How to emulate git status to see staged changes

[AndyBaay]

I've looked around and can't find an example of how to get the staged file changes. I'm looking for the equivalent of git diff HEAD --name-only or the "Changes to be committed" section of git status. For example:

$ git status
On branch main
Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
        modified:   README.txt
        new file:   new_file.sh
        new file:   subdir2/README.txt

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        ignored.txt

I want to get the 3 staged changes: README.txt, new_file.sh, subdir2/README.txt.

I've tried this:

            let index_file = repo.open_index()?;
            let state = gix::index::State::from(index_file);
            for entry in state.entries() {
                info!("{} -> {}", entry.path(&state), entry.stage());
            }

But that gives me all files committed and staged, with the same value 0 for entry.stage().

Is there a way to get a list of the staged changes? Ideally I would be able to see the line-level diff, but file-level is fine too.

[Byron]

Here a diff between a tree (HEAD^{tree}) and the index would be required, or a diff between two indices, but none of these facilities currently exists.

I have been meaning to implement this for a quite a while now, but other things keep popping up.