PHP - Inconsistent mergeFromJsonString behavior

[FabioBatSilva]

The PHP C extension implementation native PHP implementation have different behavior when deserializing a empty JSON object/array.

The native php implementation threats both '{}' and [] as valid inputs.
And the C extension allow only {} (I believe that is the correct behaviour)

This happens BC In php the function json_encode will encode a empty associative array as []

php -r "var_dump(json_encode(array_filter(['foo' => null])));"
string(2) "[]"

And we also get back the same php value when decoding both {} and []:

$php -r "var_dump(json_decode('[]', true, 512, JSON_BIGINT_AS_STRING));"
array(0) {
}

$ php -r "var_dump(json_decode('{}', true, 512, JSON_BIGINT_AS_STRING));"
array(0) {
}

PHP Implementation :

protobuf/php/src/Google/Protobuf/Internal/Message.php

Line 1324 in e3ac4c9

$array = json_decode($input->getData(), true, 512, JSON_BIGINT_AS_STRING);

---

What version of protobuf and what language are you using?
Version: main
Language: php
OS: Linux

What did you do?

<?php

require_once (dirname(__DIR__) . '/vendor/autoload.php');
require_once (__DIR__ . '/test_util.php');

use Foo\TestMessage;

$message = new TestMessage();
$values = array_filter([
    'true_optional_string' => null,
]);

$message->mergeFromJsonString(json_encode($values));
//$message->mergeFromJsonString('[]');

var_dump($message->hasTrueOptionalString());

#### Compile the extension 
./php/tests/compile_extension.sh

# Run script
php -d display_errors=on -dextension=../ext/google/protobuf/modules/protobuf.so json_encode_test.php

What did you expect to see ?

Error parsing JSON

What did you see instead?
C extension:

Fatal error: Uncaught Exception: Error occurred during parsing: Error parsing JSON @1:0: Expected: '{'

PHP implementation:

bool(false)