Follow-up for #3033123: PHP 5.5 + Drupal 8.7 test runs are suddenly failing

Let's trigger the failure.

Based on https://www.drupal.org/pift-ci-job/1188059, we know that at least on Feb 1 this was still passing tests just fine. Core's composer.json and composer.lock were last changed on Jan 15 in SA-CORE-2019-002 (commit 7e1a53c). I have no idea how this is possible. The detailed logs for old test runs aren't available.

Installing PHP 5…

Testbot--
Testbot--
Testbot--

Testing started at 21:20 ...
/usr/local/bin/php /private/var/folders/4l/5sndwsz50tqgxjh2525n10br0000gp/T/ide-phpunit.php --configuration /Users/wim.leers/Work/d8/core/phpunit.xml Drupal\Tests\jsonapi\Kernel\Normalizer\JsonApiDocumentTopLevelNormalizerTest /Users/wim.leers/Work/d8/modules/jsonapi/tests/src/Kernel/Normalizer/JsonApiDocumentTopLevelNormalizerTest.php
#!/usr/bin/env php
PHPUnit 4.8.36 by Sebastian Bergmann and contributors.

Testing Drupal\Tests\jsonapi\Kernel\Normalizer\JsonApiDocumentTopLevelNormalizerTest
EIE.......

Time: 14.64 seconds, Memory: 8.75MB

There were 2 errors:

1) Drupal\Tests\jsonapi\Kernel\Normalizer\JsonApiDocumentTopLevelNormalizerTest::testNormalize
PHPUnit_Framework_Exception: PHP Fatal error:  Default value for parameters with a class type hint can only be NULL in /Users/wim.leers/Work/d8/modules/jsonapi/src/JsonApiResource/ResourceObjectData.php on line 25
Fatal error: Default value for parameters with a class type hint can only be NULL in /Users/wim.leers/Work/d8/modules/jsonapi/src/JsonApiResource/ResourceObjectData.php on line 25

/Users/wim.leers/Work/d8/vendor/phpunit/phpunit/phpunit:52

2) Drupal\Tests\jsonapi\Kernel\Normalizer\JsonApiDocumentTopLevelNormalizerTest::testNormalizeUuid
PHPUnit_Framework_Exception: PHP Fatal error:  Default value for parameters with a class type hint can only be NULL in /Users/wim.leers/Work/d8/modules/jsonapi/src/JsonApiResource/ResourceObjectData.php on line 25
Fatal error: Default value for parameters with a class type hint can only be NULL in /Users/wim.leers/Work/d8/modules/jsonapi/src/JsonApiResource/ResourceObjectData.php on line 25

/Users/wim.leers/Work/d8/vendor/phpunit/phpunit/phpunit:52

FAILURES!
Tests: 10, Assertions: 67, Errors: 2, Incomplete: 1.

At last, actionable feedback.

#3033123: Add ResourceObjectData, IncludedData, and RelationshipData specializations of Data introduced a PHP 7 typehint. This is what apparently caused all this. And because d.o once again forgot about our configured daily test runs (sadly only one environment combination possible for on-commit test runs), we weren't notified of this PHP 5 failure. 😢

🥳 Green! ✅