Fix for bug #39344 (Gnus selecting deleted buffer) incomplete.

Fix for bug #39344 (Gnus selecting deleted buffer) incomplete.

[Karl Fogel]

Hi.  I just encountered bug#39344 today (get a "Selecting deleted buffer" error when quitting Gnus).  While I was debugging it, coming to the exact same initial workaround that Steve Berman came to in the bug ticket, Sam Steingold committed this intended fix:

  commit bb3b0990d8505342ae14841144778df9e650ebdc
  Commit:     Sam Steingold <sds@gnu.org>
  CommitDate: Wed Jan 29 11:17:50 2020 -0500
  
      fix bug#39344
      
      * gnus.el (gnus-add-buffer): Use `cl-pushnew' instead of `push' to
        avoid duplicate entries.

I recompiled to get Sam's fix, but the bug is still present.  

After some debugging, I still don't know why the bug remains, though I've learned a lot about Gnus buffer management, so that's nice.  My guess is that this problem is related to earlier commit 5ee3c37634f, in which many functions in Gnus were changed to use `gnus-get-buffer-create' and thus now store the created buffer in in `gnus-buffers'.  I did wonder about the fact that `gnus-buffers' is both a variable and a function (with only the latter pruning out the killed buffers) -- that seems like it could a potential confusion source and/or bug source in general, but I don't know if it has anything to do with the current bug.

Anyway, before I go deeper, Sam, I thought I'd post this in case your fix is working for you and you didn't realize that it isn't working for someone else.  If you can't reproduce the problem anymore after commit bb3b0990d, then I will continue to debug.  However, if you can reproduce it, then I'll assume you are working on it (and you surely would do so much more efficiently then I would).

Best regards,
-Karl

Re: Fix for bug #39344 (Gnus selecting deleted buffer) incomplete.

[Andreas Schwab]

On Jan 29 2020, Karl Fogel wrote:

> After some debugging, I still don't know why the bug remains, though I've
> learned a lot about Gnus buffer management, so that's nice.  My guess is
> that this problem is related to earlier commit 5ee3c37634f, in which many
> functions in Gnus were changed to use `gnus-get-buffer-create' and thus
> now store the created buffer in in `gnus-buffers'.

But it adds only new buffers to gnus-buffers, so that it cannot create
duplicates.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

Re: Fix for bug #39344 (Gnus selecting deleted buffer) incomplete.

[Karl Fogel]

On 29 Jan 2020, Andreas Schwab wrote:
>On Jan 29 2020, Karl Fogel wrote:
>
>> After some debugging, I still don't know why the bug remains, though I've
>> learned a lot about Gnus buffer management, so that's nice.  My guess is
>> that this problem is related to earlier commit 5ee3c37634f, in which many
>> functions in Gnus were changed to use `gnus-get-buffer-create' and thus
>> now store the created buffer in in `gnus-buffers'.
>
>But it adds only new buffers to gnus-buffers, so that it cannot create
>duplicates.

Well, yes, that makes sense to me too but occasionally I get surprised by an unexpected side effect in Emacs.

However, I think Sam's commit bb3b0990d really did fix bug#39344 after all.  I did a *full* rebuild this time, i.e.,

  $ make distclean && ./autogen.sh && ./configure && make bootstrap

and now the bug is gone.  Previously I had just done a plain 'make', after 'git pull' into a just-built tree had pulled down exactly that one change from Sam.  Probably the persistence of the buggy behavior was an artifact of the quick build process.

Best regards,
-Karl