Re: find-file-hook, recenter, scroll-conservatively and save-place

[Gergely Risko <gergely@risko.hu>]

On 2019-01-31 19:44 (Thursday), martin rudalics <rudalics@gmx.at> writes:
> When 'display-buffer' finds a '(window-start . recenter) ALIST entry
> it would call 'recenter' after assigning the window buffer.

I reproduced this behavior with advices and hooks in current Emacs, so
we can play with it.  This is a self-contained ~/.emacs (that I'm
testing with --no-site-file --no-site-lisp --no-splash):

-=-=-=-=-=-=-=-=-=-=-
(save-place-mode 1)
(setq vc-follow-symlinks t)
(setq scroll-margin 3)
(setq scroll-conservatively 101)

(defvar-local nce/flagged-for-recenter nil)
(defun nce/flag-for-recenter ()
  (setq-local nce/flagged-for-recenter t))

(defun nce/recenter-if-flagged (ad-do-it buffer &rest args)
  (let ((window (apply ad-do-it buffer args)))
    (when (buffer-local-value 'nce/flagged-for-recenter buffer)
      (setq-local nce/flagged-for-recenter nil)
      (with-selected-window window
        (with-current-buffer buffer
          (condition-case nil (recenter) ('error t)))))
    window))

(add-hook 'find-file-hook 'nce/flag-for-recenter)
(advice-add 'display-buffer :around 'nce/recenter-if-flagged)
-=-=-=-=-=-=-=-=-=-=-

It works quite well and it's a lot better than my previous find-file
based solution (sent to Eli), because we only need one advice on
display-buffer and not on all the various find file stuff.

I only discovered one issue, startup.el contains this regarding
command line parsing:
-=-=-=-=-=-=-=-=-=-=-
    (let ((displayable-buffers-len (length displayable-buffers))
          ;; `nondisplayed-buffers-p' is true if there exist buffers
          ;; in `displayable-buffers' that were not displayed to the
          ;; user.
          (nondisplayed-buffers-p nil))
      (when (> displayable-buffers-len 0)
        (switch-to-buffer (car displayable-buffers)))   <------
      (when (> displayable-buffers-len 1)
        (switch-to-buffer-other-window (car (cdr displayable-buffers)))
        ;; Focus on the first buffer.
        (other-window -1))
      (when (> displayable-buffers-len 2)
-=-=-=-=-=-=-=-=-=-=-

Here, the second file is properly recenterd, because it uses
switch-to-buffer-other-window (so our display-buffer is called), but
the first file is simply displayed with switch-to-buffer.  So I guess
we would have to put a recenter here in startup.el conditional on the
buffer-local variable that was meant to display-buffer by the
save-place hook.  Or maybe replace the marked switch-to-buffer call
with: (display-buffer (...) '(display-buffer-same-window))

Gergely