Repair wp/6.0 branch Actions: Resolve Composer dependencies against the lowest tested PHP version - #84282

Part of #82933.

What?

Makes Composer resolve this branch's dependencies against PHP 5.6.20, the lowest PHP version the unit-test matrix runs and WordPress's minimum PHP version for this release:

• Changes composer.json's config.platform.php from 7.4 to 5.6.20.
• Adds "php": ">=5.6.20" to require.
• Regenerates composer.lock with composer update phpunit/phpunit --with-all-dependencies. The only package changes are:
  • 9 downgrades:
    • symfony/yaml v4.4.45 → v3.4.47
    • doctrine/instantiator 1.5.0 → 1.0.5
    • myclabs/deep-copy 1.13.4 → 1.7.0
    • phpdocumentor/reflection-common 2.2.0 → 1.0.1
    • phpdocumentor/reflection-docblock 5.6.7 → 3.3.2
    • phpdocumentor/type-resolver 1.12.0 → 0.4.0
    • phpunit/php-token-stream 2.0.2 → 1.4.12
    • symfony/polyfill-ctype v1.37.0 → v1.19.0
    • webmozart/assert 1.12.1 → 1.9.1
  • 2 removals:
    • doctrine/deprecations
    • phpstan/phpdoc-parser

This is the wp/6.0 counterpart of #84251 (wp/6.1) and #84227 (wp/6.2).

Why?

With the platform set to 7.4, Composer installs symfony/yaml 4.4, which requires PHP 7.1. The PHP 7.0 jobs run the PHPUnit 6.5 phar from the wp-env image, and the plugin's Composer autoloader is registered in front of the phar's own. When PHPUnit prints a failure diff, it loads Symfony\Component\Yaml\Yaml from the plugin's vendor directory, and PHP 7.0 cannot parse it. Every failing assertion then becomes a fatal error on the PHP 7.0 jobs:

Fatal error: Method PHPUnit\Framework\ExpectationFailedException::__toString() must not throw an exception, caught ParseError: syntax error, unexpected 'const' (T_CONST), expecting variable (T_VARIABLE) in phar:///usr/local/bin/phpunit/phpunit/TextUI/ResultPrinter.php on line 0

Resolving against 5.6.20 picks versions that every job in the matrix can load.

How?

#84251 and #84227 remove config.platform.php entirely and let Composer detect the running PHP version. That doesn't work here. Those branches have no composer.lock and run composer install on the runner at the job's own PHP version. This branch commits a composer.lock and installs inside wp-env's composer container, which runs PHP 8.5. Without a platform value, composer install would check the lock against PHP 8.5 and reject it, because PHPUnit 5.7 and its dependencies don't allow PHP 8. So this branch keeps config.platform.php, sets it to the lowest PHP version the tests run under, and adds the same require.php floor as the other branches.

Use of AI Tools

This PR was created by Claude Code under my supervision. All code should be treated as AI-produced and not yet reviewed by a human until this PR is marked Ready for Review.

🤖 Generated with Claude Code