nested submodules detection w/o .gitmodules file

Hello Git,

I have a pretty long investigation has been started from usage 3dparty projects related directly or indirectly to the git submodules:

`svn externals replacement` : https://github.com/chronoxor/gil/issues/6 `svn complete replacement for externals` : https://github.com/dirk-thomas/vcstool/issues/243

And stumbled on this discussion:

`nested submodules detection w/o .gitmodules file` : https://github.com/gitextensions/gitextensions/discussions/10644 (https://github.com/gitextensions/gitextensions/issues/10642)

The main question here is that, could the git have has submodules without `.submodules` file?

If no, then all side projects which utilizes it's own input file for the externals may subsequentially fail:

https://github.com/chronoxor/gil https://github.com/dirk-thomas/vcstool https://github.com/ingydotnet/git-subrepo

If yes, then other projects which does rely on the `.submodules` would have not actual or even invalid state:

https://github.com/gitextensions/gitextensions

Or even the github itself: 

`Zip archive to include submodule` : https://github.com/dear-github/dear-github/issues/214

(`[PATCH] archive: add –recurse-submodules to git-archive command` : https://git.github.io/rev_news/2022/11/30/edition-93/, https://lore.kernel.org/git/pull.1359.git.git.1665597148042.gitgitgadget@gmail.com/)

Mine point here is that:

Git database is a primary storage. The `.gitmodules` file is not a primary storage, so can be in not an actual or desync state with the database. And any application or a 3dparty project must read the database directly.

But another problem here is that the git still does not have a stable API for that. For example, a submodule can be declared directly from the `.git/config` file in a working copy:

https://git-scm.com/docs/git-submodule#Documentation/git-submodule.txt-init--ltpathgt82308203 https://git-scm.com/docs/gitsubmodules#_active_submodules

So, who is right and what is wrong here?