Subject: bug#60333: [PATCH] whitespace: Update bob, eob markers in base and indirect buffers

From: Richard Hansen <[email-masked]>
Date: Thu, 29 Dec 2022 03:11:11 -0500

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