ox-publish: Allow linking to encrypted Org files

* lisp/ox-html.el (org-html-link): Convert .org.gpg file links to
.html, in addition to previously performed .org -> .html convertion.
(org-html-link-org-files-as-html): Update the docstring.
* doc/org-manual.org (Publishing links):
* etc/ORG-NEWS (Publishing now supports links to encrypted Org files):
Document the new feature.

doc/org-manual.org

@@ -16472,13 +16472,16 @@ Settings]]), however, override everything.
 #+cindex: links, publishing
 
 To create a link from one Org file to another, you would use something
-like =[[file:foo.org][The foo]]= or simply =[[file:foo.org]]= (see [[*External Links]]).  When
-published, this link becomes a link to =foo.html=.  You can thus
-interlink the pages of your "Org web" project and the links will work
-as expected when you publish them to HTML.  If you also publish the
-Org source file and want to link to it, use an =http= link instead of
-a =file:= link, because =file= links are converted to link to the
-corresponding =.html= file.
+like =[[file:foo.org][The foo]]= or simply =[[file:foo.org]]= (see
+[[*External Links]]).  When published, this link becomes a link to
+=foo.html=.  You can thus interlink the pages of your "Org web"
+project and the links will work as expected when you publish them to
+HTML.  If you also publish the Org source file and want to link to it,
+use an =http= link instead of a =file:= link, because =file= links are
+converted to link to the corresponding =.html= file.
+
+Links to encrypted Org files, like =[[file:foo.org.gpg]]= are also
+supported.
 
 You may also link to related files, such as images.  Provided you are
 careful with relative file names, and provided you have also

etc/ORG-NEWS

@@ -143,6 +143,12 @@ discouraged when working with Org files.
 *** Clock table can now produce quarterly reports
 
 =:step= clock table parameter can now be set to =quarter=.
+*** Publishing now supports links to encrypted Org files
+
+Links to other published Org files are automatically converted to the
+corresponding html links.  Now, this feature is also available when
+links point to encrypted Org files, like
+=[[file:foo.org.gpg::Heading]]=.
 
 *** Interactive commands now support escaping text inside comment blocks
 

lisp/ox-html.el

@@ -839,6 +839,8 @@ are directly put into a \"href\" tag in HTML.  However, links to other Org files
 (recognized by the extension \".org\") should become links to the corresponding
 HTML file, assuming that the linked Org file will also be converted to HTML.
 
+Links to \"file.org.gpg\" are also converted.
+
 When nil, the links still point to the plain \".org\" file."
   :group 'org-export-html
   :type 'boolean)
@@ -3066,12 +3068,13 @@ INFO is a plist holding contextual information.  See
 	  (lambda (raw-path info)
 	    ;; Treat links to `file.org' as links to `file.html', if
 	    ;; needed.  See `org-html-link-org-files-as-html'.
-	    (cond
-	     ((and (plist-get info :html-link-org-files-as-html)
-		   (string= ".org"
-			    (downcase (file-name-extension raw-path "."))))
-	      (concat (file-name-sans-extension raw-path) dot html-ext))
-	     (t raw-path))))
+            (save-match-data
+	      (cond
+	       ((and (plist-get info :html-link-org-files-as-html)
+                     (let ((case-fold-search t))
+                       (string-match "\\(.+\\)\\.org\\(?:\\.gpg\\)?$" raw-path)))
+	        (concat (match-string 1 raw-path) dot html-ext))
+	       (t raw-path)))))
 	 (type (org-element-property :type link))
 	 (raw-path (org-element-property :path link))
 	 ;; Ensure DESC really exists, or set it to nil.