>> Fixing the described problem will remove this comment,
>> but I have no idea how better to do this.  The problem is that
>> we need to provide own created buffer to the call to `vc-find-revision'.
>> Currently it has the following function signature:
>>
>>    (defun vc-find-revision (file revision &optional backend)
>>
>> But VC API in the comments in the beginning of vc.el
>> is documented with a different function signature:
>>
>>    ;; * find-revision (file rev buffer)
>>    ;;
>>    ;;   Fetch revision REV of file FILE and put it into BUFFER.
>>    ;;   If REV is the empty string, fetch the head of the trunk.
>>    ;;   The implementation should pass the value of vc-checkout-switches
>>    ;;   to the backend command.
>
> That is the VC backend API, not the signatures of public functions in vc.el
> (which would be kinda pointless).
>
> vc-git-find-revision and friends do indeed have this signature.
>
> Take a look at the uses of vc-call-backend in
> vc-find-revision[-no]-save. Maybe you need to write a new ???-find-revision
> function that does what you need.

Thanks, I see now that we can freely add a new optional arg: