How to make top-level git to track all the files under another sub-directory git

Question

command sequence

mkdir topdir
mkdir another-git-directory
touch fileC
touch fileD
git add .
git commit -m "sub-dir init"
cd ..
touch fileA
touch fileB
git add .
git commit -m "top-dir init"
git ls-files
// now we can see that fileC and fileD is not tracked by top-level git //
git ls-files -o
// this would not show us the fileC and fileD as untracked files//

my question is: how can we make "git ls-files -o" to show the untracked files inside sub-directory? why git is behaved such, as i expect git ls-files to show all untracked file (even it is inside another sub-dir git)?

I know that I could make the top git to track the sub-dir files using "git add */."... but I am interested to know why for the question above. Thanks!

directory structure

  topdir + +-- .git +-- fileA +-- fileB + another-git-directory +-- .git +-- fileC +-- fileD 

update (26 Jun)

I found this thread Unable to track files within Git submodules and this url (cn) http://blog.ossxp.com/2010/01/425/ which explains how to resolve the problem.

the solution:

git rm --cached another-git-directory #no trailing slash
git add another-git-directory/.
git commit

the 'git rm --cached path/to/sub-dir-or-sub-module' will tell the top-dir not to treat the sub-dir as a submodule... I think....

Answer 1

A nested repo is by default untracked .
(actually it tracks the submodule root folder as a gitlink , special entry in the index )
Git will detect the nested .git repo, and the parent repo will delegate any file status to the nested one.

To show them tracked, you may have to:

• remove the gitlink: git rm --cached mysubmodule .
  Note the lack of trailing slash: mysubmodule represents the gitlink, while mysubmodule/ is the folder created by the checked out submodule.
• add it back to the index of the parent repo: git add mysubmodule (here, you can add or not a trailing slash, it does not matter)
• commit the new files added and present in mysubmodule .