make live-preview follow min or max point

Author: Danny McClanahan

markdown-mode.el

@@ -5872,21 +5872,63 @@ buffer. Inverse of `markdown-live-preview-buffer'.")
         (get-buffer "*eww*"))
     (error "eww is not present or not loaded on this version of emacs")))
 
+(defun markdown-visual-lines-between-points (beg end)
+  (save-excursion
+    (goto-char beg)
+    (cl-loop with count = 0
+             while (progn (end-of-visual-line)
+                          (and (< (point) end) (line-move-visual 1 t)))
+             do (cl-incf count)
+             finally return count)))
+
 (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))))
+live."
+  (when (buffer-live-p buf)
+    (with-current-buffer buf
+      (mapcar
+       (lambda (win)
+         (with-selected-window win
+           (let* ((start (window-start))
+                  (pt (window-point))
+                  (pt-or-sym (cond ((= pt (point-min)) 'min)
+                                   ((= pt (point-max)) 'max)
+                                   (t pt)))
+                  (diff (markdown-visual-lines-between-points
+                         start pt)))
+             (message "serialize: start=%d, pt=%d, pt-or-sym=%S, diff=%d"
+                      start pt pt-or-sym diff)
+             (list win pt-or-sym diff))))
+       (get-buffer-window-list buf)))))
+
+(defun markdown-get-point-back-lines (pt num-lines)
+  (save-excursion
+    (goto-char pt)
+    (line-move-visual (- num-lines) t)
+    ;; in testing, can occasionally overshoot the number of lines to traverse
+    (let ((actual-num-lines (markdown-visual-lines-between-points (point) pt)))
+      (when (> actual-num-lines num-lines)
+        (line-move-visual (- actual-num-lines num-lines) t)))
+    (point)))
 
 (defun markdown-live-preview-window-deserialize (window-posns)
   "Apply window point and scroll data from WINDOW-POSNS, given by
 `markdown-live-preview-window-serialize'."
-  (cl-destructuring-bind (win pt start) window-posns
+  (cl-destructuring-bind (win pt-or-sym diff) 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))))
+      (with-current-buffer markdown-live-preview-buffer
+        (set-window-buffer win (current-buffer))
+        (cl-destructuring-bind (actual-pt actual-diff)
+            (cl-case pt-or-sym
+              (min (list (point-min) 0))
+              (max (list (point-max) diff))
+              (t (list pt-or-sym diff)))
+          (message "deserialize: pt-or-sym=%S, diff=%d" pt-or-sym actual-diff)
+          (message "point-back-lines: %d"
+                   (markdown-get-point-back-lines actual-pt actual-diff))
+          (set-window-start
+           win (markdown-get-point-back-lines actual-pt actual-diff))
+          (set-window-point win actual-pt))))))
 
 (defun markdown-live-preview-export ()
   "Export to XHTML using `markdown-export' and browse the resulting file within

tests/markdown-test.el

@@ -3767,25 +3767,30 @@ Detail: https://github.com/jrblevin/markdown-mode/issues/79"
         (kill-buffer)))))
 
 (defadvice markdown-live-preview-window-eww
-    (around markdown-create-fake-eww disable)
+    (around markdown-test-create-fake-eww disable)
   (setq ad-return-value (get-buffer-create "*eww*")))
 
-(defmacro markdown-temp-eww (&rest body)
+(defmacro markdown-test-fake-eww (&rest body)
   `(progn
-     ,@(if (featurep 'eww) body
+     ,@(if (require 'eww nil t) body
          `((ad-enable-advice #'markdown-live-preview-window-eww
-                             'around 'markdown-create-fake-eww)
+                             'around 'markdown-test-create-fake-eww)
            (ad-activate #'markdown-live-preview-window-eww)
            ,@body
            (ad-disable-advice #'markdown-live-preview-window-eww
-                              'around 'markdown-create-fake-eww)
+                              'around 'markdown-test-create-fake-eww)
            (ad-activate #'markdown-live-preview-window-eww)))))
 
+(defmacro markdown-test-eww-or-nothing (test &rest body)
+  (if (require 'eww nil t) `(progn ,@body)
+    (message "no eww found: skipping %s" test)
+    nil))
+
 (ert-deftest test-markdown-ext/live-preview-exports ()
   (markdown-test-temp-file "inline.text"
     (unless (require 'eww nil t)
       (should-error (markdown-live-preview-mode)))
-    (markdown-temp-eww
+    (markdown-test-fake-eww
      (markdown-live-preview-mode)
      (should (buffer-live-p markdown-live-preview-buffer))
      (should (eq (current-buffer)
@@ -3798,7 +3803,7 @@ Detail: https://github.com/jrblevin/markdown-mode/issues/79"
      (should (buffer-live-p markdown-live-preview-buffer)))))
 
 (ert-deftest test-markdown-ext/live-preview-delete-exports ()
-  (markdown-temp-eww
+  (markdown-test-fake-eww
    (let ((markdown-live-preview-delete-export 'delete-on-destroy)
          file-output)
      (markdown-test-temp-file "inline.text"
@@ -3820,6 +3825,49 @@ Detail: https://github.com/jrblevin/markdown-mode/issues/79"
            (should (file-exists-p file-output)))
        (delete-file file-output)))))
 
+(ert-deftest test-markdown-ext/live-preview-follow-min-max ()
+  (markdown-test-eww-or-nothing "live-preview-follow-min-max"
+   (markdown-test-temp-file "inline.text"
+     (markdown-live-preview-mode)
+     (should (buffer-live-p markdown-live-preview-buffer))
+     (should (window-live-p (get-buffer-window markdown-live-preview-buffer)))
+     (with-selected-window (get-buffer-window markdown-live-preview-buffer)
+       (goto-char (point-min)))
+     (goto-char (point-min))
+     (insert "a test ")
+     (markdown-live-preview-export)
+     (let (final-pt final-win-st-diff)
+       ;; test that still starts at point-min
+       (with-selected-window (get-buffer-window markdown-live-preview-buffer)
+         (should (= (window-point) 1))
+         (should (= (markdown-visual-lines-between-points
+                     (window-start) (window-point))
+                    0))
+         (set-window-point (selected-window) (point-max))
+         (setq final-pt (window-point)
+               final-win-st-diff (markdown-visual-lines-between-points
+                                  (window-start) (window-point))))
+       (goto-char (point-min))
+       (insert "this is ")
+       (markdown-live-preview-export)
+       (with-selected-window (get-buffer-window markdown-live-preview-buffer)
+         (should (= (window-point) (+ final-pt (length "this is "))))
+         (should (= (markdown-visual-lines-between-points
+                     (window-start) (window-point))
+                    final-win-st-diff))
+         ;; test that still starts at point-max, with correct line difference
+         (goto-char (floor (/ (float (- (point-max) (point-min))) 2)))
+         (setq final-pt (window-point)
+               final-win-st-diff (markdown-visual-lines-between-points
+                                  (window-start) final-pt)))
+       (markdown-live-preview-export)
+       ;; test that still starts at same point, with correct line difference
+       (with-selected-window (get-buffer-window markdown-live-preview-buffer)
+         (should (= (window-point) final-pt))
+         (should (= (markdown-visual-lines-between-points
+                     (window-start) (window-point))
+                    final-win-st-diff)))))))
+
 (provide 'markdown-test)
 
 ;;; markdown-test.el ends here