PHP 8 and Legacy Code

Presented on January 21st 2021 at the PHPcc Online Conference.
https://thephp.cc/dates/2021/01/the-online-php-conference
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With the release of PHP 8, unit tests have become more important than ever before as there are numerous changes which can only be detected via tests.

But what if you maintain a legacy project which is still using PHPUnit 5? And what about extensions to this software running integration tests using (parts of) your test set up?

Using WordPress as an example, let's take a look at how a legacy project can prepare for compatibility with PHP 8 and at the problems they run into when paying up some of their technical debt. What are the extra complications they run into? And how to set priorities with the added time pressure of the PHP 8 release being around the corner?
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Transcript

1. PHP 8 and Legacy Code A case-study Juliette Reinders Folmer Tweet about it: @jrf_nl #OnlinePHPConference © Sebastian Bergmann
2. PHP 8 26 November 2020 © FlyClipArt
3. New in PHP 8.0 Match control structure Attributes Nullsafe object operator Trailing comma in closure use Constructor property promotion Non capturing catch Union types Mixed type Static return type Throw expressions Stringable Magic method signature check Stable sorting ::class on objects Syntax tweaks Named arguments Reclassify engine warnings Saner numeric strings Saner string to number comparisons Locale independent float to string cast Stricter type check for arithmetic/ bitwise operators Consistent type errors for internal functions "bug fixes"
4. An Example <?php declare(strict_types = 1); vprintf( 'The %s', 'dog' ); vprintf( 'The %s', ['dog'] ); PHP < 8.0 PHP 8.0 The dog Uncaught TypeError: vprintf(): The dog Argument #2 ($values) must be of type array, string given
5. “ As a rare exception, this BC break will probably hit php-src harder than actual users of PHP "Backward Incompatible Changes" as per the Consistent type errors for internal functions RFC
6. Another example <?php $sub = substr('abcdef', 4, -4); if ($sub === false) { echo 'fail'; } else { echo 'do something with $sub'; } PHP < 8.0 PHP 8.0 fail do something with $sub
7. test Test TEST
8. Test Requirements Have tests Strict assertions High code coverage, strictly measured Happy & unhappy path
9. PHP 8 Compatibility Checklist ❑ Wait for PHP 8 compatible tooling ❑ Get the test suite running on PHP 8 ❑ Run static analysis ❑ Fix every issue ❑ Update external dependencies ❑ Review public parameter names
10. WordPress A case-study
11. WordPress Test Suite Have tests Strict assertions High code coverage, strictly measured Happy & unhappy path
12. Testing WordPress on PHP 8 July August September October November December First PHP 8 tickets opened
13. PHPUnit vs PHP PHPUnit / PHP 5.6 7.0 7.1 7.2 7.3 7.4 8.0 5.x 6.x 7.x 8.x 9.x 9.3+ void
14. Testing WordPress on PHP 8 July August September October November December First PHP 8 tickets opened Drop PHP < 7.1 ?
15. Let's Look at the Stats
16. Let's Look at the Stats
17. Let's Look at the Stats
18. Let's Look at the Stats
19. Let's Look at the Stats
20. Testing WordPress on PHP 8 July August September October November December First PHP 8 tickets opened Drop PHP < 7.1 ? Fixed rolling schedule proposal
21. Constraints and Roadblocks ▪ Supporting PHP 5.6 + 7.0 still required ▪ Plugin tests often extend WP integration test suite ▪ PHPUnit < 9.3 not compatible with PHP 8.0 - Mocking - @runInSeparateProcess ▪ PHPUnit 7 Phar will not run on PHP 8.0 ▪ Committed composer.lock file
22. Solution "autoload-dev": { "files": [ "tests/includes/MockObject/Builder/NamespaceMatch.php", "tests/includes/MockObject/Builder/ParametersMatch.php", "tests/includes/MockObject/InvocationMocker.php", "tests/includes/MockObject/MockMethod.php" ], "exclude-from-classmap": [ "vendor/phpunit/…/MockObject/Builder/NamespaceMatch.php", "vendor/phpunit/…/MockObject/Builder/ParametersMatch.php", "vendor/phpunit/…/MockObject/InvocationMocker.php", "vendor/phpunit/…/MockObject/MockMethod.php" ] }, ▪ Composer, not phar ▪ Lock at PHPUnit 7.5 ▪ Downgrade to PHPUnit 5 in CI for PHP 5.6, 7.0 ▪ Use MockObject classes from PHPUnit 9.3 ▪ Separate process => separate group
23. Testing WordPress on PHP 8 July August September October November December First PHP 8 tickets opened Drop PHP < 7.1 ? Fixed rolling schedule proposal Tests running on PHP 8 Tests passing on PHP 8
24. WordPress Test Suite Have tests Strict assertions High code coverage, strictly measured Happy & unhappy path
25. Testing WordPress on PHP 8 July August September October November December First PHP 8 tickets opened Drop PHP < 7.1 ? Fixed rolling schedule proposal Tests running on PHP 8 Tests passing on PHP 8 WP/ PHP 8 compat report External dependency updates WP.5.6 released "beta" compatible with PHP 8
26. "beta-compatible" Fix all KNOWN issues Undiscovered issues ? Parameter name review Plugins & themes not being compatible Plugins & themes doing it wrong™
27. WordPress Plugins & Themes
28. Test Requirements Happy & unhappy path High code coverage, strictly measured Strict assertions Have tests
29. Constraints Support multiple WP versions Support multiple PHP versions No control over run environment
30. Mock-based Tests PHPUnit 5.x composer.lock Platform - php 5.6 PHPUnit 5.x – 9.x CI: composer update … --ignore-platform-reqs Needs PHPUnit cross-version compatibility layer
31. WP Integration Tests PHPUnit 5.x composer.lock Platform - php 5.6 PHPUnit 5.x – 7.x CI: composer update … --ignore-platform-reqs Need PHPUnit cross-version compatibility layer Need custom autoload for MockObject
32. New Tooling PHPUnit Polyfills WP Test Utils Sponsored by: Alternative: Symfony Bridge * Supports PHPUnit 4.8 – 9.x, PHP 5.5 – 8.0
33. “ The barrier for updating legacy code to use a more modern PHP version has gone up exponentially and for some, may even have become insurmountable. Juliette Reinders Folmer "A Perfect Storm"
34. Further Reading ▪ The 2020 WordPress and PHP 8 Compatibility Report https://developer.yoast.com/blog/the-2020-wordpress-and-php-8- compatibility-report/ ▪ A Perfect Storm https://24daysindecember.net/2020/12/21/a-perfect-storm/ ▪ PHPUnit Polyfills https://packagist.org/packages/yoast/phpunit-polyfills ▪ WP Test Utils https://packagist.org/packages/yoast/wp-test-utils
35. Thanks! Any questions ? Slides: https://speakerdeck.com/jrf Feedback: https://joind.in/talk/dafa1 @jrf_nl @jrfnl