git diff --text does not work during rebase for binary files

["Дилян Палаузов" <dilyan.palauzov@aegee.org>]

Hello,

I create a small text file ending with \0 and add it to git:

In .gitattributes I specify:

*.txt diff merge=text text

I create several commits by changing the small text file.

The result is at https://github.com/dilyanpalauzov/git-diff-biinary .

I do now

  git rebase -i HEAD~2
and before the “second commit” type E to edit that commit.

I change the small file.

git add a.txt && git rebase --continue

git says:

[detached HEAD bc00e34] second commit
 Date: Sun Mar 21 19:16:15 2021 +0200
 1 file changed, 2 insertions(+), 1 deletion(-)
warning: Cannot merge binary files: a.txt (HEAD vs. 04c77de (third
commit))
Auto-merging a.txt
CONFLICT (content): Merge conflict in a.txt
error: could not apply 04c77de... third commit
Resolve all conflicts manually, mark them as resolved with
"git add/rm <conflicted_files>", then run "git rebase --continue".
You can instead skip this commit: run "git rebase --skip".
To abort and get back to the state before "git rebase", run "git rebase
--abort".
Could not apply 04c77de... third commit


'git diff' and 'git diff --text' show:

diff --cc a.txt
index 7a61015,dc817ec..0000000
--- a/a.txt
+++ b/a.txt

The file does not contain <<HEAD===>>> markers, despite having
merge=text attribute.

HOW CAN I force git diff to show the differences and git merge to
include the <<<===>>> markers?

I have to say, that at different occassions git diff --text does work
ass expected (e.g. when I call git diff --cached --text).

I call now 
git rebase --abort
git log -p

git shows the differences in the small text file ending with \0.  So
apparently log reads the option, but diff does not.

Using git 2.30.2.

Greetings
  Дилян