org-export: Do not strip link type by default during export

* lisp/ox-html.el (org-html-link):
* lisp/ox-latex.el (org-latex-link):
* lisp/ox-man.el (org-man-link):
* lisp/ox-md.el (org-md-link):
* lisp/ox-odt.el (org-odt-link--inline-image):
* lisp/ox-texinfo.el (org-texinfo-link): Preserve link type during
export for all the links, not just for a hard-coded subset.
* etc/ORG-NEWS (Built-in HTML, LaTeX, Man, Markdown, ODT, and Texinfo
exporters preserve the link protocol during export): Document the
breaking change.

Link: https://list.orgmode.org/orgmode/878r9nofpw.fsf@localhost/

etc/ORG-NEWS

@@ -13,6 +13,24 @@ Please send Org bug reports to mailto:emacs-orgmode@gnu.org.
 
 * Version 9.7 (not released yet)
 ** Important announcements and breaking changes
+*** Built-in HTML, LaTeX, Man, Markdown, ODT, and Texinfo exporters preserve the link protocol during export
+
+Previously, some link types where not exported as =protocol:uri= but
+as bare =uri=. This is now changed.
+
+When a link is known by Org mode and does not have a custom ~:export~
+parameter (see A.3 Adding Hyperlink Types section of the manual), the
+link protocol is now not stripped.
+
+For example, if one adds a link type =tel=, but does not define
+~:export~ parameter
+: (org-link-set-parameters "tel")
+=[[tel:12345][John Doe]]= link will be correctly exported to LaTeX as
+=\href{tel:12345}{John Doe}=, not =\href{12345}{John Doe}=.
+
+However, links like =[[elisp:(+ 1 2)]]= will be exported as
+=\url{elisp:(+ 1 2)}=, which may be somewhat unexpected.
+
 *** When ~org-link-file-path-type~ is a function, its argument is now a filename as it is read by ~org-insert-link~; not an absolute path
 
 Previously, when ~org-link-file-path-type~ is set to a function, the

lisp/ox-html.el

@@ -3231,8 +3231,6 @@ INFO is a plist holding contextual information.  See
 	 (desc (org-string-nw-p desc))
 	 (path
 	  (cond
-	   ((member type '("http" "https" "ftp" "mailto" "news"))
-	    (url-encode-url (concat type ":" raw-path)))
 	   ((string= "file" type)
 	    ;; During publishing, turn absolute file names belonging
 	    ;; to base directory into relative file names.  Otherwise,
@@ -3259,7 +3257,7 @@ INFO is a plist holding contextual information.  See
 		  (concat raw-path
 			  "#"
 			  (org-publish-resolve-external-link option path t))))))
-	   (t raw-path)))
+	   (t (url-encode-url (concat type ":" raw-path)))))
 	 (attributes-plist
 	  (org-combine-plists
 	   ;; Extract attributes from parent's paragraph.  HACK: Only

lisp/ox-latex.el

@@ -2943,12 +2943,10 @@ INFO is a plist holding contextual information.  See
 		  link (plist-get info :latex-inline-image-rules)))
 	 (path (org-latex--protect-text
 		(pcase type
-		  ((or "http" "https" "ftp" "mailto" "doi")
-		   (concat type ":" raw-path))
 		  ("file"
 		   (org-export-file-uri raw-path))
 		  (_
-		   raw-path)))))
+		   (concat type ":" raw-path))))))
     (cond
      ;; Link type is handled by a special function.
      ((org-export-custom-protocol-maybe link desc 'latex info))

lisp/ox-man.el

@@ -615,10 +615,8 @@ INFO is a plist holding contextual information.  See
          ;; Ensure DESC really exists, or set it to nil.
          (desc (and (not (string= desc "")) desc))
          (path (pcase type
-                 ((or "http" "https" "ftp" "mailto")
-                  (concat type ":" raw-path))
                  ("file" (org-export-file-uri raw-path))
-                 (_ raw-path))))
+                 (_ (concat type ":" raw-path)))))
     (cond
      ;; Link type is handled by a special function.
      ((org-export-custom-protocol-maybe link desc 'man info))

lisp/ox-md.el

@@ -544,11 +544,9 @@ INFO is a plist holding contextual information.  See
 	 (type (org-element-property :type link))
 	 (raw-path (org-element-property :path link))
 	 (path (cond
-		((member type '("http" "https" "ftp" "mailto"))
-		 (concat type ":" raw-path))
 		((string-equal  type "file")
 		 (org-export-file-uri (funcall link-org-files-as-md raw-path)))
-		(t raw-path))))
+		(t (concat type ":" raw-path)))))
     (cond
      ;; Link type is handled by a special function.
      ((org-export-custom-protocol-maybe link desc 'md info))

lisp/ox-odt.el

@@ -2246,11 +2246,9 @@ used as a communication channel."
   (cl-assert (org-element-type-p element 'link))
   (let* ((src (let* ((type (org-element-property :type element))
 		     (raw-path (org-element-property :path element)))
-		(cond ((member type '("http" "https"))
-		       (concat type ":" raw-path))
-		      ((file-name-absolute-p raw-path)
+		(cond ((file-name-absolute-p raw-path)
 		       (expand-file-name raw-path))
-		      (t raw-path))))
+		      (t (concat type ":" raw-path)))))
 	 (src-expanded (if (file-name-absolute-p src) src
 			 (expand-file-name src (file-name-directory
 						(plist-get info :input-file)))))

lisp/ox-texinfo.el

@@ -1326,11 +1326,9 @@ INFO is a plist holding contextual information.  See
 	 (desc (and (not (string= desc "")) desc))
 	 (path (org-texinfo--sanitize-content
 		(cond
-		 ((member type '("http" "https" "ftp"))
-		  (concat type ":" raw-path))
 		 ((string-equal type "file")
 		  (org-export-file-uri raw-path))
-		 (t raw-path)))))
+		 (t (concat type ":" raw-path))))))
     (cond
      ((org-export-custom-protocol-maybe link desc 'texinfo info))
      ((org-export-inline-image-p link org-texinfo-inline-image-rules)