Yesterday Jorgi Boggiano, a co-founder of Packagist, the PHP Package Repository for Composer, announced that Composer 2.3 is ready to be released and requested assistance in testing the new version. He reminded that you need to run the command  composer self-update --preview to install the pre-release. Please note that it is available only if you’re using PHP 7.2.5 or higher.

The new release contains significant internal changes targeted to modernize the PHP code. The most important changes include:

• the minimum supported PHP version was changed from 5.3.2 to 7.2.5;
• Symfony component dependencies were upgraded from 2.8.x to 5.4.x;
• added declare(strict_types=1) to all the files. It might cause issues in some cases;
• added return types wherever possible (except the classes and interfaces that are being extended often, to keep backward compatibility). This change will likely cause issues with the code that extends the modified classes and interfaces and does not declare the same return types.

The complete list of changes is available here. However, it is clear that many of them might cause issues on some projects. That’s why it is important to test the release candidate to prepare for the changes that will be introduced in the upcoming version. For now, it is still possible to get back onto the latest stable version, 2.2, using the command composer self-update --stable.