bug#74352: 29.4; emerge-files with tramp + local file fails

[Michael Albinus via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Jörg Sommer <joerg@jo-so.de> writes:

> Hi,

Hi Jörg,

> when running `emerge-files` with `/ssh:remote:file` and `~/local-file` I get
> the buffer `*emerge-diff-errors*` with:
>
> ```
> diff: /tmp/tramp.wlcRNL: No such file or directory
> diff: /home/joerg/local-file: No such file or directory
> ```

I can reproduce the problem if file-A is remote, and file-B is
local. Also, if both file-A and file-B are remote.

If both files are local, or file-A is local and file-B is remote, emerge
works as exptected.

The crucial point seems to be that file-A is a remote one.

> This change solves the problem:
>
> ```diff
> diff --git lisp/vc/emerge.el lisp/vc/emerge.el
> index ca48f2f3c7b..562041e4232 100644
> --- lisp/vc/emerge.el
> +++ lisp/vc/emerge.el
> @@ -581,6 +581,7 @@ emerge-make-diff-list
>    (setq emerge-diff-buffer (get-buffer-create "*emerge-diff*"))
>    (with-current-buffer
>        emerge-diff-buffer
> +    (setq default-directory (file-name-directory file-A))
>      (erase-buffer)
>      (shell-command
>       (format "%s %s %s %s"
> ```

The point is, that emerge calls the 'diff' program for either the file
itself (if local), or a local copy of the file (if remote). A consistent
solution is therefore to set a local default directory, like

--8<---------------cut here---------------start------------->8---
    (setq default-directory temporary-file-directory)
--8<---------------cut here---------------end--------------->8---

instead of your change. Would you like to check?

However, this won't be a complete solution. There are other places in
emerge.el, where the temporary buffer for calling 'diff' must have a
local default directory. I'm not an emerge aficionado (haven't used it
until now). Would you like to produce a complete patch, based on my
proposal above?

> Regards Jörg

Best regards, Michael.