Explore why PHP 8.4 polyfill is not loaded for test runs on PHP 8.3

Yep, the PHP 8.4 polyfill is not loaded by composer. Weirdly, the PHP 8.5 one is.

https://git.drupalcode.org/issue/drupal-3563359/-/jobs/7679099

Is there a package with symfony/polyfill-php84 in the replace section, perhaps?

Short answer to #8 is no. I will push an MR shortly. More info below.

I set the robots to work on this to answer the question and was able to replicate and pinpoint the issue.

\Drupal\Tests\package_manager\Build\TemplateProjectTestBase::createTestProject disables packagist and points at a locally generated repo. That repo is generated in ::createVendorRepository which explicitly unsets symfony/polyfill-php84 from the requirements. This also explains why symfony/polyfill-php85 is still available. There is also a comment before the unset:

// These polyfills are dependencies of some packages, but for reasons we
// don't understand, they are not installed in code bases built on PHP
// versions that are newer than the ones being polyfilled, which means we
// won't be able to build our test project because these polyfills aren't
// available in the local code base. Since we're guaranteed to be on PHP
// 8.3 or later, no package should need to polyfill older versions.

There is a simple explanation to this. They are not installed on newer versions because they appear in replace section of drupal/drupal.

I think we should restore the array_any call, remove the line that unsets polyfill-php84, fix the comment that says we don't know what this does and then potentially look at dynamically populating that list to be unset, from the replace section of drupal/drupal.

FWIW #9 is mostly about 11.x, but it makes sense to resolve the @todo comment in main, and to provide a better explanation. I've created 2 MRs, one for main, one for 11.x.

We need a better issue title so it makes sense for main, but I couldn't think of how to word it.

Think the title is fine?

This list should be kept in sync with the replace section of composer.json.

Should we have a test around this? Would be out of scope here but asking.

I'm being awful about using that tag sorry for the noise

I'm not sure how easy it would be to write a test that doesn't need to be kept up to date when we change minimum PHP versions / new polyfills are added (which would have the same problem), we could open a follow-up issue if someone has an idea how to do it.

Committed/pushed the respective MRs to main, 12.0.x and 11.x, thanks!