Create `org-link-parameters'

* lisp/org-element.el: Replace `org-link-types' variable with
  `org-link-types' function.

* lisp/org.el: Replace the `org-link-types' variable with
  `org-link-types' function. Create `org-link-get-parameter' and
  `org-link-set-parameters' functions. Remove `org-add-link-type'. Add
  `org-store-link-functions' function and remove
  `org-store-link-functions' variable. Add `org--open-file-link' for use
  as a :follow function for file type links.

* lisp/org.el: Set :follow functions for file links in `org-link-parameters.
Define `org-open-file-link' that opens a file link with an app.

* testing/lisp/test-ox.el: Remove usage of the `org-link-types'
  variable.

* lisp/org-compat.el: Move `org-add-link-type' and mark it as obsolete.

* lisp/ox.el: Change org-add-link-type comment in ox.el.

lisp/org-compat.el

@@ -195,6 +195,37 @@ is, use SPECS to define the face."
     specs))
 (make-obsolete 'org-compatible-face "you can remove it." "Org 9.0")
 
+(defun org-add-link-type (type &optional follow export)
+  "Add a new TYPE link.
+FOLLOW and EXPORT are two functions.
+
+FOLLOW should take the link path as the single argument and do whatever
+is necessary to follow the link, for example find a file or display
+a mail message.
+
+EXPORT should format the link path for export to one of the export formats.
+It should be a function accepting three arguments:
+
+  path    the path of the link, the text after the prefix (like \"http:\")
+  desc    the description of the link, if any
+  format  the export format, a symbol like `html' or `latex' or `ascii'.
+
+The function may use the FORMAT information to return different values
+depending on the format.  The return value will be put literally into
+the exported file.  If the return value is nil, this means Org should
+do what it normally does with links which do not have EXPORT defined.
+
+Org mode has a built-in default for exporting links.  If you are happy with
+this default, there is no need to define an export function for the link
+type.  For a simple example of an export function, see `org-bbdb.el'.
+
+If TYPE already exists, update it with the arguments.
+See `org-link-parameters' for documentation on the other parameters."
+  (org-link-set-parameters type :follow follow :export export)
+  (message "Created %s link." type))
+
+(make-obsolete 'org-add-link-type "org-link-add." "Org 9.0")
+
 
 ;;; Miscellaneous functions
 

lisp/org-element.el

@@ -185,7 +185,7 @@ specially in `org-element--object-lex'.")
 		"\\)\\)")
 	org-element--object-regexp
 	(mapconcat #'identity
-		   (let ((link-types (regexp-opt org-link-types)))
+		   (let ((link-types (regexp-opt (org-link-types))))
 		     (list
 		      ;; Sub/superscript.
 		      "\\(?:[_^][-{(*+.,[:alnum:]]\\)"
@@ -3108,7 +3108,7 @@ Assume point is at the beginning of the link."
 	      (string-match "\\`\\.\\.?/" raw-link))
 	  (setq type "file")
 	  (setq path raw-link))
-	 ;; Explicit type (http, irc, bbdb...).  See `org-link-types'.
+	 ;; Explicit type (http, irc, bbdb...).
 	 ((string-match org-link-types-re raw-link)
 	  (setq type (match-string 1 raw-link))
 	  (setq path (substring raw-link (match-end 0))))

lisp/org.el

@@ -1758,6 +1758,73 @@ calls `table-recognize-table'."
   "Buffer-local version of `org-link-abbrev-alist', which see.
 The value of this is taken from the #+LINK lines.")
 
+(defcustom org-link-parameters
+  '(("file" :complete org-file-complete-link)
+    ("file+emacs" :follow (lambda (path) (org--open-file-link path '(4))))
+    ("file+sys" :follow (lambda (path) (org--open-file-link path 'system)))
+    ("http") ("https") ("ftp") ("mailto")
+    ("news") ("shell") ("elisp")
+    ("doi") ("message") ("help"))
+  "An alist of properties that defines all the links in Org mode.
+The key in each association is a string of the link type.
+Subsequent optional elements make up a p-list of link properties.
+
+:follow - A function that takes the link path as an argument.
+
+:export - A function that takes the link path, description and
+export-backend as arguments.
+
+:store - A function responsible for storing the link.  See the
+function `org-store-link-functions'.
+
+:complete - A function that inserts a link with completion.  The
+function takes one optional prefix arg.
+
+:face - A face for the link, or a function that returns a face.
+The function takes one argument which is the link path.  The
+default face is `org-link'.
+
+:mouse-face - The mouse-face. The default is `highlight'.
+
+:display - `full' will not fold the link in descriptive
+display.  Default is `org-link'.
+
+:help-echo - A string or function that takes (window object position)
+as arguments and returns a string.
+
+:keymap - A keymap that is active on the link.  The default is
+`org-mouse-map'.
+
+:htmlize-link - A function for the htmlize-link.  Defaults
+to (list :uri \"type:path\")
+
+:activate-func - A function to run at the end of font-lock
+activation.  The function must accept (link-start link-end path bracketp)
+as arguments."
+  :group 'org-link
+  :type '(alist :tag "Link display parameters"
+		:value-type plist))
+
+(defun org-link-get-parameter (type key)
+  "Get TYPE link property for KEY.
+TYPE is a string and KEY is a plist keyword."
+  (plist-get
+   (cdr (assoc type org-link-parameters))
+   key))
+
+(defun org-link-set-parameters (type &rest parameters)
+  "Set link TYPE properties to PARAMETERS.
+  PARAMETERS should be :key val pairs."
+  (let ((data (assoc type org-link-parameters)))
+    (if data (setcdr data (org-combine-plists (cdr data) parameters))
+      (push (cons type parameters) org-link-parameters)
+      (org-make-link-regexps)
+      (org-element-update-syntax))))
+
+(defun org-link-types ()
+  "Return a list of known link types."
+  (mapcar #'car org-link-parameters))
+
 (defcustom org-link-abbrev-alist nil
   "Alist of link abbreviations.
 The car of each element is a string, to be replaced at the start of a link.
@@ -5490,7 +5557,7 @@ The following commands are available:
      org-display-table 4
      (vconcat (mapcar
 	       (lambda (c) (make-glyph-code c (and (not (stringp org-ellipsis))
-					      org-ellipsis)))
+						   org-ellipsis)))
 	       (if (stringp org-ellipsis) org-ellipsis "..."))))
     (setq buffer-display-table org-display-table))
   (org-set-regexps-and-options)
@@ -5658,9 +5725,6 @@ the rounding returns a past time."
 (require 'font-lock)
 
 (defconst org-non-link-chars "]\t\n\r<>")
-(defvar org-link-types '("http" "https" "ftp" "mailto" "file" "file+emacs"
-			 "file+sys" "news" "shell" "elisp" "doi" "message"
-			 "help"))
 (defvar org-link-types-re nil
   "Matches a link that has a url-like prefix like \"http:\"")
 (defvar org-link-re-with-space nil
@@ -5727,8 +5791,8 @@ stacked delimiters is N.  Escaping delimiters is not possible."
 
 (defun org-make-link-regexps ()
   "Update the link regular expressions.
-This should be called after the variable `org-link-types' has changed."
-  (let ((types-re (regexp-opt org-link-types t)))
+This should be called after the variable `org-link-parameters' has changed."
+  (let ((types-re (regexp-opt (org-link-types) t)))
     (setq org-link-types-re
 	  (concat "\\`" types-re ":")
 	  org-link-re-with-space
@@ -5766,7 +5830,7 @@ This should be called after the variable `org-link-types' has changed."
 	  org-bracket-link-analytic-regexp++
 	  (concat
 	   "\\[\\["
-	   "\\(" (regexp-opt (cons "coderef" org-link-types) t) ":\\)?"
+	   "\\(" (regexp-opt (cons "coderef" (org-link-types)) t) ":\\)?"
 	   "\\([^]]+\\)"
 	   "\\]"
 	   "\\(\\[" "\\([^]]+\\)" "\\]\\)?"
@@ -7393,7 +7457,7 @@ a block.  Return a non-nil value when toggling is successful."
 ;; Remove overlays when changing major mode
 (add-hook 'org-mode-hook
 	  (lambda () (add-hook 'change-major-mode-hook
-			  'org-show-block-all 'append 'local)))
+			       'org-show-block-all 'append 'local)))
 
 ;;; Org-goto
 
@@ -9666,60 +9730,32 @@ The refresh happens only for the current tree (not subtree)."
 (defvar org-store-link-plist nil
   "Plist with info about the most recently link created with `org-store-link'.")
 
-(defvar org-link-protocols nil
-  "Link protocols added to Org-mode using `org-add-link-type'.")
+(defun org-store-link-functions ()
+  "Return a list of functions that are called to create and store a link.
+The functions defined in the :store property of
+`org-link-parameters'.
 
-(defvar org-store-link-functions nil
-  "List of functions that are called to create and store a link.
 Each function will be called in turn until one returns a non-nil
-value.  Each function should check if it is responsible for creating
-this link (for example by looking at the major mode).
-If not, it must exit and return nil.
-If yes, it should return a non-nil value after a calling
-`org-store-link-props' with a list of properties and values.
-Special properties are:
+value.  Each function should check if it is responsible for
+creating this link (for example by looking at the major mode).
+If not, it must exit and return nil.  If yes, it should return
+a non-nil value after calling `org-store-link-props' with a list
+of properties and values.  Special properties are:
 
 :type         The link prefix, like \"http\".  This must be given.
 :link         The link, like \"http://www.astro.uva.nl/~dominik\".
               This is obligatory as well.
 :description  Optional default description for the second pair
-              of brackets in an Org-mode link.  The user can still change
-              this when inserting this link into an Org-mode buffer.
+              of brackets in an Org mode link.  The user can still change
+              this when inserting this link into an Org mode buffer.
 
 In addition to these, any additional properties can be specified
-and then used in capture templates.")
-
-(defun org-add-link-type (type &optional follow export)
-  "Add TYPE to the list of `org-link-types'.
-Re-compute all regular expressions depending on `org-link-types'
-
-FOLLOW and EXPORT are two functions.
-
-FOLLOW should take the link path as the single argument and do whatever
-is necessary to follow the link, for example find a file or display
-a mail message.
-
-EXPORT should format the link path for export to one of the export formats.
-It should be a function accepting three arguments:
-
-  path    the path of the link, the text after the prefix (like \"http:\")
-  desc    the description of the link, if any
-  format  the export format, a symbol like `html' or `latex' or `ascii'.
-
-The function may use the FORMAT information to return different values
-depending on the format.  The return value will be put literally into
-the exported file.  If the return value is nil, this means Org should
-do what it normally does with links which do not have EXPORT defined.
-
-Org mode has a built-in default for exporting links.  If you are happy with
-this default, there is no need to define an export function for the link
-type.  For a simple example of an export function, see `org-bbdb.el'."
-  (add-to-list 'org-link-types type t)
-  (org-make-link-regexps)
-  (org-element-update-syntax)
-  (if (assoc type org-link-protocols)
-      (setcdr (assoc type org-link-protocols) (list follow export))
-    (push (list type follow export) org-link-protocols)))
+and then used in capture templates."
+  (cl-loop for link in org-link-parameters
+	   with store-func
+	   do (setq store-func (org-link-get-parameter (car link) :store))
+	   if store-func
+	   collect store-func))
 
 (defvar org-agenda-buffer-name) ; Defined in org-agenda.el
 (defvar org-id-link-to-org-use-id) ; Defined in org-id.el
@@ -9764,7 +9800,7 @@ active region."
 		    (delq
 		     nil (mapcar (lambda (f)
 				   (let (fs) (if (funcall f) (push f fs))))
-				 org-store-link-functions))
+				 (org-store-link-functions)))
 		    sfunsn (mapcar (lambda (fu) (symbol-name (car fu))) sfuns))
 	      (or (and (cdr sfuns)
 		       (funcall (intern
@@ -10325,7 +10361,7 @@ Use TAB to complete link prefixes, then RET for type-specific completion support
 	(and (window-live-p cw) (select-window cw)))
       (setq all-prefixes (append (mapcar 'car abbrevs)
 				 (mapcar 'car org-link-abbrev-alist)
-				 org-link-types))
+				 (org-link-types)))
       (unwind-protect
 	  ;; Fake a link history, containing the stored links.
 	  (let ((org--links-history
@@ -10601,6 +10637,30 @@ they must return nil.")
 
 (defvar org-link-search-inhibit-query nil) ;; dynamically scoped
 (defvar clean-buffer-list-kill-buffer-names) ; Defined in midnight.el
+(defun org--open-file-link (path app)
+  "Open PATH using APP.
+
+PATH is from a file link, and can have the following syntax:
+     [[file:~/code/main.c::255]]
+     [[file:~/xx.org::My Target]]
+     [[file:~/xx.org::*My Target]]
+     [[file:~/xx.org::#my-custom-id]]
+     [[file:~/xx.org::/regexp/]]
+
+If APP is non-nil, open PATH in Emacs.  If it is `system', use
+a system application instead."
+  (let* ((fields (split-string path "::"))
+	 (option (and (cdr fields)
+		      (mapconcat #'identity (cdr fields) ""))))
+    (apply #'org-open-file
+	   (car fields)
+	   app
+	   (cond ((not option) nil)
+		 ((string-match-p "\\`[0-9]+\\'" option)
+		  (list (string-to-number option)))
+		 (t (list nil
+			  (org-link-unescape option)))))))
+
 (defun org-open-at-point (&optional arg reference-buffer)
   "Open link, timestamp, footnote or tags at point.
 

lisp/ox.el

@@ -4073,7 +4073,7 @@ meant to be translated with `org-export-data' or alike."
 ;;;; For Links
 ;;
 ;; `org-export-custom-protocol-maybe' handles custom protocol defined
-;; with `org-add-link-type', which see.
+;; in `org-link-parameters'.
 ;;
 ;; `org-export-get-coderef-format' returns an appropriate format
 ;; string for coderefs.

testing/lisp/test-ox.el

@@ -2571,8 +2571,8 @@ Para2"
   (should
    (string-match
     "success"
-    (let ((org-link-types (copy-sequence org-link-types)))
-      (org-add-link-type "foo" nil (lambda (p d f) "success"))
+    (progn
+      (org-link-set-parameters "foo" :export (lambda (p d f) "success"))
       (org-export-string-as
        "[[foo:path]]"
        (org-export-create-backend
@@ -2586,9 +2586,9 @@ Para2"
   (should-not
    (string-match
     "success"
-    (let ((org-link-types (copy-sequence org-link-types)))
-      (org-add-link-type
-       "foo" nil (lambda (p d f) (and (eq f 'test) "success")))
+    (progn
+      (org-link-set-parameters
+       "foo" :export (lambda (p d f) (and (eq f 'test) "success")))
       (org-export-string-as
        "[[foo:path]]"
        (org-export-create-backend
@@ -2603,9 +2603,9 @@ Para2"
   (should-not
    (string-match
     "success"
-    (let ((org-link-types (copy-sequence org-link-types)))
-      (org-add-link-type
-       "foo" nil (lambda (p d f) (and (eq f 'test) "success")))
+    (progn
+      (org-link-set-parameters
+       "foo" :export (lambda (p d f) (and (eq f 'test) "success")))
       (org-export-string-as
        "[[foo:path]]"
        (org-export-create-backend