default file for diff-backup

default file for diff-backup

[Alfred M. Szmidt]

This makes diff-backup supply a default file name, making the
default behaviour a bit more useful.

*** lisp/vc/diff.el.~1~
--- lisp/vc/diff.el
***************
*** 187,194 ****
  If this file is a backup, diff it with its original.
  The backup file is the first file given to `diff'.
  With prefix arg, prompt for diff switches."
!   (interactive (list (read-file-name "Diff (file with backup): ")
! 		     (diff-switches)))
    (let (bak ori)
      (if (backup-file-name-p file)
  	(setq bak file
--- 187,201 ----
  If this file is a backup, diff it with its original.
  The backup file is the first file given to `diff'.
  With prefix arg, prompt for diff switches."
!   (interactive
!    (list
!     (if (and buffer-file-name (file-exists-p buffer-file-name))
! 	(read-file-name
! 	 (concat "Diff file with backup (default "
! 		 (file-name-nondirectory buffer-file-name) "): ")
! 	 nil buffer-file-name t)
!       (read-file-name "Diff file with backup: " nil nil t))
!     (diff-switches)))
    (let (bak ori)
      (if (backup-file-name-p file)
  	(setq bak file

Diff finished.  Fri Jun 20 14:06:26 2014

Re: default file for diff-backup

[Stefan Monnier]

> This makes diff-backup supply a default file name, making the
> default behaviour a bit more useful.

Looks OK, feel free to install into trunk.


        Stefan

Re: default file for diff-backup

[Alfred M. Szmidt]

   > This makes diff-backup supply a default file name, making the
   > default behaviour a bit more useful.

   Looks OK, feel free to install into trunk.

Someone other than me will have to do that since I don't have commit
access.

RE: default file for diff-backup

[Herring, Davis]

> This makes diff-backup supply a default file name, making the
> default behaviour a bit more useful.

Is the idea to handle `insert-default-directory' being nil?  `diff-backup' already has the obvious default otherwise.  If so: you could just let-bind it, I guess, although overriding customization is not usually a good thing.

Davis

Re: default file for diff-backup

[Alfred M. Szmidt]

The idea is to supply the current file name of the buffer if you just
hit enter, i.e exact same behaviour as for M-x diff RET.

RE: default file for diff-backup

[Herring, Davis]

> The idea is to supply the current file name of the buffer if you just
> hit enter, i.e exact same behaviour as for M-x diff RET.

I get that already (even though it doesn't explicitly say so in the prompt).  Just like, say, `copy-file'.

Davis

Re: default file for diff-backup

[Alfred M. Szmidt]

   > The idea is to supply the current file name of the buffer if you just
   > hit enter, i.e exact same behaviour as for M-x diff RET.

   I get that already (even though it doesn't explicitly say so in the prompt).  Just like, say, `copy-file'.

There are quite a few cases where the default could be improved for
the "RET" case, copy-file, rename-file, delete-file, ...

RE: default file for diff-backup

[Herring, Davis]

> There are quite a few cases where the default could be improved for
> the "RET" case, copy-file, rename-file, delete-file, ...

But they all already work!

At least, if `insert-default-directory' is non-nil, as is the default.  That's why I asked whether your patch was meant to address the other case.

Davis

Re: default file for diff-backup

[Alfred M. Szmidt]

   > There are quite a few cases where the default could be improved for
   > the "RET" case, copy-file, rename-file, delete-file, ...

   But they all already work!

So they seem! Though not clear that they do, it would be nicer if
there was some hint that one could just hint RET.  It is not the
behaviour that `diff' exhibits, where you are at least shown
something.

   At least, if `insert-default-directory' is non-nil, as is the
   default.  That's why I asked whether your patch was meant to
   address the other case.

I think I see what you are saying now, it was unclear to me.  What is
annoying to me, is that there is no mention of a "default" when you
invoke M-x diff-backup (or for the matter, M-x copy-file, rename-file,
...).  M-x diff does have one though, which is really all I want.

I.e.:

  C-x C-f ~/.emacs RET
  M-x copy-file RET
  Copy file: ~/

~/ isn't a file, why would I copy it?  So I type the file I want
instead of just hitting RET, which would give me the default file as
you note.  Where as with the simple modification to diff-backup:

  C-x C-f ~/.emacs RET
  M-x diff-backup RET
  Diff file with backup (default .emacs): ~/

This is far clearer.

RE: default file for diff-backup

[Herring, Davis]

> Diff file with backup (default .emacs): ~/

You can address all use cases at once (and make it respect `insert-default-directory') by making this change in `read-file-name' instead.

Davis