Add org-mode link-type "https" to open local copies

The https link-type opens the local copies of the Spacemacs documentation files with
the spacemacs/view-org-file function. It supports GitHub style heading links

For example, the link:

https://github.com/syl20bnr/spacemacs/blob/develop/layers/org/README.org#links

Will be handled similary to as if it was:

file:~/.emacs.d/layers/org/README.org::*links

Also the `space-doc' mode will be applied.

Refactored GH style anchor search.

core/core-funcs.el

@@ -171,12 +171,30 @@ Supported properties:
   (find-file file)
   (org-indent-mode)
   (view-mode)
-  (when(and(boundp 'space-doc-mode)(fboundp 'space-doc-mode)(space-doc-mode)))
+
+  ;; Enable `space-doc-mode' if defined.
+  (when (and (boundp 'space-doc-mode)
+             (fboundp 'space-doc-mode))
+    (space-doc-mode))
+
   (goto-char (point-min))
 
   (when anchor-text
-    (re-search-forward anchor-text))
-  (beginning-of-line)
+    ;; If `anchor-text' is GitHub style link.
+    (if (string-prefix-p "#" anchor-text)
+        ;; If the toc-org package is loaded.
+        (if (configuration-layer/package-usedp 'toc-org)
+            ;; For each heading. Search the heading that corresponds to `anchor-text'.
+            (while (and (re-search-forward "^[\\*]+\s\\(.*\\).*$" nil t)
+                        (not (string= (toc-org-hrefify-gh (match-string 1))
+                                      anchor-text))))
+          ;; This is not a problem because without the space-doc package
+          ;; those links will be opened in the browser.
+          (message (format "Can't follow the GitHub style anchor: '%s' without the org layer." anchor-text)))
+
+      (re-search-forward anchor-text)))
+
+(beginning-of-line)
 
   (cond
    ((eq expand-scope 'subtree)

layers/org/local/space-doc/space-doc.el

@@ -7,6 +7,22 @@
 ;;
 ;; This file is not part of GNU Emacs.
 ;;
+;; Description:
+;; This package provides:
+;;   - `space-doc-mode' - buffer local minor mode
+;; for viewing the Spacemacs documentation files.
+;; The mode hides org meta tags to improve readability.
+;;   - `org-mode' link-type "https" that opens the local
+;; copies of the Spacemacs documentation files with
+;; `spacemacs/view-org-file' and supports GitHub style
+;; heading links.
+;;
+;; For example, the link:
+;;  https://github.com/syl20bnr/spacemacs/blob/develop/layers/org/README.org#links
+;; Will be handled similary to as if it was:
+;; file:~/.emacs.d/layers/org/README.org::*links
+;; Also the `space-doc' mode will be applied.
+
 ;;; License: GPLv3
 ;;; Code:
 (require 'face-remap)
@@ -42,5 +58,23 @@ keeping their content visible."
     (progn (message (format "space-doc-mode error:%s isn't an org-mode buffer" (buffer-name)))
            (setq org-mode nil))))
 
+(defun spacemacs//space-doc-open (path)
+  "If the `path' argument is a link to an .org file that is located
+in the Spacemacs GitHub repository - Visit the local copy
+of the file with `spacemacs/view-org-file'.
+Open all other links with `browse-url'."
+  (let ((git-url-root-regexp
+         (concat "\\/\\/github\\.com\\/syl20bnr"
+                 "\\/spacemacs\\/blob\\/[^/]+\\/\\(.*\\.org\\)\\(\\#.*\\)?")))
+    (if (string-match git-url-root-regexp path)
+        (spacemacs/view-org-file (concat user-emacs-directory
+                                         (match-string 1 path))
+                                 (or (match-string 2 path)
+                                     "^")
+                                 'subtree)
+      (browse-url (concat "https://" path)))))
+
+(org-add-link-type "https" 'spacemacs//space-doc-open)
+
 (provide 'space-doc)
 ;;; space-doc.el ends here