Eli Zaretskii <eliz@gnu.org> writes:

>> But how can I get the SHA of the current revision when I am in a buffer
>> opened by =vc-find-revision=?
>
> That's the argument with which vc-find-revision was called, right?  So
> the only change we might need is to record the revision in some
> buffer-local variable, if we don't already do that (don't we show the
> revision of the mode line?).
Yes a buffer-local.

the 'revision' on the mode line is part of buffer name, not always a
revision.

(vc-find-revision "doc/lispref/help.texi" "remotes/origin/emacs-29"
'Git)