Re: diff-find-file-name and /dev/null

[Glenn Morris]

Nikolaj Schumacher wrote:

> Since there's nothing to view or edit in /dev/null.

How about this patch then:

diff -c -c -w -r1.99.2.3 diff-mode.el
*** diff-mode.el        6 Aug 2007 20:08:07 -0000       1.99.2.3
--- diff-mode.el        25 Aug 2007 01:41:53 -0000
***************
*** 646,652 ****
           ((or (null files)
                (setq file (do* ((files files (cdr files))
                                 (file (car files) (car files)))
!                              ((or (null file) (file-exists-p file))
                                file))))
            file))
         ;; <foo>.rej patches implicitly apply to <foo>
--- 646,652 ----
           ((or (null files)
                (setq file (do* ((files files (cdr files))
                                 (file (car files) (car files)))
!                              ((or (null file) (file-regular-p file))
                                file))))
            file))
         ;; <foo>.rej patches implicitly apply to <foo>

> Also in a usual diff file
>
> --- /dev/null 2007-08-17 06:03:27.000000000 +0200
> +++ /foo/bar.c        2007-08-18 00:48:25.000000000 +0200
>
> `diff-goto-source' would visit /foo/bar.c

It's easy to produce a non-git diff that has the same behaviour. Just
do a diff between /dev/null and a relative filename:

diff -u /dev/null foo/somefile > foo/some.diff

Then open foo/some.diff in Emacs and try to jump to source. I'd never
make a hideous diff like that though...

> I admit the actual fault could be the fact that it looks for first
> one at all (or at least _before_ chopping off prefixes of the second
> one), even when diff-jump-to-old-file is nil. /dev/null is just the
> only cause of such behavior.

Yes, I don't see why diff-find-file-name does that, and I don't think
/dev/null is the only cause. Eg repeating the above example, but with
regular files:

diff -u /tmp/file1 foo/file2 > foo/file.diff

diff-goto-source will open file1 rather than file2.


Stefan, is there a reason why diff-find-file-name can return the old
file, even when OLD is nil? Why doesn't it just consider
(car (diff-hunk-file-names old))?

If it should consider both old and new in each case, should it not try
dropping the directory entries from the new/old file first, before
going on to check the old/new one in the same way only it it does not
find a match?