From 57dfd337e97eadd7366b71545627d32a5325e0bb Mon Sep 17 00:00:00 2001
From: Neil <nyamatongwe@gmail.com>
Date: Tue, 2 Jan 2024 10:25:50 +1100
Subject: Simplify choosing caret position when undoing contiguous deletions.
 Stop considering container actions as they are supposed to be transparent.
 The mayCoalesce flag is private to the undo code and may be removed in the
 future. Use Range type to unify state implementing coalescing.

---
 src/Document.cxx | 28 ++++++----------------------
 1 file changed, 6 insertions(+), 22 deletions(-)

diff --git a/src/Document.cxx b/src/Document.cxx
index aea2cfd0b..1a8c4020f 100644
--- a/src/Document.cxx
+++ b/src/Document.cxx
@@ -1363,10 +1363,7 @@ Sci::Position Document::Undo() {
 			bool multiLine = false;
 			const int steps = cb.StartUndo();
 			//Platform::DebugPrintf("Steps=%d\n", steps);
-			Sci::Position coalescedRemovePos = -1;
-			Sci::Position coalescedRemoveLen = 0;
-			Sci::Position prevRemoveActionPos = -1;
-			Sci::Position prevRemoveActionLen = 0;
+			Range coalescedRemove;	// Default is empty at 0
 			for (int step = 0; step < steps; step++) {
 				const Sci::Line prevLinesTotal = LinesTotal();
 				const Action &action = cb.GetUndoStep();
@@ -1377,12 +1374,6 @@ Sci::Position Document::Undo() {
 					DocModification dm(ModificationFlags::Container | ModificationFlags::Undo);
 					dm.token = action.position;
 					NotifyModified(dm);
-					if (!action.mayCoalesce) {
-						coalescedRemovePos = -1;
-						coalescedRemoveLen = 0;
-						prevRemoveActionPos = -1;
-						prevRemoveActionLen = 0;
-					}
 				} else {
 					NotifyModified(DocModification(
 									ModificationFlags::BeforeDelete | ModificationFlags::Undo, action));
@@ -1398,22 +1389,15 @@ Sci::Position Document::Undo() {
 				if (action.at == ActionType::remove) {
 					newPos += action.lenData;
 					modFlags |= ModificationFlags::InsertText;
-					if ((coalescedRemoveLen > 0) &&
-						(action.position == prevRemoveActionPos || action.position == (prevRemoveActionPos + prevRemoveActionLen))) {
-						coalescedRemoveLen += action.lenData;
-						newPos = coalescedRemovePos + coalescedRemoveLen;
+					if (coalescedRemove.Contains(action.position)) {
+						coalescedRemove.end += action.lenData;
+						newPos = coalescedRemove.end;
 					} else {
-						coalescedRemovePos = action.position;
-						coalescedRemoveLen = action.lenData;
+						coalescedRemove = Range(action.position, action.position + action.lenData);
 					}
-					prevRemoveActionPos = action.position;
-					prevRemoveActionLen = action.lenData;
 				} else if (action.at == ActionType::insert) {
 					modFlags |= ModificationFlags::DeleteText;
-					coalescedRemovePos = -1;
-					coalescedRemoveLen = 0;
-					prevRemoveActionPos = -1;
-					prevRemoveActionLen = 0;
+					coalescedRemove = Range(); 
 				}
 				if (steps > 1)
 					modFlags |= ModificationFlags::MultiStepUndoRedo;
-- 
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