Re: master f450798: Don't move point in vc-dir on vc-register/vc-checkin (bug#43188)

[Andrii Kolomoiets <andreyk.mad@gmail.com>]

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Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> -    (save-excursion
>> +    (let ((p (point)))
>>        (dolist (node nodes)
>> -        (ewoc--refresh-node pp node dll)))))
>> +        (ewoc--refresh-node pp node dll))
>> +      (goto-char p))))
>
> Hmm... I think this is an improvement when point is within the refreshed
> node, but a regression when it's further down in the buffer.

You are right.

Take a look at the new patch.  ewoc-invalidate now save and restore
point line and column offset in the current node.

testewoc.el is the code I used to test the patch:

1. emacs -Q
2. M-x load-file testewoc.el
3. M-x testewoc
4. move point somewhere and M-x testewoc-invalidate
Point must remain in the same line and column within the node.  The
nodes is represented with characters "0", "1" and "2".


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From 0b43d95581c36d43995fc27fdb965327937455ae Mon Sep 17 00:00:00 2001
From: Andrii Kolomoiets <andreyk.mad@gmail.com>
Date: Sat, 5 Sep 2020 22:18:59 +0300
Subject: [PATCH] Save and restore point in ewoc-invalidate

* lisp/emacs-lisp/ewoc.el (ewoc-invalidate): Save and restore point line and
column offset.
* lisp/vc/vc-dir.el (vc-dir-update): Don't save/restore point on calling
'ewoc-invalidate'.
---
 lisp/emacs-lisp/ewoc.el | 37 ++++++++++++++++++++++++++++++++++---
 lisp/vc/vc-dir.el       |  6 +-----
 2 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/lisp/emacs-lisp/ewoc.el b/lisp/emacs-lisp/ewoc.el
index 78ada3e076..6a37309eb1 100644
--- a/lisp/emacs-lisp/ewoc.el
+++ b/lisp/emacs-lisp/ewoc.el
@@ -461,9 +461,40 @@ ewoc-invalidate
 Delete current text first, thus effecting a \"refresh\"."
   (ewoc--set-buffer-bind-dll-let* ewoc
       ((pp (ewoc--pretty-printer ewoc)))
-    (save-excursion
-      (dolist (node nodes)
-        (ewoc--refresh-node pp node dll)))))
+    (let ((point (point))
+	  (footer-start (ewoc-location (ewoc--footer ewoc)))
+	  (refresh-nodes (lambda ()
+			   (dolist (node nodes)
+			     (ewoc--refresh-node pp node dll)))))
+      (cond
+       ((= point footer-start)
+	(funcall refresh-nodes))
+       ((or (> point footer-start)
+            (<= point (ewoc-location (ewoc-nth ewoc 0))))
+	(save-excursion
+	  (funcall refresh-nodes)))
+       (t
+	(let* ((node-start (ewoc-location (ewoc-locate ewoc)))
+	       (line (- (line-number-at-pos point)
+			(line-number-at-pos node-start)))
+	       (column (min (- point node-start)
+                            (- point (line-beginning-position)))))
+	  (funcall refresh-nodes)
+	  (goto-char node-start)
+	  (let* ((node-end (1- (ewoc-location
+                                (ewoc--node-right (ewoc-locate ewoc)))))
+		 (line-start (line-number-at-pos node-start))
+		 (line-end (line-number-at-pos node-end))
+		 (line (min line (- line-end line-start)))
+                 (line-beginning-position (line-beginning-position))
+                 (line-end-position (line-end-position)))
+            (when (> line 0)
+	      (forward-line line))
+	    (forward-char (min column
+			       (- node-end node-start)
+			       (- node-end line-beginning-position)
+			       (- line-end-position line-beginning-position)
+			       (- line-end-position node-start))))))))))
 
 (defun ewoc-goto-prev (ewoc arg)
   "Move point to the ARGth previous element in EWOC.
diff --git a/lisp/vc/vc-dir.el b/lisp/vc/vc-dir.el
index 6c219005ce..cdf8ab984e 100644
--- a/lisp/vc/vc-dir.el
+++ b/lisp/vc/vc-dir.el
@@ -451,11 +451,7 @@ vc-dir-update
 		      (setf (vc-dir-fileinfo->state (ewoc-data node)) (nth 1 entry))
 		      (setf (vc-dir-fileinfo->extra (ewoc-data node)) (nth 2 entry))
 		      (setf (vc-dir-fileinfo->needs-update (ewoc-data node)) nil)
-                      ;; `ewoc-invalidate' will kill line and insert new text,
-                      ;; let's keep point column.
-                      (let ((p (point)))
-		        (ewoc-invalidate vc-ewoc node)
-                        (goto-char p)))
+		      (ewoc-invalidate vc-ewoc node))
 		  ;; If the state is nil, the file does not exist
 		  ;; anymore, so remember the entry so we can remove
 		  ;; it after we are done inserting all ENTRIES.
-- 
2.15.1