Read the Composer 2.3 Release Announcement for more details on the release highlights.

Complete Changelog

• BC Break: the minimum PHP version is now 7.2.5+, use the Composer 2.2 LTS if you are stuck with an older PHP (#10343)
• BC Break: added native parameter & return types to many internal APIs, we explicitly left the most extended/implemented symbols untouched but if this causes problems nonetheless please report it ASAP (#10547, #10561)
• BC Break: added visibility to all constants, a few internal ones have been made private/protected, if this causes problems please report it ASAP (#10550)
• BC Break: the minimum supported Symfony components version is now 5.4, this only affects you if you are requiring composer/composer directly however, which is generally frowned upon
• Bumped composer-plugin-api to 2.3.0
• Bumped bundled Symfony components from 2.8 to 5.4 🥳
• Added declare(strict_types=1) to all the classes, which for sure could cause regressions in edge cases, please report with stack traces (#10567)
• Added --patch-only to the outdated command to only show updates to patch versions and ignore new major/minor versions (#10589)
• Added clickable links to various commands for terminals which support it (#10430)
• Added ProcessExecutor ability to receive commands as arrays by (internals/plugin change only) (#10435)
• Added abandoned flag to show/outdated commands JSON-formatted output (#10485)
• Added config.reference option to path repositories to configure the way the reference is generated, and possibly reduce composer.lock conflicts (#10488)
• Added automatic removal of allow-plugins rules when removing a plugin via the remove command (#10615)
• Added COMPOSER_IGNORE_PLATFOR_REQ & COMPOSER_IGNORE_PLATFOR_REQS env vars to configure the equivalent flags (#10616)
• Added support for Symfony 6.0 components
• Added support for psr/log 3.x (#10454)
• Fixed symlink creation in linux VM guest filesystems to be recognized by Windows (#10592)
• Performance improvement in pool optimization step (#10585)
• Performance improvement in Composer bootstrapping (version guessing) when on a feature branch (#10632)