Force git diff to create a binary patch?

Hello everyone,

Here are two small files with non-ASCII data, yet git diff considers
them text instead of binary.

    echo -n -e '\x01\xff\xdf' > bin1
    echo -n -e '\x01\xdf\xff' > bin2
    git diff --binary bin1 bin2

Result:

    diff --git a/bin1 b/bin2
    index 802dc8e..c39b638 100644
    --- a/bin1
    +++ b/bin2
    @@ -1 +1 @@
    -^A<FF><DF>
    \ No newline at end of file
    +^A<DF><FF>
    \ No newline at end of file

I think `--binary` for `git diff` should force the creation of git
binary patches if there are any non-printable-ASCII characters, since
my understanding is that `--binary` is for safe encoding for email.
Otherwise `-a` can be used.

Original post: https://stackoverflow.com/questions/62858327/how-can-i-force-git-diff-to-create-a-git-binary-patch

Thanks