6

I've read What is inhibit-point-motion-hooks?.

Assume some minor-mode my-mode that wants to do point-motion-y things.

Assume my--point-entered and my--point-left functions that work fine in Emacs < 25, when my-mode sets point-entered and point-left props to use them.

Assume I'd like to have the mode keep working on Emacs < 25, but also do the right thing if it finds itself on 25+. What is the right thing to do?

I could (setq-local inhibit-point-motion-hooks nil) and call it a day. But that var is described as "obsolete", which seems stronger than "deprecated". So that seems like not the right thing.

Is the following a good template to use instead?

;; When mode is enabled
(when (fboundp 'cursor-sensor-mode)
  (cursor-sensor-mode 1))

;; When mode is disabled
(when (fboundp 'cursor-sensor-mode)
  (cursor-sensor-mode -1))

(defun my--cursor-sensor-function (window old dir)
  (let ((new (window-point window))) ;is this correct ???
    (pcase dir
      (`entered (my--point-entered old new))
      (`left    (my--point-left    old new)))))
;; where my--point-* are existing point motion functions

;; Where the props are added:
(let ((motion-props (if (fboundp 'cursor-sensor-mode)
                              (list 'cursor-sensor-functions
                                    (list #'my--cursor-sensor-function))
                            (list 'point-entered #'my--point-entered
                                  'point-left    #'my--point-left))))
  (add-text-properties beg
                       end
                       (append (list 'some-other-prop some-val)
                               motion-props)))

Or if that's not a good approach, what is the recommended way to work with both older and newer versions of Emacs?

  • 1. Your second sexp overrides the first one: if cursor-sensor-mode is defined then the function is ultimately called with a nil argument. 2. Calling it with a nil arg or a t arg has the same effect, anyway. Use 1 and -1 to turn it on and off, respectively. – Drew Jan 4 '17 at 17:40
  • @Drew Oops. I (thought I) already knew that detail about mode functions but managed to get that wrong in my example. Thanks! I'll edit. – Greg Hendershott Jan 4 '17 at 18:58
3

The two systems work in fundamentally different ways, so you can't easily have a 100% solution that unifies the two, but your approach looks OK. The only thing I'd recommend is to do the emulation the other way around: write your code for cursor-sensor-mode mostly and then write my-point-entered and my-point-left functions that call my-cursor-sensor-function. The reason for that is that it is "optimized for the future" rather than "optimized for the past".

| improve this answer | |
  • Thanks! I'll take your advice and reverse the emulation. Just to confirm, is it reliable to use window-point to get the new position (that's no longer provided as an argument); was that your intent? – Greg Hendershott Jan 5 '17 at 15:20
  • 1
    Yes, window-point is what you want for that. – Stefan Jan 5 '17 at 21:17
  • Sorry a follow-up point: I'm seeing cursor-sensor-mode work only when entering a region using forward motion. Backing into a region with e.g. backward-char, my cursor sensor function is not called. Is this as-expected, a bug, or a mistake on my end? – Greg Hendershott Jan 9 '17 at 16:25
  • @GregHendershott: your description is not precise enough for me to decide if it sounds like a bug or a misunderstanding. – Stefan Jan 9 '17 at 20:27
  • Actually the issue seems to be that c-s-m occurs one position sooner than a p-e when moving backwards. Something like treating the property end as inclusive vs. exclusive. Will report back with simpler recipe. – Greg Hendershott Jan 9 '17 at 22:20

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