C-x C-v considered harmful

[Bob Rogers]

   From: "Drew Adams" <drew.adams@...>
   Date: Thu, 9 Jul 2009 16:21:49 -0700

   > I have no opinion about a more general option.

   Nor I.

Personally, I think I would be content if we added a query only for
active process buffers.

   . . .

   FWIW, I've been taking advantage of `kill-buffer''s lack of query for
   process buffers as a _feature_, to avoid having to type `yes' (or is
   it `y'?) when I kill Emacs to confirm that I want to kill any active
   processes. I've gotten in the habit of using `C-x k' or `C-x C-v'
   when I'm through with a *shell* buffer, for instance. (Yes, I realize
   that's as much typing as `yes'/`y', but it somehow feels less
   annoying.) ;-)

I just type "quit RET" to the shell.  And if I'm in an SSH session with
open tunneled connections, it won't exit immediately, so I'm reminded
that I have other state to take care of before doing C-x C-c.

                                        -- Bob

[Stefan Monnier]

>    I've just made C-x C-v obey confirm-nonexistent-file-or-buffer (as they
>    should have from the beginning) which should fix the OP's problem.

> I'm sorry, but you seem to have misunderstood:  My problem with C-x C-v
> is its behavior in killing buffers, not in how it finds files.  (That is
> why I did not respond to your earlier post; as one who has never
> *deliberately* invoked C-x C-v, I have no opinion.)

But it does fix the OP's particular case because the RET would have
asked to "[Confirm]" since here was no "d" file (or directory).


        Stefan

[Juri Linkov]

> The variable `kill-buffer-query-functions' is nil by default,
> so maybe it's better to implement this confirmation in Fkill_buffer
> instead of the hook `kill-buffer-query-functions'?

Looking again at `find-alternate-file' convinces me that the right
solution is to use the `kill-buffer-query-functions' hook.

`find-alternate-file' explicitly runs this hook as:

  (run-hook-with-args-until-failure 'kill-buffer-query-functions)

and binds it to nil around killing the buffer to not ask again:

  (let ((kill-buffer-query-functions))
    (kill-buffer obuf))

So there is no good way to prevent asking a confirmation about a running
process in Fkill_buffer.

Asking a confirmation about a modified file buffer could be moved to the
`kill-buffer-query-functions' hook as well because this will avoid
duplicating this question in `find-alternate-file'.  But at least now
I propose to add a process confirmation to `kill-buffer-query-functions':

Index: lisp/files.el
===================================================================
RCS file: /sources/emacs/emacs/lisp/files.el,v
retrieving revision 1.1055
diff -u -r1.1055 files.el
--- lisp/files.el 5 Jul 2009 22:15:37 -0000 1.1055
+++ lisp/files.el 13 Jul 2009 20:03:47 -0000
@@ -1441,6 +1441,16 @@
       (other-window 1)
       (find-alternate-file filename wildcards))))
 
+(defun process-kill-buffer-query-function ()
+  "Ask before killing a buffer that has a running process."
+  (let ((process (get-buffer-process (current-buffer))))
+    (or (not process)
+        (not (memq (process-status process) '(run stop open listen)))
+        (not (process-query-on-exit-flag process))
+        (yes-or-no-p "Buffer has a running process; kill it? "))))
+
+(add-hook 'kill-buffer-query-functions 'process-kill-buffer-query-function)
+
 (defun find-alternate-file (filename &optional wildcards)
   "Find file FILENAME, select its buffer, kill previous buffer.
 If the current buffer now contains an empty file that you just visited

--
Juri Linkov
http://www.jurta.org/emacs/

[Bob Rogers]

   From: Stefan Monnier <monnier@...>
   Date: Sat, 11 Jul 2009 06:06:40 -0400

   >    I've just made C-x C-v obey confirm-nonexistent-file-or-buffer (as they
   >    should have from the beginning) which should fix the OP's problem.

   > I'm sorry, but you seem to have misunderstood:  My problem with C-x C-v
   > is its behavior in killing buffers, not in how it finds files.  (That is
   > why I did not respond to your earlier post; as one who has never
   > *deliberately* invoked C-x C-v, I have no opinion.)

   But it does fix the OP's particular case because the RET would have
   asked to "[Confirm]" since here was no "d" file (or directory).

           Stefan

This did not occur to me.  But I notice that typing "C-x C-v d RET"
fails to require a "[Confirm]" if the value of
confirm-nonexistent-file-or-buffer is after-completion.  Since this is
the default, that is no help for those who have not yet been bitten by
this problem.  (It would in fact have helped me, as the OP, because I do
set confirm-nonexistent-file-or-buffer to t, but I have been flogging
this thread in the hope of making Emacs friendlier by default.)

   It is also unlikely to help if you had meant to type "C-x C-f"
instead of "C-x C-v"; both commands behave the same, regardless of the
confirm-nonexistent-file-or-buffer setting, up until the point the
previous buffer is killed.

   And it doesn't help at all with the fact that even "C-x k" is skimpy
in the warning department.  Are you rejecting Drew's argument that it is
really kill-buffer that needs attention (at least when invoked
interactively)?

                                        -- Bob

[Stefan Monnier]

> This did not occur to me.  But I notice that typing "C-x C-v d RET"
> fails to require a "[Confirm]" if the value of
> confirm-nonexistent-file-or-buffer is after-completion.  Since this is

Oops, indeed, I forgot about this "detail".  Thanks for reminding me.

>    And it doesn't help at all with the fact that even "C-x k" is skimpy
> in the warning department.  Are you rejecting Drew's argument that it is
> really kill-buffer that needs attention (at least when invoked
> interactively)?

I do not oppose the change to kill-buffer, no.
I'm just happy that this thread pointed out the lack of support for
confirm-nonexistent-file-or-buffer in C-x C-v (and did so before the
release).


        Stefan

[Juri Linkov]

> Looking again at `find-alternate-file' convinces me that the right
> solution is to use the `kill-buffer-query-functions' hook.

I found a better place for this piece of code.  subr.el has a special
section "Process stuff".

Also the docstring of `set-process-query-on-exit-flag' should be
modified to mention its effect on buffer killing.

Index: lisp/subr.el
===================================================================
RCS file: /sources/emacs/emacs/lisp/subr.el,v
retrieving revision 1.641
diff -c -r1.641 subr.el
*** lisp/subr.el 14 Jul 2009 07:45:59 -0000 1.641
--- lisp/subr.el 16 Jul 2009 21:55:24 -0000
***************
*** 1722,1727 ****
--- 1722,1737 ----
      (set-process-query-on-exit-flag process nil)
      old))
 
+ (defun process-kill-buffer-query-function ()
+   "Ask before killing a buffer that has a running process."
+   (let ((process (get-buffer-process (current-buffer))))
+     (or (not process)
+         (not (memq (process-status process) '(run stop open listen)))
+         (not (process-query-on-exit-flag process))
+         (yes-or-no-p "Buffer has a running process; kill it? "))))
+
+ (add-hook 'kill-buffer-query-functions 'process-kill-buffer-query-function)
+
  ;; process plist management
 
  (defun process-get (process propname)

Index: src/process.c
===================================================================
RCS file: /sources/emacs/emacs/src/process.c,v
retrieving revision 1.589
diff -c -r1.589 process.c
*** src/process.c 28 Jun 2009 20:25:49 -0000 1.589
--- src/process.c 16 Jul 2009 21:55:57 -0000
***************
*** 1133,1139 ****
         2, 2, 0,
         doc: /* Specify if query is needed for PROCESS when Emacs is exited.
  If the second argument FLAG is non-nil, Emacs will query the user before
! exiting if PROCESS is running.  */)
       (process, flag)
       register Lisp_Object process, flag;
  {
--- 1133,1139 ----
         2, 2, 0,
         doc: /* Specify if query is needed for PROCESS when Emacs is exited.
  If the second argument FLAG is non-nil, Emacs will query the user before
! exiting or killing a buffer if PROCESS is running.  */)
       (process, flag)
       register Lisp_Object process, flag;
  {

--
Juri Linkov
http://www.jurta.org/emacs/