[kasper-agg]

Description

composer.json maps the empty PSR-4 prefix to src/:

"psr-4": {
    "": "src/"
}

An empty prefix is a fallback for every class. Unless a project uses an authoritative classmap (classmap-authoritative), Composer's autoloader therefore checks vendor/openmage/composer-plugin/src/<Class>.php for every class it doesn't find in its classmap. In OpenMage that's every Magento class (app/code, lib/Varien, zf1), on every request. Composer's autoloader is registered before Varien_Autoload, so this lookup happens first, for each class.

Traced on a stock OpenMage install (strace -e trace=%file, loading five classes):

access(".../vendor/openmage/composer-plugin/src/Mage_Core_Model_App.php", F_OK) = -1 ENOENT
access(".../vendor/openmage/composer-plugin/src/Varien_Object.php", F_OK) = -1 ENOENT
access(".../vendor/openmage/composer-plugin/src/Mage_Catalog_Model_Product.php", F_OK) = -1 ENOENT
access(".../vendor/openmage/composer-plugin/src/Zend_Db_Select.php", F_OK) = -1 ENOENT
access(".../vendor/openmage/composer-plugin/src/Foo_Missing_Class.php", F_OK) = -1 ENOENT

One failed file lookup per class. PHP doesn't cache paths that don't exist, so each one reaches the filesystem.

All classes in src/ are in the OpenMage\ComposerPlugin namespace, so this PR maps only that prefix:

"psr-4": {
    "OpenMage\\ComposerPlugin\\": "src/OpenMage/ComposerPlugin/"
}

Effect

• With this mapping, the same trace shows 0 lookups in vendor/openmage/composer-plugin/src/.
• The plugin's own classes load as before. Checked on a stock OpenMage install with the mapping applied: class_exists() finds OpenMage\ComposerPlugin\Plugin and the copy plugins, and Composer still loads the plugin (composer -vvv shows "Loading plugin OpenMage\ComposerPlugin\Plugin").
• No code changes. Plugin::getPlugins() derives class names from the files' namespace lines, and those are unchanged.
• Shops that already use classmap-authoritative see no difference.

OpenMage gets the benefit after a release of this package and a composer update openmage/composer-plugin.

Checks

• composer phpunit:test: OK (50 tests, 50 assertions).
• composer phpstan: no errors.
• composer validate: valid. It only warns about the existing unbound * constraints for symfony/filesystem and symfony/finder.
• composer rector:test fails with Unknown named parameter $strictBooleans, also without this change. .rector.php uses a parameter that newer Rector versions (allowed by ^2.1.2) no longer accept. This is unrelated to this PR, so I've left it alone.

Context

Found while looking into failed file lookups in OpenMage's autoloading, see OpenMage/magento-lts#5722 and OpenMage/magento-lts#5787.