Merge branch 'json-view/08-view-builder' into json-view/11-view-access

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

tests/fuzzing.md

@@ -6,7 +6,10 @@ Each parser of the library (JSON, BJData, BON8, BSON, CBOR, MessagePack, and UBJ
 Additionally, `parse_json_view_fuzzer` (`tests/src/fuzzer-parse_json_view.cpp`) cross-checks `json_document`/`json_view`
 (the zero-copy, read-only view declared in `json_view.hpp`) against `basic_json` on the same JSON text: it asserts that
 `json_document::accept` agrees with `json::accept`, that an accepted input materializes to the same value `json::parse`
-produces, and that a rejected input makes both parsers throw with an identical `what()`. It takes plain JSON text, so it
+produces, and that a rejected input makes both parsers throw with an identical `what()`. It checks this for a
+`std::string` input (borrowed, with a NUL after the last byte) and for an exact-size `std::vector<std::uint8_t>`
+(borrowed, with nothing after the last byte), and for the `ignore_comments` and `ignore_trailing_commas` options, which
+are taken from the low bits of the first input byte (the byte stays part of the text). It takes plain JSON text, so it
 reuses the `corpus_json` corpus rather than a format of its own.
 
 ## What the fuzzers check

tests/src/fuzzer-parse_json_view.cpp

@@ -9,7 +9,9 @@
 /*
 This file implements a parser test suitable for fuzz testing. It checks that
 json_document (the zero-copy, read-only view of a parsed JSON text declared in
-json_view.hpp) agrees with basic_json on every input:
+json_view.hpp) agrees with basic_json on every input, for the parse options
+selected by the low bits of the first input byte (bit 0: ignore_comments, bit 1:
+ignore_trailing_commas; the byte stays part of the text):
 
 - json_document::accept(data) must equal json::accept(data)
 - if the input is accepted, json_document::parse(data).root().materialize()
@@ -18,12 +20,20 @@ json_view.hpp) agrees with basic_json on every input:
   enabled) must throw a json::parse_error or json::out_of_range whose what()
   is identical to the one json::parse(data) throws
 
+This is checked for two kinds of input: a std::string, which the document
+borrows and which ends in the NUL the parser uses as sentinel, and an
+exact-size byte vector, which has no NUL after its last byte and takes the
+parser's bounds-checked path (AddressSanitizer reports any read past the end).
+
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
 #include <cassert>
+#include <cstddef>
+#include <cstdint>
 #include <string>
+#include <vector>
 #include <nlohmann/json.hpp>
 #include <nlohmann/json_view.hpp>
 
@@ -35,65 +45,110 @@ drivers.
 using json = nlohmann::json;
 using json_document = nlohmann::json_document;
 
-// see http://llvm.org/docs/LibFuzzer.html
-extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+namespace
 {
-    // json_document::accept only has a single-argument overload; wrap the raw
-    // bytes in a (borrowed) std::string so the same bytes can be handed to it
-    const std::string input(reinterpret_cast<const char*>(data), size); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+// what json::parse does with a text: the value, or the message of the exception
+struct reference_result
+{
+    bool accepted = false;
+    json value{};
+    std::string what{}; // NOLINT(readability-redundant-member-init)
+};
 
-    const bool accepted_by_json = json::accept(data, data + size);
-    const bool accepted_by_view = json_document::accept(input);
+reference_result parse_reference(const std::uint8_t* data, std::size_t size, bool comments, bool trailing_commas)
+{
+    reference_result r;
+    r.accepted = json::accept(data, data + size, comments, trailing_commas);
+    bool json_threw = false;
+    try
+    {
+        r.value = json::parse(data, data + size, nullptr, true, comments, trailing_commas);
+    }
+    catch (const json::parse_error& e)
+    {
+        r.what = e.what();
+        json_threw = true;
+    }
+    catch (const json::out_of_range& e)
+    {
+        r.what = e.what();
+        json_threw = true;
+    }
+    // json::accept and json::parse must agree
+    assert(json_threw == !r.accepted);
+    static_cast<void>(json_threw);
+    return r;
+}
 
+// json_document must agree with the reference for this input (a container
+// that json_document::parse borrows)
+template<typename Input>
+void check_input(const Input& input, const reference_result& expected, bool comments, bool trailing_commas)
+{
     // json_document::accept must agree with json::accept on every input
-    assert(accepted_by_json == accepted_by_view);
+    const bool accepted_by_view = json_document::accept(input, comments, trailing_commas);
+    assert(expected.accepted == accepted_by_view);
+    static_cast<void>(accepted_by_view);
 
-    if (accepted_by_json)
+    if (expected.accepted)
     {
         // both parsers must agree on the resulting value
-        json const j1 = json::parse(data, data + size);
-        json_document const doc = json_document::parse(input);
+        json_document const doc = json_document::parse(input, true, comments, trailing_commas);
+        assert(!doc.is_discarded());
         json const j2 = doc.root().materialize();
-        assert(j1 == j2);
+        assert(expected.value == j2);
+        static_cast<void>(j2);
+
+        // (without exceptions, the same document)
+        json_document const quiet = json_document::parse(input, false, comments, trailing_commas);
+        assert(!quiet.is_discarded());
+        assert(quiet.node_count() == doc.node_count());
     }
     else
     {
         // both parsers must reject the input the same way when exceptions are used
-        std::string expected_what;
-        bool json_threw = false;
-        try
-        {
-            static_cast<void>(json::parse(data, data + size));
-        }
-        catch (const json::parse_error& e)
-        {
-            expected_what = e.what();
-            json_threw = true;
-        }
-        catch (const json::out_of_range& e)
-        {
-            expected_what = e.what();
-            json_threw = true;
-        }
-        assert(json_threw);
-
         bool view_threw = false;
         try
         {
-            static_cast<void>(json_document::parse(input));
+            static_cast<void>(json_document::parse(input, true, comments, trailing_commas));
         }
         catch (const json::parse_error& e)
         {
-            assert(e.what() == expected_what);
+            assert(e.what() == expected.what);
             view_threw = true;
         }
         catch (const json::out_of_range& e)
         {
-            assert(e.what() == expected_what);
+            assert(e.what() == expected.what);
             view_threw = true;
         }
         assert(view_threw);
+        static_cast<void>(view_threw);
+
+        // and without exceptions, the document is discarded
+        json_document const quiet = json_document::parse(input, false, comments, trailing_commas);
+        assert(quiet.is_discarded());
+        static_cast<void>(quiet);
     }
+}
+} // namespace
+
+// see http://llvm.org/docs/LibFuzzer.html
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+{
+    // the parse options are taken from the low bits of the first byte
+    const bool comments = size > 0 && (data[0] & 1U) != 0;
+    const bool trailing_commas = size > 0 && (data[0] & 2U) != 0;
+
+    const reference_result expected = parse_reference(data, size, comments, trailing_commas);
+
+    // a std::string: borrowed, with the NUL of std::string as sentinel
+    const std::string input(reinterpret_cast<const char*>(data), size); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    check_input(input, expected, comments, trailing_commas);
+
+    // an exact-size byte vector: borrowed, with nothing after its last byte
+    const std::vector<std::uint8_t> exact(data, data + size);
+    check_input(exact, expected, comments, trailing_commas);
 
     // return 0 - non-zero return values are reserved for future use
     return 0;

tests/src/unit-class_lexer.cpp

@@ -1792,4 +1792,11 @@ TEST_CASE("string scanning kernels")
         CHECK(nlohmann::detail::count_trailing_zeros(bit) == k);
         CHECK(nlohmann::detail::count_trailing_zeros(bit | (bit << 1u) | 0x8000000000000000u) == k);
     }
+
+    // eight bytes as a little-endian word, at any alignment
+    const unsigned char bytes[16] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF};
+    CHECK(nlohmann::detail::read_eight_bytes(bytes) == 0x0807060504030201u);
+    CHECK(nlohmann::detail::read_eight_bytes(bytes + 1) == 0x0908070605040302u);
+    CHECK(nlohmann::detail::read_eight_bytes(bytes + 8) == 0xFF0F0E0D0C0B0A09u);
+    CHECK(nlohmann::detail::read_eight_bytes(reinterpret_cast<const char*>(bytes) + 3) == 0x0B0A090807060504u);
 }

tests/src/unit-json_view.cpp

@@ -19,6 +19,7 @@ using nlohmann::ordered_json_view;
 #include <algorithm>
 #include <array>
 #include <cmath>
+#include <cstddef>
 #include <cstdint>
 #include <cstdio>
 #include <cstring>
@@ -29,6 +30,7 @@ using nlohmann::ordered_json_view;
 #include <random>
 #include <sstream>
 #include <string>
+#include <type_traits>
 #include <unordered_map>
 #include <utility>
 #include <vector>
@@ -39,6 +41,55 @@ using nlohmann::ordered_json_view;
 
 namespace
 {
+// the value of a text, through a named document: the views of a temporary
+// document would dangle (root() of an rvalue document does not compile)
+template<typename Document, typename... Args>
+auto materialized(Args&& ... args) -> decltype(std::declval<typename Document::view_type>().materialize())
+{
+    const Document d = Document::parse(std::forward<Args>(args)...);
+    return d.root().materialize();
+}
+
+template<typename Document, typename Input>
+auto materialized_copy(Input&& input) -> decltype(std::declval<typename Document::view_type>().materialize())
+{
+    const Document d = Document::parse_copy(std::forward<Input>(input));
+    return d.root().materialize();
+}
+
+// a "byte container" that claims to hold `size` bytes, to reach the limit on
+// the size of the input without allocating gigabytes; nothing past the first
+// bytes is ever read, because the size is checked before the parse starts
+struct oversized_input
+{
+    using value_type = char;
+    std::size_t claimed;
+
+    const char* data() const
+    {
+        return "[1]";
+    }
+
+    std::size_t size() const
+    {
+        return claimed;
+    }
+};
+
+// detection of calls that must not compile
+template<typename... Args>
+using parse_call_t = decltype(json_document::parse(std::declval<Args>()...));
+template<typename... Args>
+using parse_copy_call_t = decltype(json_document::parse_copy(std::declval<Args>()...));
+template<typename... Args>
+using accept_call_t = decltype(json_document::accept(std::declval<Args>()...));
+template<typename... Args>
+using read_call_t = decltype(std::declval<json_document&>().read(std::declval<Args>()...));
+template<typename Document>
+using root_call_t = decltype(std::declval<Document>().root());
+template<typename View>
+using bool_conversion_t = decltype(static_cast<bool>(std::declval<View>()));
+
 #if !defined(JSON_NOEXCEPTION)
 // the exception parse() throws for a text, or "" if it accepts it
 std::string parse_exception(const std::string& text, bool comments = false, bool trailing_commas = false)
@@ -152,7 +203,6 @@ TEST_CASE("json_view")
             CHECK(v.is_primitive() == j.is_primitive());
             CHECK(v.is_structured() == j.is_structured());
             CHECK(!v.is_discarded());
-            CHECK(static_cast<bool>(v));
             CHECK(v.size() == j.size());
             CHECK(v.empty() == j.empty());
             CHECK(v.materialize() == j);
@@ -160,7 +210,6 @@ TEST_CASE("json_view")
 
         const json_view invalid{};
         CHECK(invalid.is_discarded());
-        CHECK(!static_cast<bool>(invalid));
         CHECK(invalid.type() == json::value_t::discarded);
         CHECK(invalid.size() == 0);
         CHECK(invalid.empty());
@@ -176,19 +225,19 @@ TEST_CASE("json_view")
             std::string text;
             g.value(text, 0);
             CAPTURE(text)
-            CHECK(json_document::parse(text).root().materialize() == json::parse(text));
+            CHECK(materialized<json_document>(text) == json::parse(text));
             // member order as ordered_json::parse keeps it
-            CHECK(ordered_json_document::parse(text).root().materialize().dump() == ordered_json::parse(text).dump());
+            CHECK(materialized<ordered_json_document>(text).dump() == ordered_json::parse(text).dump());
         }
         // duplicate keys: the last value, at the position of the first key
-        CHECK(json_document::parse(R"({"a":1,"b":2,"a":3})").root().materialize() == json::parse(R"({"a":1,"b":2,"a":3})"));
-        CHECK(ordered_json_document::parse(R"({"a":1,"b":2,"a":3})").root().materialize().dump() == R"({"a":3,"b":2})");
+        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})");
         // very deep nesting (iterative, as parse())
         const std::string deep = std::string(100000, '[') + std::string(100000, ']');
-        CHECK(json_document::parse(deep).root().materialize() == json::parse(deep));
+        CHECK(materialized<json_document>(deep) == json::parse(deep));
 #if JSON_DIAGNOSTICS
         // the parents are set, so errors name the path
-        const json m = json_document::parse(R"({"a":{"b":[1]}})").root().materialize();
+        const json m = materialized<json_document>(R"({"a":{"b":[1]}})");
         CHECK_THROWS_WITH_AS(m.at("a").at("b").at(0).at("x"), "[json.exception.type_error.304] (/a/b/0) cannot use at() with number", json::type_error&);
 #endif
     }
@@ -261,7 +310,7 @@ TEST_CASE("json_view")
             CHECK(json_document::accept(text));
             if (accepted)
             {
-                CHECK(float_document::parse(text).root().materialize() == json_float::parse(text));
+                CHECK(materialized<float_document>(text) == json_float::parse(text));
             }
         }
         float_document f;
@@ -275,7 +324,7 @@ TEST_CASE("json_view")
         CHECK(json_document::accept(with_nul) == json::accept(with_nul));
         const std::string nul_in_comment("[1, // c\0\n2]", 12);
         CHECK(json_document::accept(nul_in_comment, true) == json::accept(nul_in_comment, true));
-        CHECK(json_document::parse("\xEF\xBB\xBF[1]").root().materialize() == json::parse("\xEF\xBB\xBF[1]"));
+        CHECK(materialized<json_document>("\xEF\xBB\xBF[1]") == json::parse("\xEF\xBB\xBF[1]"));
 #if !defined(JSON_NOEXCEPTION)
         CHECK(view_exception("\xEF\xBB") == parse_exception("\xEF\xBB"));
 #endif
@@ -291,18 +340,18 @@ TEST_CASE("json_view")
         CHECK(!borrowed.owns_source());
         CHECK(borrowed.source().data() == text.data());
         CHECK(borrowed.root().materialize() == expected);
-        CHECK(json_document::parse(text.c_str()).root().materialize() == expected);
-        CHECK(json_document::parse(R"([1, "two", {"three": 3.5}])").root().materialize() == expected);
-        CHECK(json_document::parse(text.data(), text.data() + text.size()).root().materialize() == expected);
+        CHECK(materialized<json_document>(text.c_str()) == expected);
+        CHECK(materialized<json_document>(R"([1, "two", {"three": 3.5}])") == expected);
+        CHECK(materialized<json_document>(text.data(), text.data() + text.size()) == expected);
         const std::vector<char> chars(text.begin(), text.end());
         CHECK(!json_document::parse(chars).owns_source());
-        CHECK(json_document::parse(chars).root().materialize() == expected);
+        CHECK(materialized<json_document>(chars) == expected);
         const std::vector<std::uint8_t> bytes(text.begin(), text.end());
-        CHECK(json_document::parse(bytes).root().materialize() == expected);
+        CHECK(materialized<json_document>(bytes) == expected);
 #ifdef JSON_HAS_CPP_17
         const std::string_view sv = text;
         CHECK(!json_document::parse(sv).owns_source());
-        CHECK(json_document::parse(sv).root().materialize() == expected);
+        CHECK(materialized<json_document>(sv) == expected);
 #endif
 
         // owned
@@ -311,15 +360,28 @@ TEST_CASE("json_view")
         CHECK(from_rvalue.owns_source());
         CHECK(from_rvalue.root().materialize() == expected);
         CHECK(json_document::parse(std::vector<char>(text.begin(), text.end())).owns_source());
+        // a const rvalue cannot be moved from, and is not borrowed (it may be a
+        // temporary): it is copied, as is a const rvalue of any container
+        const std::string const_text = text;
+        const json_document from_const_rvalue = json_document::parse(std::move(const_text)); // NOLINT(performance-move-const-arg,hicpp-move-const-arg)
+        CHECK(from_const_rvalue.owns_source());
+        CHECK(from_const_rvalue.source().data() != const_text.data());
+        CHECK(from_const_rvalue.root().materialize() == expected);
+        json_document read_const_rvalue;
+        read_const_rvalue.read(std::move(const_text)); // NOLINT(performance-move-const-arg,hicpp-move-const-arg)
+        CHECK(read_const_rvalue.owns_source());
+        CHECK(read_const_rvalue.root().materialize() == expected);
+        const std::vector<char> const_chars(text.begin(), text.end());
+        CHECK(json_document::parse(std::move(const_chars)).owns_source()); // NOLINT(performance-move-const-arg,hicpp-move-const-arg)
         CHECK(json_document::parse_copy(text).owns_source());
-        CHECK(json_document::parse_copy(text).root().materialize() == expected);
+        CHECK(materialized_copy<json_document>(text) == expected);
         std::istringstream stream(text);
         const json_document from_stream = json_document::parse(stream);
         CHECK(from_stream.owns_source());
         CHECK(from_stream.root().materialize() == expected);
         const std::list<char> list(text.begin(), text.end());
         CHECK(json_document::parse(list.begin(), list.end()).owns_source());
-        CHECK(json_document::parse(list.begin(), list.end()).root().materialize() == expected);
+        CHECK(materialized<json_document>(list.begin(), list.end()) == expected);
 
         // iterator pairs: pointers are borrowed, and so are contiguous library
         // iterators where the input adapter detects them (C++20)
@@ -330,14 +392,85 @@ TEST_CASE("json_view")
         CHECK((from_iterators.source().data() == chars.data()) == contiguous);
         CHECK(from_iterators.root().materialize() == expected);
         const std::string padded = "x" + text + "x";
-        CHECK(json_document::parse(padded.begin() + 1, padded.end() - 1).root().materialize() == expected);
+        CHECK(materialized<json_document>(padded.begin() + 1, padded.end() - 1) == expected);
         CHECK(json_document::parse(chars.cbegin(), chars.cbegin(), false).is_discarded());
         const std::wstring wide = L"[\"\u00e4\u20ac\", 1]";
-        CHECK(json_document::parse(wide).root().materialize() == json::parse(wide));
+        CHECK(materialized<json_document>(wide) == json::parse(wide));
         CHECK(json_document::parse(static_cast<const char*>(nullptr), false).is_discarded());
         CHECK(json_document::parse("", false).is_discarded());
     }
 
+    SECTION("integer arguments do not compile")
+    {
+        using nlohmann::detail::is_detected;
+
+        // a length is not a flag: parse(ptr, len) would convert len to
+        // allow_exceptions and read ptr as a C string, which need not end
+        static_assert(is_detected<parse_call_t, const char*, bool>::value, "parse(ptr, bool) is valid");
+        static_assert(is_detected<parse_call_t, const char*, bool, bool, bool>::value, "parse(ptr, bool, bool, bool) is valid");
+        static_assert(is_detected<parse_call_t, const char*, const char*>::value, "parse(first, last) is valid");
+        static_assert(is_detected<parse_call_t, const char*, const char*, bool>::value, "parse(first, last, bool) is valid");
+        static_assert(!is_detected<parse_call_t, const char*, std::size_t>::value, "parse(ptr, len) must not compile");
+        static_assert(!is_detected<parse_call_t, const char*, int>::value, "parse(ptr, int) must not compile");
+        static_assert(!is_detected<parse_call_t, const char*, char>::value, "parse(ptr, char) must not compile");
+        static_assert(!is_detected<parse_call_t, const char*, std::size_t, bool>::value, "parse(ptr, len, bool) must not compile");
+        static_assert(!is_detected<parse_call_t, const std::string&, std::size_t>::value, "parse(string, len) must not compile");
+        static_assert(!is_detected<parse_call_t, const std::vector<char>&, std::size_t>::value, "parse(vector, len) must not compile");
+
+        static_assert(is_detected<parse_copy_call_t, const char*, bool>::value, "parse_copy(ptr, bool) is valid");
+        static_assert(!is_detected<parse_copy_call_t, const char*, std::size_t>::value, "parse_copy(ptr, len) must not compile");
+
+        static_assert(is_detected<accept_call_t, const char*, bool>::value, "accept(ptr, bool) is valid");
+        static_assert(!is_detected<accept_call_t, const char*, std::size_t>::value, "accept(ptr, len) must not compile");
+
+        static_assert(is_detected<read_call_t, const char*, bool>::value, "read(ptr, bool) is valid");
+        static_assert(!is_detected<read_call_t, const char*, std::size_t>::value, "read(ptr, len) must not compile");
+
+        // json_view has no conversion to bool: unlike basic_json's, it would
+        // mean "exists", not "is not null"; use is_discarded()
+        static_assert(!is_detected<bool_conversion_t, json_view>::value, "json_view must not convert to bool");
+
+        // the valid calls still work
+        const char* const text = "[1]";
+        CHECK(materialized<json_document>(text, true) == json::parse(text));
+        CHECK(json_document::accept(text, true, true));
+    }
+
+    SECTION("root of a temporary document does not compile")
+    {
+        using nlohmann::detail::is_detected;
+
+        // the view would dangle: auto v = json_document::parse(text).root();
+        static_assert(is_detected<root_call_t, json_document&>::value, "root() of an lvalue is valid");
+        static_assert(is_detected<root_call_t, const json_document&>::value, "root() of a const lvalue is valid");
+        static_assert(!is_detected<root_call_t, json_document>::value, "root() of an rvalue must not compile");
+        static_assert(!is_detected < root_call_t, json_document && >::value, "root() of an rvalue must not compile");
+        static_assert(!is_detected < root_call_t, const json_document && >::value, "root() of a const rvalue must not compile");
+        static_assert(!is_detected<root_call_t, ordered_json_document>::value, "root() of an rvalue must not compile");
+
+        // a named document is fine, also after a move
+        json_document d = json_document::parse("[1]");
+        CHECK(d.root().size() == 1);
+        const json_document moved = std::move(d);
+        CHECK(moved.root().size() == 1);
+    }
+
+    SECTION("input size limit")
+    {
+        // 32-bit offsets: the limit is 4 GiB minus 16 bytes (a margin below 2^32),
+        // which is what the exception message and the documentation say
+        const std::size_t limit = nlohmann::detail::view::max_input_size;
+        CHECK(limit == std::size_t{4294967279u});
+
+        const oversized_input input{limit + 1};
+        CHECK(!json_document::accept(input));
+        CHECK(json_document::parse(input, false).is_discarded());
+#if !defined(JSON_NOEXCEPTION)
+        json_document d;
+        CHECK_THROWS_WITH_AS(d = json_document::parse(input), "[json.exception.out_of_range.416] input of 4294967280 bytes or more is not supported by json_document", json::out_of_range&);
+#endif
+    }
+
     SECTION("document lifetime and reuse")
     {
         json_document d;

tests/src/unit-json_view_builder.cpp

@@ -19,8 +19,10 @@ using nlohmann::json;
 
 #include <cstdint>
 #include <fstream>
+#include <limits>
 #include <map>
 #include <memory>
+#include <new>
 #include <random>
 #include <sstream>
 #include <string>
@@ -401,3 +403,89 @@ TEST_CASE("json_view builder")
         }
     }
 }
+
+TEST_CASE("json_view node integer bits")
+{
+    using nlohmann::detail::view::integer_bits;
+    using nlohmann::detail::view::set_integer_bits;
+
+    // an integer lives in len (low half) and next (high half), on any byte
+    // order; a big-endian target must not store the native word over both
+    SECTION("set_integer_bits and integer_bits")
+    {
+        node n = {};
+        for (const std::uint64_t v :
+                {
+                    std::uint64_t{0}, std::uint64_t{1}, std::uint64_t{0xFFFFFFFFu}, std::uint64_t{0x100000000u},
+                    std::uint64_t{0x0000000200000003u}, std::uint64_t{0x0123456789ABCDEFu}, std::uint64_t{0xFFFFFFFFFFFFFFFEu}
+                })
+        {
+            CAPTURE(v)
+            n.kind = 0x5A;
+            n.flags = 0xA5;
+            n.extra = 0x1234;
+            n.off = 0x89ABCDEFu;
+            set_integer_bits(n, v);
+            CHECK(integer_bits(n) == v);
+            CHECK(n.len == static_cast<std::uint32_t>(v));
+            CHECK(n.next == static_cast<std::uint32_t>(v >> 32));
+            // the other fields are untouched
+            CHECK(n.kind == 0x5A);
+            CHECK(n.flags == 0xA5);
+            CHECK(n.extra == 0x1234);
+            CHECK(n.off == 0x89ABCDEFu);
+        }
+    }
+
+    SECTION("parsed integers")
+    {
+        struct integer_case
+        {
+            const char* text;
+            std::uint64_t bits;
+        };
+        for (const integer_case c :
+                {
+                    integer_case{"[8589934595]", 0x0000000200000003u}, integer_case{"[4294967296]", 0x100000000u}, integer_case{"[4294967295]", 0xFFFFFFFFu},
+                    integer_case{"[-2]", 0xFFFFFFFFFFFFFFFEu}, integer_case{"[-4294967297]", 0xFFFFFFFEFFFFFFFFu}, integer_case{"[18446744073709551615]", 0xFFFFFFFFFFFFFFFFu},
+                    integer_case{"[7]", 7u}
+                })
+        {
+            CAPTURE(c.text)
+            const built b = build(c.text, false, false, true);
+            REQUIRE(b.ok);
+            const node& n = b.data->tape[1];
+            CHECK(integer_bits(n) == c.bits);
+            CHECK(n.len == static_cast<std::uint32_t>(c.bits));
+            CHECK(n.next == static_cast<std::uint32_t>(c.bits >> 32));
+        }
+    }
+}
+
+TEST_CASE("json_view node array size limit")
+{
+    // a node array larger than the address space is refused, not wrapped to a
+    // small allocation (the size computation overflows on 32-bit targets, and
+    // for absurd counts everywhere)
+    std::unique_ptr<document_data, document_data::deleter> d(document_data::create(0));
+    d->reserve(8);
+    REQUIRE(d->tape_cap >= 8);
+    d->tape_size = 2;
+    const std::size_t cap = d->tape_cap;
+    node* const tape = d->tape;
+
+#if !defined(JSON_NOEXCEPTION)
+    const std::size_t too_many = document_data::max_nodes() + 1;
+    CHECK_THROWS_AS(d->reserve(too_many), std::bad_alloc&);
+    CHECK_THROWS_AS(d->reserve((std::numeric_limits<std::size_t>::max)()), std::bad_alloc&);
+    // the array is unchanged
+    CHECK(d->tape == tape);
+    CHECK(d->tape_cap == cap);
+    CHECK(d->tape_size == 2);
+#endif
+
+    // the largest count that fits is not refused by the check (nothing is
+    // allocated for a count that is already there)
+    d->reserve(cap);
+    CHECK(d->tape == tape);
+}

tests/src/unit-to_chars.cpp

@@ -15,6 +15,7 @@
 #include <nlohmann/json.hpp>
 using nlohmann::detail::dtoa_impl::reinterpret_bits;
 
+#include <algorithm>
 #include <array>
 #include <cmath>
 #include <cstdint>
@@ -666,13 +667,24 @@ void check_shortest(double v)
     const std::string text(buf.data(), end);
     CAPTURE(text)
     CHECK(parse_double(text) == v);
-    // the layout is that of format_buffer() for the same digits
+    // the layout is that of format_buffer() for the digits of Zmij
+    const auto sd = nlohmann::detail::zmij::to_shortest(reinterpret_bits<std::uint64_t>(v));
+    const std::uint64_t significand = sd.has_digit ? (sd.integral * 10) + sd.digit : sd.integral;
+    int exponent = sd.has_digit ? sd.exponent : sd.exponent + 1;
+    std::string significand_digits = std::to_string(significand);
+    while (significand_digits.size() > 1 && significand_digits.back() == '0')
+    {
+        significand_digits.pop_back();
+        ++exponent;
+    }
     std::array<char, 64> reference{};
-    int len = 0;
-    int exponent = 0;
-    nlohmann::detail::dtoa_impl::shortest_digits(reference.data(), len, exponent, v);
-    const char* const reference_end = nlohmann::detail::dtoa_impl::format_buffer(reference.data(), len, exponent, -4, 15);
+    std::copy(significand_digits.begin(), significand_digits.end(), reference.begin());
+    const char* const reference_end = nlohmann::detail::dtoa_impl::format_buffer(reference.data(), static_cast<int>(significand_digits.size()), exponent, -4, 15);
     CHECK(text == std::string(reference.data(), static_cast<std::size_t>(reference_end - reference.data())));
+    // and write_positive() is what to_chars() calls
+    std::array<char, 64> positive{};
+    const char* const positive_end = nlohmann::detail::dtoa_impl::write_positive(positive.data(), positive.data() + positive.size(), v);
+    CHECK(text == std::string(positive.data(), static_cast<std::size_t>(positive_end - positive.data())));
     const auto de = digits_and_exponent(text);
     const std::string& digits = de.first;
     if (digits.size() > 1)
@@ -785,3 +797,58 @@ TEST_CASE("shortest digits of doubles")
         }
     }
 }
+
+TEST_CASE("choice of the conversion")
+{
+    using nlohmann::detail::dtoa_impl::is_binary64;
+
+    SECTION("by the format of the type")
+    {
+        // Zmij needs binary64 numbers; everything else uses Grisu2
+        static_assert(!is_binary64<float>::value, "float is not binary64");
+        static_assert(is_binary64<double>::value == (std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53),
+                      "double is binary64 where it is IEEE 754 with 53 digits");
+        static_assert(!is_binary64<int>::value, "integers are not binary64");
+        static_assert(is_binary64<long double>::value == (std::numeric_limits<long double>::is_iec559 && std::numeric_limits<long double>::digits == 53 && sizeof(long double) == 8),
+                      "long double is binary64 where it has the format of a double");
+        CHECK(!is_binary64<float>::value);
+        CHECK(is_binary64<double>::value);
+    }
+
+    SECTION("float: Grisu2, double: Zmij")
+    {
+        // 5.3165205877497296e+16 is one of the doubles for which Grisu2 does not find the shortest digits
+        constexpr double value = 5.3165205877497296e+16;
+        std::array<char, 64> buf{};
+        const char* const last = buf.data() + buf.size();
+
+        char* end = nlohmann::detail::dtoa_impl::write_positive(buf.data(), last, value);
+        CHECK(std::string(buf.data(), end) == "5.31652058774973e+16");
+        end = nlohmann::detail::dtoa_impl::write_positive_grisu2(buf.data(), last, value);
+        CHECK(std::string(buf.data(), end) == "5.3165205877497296e+16");
+
+        constexpr float f = 1.1754944e-38f;
+        end = nlohmann::detail::dtoa_impl::write_positive(buf.data(), last, f);
+        const std::string dispatched(buf.data(), end);
+        end = nlohmann::detail::dtoa_impl::write_positive_grisu2(buf.data(), last, f);
+        CHECK(dispatched == std::string(buf.data(), end));
+    }
+
+    SECTION("long double with the format of a double: Zmij")
+    {
+        // (on platforms where long double is wider, Grisu2 does not apply either: the snprintf fallback does)
+        if (std::numeric_limits<long double>::digits == 53 && std::numeric_limits<long double>::is_iec559)
+        {
+            using long_double_json = nlohmann::json::with_float_t<long double>;
+            for (const double d :
+                    {
+                        5.3165205877497296e+16, 1.0, 0.1, 123456.789, 2.2250738585072014e-308, 1.7976931348623157e+308, -5.3165205877497296e+16
+                    })
+            {
+                CAPTURE(d)
+                CHECK(long_double_json(static_cast<long double>(d)).dump() == nlohmann::json(d).dump());
+            }
+            CHECK(long_double_json(5.3165205877497296e+16L).dump() == "5.31652058774973e+16");
+        }
+    }
+}