Module systems
Laravel Idea uses the Module systems concept to understand the structure of applications. It helps to correctly complete the views, config, routes and more convenient code generation. Module system for the project can be configured in File | Settings | Languages & Frameworks | Laravel Idea | Module System:

Standard application
Typical Laravel application with one module in the app folder.
Simple directory modules
Module system for application with logical modules inside one directory. This article describes the reason and possible implementation: https://stitcher.io/blog/laravel-beyond-crud-01-domain-oriented-laravel
Each code generation has an Available in modules option. Database migrations usually don't need to be in the modules, but controllers do:

nWidart/laravel-modules package
Module system for application built using nWidart/laravel-modules package.
Directory modules as composer packages
This module system is for projects with modules as separated composer packages. It uses modules composer.json file for namespaces.

Sources path parameter is a location of the main module (it is app for standard application).
Root directory path parameter is the directory containing module directories.
Allow app root module in code generation dialogs also offers the main application in the module chooser of code generations.