bug#21320: diff-buffer-with-file fails on remote files

[Michael Albinus]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> If you visit a file via Tramp, then make some changes and do M-x
> diff-buffer-with-file, you'll get an error in the diff buffer because
> "diff" is executed locally with the Tramp file name.

I cannot reproduce it with "emacs -Q". The diff uses respective labels,
but that's it. It uses temporary local files. And the contents looks OK
to me, like this:

--8<---------------cut here---------------start------------->8---
diff -u --label /ssh\:ford\:/share/albinus/mail --label \#\<buffer\ mail\> 
/tmp/tramp.29783xKm /tmp/buffer-content-29783-Us
--- /ssh:ford:/share/albinus/mail
+++ #<buffer mail>
@@ -1,4 +1,4 @@
- From: Michael@RAINER.i-did-not-set--mail-host-address--so-tickle-me
+From: Michael@RAINER.i-did-not-set--mail-host-address--so-tickle-me
 To: bug-gnu-emacs@gnu.org
 Subject: 24.3.50; set-file-acl on MS Windows shall check ACL string format
 --text follows this line--

Diff finished.  Sat Aug 22 20:31:02 2015
--8<---------------cut here---------------end--------------->8---

>         Stefan

Best regards, Michael.