11.10.3.1 Warnings about style issues with modules

--warn-include-and-non-include

Warn about modules that contain both “include_module” declarations and other kinds of entities, such as types or predicates.

When a module contains both “include_module” declarations and other code, changes to that code will often cause the recompilation of all the included submodules. This is because those submodules have access to the entities declared in their parent module, so if the set of those entities changes in any way, the submodules must be checked to see whether they relied on some entity in the parent module that is not there anymore.

Modules that contain “include_module” declarations and nothing else, which are often called “packages”, do not have this problem.