[GSoC] Discussion of "Submodule related work" project

Have some questions about "Submodule related work" project

First of all, I would like to add this task to the project, if I'll take it: https://public-inbox.org/git/1488913150.8812.0@smtp.yandex.ru/T/ What do you think about this task?

 > Cleanup our test suite. Do not use a repo itself as a submodule for 
itself

Not quite familiar with submodules yet, why this is considered to be ineligible (i.e. using repo as a submodule for itself)?

 > (Advanced datastructure knowledge required?) Protect submodule from 
gc-ing
 > interesting HEADS.

Can you provide a small example that shows the problem, please? And why advanced datastructure knowledge is expected?

Maybe you have something else about this project to say.

Thanks,
  Valery Tolstov