bug#23777: 25.0.95; Throwing (error "Selecting deleted buffer") in timer

[Jiege Chen <jiegec@qq.com>]

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Begin forwarded message:

> From: Jiajie Chen <jiegec@qq.com>
> Date: June 17, 2016 at 7:27:52 PM GMT+8
> To: Noam Postavsky <npostavs@users.sourceforge.net>
> Subject: Re: bug#23777: 25.0.95; Throwing (error "Selecting deleted buffer") in timer
> 
> 
> Thanks. That works. This behaviour is only observed in Emacs daemon.
> 
> This is what I have found:
> 
> The backtrace:
> Debugger entered--Lisp error: (error "Selecting deleted buffer")
>  set-buffer(#<killed buffer>)
>  (save-current-buffer (set-buffer buf) (let* ((modified (buffer-modified-p)) (buffer-undo-list t) (inhibit-read-only t) (inhibit-modification-hooks t)) (unwind-protect (progn (remove-text-properties (point-min) (point-max) (quote (fontified)))) (if modified nil (restore-buffer-modified-p nil)))))
>  (closure (t) (buf) (save-current-buffer (set-buffer buf) (let* ((modified (buffer-modified-p)) (buffer-undo-list t) (inhibit-read-only t) (inhibit-modification-hooks t)) (unwind-protect (progn (remove-text-properties (point-min) (point-max) (quote (fontified)))) (if modified nil (restore-buffer-modified-p nil))))))(#<killed buffer>)
>  apply((closure (t) (buf) (save-current-buffer (set-buffer buf) (let* ((modified (buffer-modified-p)) (buffer-undo-list t) (inhibit-read-only t) (inhibit-modification-hooks t)) (unwind-protect (progn (remove-text-properties (point-min) (point-max) (quote (fontified)))) (if modified nil (restore-buffer-modified-p nil)))))) #<killed buffer>)
>  timer-event-handler([t 22371 54023 394400 nil (closure (t) (buf) (save-current-buffer (set-buffer buf) (let* ((modified (buffer-modified-p)) (buffer-undo-list t) (inhibit-read-only t) (inhibit-modification-hooks t)) (unwind-protect (progn (remove-text-properties (point-min) (point-max) (quote ...))) (if modified nil (restore-buffer-modified-p nil)))))) (#<killed buffer>) nil 0])
> 
> 
> Then I ran `ag 'modified
> \(buffer-modified-p\).*\n.*buffer-undo.*\n*inhib'` and got this:
> dtrt-indent-20160523.1318/dtrt-indent-diag.el:163:                    `((,modified (buffer-modified-p))
> dtrt-indent-20160523.1318/dtrt-indent-diag.el:164:                      (buffer-undo-list t)
> dtrt-indent-20160523.1318/dtrt-indent-diag.el:165:                      (inhibit-read-only t)
> markdown-mode-20160610.1745/markdown-mode.el:6321:  (let* ((modified (buffer-modified-p))
> markdown-mode-20160610.1745/markdown-mode.el:6322:         (buffer-undo-list t)
> markdown-mode-20160610.1745/markdown-mode.el:6323:         (inhibit-read-only t)
> 
> Then reading the code in those files, the code turned out to be in a macro:
> 
> (defmacro save-buffer-state (varlist &rest body)
>  "Bind variables according to VARLIST and eval BODY restoring buffer state."
>  (declare (indent 1) (debug let))
>  (let ((modified (make-symbol "modified")))
>    `(let* ,(append varlist
>                    `((,modified (buffer-modified-p))
>                      (buffer-undo-list t)
>                      (inhibit-read-only t)
>                      (inhibit-point-motion-hooks t)
>                      (inhibit-modification-hooks t)
>                      deactivate-mark
>                      buffer-file-name
>                      buffer-file-truename))
>       (progn
>         ,@body)
>       (unless ,modified
>         (restore-buffer-modified-p nil)))))
> 
> 
> But I have found only one occurrence in dtrt-indent:
> 
> (defun dtrt-indent-highlight ()
>  "Highlight non-excluded indentation in the current buffer."
>  (interactive)
>  (let ((language-and-variable
>         (cdr (dtrt-indent--search-hook-mapping major-mode))))
>    (if (null language-and-variable)
>        (message "Major mode %s not supported by dtrt-indent" major-mode)
>      (save-buffer-state nil
>        (dtrt-indent--for-each-indentation
>         (car language-and-variable)
>         (lambda (histogram)
>           (put-text-property (save-excursion (beginning-of-line) (point))
>                              (point)
>                              'face '(background-color . "red"))
>           t)
>         nil)))))
> 
> Dunno how it is related to that timer execution. But according to the
> comment above `save-buffer-state`, there might be a similar macro in
> font-lock.el. Yes there is.
> I did a grep in emacs source and found lots of them. Then I look at the
> body part of that macro expansion: `(unwind-protect (progn
> (remove-text-properties (point-min) (point-max) 'fontified)))`. However
> I failed to find any occurrence. It might be another macro expansion
> here. So I decide to put it aside and will investigate later.
> 
> Best regards,
> Jiege CHen

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