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Merged
jviotti merged 1 commit into from
Jun 27, 2026
Merged

Implement a helper to check equality of JSON object keys #2546

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22 changes: 22 additions & 0 deletions src/core/json/include/sourcemeta/core/json_object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,28 @@ template <typename Key, typename Value, typename Hash> class JSONObject {
key_type first;
mapped_type second;
hash_type hash;

/// Check whether this entry's key equals the given key, comparing the
/// precomputed hashes first and only falling back to a string comparison
/// when the hash is not perfect. For example:
///
/// ```cpp
/// #include <sourcemeta/core/json.h>
/// #include <cassert>
///
/// const sourcemeta::core::JSON document =
/// sourcemeta::core::parse_json("{ \"foo\": 1 }");
/// const auto &entry{*document.as_object().cbegin()};
/// assert(entry.key_equals(
/// "foo", sourcemeta::core::JSON::Object::hash("foo")));
/// ```
[[nodiscard]] inline auto key_equals(const KeyView key,
const hash_type key_hash) const
-> bool {
assert(JSONObject::hash(key) == key_hash);
return this->hash == key_hash &&

@augmentcode augmentcode Bot Jun 27, 2026 •
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src/core/json/include/sourcemeta/core/json_object.h:58: key_equals can return a false positive if a caller accidentally passes a key_hash that doesn’t correspond to the provided key (especially in the is_perfect case where the string comparison is skipped). Other APIs that accept a precomputed hash typically assert(hash(key) == key_hash), so it may be worth adding a similar defensive check here to catch misuse in debug builds.

Severity: medium

Fix This in Augment

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cubic-dev-ai[bot] marked this conversation as resolved.
(hasher.is_perfect(key_hash) || this->first == key);
}
};

using underlying_type = std::vector<Entry>;
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36 changes: 36 additions & 0 deletions test/json/json_object_test.cc
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Expand Up @@ -1478,3 +1478,39 @@ TEST(JSON_object, assign_if_missing_with_string_view) {
EXPECT_EQ(document.at("foo").to_integer(), 1);
EXPECT_EQ(document.at("bar").to_integer(), 2);
}

TEST(JSON_object, entry_key_equals_perfect_match) {
const auto document{sourcemeta::core::parse_json(R"({ "foo": 1 })")};
const auto &entry{*document.as_object().cbegin()};
EXPECT_TRUE(
entry.key_equals("foo", sourcemeta::core::JSON::Object::hash("foo")));
}

TEST(JSON_object, entry_key_equals_perfect_mismatch) {
const auto document{sourcemeta::core::parse_json(R"({ "foo": 1 })")};
const auto &entry{*document.as_object().cbegin()};
EXPECT_FALSE(
entry.key_equals("bar", sourcemeta::core::JSON::Object::hash("bar")));
}

TEST(JSON_object, entry_key_equals_imperfect_match) {
const std::string key(40, 'a');
sourcemeta::core::JSON document{sourcemeta::core::JSON::make_object()};
document.assign(key, sourcemeta::core::JSON{1});
const auto &entry{*document.as_object().cbegin()};
EXPECT_FALSE(document.as_object().hash(key) ==
sourcemeta::core::JSON::Object::hash("a"));
EXPECT_TRUE(entry.key_equals(key, sourcemeta::core::JSON::Object::hash(key)));
}

TEST(JSON_object, entry_key_equals_imperfect_collision_is_rejected) {
const std::string stored{std::string(31, 'a') + "11111110" + "z"};
const std::string other{std::string(31, 'a') + "22222220" + "z"};
sourcemeta::core::JSON document{sourcemeta::core::JSON::make_object()};
document.assign(stored, sourcemeta::core::JSON{1});
const auto &entry{*document.as_object().cbegin()};
EXPECT_EQ(sourcemeta::core::JSON::Object::hash(stored),
sourcemeta::core::JSON::Object::hash(other));
EXPECT_FALSE(
entry.key_equals(other, sourcemeta::core::JSON::Object::hash(other)));
}
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