thing-at-point does not bound url properly due to backslash in url

Question

I am trying to filter URLs and elisp thing-at-point 'url doesn't bounds a url properly because it has backslashes \in it. I believe that backslashes are unsafe in urls, but that's a separate topic. The fact is that I am receiving emails with URLs that have them. So my question is if there is any way to ensure that thing-at-point allows backslashes, so that urls can be properly bounded? The relevant functions should be available at thingatpt.el Thank you in advance.

Update

This is phils' solution

(defun thing-at-point-bounds-of-url-at-point (&optional lax)
  "Return a cons cell containing the start and end of the URI at point.
     Try to find a URI using `thing-at-point-markedup-url-regexp'.
     If that fails, try with `thing-at-point-beginning-of-url-regexp'.
     If that also fails, and optional argument LAX is non-nil, return
     the bounds of a possible ill-formed URI (one lacking a scheme)."
  ;; Look for the old <URL:foo> markup.  If found, use it.
  (or (thing-at-point--bounds-of-markedup-url)
      ;; Otherwise, find the bounds within which a URI may exist.  The
      ;; method is similar to `ffap-string-at-point'.  Note that URIs
      ;; may contain parentheses but may not contain spaces (RFC3986).
      (let* ((allowed-chars "--:=&?$+@-Z_[:alpha:]~#,%;*()!'\\\\")
         (skip-before "^[0-9a-zA-Z]")
         (skip-after  ":;.,!?")
         (pt (point))
         (beg (save-excursion
            (skip-chars-backward allowed-chars)
            (skip-chars-forward skip-before pt)
            (point)))
         (end (save-excursion
            (skip-chars-forward allowed-chars)
            (skip-chars-backward skip-after pt)
            (point))))
    (or (thing-at-point--bounds-of-well-formed-url beg end pt)
        (if lax (cons beg end))))))

and this is the original and url bounded by thing-at-point-bounds-of-url-at-point (both edited)

original:

https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.disney.com%2F&amp\;data=02%7C01%7CDonald.Duck%40disney.com%7Cfd8a40dd8138470286be08d8020da460%7C07ef1208413c4b5e9cdd64ef305754f0%7C0%7C0%7C637261604914185764&amp\;sdata=UdFaQR32cGXKu7ZrBU%2BGg8TJ%2BOeTZUMBV9N%2BE8Vi22s%3D&amp\;reserved=0

bounded:

https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.disney.com%2F&amp

Answer 1

In Emacs 26.3 at least, the allowed characters are hard-coded in thing-at-point-bounds-of-url-at-point; so you would need to modify that function accordingly, to add a backslash to the allowed-chars binding. The comments below on escaping would apply here too: use "\\\\". (And likewise for having no idea whether or not this will have unwanted side-effects.)

Edit: Initial answer follows, before I'd realised that thing-at-point doesn't use url-get-url-at-point at all...

---

url-get-url-filename-chars is a variable defined in `url-util.el'.
Its value is "-%.?@a-zA-Z0-9()_/:~=&"

Documentation:
Valid characters in a URL.

It's used (by url-get-url-at-point) both in a regexp character alternative, and also with skip-chars-*, which means you'd need to use the latter's escaping for a backslash: "\\\\" (which is merely redundant for the former).

I don't know what all of the practical consequences of modifying this value might be.