Re: [elpa] externals/vertico a962a8b 2/3: Implement deferred highlighting for all completion styles

[Daniel Mendler]

Hi Stefan!

On 4/11/21 6:37 PM, Stefan Monnier wrote:
> > +(declare-function orderless-highlight-matches "ext:orderless")
> > +(defun vertico--all-completions (&rest args)
> > +  "Compute all completions for ARGS with deferred highlighting."
> > +  (cl-letf* ((orig-pcm (symbol-function #'completion-pcm--hilit-commonality))
> > +             (orig-flex (symbol-function #'completion-flex-all-completions))
> > +             ((symbol-function #'completion-flex-all-completions)
> > +              (lambda (&rest args)
> > +                ;; Unfortunately for flex we have to undo the deferred 
> > highlighting, since flex uses
> > +                ;; the completion-score for sorting, which is applied during 
> > highlighting.
> > +                (cl-letf (((symbol-function 
> > #'completion-pcm--hilit-commonality) orig-pcm))
> > +                  (apply orig-flex args))))
> > +             ;; Defer the following highlighting functions
> > +             (hl #'identity)
> > +             ((symbol-function #'completion-hilit-commonality)
> > +              (lambda (cands prefix &optional base)
> > +                (setq hl (lambda (x) (nconc (completion-hilit-commonality x 
> > prefix base) nil)))
> > +                (and cands (nconc cands base))))
> > +             ((symbol-function #'completion-pcm--hilit-commonality)
> > +              (lambda (pattern cands)
> > +                (setq hl (lambda (x) (completion-pcm--hilit-commonality 
> > pattern x)))
> > +                cands))
> > +             ((symbol-function #'orderless-highlight-matches)
> > +              (lambda (pattern cands)
> > +                (setq hl (lambda (x) (orderless-highlight-matches pattern x)))
> > +                cands)))
> > +    (cons (apply #'completion-all-completions args) hl)))
>
> Yuck!
> I think this should have a bug#NNN attached to make sure it's only used
> on a temporary basis (i.e. until Emacs's minibuffer.el provides the
> corresponding functionality).

I wasn't aware that you are monitoring this so closely. This is 
basically the prototype of how the deferred highlighting could look 
like, instead of my proposal 8, `completion-skip-highlighting`, which 
can hardly be generalized. It works well for Orderless 
(`orderless-skip-highlighting`), but that's about it.

One can introduce a function 
`completion-all-completions-deferred-highlighting` or alternatively add 
an optional argument to `completion-all-completions`, which signals that 
the function should return the list of completions and the deferred 
highlighting function/highlighting data. (One may also consider 
returning the base directly or is there a particular reason to put it 
into the last cdr?)

The function `completion-all-completions-deferred-highlighting` can 
return a special highlighting function, registered in 
`completion-styles-alist`.

Daniel