Your requirements could not be resolved to an installable set of packages. Problem 1 - Conclusion: don't install vimeo/psalm 6.1.0 (conflict analysis result) - Conclusion: don't install infection/infection 0.26.19 (conflict analysis result) - Root composer.json requires vimeo/psalm ^6.1.0 -> satisfiable by vimeo/psalm[6.1.0, 6.x-dev]. - Conclusion: don't install nikic/php-parser v4.18.0 (conflict analysis result) - Conclusion: don't install nikic/php-parser[v4.15.1] | install nikic/php-parser[v5.0.0] (conflict analysis result) - Conclusion: don't install nikic/php-parser v5.0.0 (conflict analysis result) - Root composer.json requires infection/infection ^0.26.19 -> satisfiable by infection/infection[0.26.19, 0.26.20, 0.26.21, 0.26.x-dev]. - infection/infection[0.26.20, ..., 0.26.x-dev] require nikic/php-parser ^4.15.1 -> satisfiable by nikic/php-parser[v4.15.1, ..., 4.x-dev]. - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.6.0, ..., 4.x-dev, v5.0.0alpha1, ..., v5.4.0]. - vimeo/psalm 6.x-dev requires nikic/php-parser ^5.0.0 -> satisfiable by nikic/php-parser[v5.0.0alpha1, ..., v5.4.0]. - Conclusion: don't install nikic/php-parser v5.1.0 (conflict analysis result) Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.