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Move the dump, comparison, and large-object tests to unit-json_view_dump.cpp

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The dump and comparison tests moved to their own file in the dump pull
request; the hash index tests of this branch join them there.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-11 11:31:08 +02:00
1 parent ae04acbf33
commit c755fc0642
2 files changed
+263 -485
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tests/src/unit-json_view_dump.cpp
+263
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@@ -20,6 +20,7 @@ using nlohmann::ordered_json_view;
using json_view_test::generator;
using json_view_test::has_duplicate_keys;
#include <array>
#include <cmath>
#include <cstddef>
#include <cstdint>
@@ -273,3 +274,265 @@ TEST_CASE("json_view comparison")
CHECK(a.root() != c.root());
}
}
TEST_CASE("json_view large objects")
{
// objects with 128 members or more are looked up with a hash index
for (const std::size_t members :
{
127u, 128u, 129u, 10000u
})
{
CAPTURE(members)
std::string text = "{";
for (std::size_t i = 0; i < members; ++i)
{
text += (i != 0 ? ",\"" : "\"") + std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\\n" : "") + "\":" + std::to_string(i);
}
text += R"(,"":"empty key","k1":"a duplicate of an earlier key"})";
const json_document d = json_document::parse(text);
const json_view v = d.root();
const json j = json::parse(text);
for (std::size_t i = 0; i < members; ++i)
{
const std::string key = std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\n" : "");
CHECK(v[key].get<std::size_t>() == i);
CHECK(v.contains(key));
CHECK(v.find(key).key() == key);
CHECK(v.at(key).get<std::size_t>() == i);
CHECK(!v.contains(key + "x"));
}
CHECK(v[""].get_string() == "empty key");
CHECK(v["k1"].get<int>() == 1); // the first of duplicate keys, as for small objects
CHECK(!v.contains("missing"));
CHECK_THROWS_WITH_AS(v.at("missing"), "[json.exception.out_of_range.403] key 'missing' not found", json::out_of_range&);
CHECK(v == j);
CHECK(v.materialize() == j);
}
SECTION("duplicate keys: the first member wins, with and without a table")
{
// an object of `total` members: the keys "k0".."k<n-1>" in order, then
// three keys repeated twice more (one copy in the middle, one at the
// end), and two keys repeated once; the value of a member is its
// position, so that the first member of a key can be told apart
struct member
{
std::string key;
std::size_t position;
};
const auto make_members = [](std::size_t total)
{
std::vector<std::string> keys;
for (std::size_t i = 0; i + 8 < total; ++i)
{
keys.push_back("k" + std::to_string(i));
}
const std::size_t n = keys.size();
const std::array<std::size_t, 3> triple = {{3, 17, n - 1}};
const std::array<std::size_t, 2> twice = {{5, n / 2}};
std::vector<std::string> ordered = keys;
for (const std::size_t i : triple)
{
ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 2), keys[i]);
}
for (const std::size_t i : twice)
{
ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 3), keys[i]);
}
for (const std::size_t i : triple)
{
ordered.push_back(keys[i]);
}
std::vector<member> result;
result.reserve(ordered.size());
for (std::size_t i = 0; i < ordered.size(); ++i)
{
result.push_back({ordered[i], i});
}
return result;
};
// 100 and 127 members: no table; 128 members and more: a table
for (const std::size_t total :
{
100u, 127u, 128u, 200u, 5000u
})
{
CAPTURE(total)
const std::vector<member> members = make_members(total);
REQUIRE(members.size() >= total);
REQUIRE(members.size() >= 100);
std::string text = "{";
std::map<std::string, std::size_t> first;
std::map<std::string, std::size_t> last;
for (const member& m : members)
{
text += (text.size() > 1 ? ",\"" : "\"") + m.key + "\":" + std::to_string(m.position);
first.insert({m.key, m.position});
last[m.key] = m.position;
}
text += '}';
REQUIRE(first.size() < members.size());
const json_document d = json_document::parse(text);
const json_view v = d.root();
const json j = json::parse(text);
CHECK(v.size() == members.size()); // every occurrence is visited
const json m = v.materialize();
for (const auto& entry : first)
{
CAPTURE(entry.first)
const std::size_t expected = entry.second;
CHECK(v[entry.first].get<std::size_t>() == expected);
CHECK(v.at(entry.first).get<std::size_t>() == expected);
CHECK(v.find(entry.first).value().get<std::size_t>() == expected);
CHECK(v.value(entry.first, std::size_t{0}) == expected);
CHECK(v.contains(entry.first));
CHECK(v.count(entry.first) == 1);
const std::string pointer = "/" + entry.first;
CHECK(v[json::json_pointer(pointer)].get<std::size_t>() == expected);
CHECK(v.at(json::json_pointer(pointer)).get<std::size_t>() == expected);
CHECK(v.value(json::json_pointer(pointer), std::size_t{0}) == expected);
CHECK(v.contains(json::json_pointer(pointer)));
// materialize() and parse() keep the last value instead
CHECK(j[entry.first].get<std::size_t>() == last.at(entry.first));
CHECK(m[entry.first].get<std::size_t>() == last.at(entry.first));
}
CHECK(!v.contains("k"));
CHECK(v["missing"].is_discarded());
CHECK(v.materialize() == j);
CHECK(v == j);
}
}
SECTION("colliding keys")
{
// the hash is not seeded, so keys that all land in one place must not
// make the table build quadratic: such an object gets no table and is
// searched linearly
constexpr std::size_t members = 300;
constexpr std::size_t slots = 1024; // the table size for 300 members: the next power of two >= 600
std::vector<std::string> colliding;
std::vector<std::string> spread;
for (std::uint64_t counter = 0; colliding.size() < members || spread.size() < members; ++counter)
{
std::string key(8, 'a');
std::uint64_t x = counter;
for (std::size_t i = 0; i < 8; ++i, x /= 26)
{
key[i] = static_cast<char>('a' + (x % 26));
}
const bool lands_in_slot_zero = (nlohmann::detail::view::key_hash(key.data(), key.size()) & (slots - 1)) == 0;
if (lands_in_slot_zero && colliding.size() < members)
{
colliding.push_back(key);
}
else if (!lands_in_slot_zero && spread.size() < members)
{
spread.push_back(key);
}
}
const auto make_text = [](const std::vector<std::string>& keys)
{
std::string text = "{";
for (std::size_t i = 0; i < keys.size(); ++i)
{
text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i % 10);
}
return text + "}";
};
const std::string colliding_text = make_text(colliding);
const std::string spread_text = make_text(spread);
json_document with_collisions = json_document::parse(colliding_text);
json_document without_collisions = json_document::parse(spread_text);
for (const auto* pair :
{
&colliding, &spread
})
{
const json_view v = (pair == &colliding ? with_collisions : without_collisions).root();
for (std::size_t i = 0; i < members; ++i)
{
CAPTURE(i)
CHECK(v[(*pair)[i]].get<std::size_t>() == i % 10);
CHECK(v.at((*pair)[i]).get<std::size_t>() == i % 10);
CHECK(v.find((*pair)[i]).key() == (*pair)[i]);
CHECK(!v.contains((*pair)[i] + "x"));
}
CHECK(!v.contains("missing"));
}
CHECK(with_collisions.root() == json::parse(colliding_text));
// only the object with the spread keys got a table (both texts have the
// same length, so the tables are the only difference)
with_collisions.shrink_to_fit();
without_collisions.shrink_to_fit();
CHECK(without_collisions.memory_usage() >= with_collisions.memory_usage() + (slots * sizeof(std::uint32_t)));
}
SECTION("shrink_to_fit releases the tables' spare capacity")
{
const auto make_text = [](int objects, int members)
{
std::string text = "[";
for (int object = 0; object < objects; ++object)
{
text += object != 0 ? ",{" : "{";
for (int i = 0, n = members + object; i < n; ++i)
{
text += (i != 0 ? ",\"" : "\"") + std::to_string(i) + "\":" + std::to_string(i);
}
text += '}';
}
return text + "]";
};
const std::string small_text = make_text(5, 150);
const std::string big_text = make_text(40, 400);
// reading a big text, and then a small one, leaves the spare capacity
// of the big one: shrink_to_fit() brings the document to the size of
// one parsed from the small text alone
json_document d = json_document::parse(big_text);
const std::size_t big = d.memory_usage();
d.read(small_text);
CHECK(d.memory_usage() >= big);
d.shrink_to_fit();
json_document fresh = json_document::parse(small_text);
fresh.shrink_to_fit();
CHECK(d.memory_usage() == fresh.memory_usage());
CHECK(d.memory_usage() < big / 2);
CHECK(d.root() == json::parse(small_text));
for (int object = 0; object < 5; ++object)
{
const json_view v = d.root()[static_cast<std::size_t>(object)];
for (int i = 0, n = 150 + object; i < n; ++i)
{
CHECK(v[std::to_string(i)].get<int>() == i);
}
}
}
SECTION("nested, reused, and in arrays")
{
std::string inner = "{";
for (int i = 0; i < 300; ++i)
{
inner += (i != 0 ? ",\"m" : "\"m") + std::to_string(i) + "\":" + std::to_string(i);
}
inner += '}';
const std::string text = "[" + inner + ",{\"x\":" + inner + "}," + inner + "]";
json_document d = json_document::parse(text);
CHECK(d.root()[0]["m299"].get<int>() == 299);
CHECK(d.root()[1]["x"]["m150"].get<int>() == 150);
CHECK(d.root()[2]["m0"].get<int>() == 0);
const std::size_t with_index = d.memory_usage();
d.read(std::string("{\"small\": 1}"));
CHECK(d.root()["small"].get<int>() == 1);
d.read(text);
CHECK(d.root()[2]["m7"].get<int>() == 7);
CHECK(d.memory_usage() >= with_index / 2);
}
}