Sub-project resources should be derived or otherwise marked

[thahnen]

Context

When importing a project that contains a subproject: Listing all the files of the root project via the IProject.accept(IResourceVisitor) yields not only its files but also the ones from the subproject.
This is inconvenient when working with the files of the root project only, as something like the build directory is derived but not the sub-projects main directory; on the other hand, the subprojects build directory is derived again.

Request

Finding all the folders of sub-projects in a project can be done via the Gradle tooling API as a workaround, but it is very slow once your imported project has more than one sub-project. It should be possible to derive (and exclude) the sub-project directories with Eclipse logic itself, maybe mark the resources as derived or somehow mark them differently with another attribute.

Currently, there is also no information on the .project or .classpath file linking to the sub-projects, and I found no other measure on how to check whether a project has a sub-project and at what resource location beside the tooling API.