Your requirements could not be resolved to an installable set of packages. Problem 1 - vimeo/psalm[5.26.1, ..., 5.x-dev] require nikic/php-parser ^4.17 -> satisfiable by nikic/php-parser[v4.17.0, ..., 4.x-dev]. - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.17.0, ..., 4.x-dev, v5.0.0alpha1, ..., v5.3.1]. - infection/infection[0.29.9, ..., 0.29.x-dev] require nikic/php-parser ^5.3 -> satisfiable by nikic/php-parser[v5.3.0, v5.3.1]. - Root composer.json requires infection/infection ^0.29.9 -> satisfiable by infection/infection[0.29.9, 0.29.x-dev]. - Root composer.json requires vimeo/psalm ^5.26.1 -> satisfiable by vimeo/psalm[5.26.1, 5.x-dev]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.