怎样把 MediaWiki 的 wikitext 转换为 GitHub 风格的 markdown

;; wikitext -> gfm converter
;;
;; 设计原则：
;; 1 所有规则按顺序执行
;; 2 每条规则对应一段代码
;; 3 不做抽象，优先可读性
;;
;; 规则：
;; 1 <code> 和 </code> -> ```
;; 2 <nowiki><syntaxhighlight> 和

-> ```</nowiki>

3 # -> *

4 ====== -> ######

5 ===== -> #####

6 ==== -> ####

7 === -> ###

8 == -> ##

9 -> ~~

10 ---- -> ---

(defun wikitext-convert-all (&optional start end)

 "Convert simple wikitext to GFM markdown."

 (interactive
  (if (use-region-p)
      (list (region-beginning) (region-end))
    (list (point-min) (point-max))))

 (save-excursion
   (save-restriction
     (narrow-to-region start end)

     ;; --------------------------------------------------
     ;; 1. inline 
     ;; --------------------------------------------------

     (goto-char (point-min))
     (while (re-search-forward "\\([^<\n]*\\)" nil t)
       (replace-match (concat "`" (match-string 1) "`") t t))

     (goto-char (point-min))
     (while (re-search-forward "" nil t)
       (replace-match "`"))

     (goto-char (point-min))
     (while (re-search-forward "" nil t)
       (replace-match "`"))

     ;; --------------------------------------------------
     ;; 2. syntaxhighlight
     ;; --------------------------------------------------

     (goto-char (point-min))
     (while (re-search-forward "<syntaxhighlight\\s-+lang=[\"']\\([^\"']+\\)[\"'][^>]*>" nil t)
       (replace-match (concat "```" (match-string 1)) t t))

     (goto-char (point-min))
     (while (re-search-forward "</syntaxhighlight>" nil t)
       (replace-match "```"))

     ;; --------------------------------------------------
     ;; 3. 列表 # → *
     ;; --------------------------------------------------

     (let ((in-code-block nil))
       (goto-char (point-min))
       (while (not (eobp))

         (let ((line (thing-at-point 'line t)))

           (when (string-match "^```" line)
             (setq in-code-block (not in-code-block)))

           (unless in-code-block
             (beginning-of-line)
             (while (search-forward "#" (line-end-position) t)
               (replace-match "*"))))

         (forward-line 1)))

     ;; --------------------------------------------------
     ;; 4. headings
     ;; --------------------------------------------------

     (dolist (n '(6 5 4 3 2))
       (goto-char (point-min))
       (let ((pat (format "^=\\{%d\\}[ \t]*\\(.*?\\S-\\)[ \t]*=\\{%d\\}[ \t]*$" n n))
             (rep (concat (make-string n ?#) " \\1")))
         (while (re-search-forward pat nil t)
           (replace-match rep))))

     ;; --------------------------------------------------
     ;; 5. other
     ;; --------------------------------------------------

     (goto-char (point-min))
     (while (re-search-forward "" nil t)
       (replace-match "~~"))

     (goto-char (point-min))
     (while (re-search-forward "" nil t)
       (replace-match "~~"))

     (goto-char (point-min))
     (while (re-search-forward "^----[ \t]*$" nil t)
       (replace-match "---"))

     (widen))))

</syntaxhighlight>