Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires shish/phpstan-safe-rule ^1.0 -> satisfiable by shish/phpstan-safe-rule[v1.3.0, v1.3.1]. - shish/phpstan-safe-rule[v1.3.0, ..., v1.3.1] require shish/safe ^2.0 -> satisfiable by shish/safe[v2.6.0, v2.6.1, v2.6.2, v2.6.3] from composer repo (https://repo.packagist.org) but shish/safe dev-master is the root package and cannot be modified. See https://getcomposer.org/dep-on-root for details and assistance.