Re: Distinguish between regional undo and undo to the beginning in undo-equiv-table

[Yuan Fu <casouri@gmail.com>]

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> On Mar 2, 2021, at 6:50 PM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
> 
>> That means my package that constructs an undo tree from buffer-undo-list
>> cannot distinguish the two and thus cannot work incorrectly. Is it ok to map
>> one type of undo to something other than t?
> 
> I think so, yes.  It might require a few tweaks in simple.el but nothing
> major (if at all).
> 

Here is a patch, I mapped undo-in-region records to 'undo-in-region. I also fixed a bug in undo-make-selective-list: before this change, if you undo-in-region, break the undo chain, then undo-in-region again with undo-only, ulist would be set to t and it breaks at (setq undo-elt (car ulist)).

Yuan


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From 8c4d50409a7ad88eb85d51e79b04f3587cd36976 Mon Sep 17 00:00:00 2001
From: Yuan Fu <casouri@gmail.com>
Date: Wed, 3 Mar 2021 09:50:15 -0500
Subject: [PATCH] Map redo records for undo-in-region to 'undo-in-region

* lisp/simple.el (undo-equiv-table): Add explaination for
undo-in-region and undo to the beginning of undo list.
(undo): If equiv is 'undo-in-region or t, set to pending-undo-list to
t. If the redo is undo-in-region, map buffer-undo-list to
'undo-in-region instead of t.
(undo-make-selective-list): Only continue when ulist is not t or
undo-in-region.
---
 lisp/simple.el | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/lisp/simple.el b/lisp/simple.el
index f8050091d5..05bf4b8784 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2824,8 +2824,9 @@ 'advertised-undo
 
 (defconst undo-equiv-table (make-hash-table :test 'eq :weakness t)
   "Table mapping redo records to the corresponding undo one.
-A redo record for undo-in-region maps to t.
-A redo record for ordinary undo maps to the following (earlier) undo.")
+A redo record for undo-in-region maps to 'undo-in-region.
+A redo record for ordinary undo maps to the following (earlier) undo.
+An undo record that undoes to the beginning of the undo list maps to t.")
 
 (defvar undo-in-region nil
   "Non-nil if `pending-undo-list' is not just a tail of `buffer-undo-list'.")
@@ -2901,7 +2902,7 @@ undo
 	;; undo-redo-undo-redo-... so skip to the very last equiv.
 	(while (let ((next (gethash equiv undo-equiv-table)))
 		 (if next (setq equiv next))))
-	(setq pending-undo-list equiv)))
+	(setq pending-undo-list (if (consp equiv) equiv t))))
     (undo-more
      (if (numberp arg)
 	 (prefix-numeric-value arg)
@@ -2917,11 +2918,12 @@ undo
       (while (eq (car list) nil)
 	(setq list (cdr list)))
       (puthash list
-               ;; Prevent identity mapping.  This can happen if
-               ;; consecutive nils are erroneously in undo list.
-               (if (or undo-in-region (eq list pending-undo-list))
-                   t
-                 pending-undo-list)
+               (cond
+                (undo-in-region 'undo-in-region)
+                ;; Prevent identity mapping.  This can happen if
+                ;; consecutive nils are erroneously in undo list.
+                ((eq list pending-undo-list) t)
+                (t pending-undo-list))
 	       undo-equiv-table))
     ;; Don't specify a position in the undo record for the undo command.
     ;; Instead, undoing this should move point to where the change is.
@@ -3234,7 +3236,7 @@ undo-make-selective-list
         undo-elt)
     (while ulist
       (when undo-no-redo
-        (while (gethash ulist undo-equiv-table)
+        (while (consp (gethash ulist undo-equiv-table))
           (setq ulist (gethash ulist undo-equiv-table))))
       (setq undo-elt (car ulist))
       (cond
-- 
2.24.3 (Apple Git-128)


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