GNU bug report logs - #60333
[PATCH] whitespace: Update bob, eob markers in base and indirect buffers

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From: Richard Hansen <rhansen <at> rhansen.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>, Ihor Radchenko <yantar92 <at> posteo.net>
Cc: 60333 <at> debbugs.gnu.org
Subject: bug#60333: [PATCH] whitespace: Update bob, eob markers in base and indirect buffers
Date: Thu, 29 Dec 2022 03:11:11 -0500

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On 12/28/22 09:44, Stefan Monnier wrote:
>>> "Expose" is the wrong term, because we don't have that info ready to
>>> be exposed.  We'd either have to create&maintain that list, or compute
>>> it on-demand when requested.
> [...]
>> 1. Maintain internal indirect buffer list associated with buffers in C
> 
> That's the "create&maintain that list" option.
> Personally I don't like it: I'd like to reduce the amount of support we
> provide in C for indirect buffers rather than increase it.

What alternative would you prefer?

How about something like this in a shared location (e.g., simple.el next 
to `clone-indirect-buffer'):

    (defvar indirect-buffers--cached nil)

    (defun indirect-buffers--invalidate-cache ()
      (setq indirect-buffers--cached nil)
      (remove-hook 'buffer-list-update-hook
                   #'indirect-buffers--invalidate-cache))

    (defun indirect-buffers ()
      (unless indirect-buffers--cached
        (setq indirect-buffers--cached '(nil nil))
        (dolist (buf (buffer-list))
          (let ((base (buffer-base-buffer buf)))
             (when base
              (push buf (plist-get indirect-buffers--cached base)))))
        (add-hook 'buffer-list-update-hook
                  #'indirect-buffers--invalidate-cache))
      indirect-buffers--cached)

Other options I can see:

  #1: Apply this patch as-is, keep Org as-is, and live with the code 
duplication.
  #2: Reject this patch and keep Org as-is.
  #3: Advise `make-indirect-buffer'.  The advice would record new 
indirect buffers and add a `kill-buffer-hook' function to clean up the 
entry.  (Note, however, that `make-indirect-buffer' is a primitive 
function.)
  #4: Fix Bug#46982.  (One possible approach that maintains backwards 
compatibility:  Teach `after-change-functions' to look for a symbol 
property that means "run me not just for changes made in this buffer, 
but also if a change is made in this buffer's base/indirect buffer".)

Thanks,
Richard

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