How to make `git log --stat -- <path>` show *all* files in selected commits?

Question

When I use a <path> argument with git log --stat to limit the log to commits modifying <path>, git lists <path> as the only modified file when displaying the selected commits. I would instead like to see all modified paths listed for each selected commit.

For example:

$ echo test > a.txt
$ echo test > b.txt
$ git add a.txt b.txt
$ git commit -m test
 [...]
 2 files changed, 2 insertions(+), 0 deletions(-)
 [...]
$ git log -n1 --stat
 [...]

 a.txt |    1 +
 b.txt |    1 +
 2 files changed, 2 insertions(+), 0 deletions(-)
$ git log -n1 --stat -- a.txt
 [...]

 a.txt |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

Note that the second git log, with the path argument a.txt, says "1 files changed", when in fact "2 files changed". I would like git to tell me that both a.txt and b.txt changed, even though I selected the commit based on the path a.txt.

UPDATE: @jacknagel answered my question, but it turns out his solution doesn't work in my real use case. In my real use case, I'm looking for all commits that modified a file, including renames, in a case where two related projects diverged. I need to figure out what changes in one project imply corresponding changes (I need to make) in the other project. Unfortunately, git complains when I try to use --full-diff and --follow at the same time.

So, in my real situation, I'm trying to run:

git log --stat --follow -- a.txt

and a solution that works in this case is:

git log --format='%H' --follow -- a.txt | xargs git show --stat -C

Answer 1

You can get this behavior using the --full-diff option:

   --full-diff
       Without this flag, "git log -p <path>..." shows commits that touch
       the specified paths, and diffs about the same specified paths. With
       this, the full diff is shown for commits that touch the specified
       paths; this means that "<path>..." limits only commits, and doesn't
       limit diff for those commits.

       Note that this affects all diff-based output types, e.g. those
       produced by --stat etc.