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Re: Public API change: How to handle function signature change gracefull

From: John Kitchin
Subject: Re: Public API change: How to handle function signature change gracefully
Date: Tue, 21 Apr 2020 16:07:30 -0400

I think what Nicolas suggests is probably the easiest path. Here is one example that does what I think you are looking for. I use a simple string comparison on the contents, you could do something more sophisticated.

#+BEGIN_SRC emacs-lisp
(defun fruit-link-face (path)
  (let* ((ln (org-element-context))
(start (org-element-property :contents-begin ln))
(end (org-element-property :contents-end ln))
(contents (if (and start end)
      (buffer-substring start end)
    (if (and contents (stringp contents))
(if (string> contents "j")
   '(:foreground "red")
 '(:foreground "blue"))

(org-link-set-parameters "fruit"
                         :face 'fruit-link-face)

| :face | fruit-link-face |

[[fruit:mango ][test]].  # this will be red

  fruit:apple. # regular org link.

 [[fruit:apple][bera]]. # this will be blue

Professor John Kitchin 
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213

On Tue, Apr 21, 2020 at 1:57 PM Nicolas Goaziou <address@hidden> wrote:

Benjamin Andresen writes:
> I would like to change the public API of the :face part of `org-link-set-parameters':
>         (org-link-set-parameters "file" :face 'org-link)
> My ultimate goal is to have org-links be able to be have their face changed based on the contents, not just the path of the link.
> I found the relevant code in org.el in the function `org-activate-links':
>    'face (pcase (org-link-get-parameter type :face)
>    ((and (pred functionp) face) (funcall face path))
>    ((and (pred facep) face) face)
>    ((and (pred consp) face) face) ;anonymous
>    (_ 'org-link))
> and would like to change this to
>    'face (pcase (org-link-get-parameter type :face)
>    ((and (pred functionp) face) (funcall face path contents)) ;; this is the change
>    ((and (pred facep) face) face)
>    ((and (pred consp) face) face) ;anonymous
>    (_ 'org-link))
> Now that will introduce a host of call issues because the callees don't expect to the amount of arguments changed under their bottom.
> I would like some guidance how I could get what I think is neat: The
> contents of the bracket-style links as an additional parameter to set
> faces on and not breaking existing hookups.

Isn't the function called with point on the link? You may just need to
extract the contents from the environment.

Otherwise, a solution is to catch `wrong-number-of-arguments' error and
call again the function with the old calling convention. See, e.g.,

> To make this more palatable I would suggest it's changed so that the
> 2nd argument will be a list of alists or keywords so to not have this
> function signature problem if someone else comes up with a reason to
> introduce yet more data.

Beware the over-engineering. At this point, someone motivated enough can
put an advice to the link fontification function.


Nicolas Goaziou

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