Annotate completion candidates (GNU Emacs)


GNU Emacs supports annotation for completion candidates. An annotation is a small bit of useful information shown next to a completion candidate which a package developer can use to provide additional help to the user while making a selection. e.g. while selecting a command, this is usually the keyboard shortcut.

In the following example, annotation is used to display a sample text with the candidate font-family applied. 

(defun test ()
  (interactive)
  (let* ((completion-extra-properties
          `(:annotation-function
        (lambda (a)
          (propertize " (OIly10)" 'face
              `(:family ,a :background "grey"))))))
    (completing-read "Font family: " (font-family-list))
    ))

 

By default, Emacs uses completions-annotations face for the annotation. Use the following patch to skip changing the face when the annotation already has a face attached.

modified   lisp/minibuffer.el
@@ -1754,8 +1754,10 @@ completion--insert-strings
               (let ((beg (point))
                     (end (progn (insert (cadr str)) (point))))
                 (put-text-property beg end 'mouse-face nil)
-                (font-lock-prepend-text-property beg end 'face
-                                                 'completions-annotations)))
+                (or (get-text-property beg 'face)
+                    (font-lock-append-text-property beg end 'face
+                                                    'completions-annotations))
+                ))
         (cond
          ((eq completions-format 'vertical)
           ;; Vertical format

 

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