; i < keys.size(); ++i)
+        {
+            text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i);
+        }
+        text += "}";
+        REQUIRE(keys.size() >= 128); // (a table is built for 128 members)
+        const json_document d = json_document::parse(text);
+        const json_view v = d.root();
+        for (std::size_t i = 0; i < keys.size(); ++i)
+        {
+            CAPTURE(keys[i])
+            CHECK(v[keys[i]].get<std::size_t>() == i);
+            CHECK(v.at(keys[i]).get<std::size_t>() == i);
+            CHECK(v.contains(keys[i]));
+            for (std::size_t at = 0; at < keys[i].size(); ++at)
+            {
+                std::string other = keys[i];
+                other[at] = other[at] == 'z' ? 'y' : 'z';
+                CAPTURE(other)
+                CHECK(v.contains(other) == (distinct.count(other) != 0));
+            }
+            CHECK(v.contains(keys[i] + "a") == (distinct.count(keys[i] + "a") != 0));
+            if (!keys[i].empty())
+            {
+                CHECK(v.contains(keys[i].substr(1)) == (distinct.count(keys[i].substr(1)) != 0));
+            }
+        }
+    }
+
     SECTION("shrink_to_fit releases the tables' spare capacity")
     {
         const auto make_text = [](int objects, int members)

tests/src/unit-json_view_edit.cpp

@@ -661,6 +661,115 @@ TEST_CASE("json_view edits: replacing arrays and objects by scalars")
     CHECK(d.root().materialize() == expected);
 }
 
+TEST_CASE("json_view edits: arrays whose elements have no subtrees")
+{
+    // such an array is indexed directly while it is in its parsed layout; edits
+    // that replace elements by scalars keep it, others move it
+    json_editable_document d = json_editable_document::parse("[10,20,30,40]");
+    json expected = json::array({10, 20, 30, 40});
+    const auto check = [&]
+    {
+        CHECK(d.root().size() == expected.size());
+        for (std::size_t i = 0; i < expected.size(); ++i)
+        {
+            CHECK(d.root()[i].materialize() == expected[i]);
+            CHECK(d.root().at(i).materialize() == expected[i]);
+        }
+        CHECK(d.root()[expected.size()].is_discarded());
+        CHECK(d.root().back().materialize() == expected.back());
+        CHECK(d.root().dump() == expected.dump());
+    };
+    check();
+    d.set(d.root()[1], "x");
+    expected[1] = "x";
+    check();
+    d.set(d.root()[3], 2.5);
+    expected[3] = 2.5;
+    check();
+    d.set(d.root()[2], json::array({1, 2}));
+    expected[2] = json::array({1, 2});
+    check();
+    d.push_back(d.root(), 50);
+    expected.push_back(50);
+    check();
+    d.insert(d.root(), 0, true);
+    expected.insert(expected.begin(), true);
+    check();
+    d.erase(d.root(), 1);
+    expected.erase(expected.begin() + 1);
+    check();
+    d.set(d.root()[2], nullptr);
+    expected[2] = nullptr;
+    check();
+}
+
+TEST_CASE("json_view edits: materializing values nested deeper than the document was parsed")
+{
+    // the stack of open containers of materialize() is sized from the nesting of the parsed text;
+    // a value added by an edit can be deeper than that (and than the stack that is local to the call)
+    json_editable_document d = json_editable_document::parse("[1,[2]]");
+    json expected = json::array({1, json::array({2})});
+    json nested = 3;
+    for (int level = 0; level < 40; ++level)
+    {
+        nested = json::array({nested, json{{"k", level}}});
+    }
+    d.push_back(d.root(), nested);
+    expected.push_back(nested);
+    CHECK(d.root().materialize() == expected);
+    CHECK(d.root()[2].materialize() == nested);
+    d.set(d.root()[1][0], nested);
+    expected[1][0] = nested;
+    CHECK(d.root().materialize() == expected);
+    CHECK(d.root().get<json>() == expected);
+}
+
+TEST_CASE("json_view edits: an editable document before and after its first edit")
+{
+    // until the first edit, an editable document is read like a read-only one; views made before the edit
+    // keep working after it
+    const std::string text = R"({"a":[1,2,{"x":"y"},4],"b":{"c":true,"d":null},"e":"text","f":[]})";
+    const json_document read_only = json_document::parse(text);
+    json_editable_document d = json_editable_document::parse(text);
+    const auto root = d.root();
+    const auto same_as_read_only = [&]
+    {
+        CHECK(root.dump() == read_only.root().dump());
+        CHECK(root.dump(2) == read_only.root().dump(2));
+        CHECK(root.materialize() == read_only.root().materialize());
+        CHECK(root["a"][2]["x"].get_string() == "y");
+        CHECK(root["a"].at(3).get<int>() == 4);
+        CHECK(root["a"].back().get<int>() == 4);
+        CHECK(root.contains("b"));
+        CHECK(!root.contains("zz"));
+        CHECK(root.find("e")->get_string() == "text");
+        CHECK(root.find("zz") == root.end());
+        CHECK(root["b"]["c"].get<bool>());
+        CHECK(root.value("e", "none") == "text");
+        std::size_t count = 0;
+        for (const auto m : root["a"])
+        {
+            CHECK(m.materialize() == read_only.root()["a"][count].materialize());
+            ++count;
+        }
+        CHECK(count == 4);
+    };
+    same_as_read_only();
+    // an edit that changes a scalar in place, then one that moves an array
+    d.set(root["e"], "other");
+    CHECK(root["e"].get_string() == "other");
+    CHECK(root["a"][2]["x"].get_string() == "y");
+    CHECK(root["a"].back().get<int>() == 4);
+    d.push_back(root["f"], 7);
+    CHECK(root["f"][0].get<int>() == 7);
+    CHECK(root["f"].back().get<int>() == 7);
+    CHECK(root.dump() == R"({"a":[1,2,{"x":"y"},4],"b":{"c":true,"d":null},"e":"other","f":[7]})");
+    d.set(root["a"], 2, json::array({1, 2}));
+    CHECK(root["a"][2][1].get<int>() == 2);
+    CHECK(root["a"].dump() == "[1,2,[1,2],4]");
+    CHECK(root.materialize() == json::parse(R"({"a":[1,2,[1,2],4],"b":{"c":true,"d":null},"e":"other","f":[7]})"));
+}
+
 namespace
 {
 // reads of "a" in an object that repeats it: the first member wins, however the

tests/src/unit-json_view_image.cpp

@@ -682,6 +682,26 @@ TEST_CASE("json_view images: ownership")
 #if !defined(JSON_NOEXCEPTION)
 TEST_CASE("json_view images: errors")
 {
+    SECTION("invalid UTF-8 of a decoded string: the compact dump writes it, the others throw")
+    {
+        const json_document d = json_document::parse(R"({"k\n":"\u00e9x"})");
+        std::vector<std::uint8_t> image = d.save();
+        const std::size_t arena = text_at(image) + header_size_field(image, 16) + 1;
+        image[arena + 3] = 0x28; // the key is "k\n"; the value starts at 3: 0xC3 0x28 is invalid
+        const json_document loaded = json_document::load(image, image_check::bounds);
+        CHECK(loaded.root().dump().size() == 13);
+        for (const int indent :
+                {
+                    0, 2
+                })
+        {
+            CHECK_THROWS_AS(loaded.root().dump(indent), json::type_error);
+            CHECK_THROWS_AS(loaded.root().dump(indent, ' ', true), json::type_error);
+        }
+        CHECK_THROWS_AS(loaded.root().dump(-1, ' ', true), json::type_error);
+        CHECK_THROWS_WITH_AS(loaded.root().dump(2), "[json.exception.type_error.316] invalid UTF-8 byte at index 1: 0x28", json::type_error&);
+    }
+
     SECTION("a literal as the root: dump() after loading")
     {
         for (const char* text :

tests/src/unit-ordered_json.cpp

@@ -12,6 +12,11 @@
 using nlohmann::json;
 using nlohmann::ordered_json;
 
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <string>
+
 TEST_CASE("ordered_json")
 {
     json j;
@@ -237,3 +242,276 @@ TEST_CASE("regression test for issue #5673 - ordered_json::emplace with a non-rv
         CHECK(oj.dump() == "{\"a\":1}");
     }
 }
+
+namespace
+{
+// the sizes around which the DOM parser changes how it stores the elements of
+// an array (16) and the members of an object in a vector (32, and 64 for the
+// key index)
+const std::array<std::size_t, 17> container_sizes = {{0, 1, 2, 3, 15, 16, 17, 18, 31, 32, 33, 34, 63, 64, 65, 66, 200}};
+
+template<typename Json>
+std::string array_text(const std::size_t n, const std::size_t depth)
+{
+    std::string text = "[";
+    for (std::size_t i = 0; i < n; ++i)
+    {
+        text += (i == 0 ? "" : ",");
+        // alternate scalars, empty containers and nested containers
+        switch (i % 4)
+        {
+            case 0:
+                text += std::to_string(i);
+                break;
+            case 1:
+                text += "\"s" + std::to_string(i) + "\"";
+                break;
+            case 2:
+                text += depth == 0 ? "[]" : array_text<Json>(n / 2, depth - 1);
+                break;
+            default:
+                text += depth == 0 ? "{}" : "{\"a\":" + array_text<Json>(n / 3, depth - 1) + ",\"b\":null}";
+                break;
+        }
+    }
+    return text + "]";
+}
+
+template<typename Json>
+std::string object_text(const std::size_t n, const std::size_t depth, const bool duplicates)
+{
+    std::string text = "{";
+    for (std::size_t i = 0; i < n; ++i)
+    {
+        text += (i == 0 ? "" : ",");
+        text += "\"key" + std::to_string(i) + "\":";
+        switch (i % 4)
+        {
+            case 0:
+                text += std::to_string(i);
+                break;
+            case 1:
+                text += depth == 0 ? "[]" : array_text<Json>(n / 2, depth - 1);
+                break;
+            case 2:
+                text += depth == 0 ? "{}" : object_text<Json>(n / 2, depth - 1, duplicates);
+                break;
+            default:
+                text += "\"value\"";
+                break;
+        }
+    }
+    if (duplicates)
+    {
+        // keys that are there already, the first and the last one, with other values
+        text += n == 0 ? "" : ",";
+        text += R"("key0":[1,2],"key)";
+        text += std::to_string(n - 1);
+        text += R"(":{"again":true})";
+    }
+    return text + "}";
+}
+
+template<typename Json>
+void check_same_dump(const std::string& text)
+{
+    // the text is what dump() writes for the parsed value, and the value
+    // survives a second round trip: arrays keep their elements in order, an
+    // ordered_json keeps its members in order of appearance
+    const Json parsed = Json::parse(text);
+    const Json again = Json::parse(parsed.dump());
+    CHECK(parsed == again);
+    CHECK(parsed.dump() == again.dump());
+    CHECK(Json::accept(text));
+}
+} // namespace
+
+TEST_CASE("parsing containers of sizes around the limits of the DOM parser")
+{
+    SECTION("arrays")
+    {
+        for (const std::size_t n : container_sizes)
+        {
+            const std::string text = array_text<json>(n, 2);
+            INFO("size ", n);
+
+            const json parsed = json::parse(text);
+            CHECK(parsed.is_array());
+            CHECK(parsed.size() == n);
+            for (std::size_t i = 0; i < n; i += 4)
+            {
+                CHECK(parsed[i] == i);
+            }
+            check_same_dump<json>(text);
+            check_same_dump<ordered_json>(text);
+            CHECK(ordered_json::parse(text).dump() == parsed.dump());
+        }
+    }
+
+    SECTION("objects")
+    {
+        for (const bool duplicates :
+                {
+                    false, true
+                })
+        {
+            for (const std::size_t n : container_sizes)
+            {
+                const std::string text = object_text<json>(n, 2, duplicates);
+                INFO("size ", n, " duplicates ", duplicates);
+
+                const json parsed = json::parse(text);
+                const ordered_json ordered = ordered_json::parse(text);
+                CHECK(parsed.is_object());
+                CHECK(ordered.is_object());
+                CHECK(parsed.size() == ordered.size());
+                // the same members, in the order of their first appearance
+                std::size_t i = 0;
+                for (auto it = ordered.begin(); it != ordered.end(); ++it, ++i)
+                {
+                    if (i < n)
+                    {
+                        CHECK(it.key() == "key" + std::to_string(i));
+                    }
+                    CHECK(parsed.at(it.key()) == json(it.value()));
+                }
+                if (duplicates && n > 1)
+                {
+                    // the later value replaced the earlier one in its place
+                    CHECK(ordered.at("key0") == ordered_json::parse("[1,2]"));
+                    CHECK(ordered.at("key" + std::to_string(n - 1)) == ordered_json::parse("{\"again\":true}"));
+                    CHECK(ordered.begin().key() == "key0");
+                    CHECK(ordered.size() == n);
+                }
+                check_same_dump<json>(text);
+                check_same_dump<ordered_json>(text);
+            }
+        }
+    }
+
+    SECTION("objects with many different and repeated keys")
+    {
+        // 300 members of which a third repeat an earlier key
+        std::string text = "{";
+        for (std::size_t i = 0; i < 300; ++i)
+        {
+            text += (i == 0 ? "" : ",");
+            text += "\"k" + std::to_string(i % 200) + "\":" + std::to_string(i);
+        }
+        text += '}';
+
+        const ordered_json ordered = ordered_json::parse(text);
+        const json parsed = json::parse(text);
+        CHECK(ordered.size() == 200);
+        CHECK(parsed.size() == 200);
+        std::size_t i = 0;
+        for (auto it = ordered.begin(); it != ordered.end(); ++it, ++i)
+        {
+            CHECK(it.key() == "k" + std::to_string(i));
+            // the last value written
+            CHECK(it.value() == (i < 100 ? i + 200 : i));
+            CHECK(parsed.at(it.key()) == json(it.value()));
+        }
+    }
+}
+
+namespace
+{
+// a deterministic source of structure for parsing tests: builds a JSON text
+// and, at the same time, the value it has to parse to
+class tree_generator
+{
+  public:
+    explicit tree_generator(std::uint32_t seed) : state(seed) {}
+
+    template<typename Json>
+    Json make(std::string& text, const std::size_t depth)
+    {
+        switch (next(depth == 0 ? 5 : 9))
+        {
+            case 0:
+                text += "null";
+                return Json(nullptr);
+            case 1:
+                text += "true";
+                return Json(true);
+            case 2:
+            {
+                const int n = static_cast<int>(next(2000)) - 1000;
+                text += std::to_string(n);
+                return Json(n);
+            }
+            case 3:
+                text += "\"text\"";
+                return Json("text");
+            case 4:
+                text += "2.5";
+                return Json(2.5);
+            case 5:
+            case 6:
+            case 7:
+            {
+                Json array = Json::array();
+                text += '[';
+                const std::size_t n = size();
+                for (std::size_t i = 0; i < n; ++i)
+                {
+                    text += (i == 0 ? "" : ",");
+                    array.push_back(make<Json>(text, depth - 1));
+                }
+                text += ']';
+                return array;
+            }
+            default:
+            {
+                Json object = Json::object();
+                text += '{';
+                const std::size_t n = size();
+                for (std::size_t i = 0; i < n; ++i)
+                {
+                    const std::string key = "k" + std::to_string(i);
+                    text += (i == 0 ? "\"" : ",\"") + key + "\":";
+                    object[key] = make<Json>(text, depth - 1);
+                }
+                text += '}';
+                return object;
+            }
+        }
+    }
+
+  private:
+    std::uint32_t next(const std::uint32_t bound)
+    {
+        state = (state * 1664525U) + 1013904223U;
+        return (state >> 8) % bound;
+    }
+
+    std::size_t size()
+    {
+        return container_sizes[next(static_cast<std::uint32_t>(container_sizes.size()))];
+    }
+
+    std::uint32_t state;
+};
+} // namespace
+
+TEST_CASE("parsing random trees of arrays and objects")
+{
+    for (std::uint32_t seed = 1; seed <= 150; ++seed)
+    {
+        INFO("seed ", seed);
+
+        std::string text;
+        std::string ordered_text;
+        const json expected = tree_generator(seed).make<json>(text, 3);
+        const auto ordered_expected = tree_generator(seed).make<ordered_json>(ordered_text, 3);
+        CHECK(text == ordered_text);
+
+        CHECK(json::parse(text) == expected);
+        CHECK(json::accept(text));
+        const ordered_json ordered = ordered_json::parse(text);
+        CHECK(ordered == ordered_expected);
+        CHECK(ordered.dump() == ordered_expected.dump());
+        CHECK(json::parse(text).dump() == expected.dump());
+    }
+}