[RFC] Change visibility for bracket links

[Nicolas Goaziou <mail@nicolasgoaziou.fr>]

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Hello,

I'd like to make the following change to bracket links display (i.e.,
when `org-highlight-links' contains `bracket', which is the default).

Basically, I want to leave a visible pair of brackets around the link,
i.e.,

  [[uri][description]]

is displayed as

  [description]

instead of

  description

and

  [[uri]]

is displayed as

  [uri]

instead of

  uri

The rationale behind this suggestion is that editing a mostly invisible
link is unintuitive when point is at the boundaries of its visible part.

More precisely, in the following visible part of a link

  description

if point hits "d" from the right, changes happen in the description of
the link, but if point comes from the left, changes happen before the
link. 

I guess I could get used to it, but sometimes, the link happens to be at
column 0. In this case, the only way to "come from the left" is to move
to the previous line and go past the newline character. This is, IMO,
very annoying, notwithstanding the fact that it is impossible to realize
at the beginning of the buffer.

Leaving a pair of brackets, OTOH, disambiguates the situation. Editing
before the opening bracket makes changes before the link. Conversely,
editing after the former makes changes to the uri or the description,
whichever is displayed.

The cost a little more visual clutter, but it seems very acceptable to
me. I attach a quick patch for testing.

Feedback welcome.

Regards,

-- 
Nicolas Goaziou                                                0x80A93738

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From 768d77be335e1e5e0a4afa9bf7dbd89f9c5ab65e Mon Sep 17 00:00:00 2001
From: Nicolas Goaziou <mail@nicolasgoaziou.fr>
Date: Wed, 5 Oct 2016 17:22:15 +0200
Subject: [PATCH] Change bracket links visibility

* lisp/org.el (org-activate-bracket-links): Leave a pair of brackets
  around bracket links so as to facilitate editing them.
---
 lisp/org.el | 49 ++++++++++++++++++-------------------------------
 1 file changed, 18 insertions(+), 31 deletions(-)

diff --git a/lisp/org.el b/lisp/org.el
index 6d5201b..25f48e3 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -6199,41 +6199,34 @@ by a #."
 			  (t
 			   `(:uri ,(format "%s:%s" type path)))))
 	   (activate-func (org-link-get-parameter type :activate-func))
-	   ;; invisible part
-	   (ip (list 'invisible (or
-				 (org-link-get-parameter type :display)
-				 'org-link)
-		     'face face
-		     'keymap keymap
-		     'mouse-face mouse-face
-		     'font-lock-multiline t
-		     'help-echo help
-		     'htmlize-link htmlize-link))
-	   ;; visible part
+	   ;; Visible part.
 	   (vp (list 'keymap keymap
 		     'face face
 		     'mouse-face mouse-face
 		     'font-lock-multiline t
 		     'help-echo help
-		     'htmlize-link htmlize-link)))
+		     'htmlize-link htmlize-link))
+	   ;; Invisible part.
+	   (ip (append (list 'invisible
+			     (or (org-link-get-parameter type :display)
+				 'org-link))
+		       vp)))
       ;; We need to remove the invisible property here.  Table narrowing
       ;; may have made some of this invisible.
       (org-remove-flyspell-overlays-in (match-beginning 0) (match-end 0))
       (remove-text-properties (match-beginning 0) (match-end 0)
 			      '(invisible nil))
-      (if (match-end 3)
+      (if (match-end 2)
 	  (progn
-	    (add-text-properties (match-beginning 0) (match-beginning 3) ip)
-	    (org-rear-nonsticky-at (match-beginning 3))
-	    (add-text-properties (match-beginning 3) (match-end 3) vp)
-	    (org-rear-nonsticky-at (match-end 3))
-	    (add-text-properties (match-end 3) (match-end 0) ip)
+	    (add-text-properties (match-beginning 0) (match-beginning 2) ip)
+	    (add-text-properties (match-beginning 2) (match-end 2) vp)
+	    (add-text-properties (match-end 2) (match-end 0) ip)
+	    ;; The following is needed so as characters inserted after
+	    ;; the closing bracket do not enter the link.
 	    (org-rear-nonsticky-at (match-end 0)))
-	(add-text-properties (match-beginning 0) (match-beginning 1) ip)
-	(org-rear-nonsticky-at (match-beginning 1))
-	(add-text-properties (match-beginning 1) (match-end 1) vp)
-	(org-rear-nonsticky-at (match-end 1))
-	(add-text-properties (match-end 1) (match-end 0) ip)
+	(add-text-properties (match-beginning 0) (1+ (match-beginning 0)) ip)
+	(add-text-properties (1+ (match-beginning 0)) (1+ (match-end 1)) vp)
+	(add-text-properties (1+ (match-end 1)) (match-end 0) ip)
 	(org-rear-nonsticky-at (match-end 0)))
       (when activate-func
 	(funcall activate-func link-start link-end path bracketp))
@@ -23762,10 +23755,7 @@ beyond the end of the headline."
 	    ;; point was already at beginning of line and command is
 	    ;; repeated.
 	    (when (and (= (point) pos) (eq last-command this-command))
-	      (goto-char after-bullet))))))))
-  (setq disable-point-adjustment
-        (or (not (invisible-p (point)))
-            (not (invisible-p (max (point-min) (1- (point))))))))
+	      (goto-char after-bullet)))))))))
 
 (defun org-end-of-line (&optional arg)
   "Go to the end of the line.
@@ -23802,10 +23792,7 @@ the cursor is already beyond the end of the headline."
 	  ;; If element is hidden, `move-end-of-line' would put point
 	  ;; after it.  Use `end-of-line' to stay on current line.
 	  (call-interactively 'end-of-line))
-	 (t (call-interactively move-fun))))))
-  (setq disable-point-adjustment
-        (or (not (invisible-p (point)))
-            (not (invisible-p (max (point-min) (1- (point))))))))
+	 (t (call-interactively move-fun)))))))
 
 (define-key org-mode-map "\C-a" 'org-beginning-of-line)
 (define-key org-mode-map "\C-e" 'org-end-of-line)
-- 
2.9.3