Tweaking Vertico candidates

One of the Emacs packages I do not seem to get used to is Marginalia.¹ There is nothing wrong with it and since Daniel Mendler is involved the ELisp underneath is great. However, to me it’s just too much information where I rarely want it. When I need that sort of documentation it’s always a quick key binding away.

Given the author it should not come as a surprise that Marginalia works rather smoothly with Vertico.² In fact, it works so well that I only see a “problem” when I use it without Marginalia. Months ago I reported this minor glitch to Daniel,³ but to cut a long story short, at the end of the current selected item vertico--format-candidate adds a newline escape sequence to which the vertico-current face is applied as well.

I know, it’s a minor thing that should not stop me from using Vertico. Still, it can be fixed quite easily. I suggested an advice in the aforementioned report, but since vertico--format-candidate is implemented as a cl-defgeneric I can do better:

(with-eval-after-load 'vertico
  (set-face-attribute 'vertico-current nil :extend nil)
  
  (cl-defmethod vertico--format-candidate (cnd pref suf idx _start)
    "Format CND given PREF, SUF, and IDX."
    (setq cnd (vertico--display-string (concat pref cnd suf "\n")))
    (when (= idx vertico--index)
      (add-face-text-property 0 (1- (length cnd)) 'vertico-current 'append cnd))
    cnd))

Beside ensuring that vertico-current does not extend beyond the selected candidate, I use the lovely named 1- function to avoid applying this face to \n as well.

Note that something like fido-vertical-mode does not need a hack like this. Yet I simply cannot resist tinkering with my favourite packages.