Autoloader cache not refreshing

[NicoleGeissinger]

Describe the bug

I found that when the class-loader-cache is created, it isn't refreshing when new (or existing) classes are created/changed. I found instances where my cache was over 2 weeks old despite many changes performed to related classes.

My solve for this was to SFTP into my WP Engine hosted server and manually delete the class-loader-cache directory to ensure it grabs the latest changes.

This results in scenarios of "works locally but not on my servers". I think this issue stems out of iterative deployments. One scenario in my testing, it worked just fine, but it was a server that we hadn't deployed any of the work to yet before any caches were created. If a cache exists and you adjust something in the autoloaded classes, the cache doesn't pick those up.

Ideally there is a mechanism to manually refresh that cache or it auto refreshes when it detects that a class has been modified. I did see the const to skip cache which will be really helpful in debugging this in the future, but ideally we have a reliable source to auto refresh it along with a manual refresh option.

Steps to Reproduce

1. Create a new class using the ModuleInterface and deploy to your server.
2. Make some changes that you can observe either from the front or backend (both affected) and deploy.
3. Double check if your changes can be observed and double check the last modified date of the class-loader-cache and your autoloaded classes.
4. If the changes aren't showing up due to the cache, deleting the class-loader-cache will fix the issue.

Screenshots, screen recording, code snippet

Observe the last modified dates not in alignment. This reflects the effect of the site working in a past state despite all the files being up to date.

Environment information

Myself and another co-worker reported this issue on WP Engine hosted sites so unsure this is relevant at all. There is a thread in the company slack around this.

WordPress information

WordPress 6.8.3

Code of Conduct

• I agree to follow this project's Code of Conduct

[claytoncollie]

@darylldoyle Can we create a hash of all PHP files in the directory and use that as the cache key? If any file changes, the hash changes and the cache is invalidated.

Potential solution

protected function get_cache_hash( string $dir ): string {
    $files = new \RecursiveIteratorIterator(
        new \RecursiveDirectoryIterator( $dir, \RecursiveDirectoryIterator::SKIP_DOTS )
    );
    
    $hash_data = [];
    foreach ( $files as $file ) {
        if ( $file->isFile() && $file->getExtension() === 'php' ) {
            // Use file path + modification time for hash
            $hash_data[] = $file->getPathname() . ':' . $file->getMTime();
        }
    }
    
    sort( $hash_data ); // Ensure consistent ordering
    return md5( implode( '|', $hash_data ) );
}

public function get_classes( $dir ) {
    $this->directory_check( $dir );

    $class_finder = Discover::in( $dir );
    $class_finder->classes();
    $class_finder->withoutChains();

    if ( $this->should_use_cache() ) {
        $cache_hash = $this->get_cache_hash( $dir );
        $class_finder->withCache(
            __NAMESPACE__ . '_' . $cache_hash,
            new FileDiscoverCacheDriver( $dir . '/class-loader-cache' )
        );
    }

    $classes = array_filter( $class_finder->get(), fn( $cl ) => is_string( $cl ) );

    return $classes;
}