bug#8163: 23.2; Feature request: dabbrev look at filenames or buffer names

[Juri Linkov]

>> Start emacs and start editing a file called abcdef:
>>
>> C-x C-f abcdef RET
>>
>> In that buffer type abcde and then press M-/ to run dabbrev-expand.
>>
>> Desired result: dabbrev looks at the buffer name (or the name of the
>> file it is visiting) and uses that to complete the string to 'abcdef'.
>> It could use the names of all open buffers as part of its pool.
>
> Makes sense to me.  I've now added this to Emacs 29.

Now dabbrev fails with:

Debugger entered--Lisp error: (error "Selecting deleted buffer")
  dabbrev--find-expansion("dabbr" -1 t)
  dabbrev-expand(nil)
  funcall-interactively(dabbrev-expand nil)
  command-execute(dabbrev-expand)

because dabbrev--last-buffer is a killed buffer in dabbrev--find-expansion:

                   (setq dabbrev--last-buffer
                         (pop dabbrev--friend-buffer-list))
                   (set-buffer dabbrev--last-buffer)

I don't see how can it not fail when the temporary buffer
"*abbrev-file*" gets added to dabbrev--friend-buffer-list:

                 (setq dabbrev--friend-buffer-list
                       (append dabbrev--friend-buffer-list
                               (list file-name-buffer))))

and then gets deleted afterwards:

           (when (buffer-live-p file-name-buffer)
             (kill-buffer file-name-buffer))))))))

So dabbrev--friend-buffer-list always contains '(... #<killed buffer>)
at the end, and at the next call to dabbrev--last-buffer causes the error.