TYPO3 Core

Composer 2.2 throws an exception when updating:

  [RuntimeException]                                         
  Cannot set the alias loader, as it is already registered!  

Exception trace:

Exception trace:
 () at /Users/st/scripts/projects/.../src/vendor/typo3/class-alias-loader/src/ClassAliasMap.php:72
 TYPO3\ClassAliasLoader\ClassAliasMap::setClassAliasLoader() at /Users/st/scripts/projects/.../src/vendor/typo3/alias-loader-include.php:9
 require() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/Autoload/AutoloadGenerator.php:1419
 Composer\Autoload\composerRequire() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/EventDispatcher/EventDispatcher.php:512
 Composer\EventDispatcher\EventDispatcher->getScriptListeners() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/EventDispatcher/EventDispatcher.php:455
 Composer\EventDispatcher\EventDispatcher->getListeners() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/EventDispatcher/EventDispatcher.php:172
 Composer\EventDispatcher\EventDispatcher->doDispatch() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/EventDispatcher/EventDispatcher.php:118
 Composer\EventDispatcher\EventDispatcher->dispatchScript() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/Installer.php:371
 Composer\Installer->run() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/Command/UpdateCommand.php:249
 Composer\Command\UpdateCommand->execute() at phar:///Users/st/.composer/vendor/bin/composer-dev/vendor/symfony/console/Command/Command.php:245
 Symfony\Component\Console\Command\Command->run() at phar:///Users/st/.composer/vendor/bin/composer-dev/vendor/symfony/console/Application.php:835
 Symfony\Component\Console\Application->doRunCommand() at phar:///Users/st/.composer/vendor/bin/composer-dev/vendor/symfony/console/Application.php:185
 Symfony\Component\Console\Application->doRun() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/Console/Application.php:332
 Composer\Console\Application->doRun() at phar:///Users/st/.composer/vendor/bin/composer-dev/vendor/symfony/console/Application.php:117
 Symfony\Component\Console\Application->run() at phar:///Users/st/.composer/vendor/bin/composer-dev/src/Composer/Console/Application.php:128
 Composer\Console\Application->run() at phar:///Users/st/.composer/vendor/bin/composer-dev/bin/composer:73
 require() at /Users/st/.composer/vendor/bin/composer-dev:30

When reverting to composer 2.1, the error vanishes.

I'm planning on creating an comment in the official discussion about this as well, but IMHO this is an issue with TYPO3 and not composer itself.

I was able to ensure that this issue was not due to additional packages like "helhum/typo3-console" or others.

1. Install composer snapshot (composer self-update --snapshot)
2. Update packages (composer update)