CtrlP: ignore files in subdirectory within a git repo

Question

For my repo, suppose it's called top

top\
  .gitignore
  foo\
  bar\

I want CtrlP to list files that are

1. Under foo\
2. Is not ignored by .gitignore defined in top\

If I cd into top\foo\, and open vim from there, 1 would be satisfied but not 2.
If I open vim on top\, 2 would be satisfied but not 1.

How do I achieve both 1 and 2?

I tried this gitignore vim script, but it only parses gitignore when I open vim in the root folder of a repo, so I can't do both 1 and 2 together.
Same for let g:ctrlp_user_command = 'ag %s -l --nocolor -g ""', ag doesn't try to go up to the repo root and read gitignore from there.
Setting g:ctrlp_working_path_mode as r let CtrlP honors .gitignore in the top folder, but everything under top\ would be listed by CtrlP. I just want files in foo\.

Thanks.

Answer 1

Seems there is no apparent way to do it, so I just followed @kamaradclimber 's suggestion, spent an hour and made this: RootIgnore
Never coded in VimScript before so it took me some time :-)

You can install it using Vundle.
It searches upward recursively for .git dir, gets the .gitignore in the same dir as the .git dir, and sets wildignore accordingly.

Update:
@jthill's method works better than mine.
But CtrlP has custom search commands while CommandT does not. So my plugin can still be useful to CommandT users.