[iliaal]

When an array or object key failed to encode, json_encode() carried on with the remaining values unless JSON_PARTIAL_OUTPUT_ON_ERROR was set, so jsonSerialize() still ran on later values and a later error could replace the one that caused the failure. Both key sites now bail out the same way a failed value already does; partial output is unchanged.

[anun333]

Quoted below: written with Claude, an LLM, as CONTRIBUTING.md asks us to mark. The builds and test runs behind it are on my machine; the commands to repeat them are under the fold.

Tested at this PR's head (7a0db18326) against today's PHP-8.4 (303bb88f1c5), debug builds. $bad = "k\xff", Probe a JsonSerializable that records its calls:

json_encode() of	PHP-8.4	this PR
[$bad => 1, 'b' => new Probe(1)]	false, Malformed UTF-8; jsonSerialize() called	false, Malformed UTF-8; not called
[$bad => 1, 'b' => new Probe(NAN)]	false, Inf and NaN	false, Malformed UTF-8
the same, JSON_THROW_ON_ERROR	JsonException code 7	code 5
the same, JSON_PARTIAL_OUTPUT_ON_ERROR	{"":1,"b":0}, Inf and NaN	the same
an object with property $bad, then NAN	false, Inf and NaN	false, Malformed UTF-8
a bad key inside one jsonSerialize() result, then NAN	false, Inf and NaN; both called	false, Malformed UTF-8; only the first called
bad key with JSON_INVALID_UTF8_SUBSTITUTE / _IGNORE	{"k�":1,"b":1} / {"k":1,"b":1}	the same
a bad value, then NAN (control)	false, Malformed UTF-8; not called	the same

So keys now stop the encoding the way values already did, and the error reported is the one that caused the failure. ext/json/tests passes at the head (90 tests), and the new test fails on PHP-8.4 without the fix.

It no longer applies to today's PHP-8.4, though: ext/json/json_encoder.c conflicts with 3584a98bda0, which changed the same two key sites, so it needs a rebase.

How this was tested

Linux x86_64, gcc 13.3, debug builds of origin/PHP-8.4 and of this PR's head as it stands (it doesn't cherry-pick onto today's branch):

./buildconf --force
./configure --enable-debug --disable-cgi --disable-phpdbg --disable-fileinfo --enable-pcntl --enable-zend-test --enable-fpm --with-curl --enable-mbstring --disable-mbregex --with-mysqli --with-pdo-mysql
make -j4

class Probe implements JsonSerializable {
    static array $calls = [];
    function __construct(public string $name, public mixed $value = 1) {}
    function jsonSerialize(): mixed { self::$calls[] = $this->name; return $this->value; }
}
// e.g. json_encode(["k\xff" => 1, 'b' => new Probe('b', NAN)]), then json_last_error_msg() and Probe::$calls

Suites: TEST_PHP_EXECUTABLE=$PWD/sapi/cli/php sapi/cli/php run-tests.php -n -q -j4 ext/json/tests on both; the new test copied into the PHP-8.4 tree for the check that it fails there.

[bukka]

I think the change makes sense - it needs rebase though...