Current status: Mitigated by pinning PHPUnit 9.5.x; task remains open so we can figure out how to properly resolve this and update to PHPUnit 9.6. (PHPUnit 10 drops support for PHP ≤8.0, so we won’t be able to update to that too soon.)
CI is failing with the following error/warning (example build):
11:26:00 There were 42 warnings: 11:26:00 11:26:00 1) DeprecatedGlobalTest::testWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 2) MediaWiki\HookContainer\HookContainerTest::testEmitDeprecationWarnings 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 3) MediaWiki\Tests\Unit\Revision\MutableRevisionRecordTest::testGetIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 4) MediaWiki\Tests\Unit\Revision\MutableRevisionRecordTest::testGetPageIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 5) MediaWiki\Tests\Unit\Revision\MutableRevisionRecordTest::testGetParentIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 6) MediaWiki\Tests\Unit\Revision\RevisionArchiveRecordTest::testGetIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 7) MediaWiki\Tests\Unit\Revision\RevisionArchiveRecordTest::testGetPageIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 8) MediaWiki\Tests\Unit\Revision\RevisionArchiveRecordTest::testGetParentIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 9) MediaWiki\Tests\Unit\Revision\RevisionStoreCacheRecordTest::testGetIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 10) MediaWiki\Tests\Unit\Revision\RevisionStoreCacheRecordTest::testGetPageIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 11) MediaWiki\Tests\Unit\Revision\RevisionStoreCacheRecordTest::testGetParentIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10. 11:26:00 11:26:00 phpvfscomposer:///workspace/src/vendor/phpunit/phpunit/phpunit:97 11:26:00 11:26:00 12) MediaWiki\Tests\Unit\Revision\RevisionStoreRecordTest::testGetIdTriggerDeprecatedWarning 11:26:00 Expecting E_DEPRECATED and E_USER_DEPRECATED is deprecated and will no longer be possible in PHPUnit 10.
Some affected patches: https://gerrit.wikimedia.org/r/c/mediawiki/core/+/884414 & https://gerrit.wikimedia.org/r/c/mediawiki/core/+/884065.