Temporary overlays in Emacs
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For some reason, no-one online seems to have a simple explanation of how to setup temporary overlays (think higlights/messages) that disappear as soon as the user moves.
This isn't some arcane art - many common emacs packages seem to use this kind of functionality, but no one (to my knowledge) has actually written this up in a neat format for others to follow.
Disclaimer: I didn't invent this - the following is basically a generalization of patterns I've seen in a couple emacs packages (i.e merlin-mode).
Sit-for
The key component for implementing this kind of functionality is the
function #(sit-for)# provided by emacs which waits for a given time
or until the user provides input and then runs the provided function:
(sit-for time after-fn)
It's usually best to wrap this with an #unwind-protect# to prevent
errors bubbling up.
Full code
Combining these two components together, we can implement a temporary highlight function as follows:
(defun temporary-highlight (bounds face)
"Temporarily highlight the region BOUNDS with FACE."
;; remove old highlights
(remove-overlays nil nil 'temporary-higlight t)
;; create overlay and setup
(lexical-let ((overlay (make-overlay (car bounds) (cdr bounds))))
(overlay-put overlay 'face face)
(overlay-put overlay 'temporary-highlight t)
;; now - keep the overlay around for 60-seconds
(unwind-protect (sit-for 60)
;; after the timeout/user-input delete overlay
(delete-overlay overlay))
))
Here we've done it just using a simple single overlay, but you can imagine how this might be used to highlight multiple separate sections temporarily - i.e highlight all matches.