combine subtree merge with sparse checkout in git

Question

I'm trying to emulate svn:externals in git. In project 'A' I need to pull down library 'B' into a sub folder of 'A'. Both A and B are separate git repos. I know I can do this with either submodules or subtree merge. However, to further complicate things, I need to pull down a subfolder of 'B' into 'A', not the whole project because it is a python module that I need to import directly and I can't have the root directory structure there or it can't be imported.

This is pretty easy to do with svn:externals. With git it seems complicated or even impossible.

Here is an example:

Project B:

-B
  - src
    __init__.py
 - test
   ...

Project A:

- A
   - src
     A.py (imports B)
     - B (partial check of sub folder 'src' as name 'B')
        __init__.py
   - test
     ...

Answer 1

B (library) must be also supermodule, which include submodule "python module"

You selected bad tool and leave on higher abstraction layer, than needed for task

Answer 2

Instead of solving it by tweaking git, why not just install B anywhere, and tell A where to find the submodule to include? If you just add to sys.path the folder containing the relevant B submodule, you can go home.

Answer 3

Git is mostly all-or-nothing. Your best bet is to clone the module elsewhere and either symlink the directory you want, or use sys.path .

- A
   - src
      - B symlink to ../../B/
- B

If you're concerned about size of submodule's clone, and you don't need to commit to it, then you can use --depth=1 when cloning to ignore history.

Unfortunately, you can't clone a subfolder. At best you could use git-filter-branch to delete everything from a repo except a selected subfolder.