Check if a Font is Available with Emacs Lisp

In Emacs Lisp, find-font function return a font-entity matching with FONT-SPEC. So we can make a helper function.

(defun font-available-p (font-name)
  (find-font (font-spec :name font-name)))

Before setting a font, we can check with this helper function.

(when (font-available-p "Fira Code")
  (set-face-attribute 'default nil :font (font-spec :family "Fira Code" :size 17)))