add markdown-native-preview-mode to view previewed output within emacs

README.md

@@ -208,10 +208,14 @@ keybindings by pressing <kbd>C-c C-h</kbd>.
     and save the result in the file `basename.html`, where
     `basename` is the name of the Markdown file with the extension
     removed.  *Export and View:* press <kbd>C-c C-c v</kbd> to export the
-    file and view it in a browser.  **For both export commands, the
-    output file will be overwritten without notice.**
-    *Open:* <kbd>C-c C-c o</kbd> will open the Markdown source file directly
-    using `markdown-open-command`.
+    file and view it in a browser.  *Open:* <kbd>C-c C-c o</kbd> will open
+    the Markdown source file directly using `markdown-open-command`.
+    *Live Export*: Press <kbd>C-c C-c l</kbd> to turn on
+    `markdown-live-preview-mode` to view the exported output
+    side-by-side with the source Markdown. **For all export commands,
+    the output file will be overwritten without notice.**
+    `markdown-live-preview-window-function` can be customized to open
+    in a browser other than `eww`.
 
     To summarize:
 
@@ -221,6 +225,7 @@ keybindings by pressing <kbd>C-c C-h</kbd>.
       - <kbd>C-c C-c v</kbd>: `markdown-command` > `basename.html` > browser.
       - <kbd>C-c C-c w</kbd>: `markdown-command` > kill ring.
       - <kbd>C-c C-c o</kbd>: `markdown-open-command`.
+      - <kbd>C-c C-c l</kbd>: `markdown-live-preview-mode` > `*eww*` buffer.
 
     <kbd>C-c C-c c</kbd> will check for undefined references.  If there are
     any, a small buffer will open with a list of undefined

markdown-mode.el

@@ -257,10 +257,14 @@
 ;;     and save the result in the file `basename.html`, where
 ;;     `basename` is the name of the Markdown file with the extension
 ;;     removed.  *Export and View:* press `C-c C-c v` to export the
-;;     file and view it in a browser.  **For both export commands, the
-;;     output file will be overwritten without notice.**
-;;     *Open:* `C-c C-c o` will open the Markdown source file directly
-;;     using `markdown-open-command'.
+;;     file and view it in a browser.  *Open:* `C-c C-c o` will open
+;;     the Markdown source file directly using `markdown-open-command'.
+;;     *Live Export*: Press `C-c C-c l` to turn on
+;;     `markdown-live-preview-mode' to view the exported output
+;;     side-by-side with the source Markdown. **For all export commands,
+;;     the output file will be overwritten without notice.**
+;;     `markdown-live-preview-window-function' can be customized to open
+;;     in a browser other than `eww'.
 ;;
 ;;     To summarize:
 ;;
@@ -270,6 +274,7 @@
 ;;       - `C-c C-c v`: `markdown-command' > `basename.html` > browser.
 ;;       - `C-c C-c w`: `markdown-command' > kill ring.
 ;;       - `C-c C-c o`: `markdown-open-command'.
+;;       - `C-c C-c l`: `markdown-live-preview-mode' > `*eww*` buffer.
 ;;
 ;;     `C-c C-c c` will check for undefined references.  If there are
 ;;     any, a small buffer will open with a list of undefined
@@ -1003,6 +1008,18 @@ to `nil' instead. See `font-lock-support-mode' for more details."
   :group 'markdown
   :type 'boolean)
 
+(defcustom markdown-live-preview-window-function 'markdown-live-preview-window-eww
+  "Function to display preview of Markdown output within Emacs. Function must
+update the buffer containing the preview and return the buffer."
+  :group 'markdown
+  :type 'function)
+
+(defcustom markdown-live-preview-delete-export t
+  "When non-nil, deleted exported html file when using
+`markdown-live-preview-export'."
+  :group 'markdown
+  :type 'boolean)
+
 
 ;;; Font Lock =================================================================
 
@@ -3543,6 +3560,7 @@ Assumes match data is available for `markdown-regex-italic'."
     (define-key map (kbd "C-c C-c e") 'markdown-export)
     (define-key map (kbd "C-c C-c v") 'markdown-export-and-preview)
     (define-key map (kbd "C-c C-c o") 'markdown-open)
+    (define-key map (kbd "C-c C-c l") 'markdown-live-preview-mode)
     (define-key map (kbd "C-c C-c w") 'markdown-kill-ring-save)
     (define-key map (kbd "C-c C-c c") 'markdown-check-refs)
     (define-key map (kbd "C-c C-c n") 'markdown-cleanup-list-numbers)
@@ -3597,6 +3615,8 @@ See also `markdown-mode-map'.")
     ["Export" markdown-export]
     ["Export & View" markdown-export-and-preview]
     ["Open" markdown-open]
+    ["Live Export" markdown-live-preview-mode
+     :style toggle :selected markdown-live-preview-mode]
     ["Kill ring save" markdown-kill-ring-save]
     "---"
     ("Headings"
@@ -4655,6 +4675,71 @@ current filename, but with the extension removed and replaced with .html."
   (interactive)
   (browse-url-of-file (markdown-export)))
 
+(defvar-local markdown-live-preview-buffer nil
+  "Buffer used to preview markdown output in `markdown-live-preview-export'.")
+
+(defun markdown-live-preview-window-eww (file)
+  "A `markdown-live-preview-window-function' for previewing with eww."
+  (eww-open-file file)
+  (get-buffer "*eww*"))
+
+(defun markdown-live-preview-window-serialize (buf)
+  "Get window point and scroll data for all windows displaying BUF if BUF is
+non-nil."
+  (when buf
+    (mapcar (lambda (win) (list win (window-point win) (window-start win)))
+            (get-buffer-window-list buf))))
+
+(defun markdown-live-preview-window-deserialize (window-posns)
+  "Apply window point and scroll data from WINDOW-POSNS, given by
+`markdown-live-preview-window-serialize'."
+  (destructuring-bind (win pt start) window-posns
+    (when (window-live-p win)
+      (set-window-buffer win markdown-live-preview-buffer)
+      (set-window-point win pt)
+      (set-window-start win start))))
+
+(defun markdown-live-preview-export ()
+  "Export to XHTML using `markdown-export' and browse the resulting file within
+Emacs using `markdown-live-preview-window-function' Return the buffer displaying
+the rendered output."
+  (interactive)
+  (let ((export-file (markdown-export))
+        ;; get positions in all windows currently displaying output buffer
+        (window-data
+         (markdown-live-preview-window-serialize markdown-live-preview-buffer))
+        (cur-buf (current-buffer)))
+    (save-window-excursion
+      ;; protect against `markdown-live-preview-window-function' changing
+      ;; `current-buffer'
+      (let ((output-buffer
+             (funcall markdown-live-preview-window-function export-file)))
+        (with-current-buffer cur-buf
+          (setq markdown-live-preview-buffer output-buffer))))
+    ;; reset all windows displaying output buffer to where they were, now with
+    ;; the new output
+    (mapc #'markdown-live-preview-window-deserialize window-data)
+    (when (and markdown-live-preview-delete-export
+               export-file (file-exists-p export-file))
+      (delete-file export-file)
+      (let ((buf (get-file-buffer export-file))) (when buf (kill-buffer buf))))
+    markdown-live-preview-buffer))
+
+(defun markdown-live-preview-remove ()
+  (when (buffer-live-p markdown-live-preview-buffer)
+    (kill-buffer markdown-live-preview-buffer))
+  (setq markdown-live-preview-buffer nil))
+
+(defun markdown-live-preview-if-markdown ()
+  (when (and (derived-mode-p 'markdown-mode)
+             markdown-live-preview-mode)
+    (markdown-live-preview-export)))
+
+(defun markdown-live-preview-remove-on-kill ()
+  (when (and (derived-mode-p 'markdown-mode)
+             markdown-live-preview-mode)
+    (markdown-live-preview-remove)))
+
 (defun markdown-open ()
   "Open file for the current buffer with `markdown-open-command'."
   (interactive)
@@ -5221,6 +5306,18 @@ before regenerating font-lock rules for extensions."
   ;; do the initial link fontification
   (markdown-fontify-buffer-wiki-links))
 
+
+;;; Live Preview Mode  ============================================
+(define-minor-mode markdown-live-preview-mode
+  "Toggle native previewing on save for a specific markdown file."
+  :lighter " MD-Preview"
+  (cond (markdown-live-preview-mode
+         (switch-to-buffer-other-window (markdown-live-preview-export)))
+        (t (markdown-live-preview-remove))))
+
+(add-hook 'after-save-hook #'markdown-live-preview-if-markdown)
+(add-hook 'kill-buffer-hook #'markdown-live-preview-remove-on-kill)
+
 
 (provide 'markdown-mode)
 ;; Local Variables:

tests/markdown-test.el

@@ -38,6 +38,10 @@
   (expand-file-name (file-name-directory
                      (or load-file-name buffer-file-name))))
 
+(defconst markdown-test-font-lock-function
+  (if (and noninteractive (fboundp 'font-lock-ensure))
+      #'font-lock-ensure #'font-lock-fontify-buffer))
+
 (defmacro markdown-test-string-mode (mode string &rest body)
   "Run BODY in a temporary buffer containing STRING in MODE."
   `(let ((win (selected-window)))
@@ -49,7 +53,7 @@
            (setq-default indent-tabs-mode nil)
            (insert ,string)
            (goto-char (point-min))
-           (font-lock-fontify-buffer)
+           (funcall markdown-test-font-lock-function)
            (prog1 ,@body (kill-buffer))))))
 
 (defmacro markdown-test-file-mode (mode file &rest body)
@@ -60,7 +64,7 @@
          (insert-file-contents fn)
          (funcall ,mode)
          (goto-char (point-min))
-         (font-lock-fontify-buffer)
+         (funcall markdown-test-font-lock-function)
          ,@body))))
 
 (defmacro markdown-test-string (string &rest body)
@@ -94,7 +98,7 @@ This file is not saved."
        (insert-file-contents fn)
        (markdown-mode)
        (goto-char (point-min))
-       (font-lock-fontify-buffer)
+       (funcall markdown-test-font-lock-function)
        ,@body
        (set-buffer-modified-p nil)
        (kill-buffer buf)
@@ -2736,7 +2740,7 @@ indented the same amount."
   "Test markdown math mode."
   (markdown-test-file "math.text"
    (markdown-enable-math t)
-   (font-lock-fontify-buffer)
+   (funcall markdown-test-font-lock-function)
    (markdown-test-range-has-face 1 32 nil)
    (markdown-test-range-has-face 33 33 markdown-markup-face)
    (markdown-test-range-has-face 34 45 markdown-math-face)