When mounting a local plugin as a volume into the wordpress service for development, changes are reflected immediately inside the container, and typos and syntax errors result in easy-to-see error messages in the browser. However, when (re-)starting the docker-compose application while there are syntax errors in the mounted plugins, startup fails when trying to activate the plugin. The output of the service in that case looks like wordpress_wordpress_1 exited with code 255 which does not point in any way towards the root of the problem.

Solution: Output more detailed error messages in docker-entrypoint.sh, indicating which part of the startup process failed more clearly.