Revert "Fix inconsistent marker boundary order"

packages/ckeditor5-engine/src/controller/datacontroller.ts

@@ -669,5 +669,45 @@ function _getMarkersRelativeToElement( element: ModelElement ): Map<string, Mode
 		}
 	}
 
+	// Sort the markers in a stable fashion to ensure that the order in which they are
+	// added to the model's marker collection does not affect how they are
+	// downcast. One particular use case that we are targeting here, is one where
+	// two markers are adjacent but not overlapping, such as an insertion/deletion
+	// suggestion pair representing the replacement of a range of text. In this
+	// case, putting the markers in DOM order causes the first marker's end to be
+	// serialized right after the second marker's start, while putting the markers
+	// in reverse DOM order causes it to be right before the second marker's
+	// start. So, we sort these in a way that ensures non-intersecting ranges are in
+	// reverse DOM order, and intersecting ranges are in something approximating
+	// reverse DOM order (since reverse DOM order doesn't have a precise meaning
+	// when working with intersecting ranges).
+	result.sort( ( [ n1, r1 ], [ n2, r2 ] ) => {
+		if ( r1.end.compareWith( r2.start ) !== 'after' ) {
+			// m1.end <= m2.start -- m1 is entirely <= m2
+			return 1;
+		} else if ( r1.start.compareWith( r2.end ) !== 'before' ) {
+			// m1.start >= m2.end -- m1 is entirely >= m2
+			return -1;
+		} else {
+			// they overlap, so use their start positions as the primary sort key and
+			// end positions as the secondary sort key
+			switch ( r1.start.compareWith( r2.start ) ) {
+				case 'before':
+					return 1;
+				case 'after':
+					return -1;
+				default:
+					switch ( r1.end.compareWith( r2.end ) ) {
+						case 'before':
+							return 1;
+						case 'after':
+							return -1;
+						default:
+							return n2.localeCompare( n1 );
+					}
+			}
+		}
+	} );
+
 	return new Map( result );
 }

packages/ckeditor5-engine/src/conversion/downcastdispatcher.ts

@@ -8,7 +8,6 @@
  */
 
 import { ModelConsumable } from './modelconsumable.js';
-import { compareMarkersForDowncast } from './comparemarkers.js';
 import { ModelRange } from '../model/range.js';
 
 import { EmitterMixin } from '@ckeditor/ckeditor5-utils';
@@ -201,23 +200,8 @@ export class DowncastDispatcher extends /* #__PURE__ */ EmitterMixin() {
 			this._convertMarkerAdd( markerName, markerRange, conversionApi );
 		}
 
-		// Sort markers in reverse DOM order so that the downcast result is deterministic
-		// regardless of the order markers were added to the collection.
-		//
-		// Example: replacing "old" with "new" creates two adjacent markers (delete + insert).
-		// With `markerToElement`, each boundary is a self-closing tag, so the processing
-		// order directly controls where they land at the shared boundary point:
-		//
-		//   Stable (reverse DOM order):   <DEL-START/>old<DEL-END/><INS-START/>new<INS-END/>
-		//   Unstable (insertion order):    <DEL-START/>old<INS-START/><DEL-END/>new<INS-END/>
-		//
-		// Non-intersecting ranges  → strict reverse DOM order.
-		// Intersecting ranges      → best-effort reverse DOM order (ambiguous by nature).
-		const markersToAdd = differ.getMarkersToAdd()
-			.sort( ( a, b ) => compareMarkersForDowncast( [ a.name, a.range ], [ b.name, b.range ] ) );
-
 		// After the view is updated, convert markers which have changed.
-		for ( const change of markersToAdd ) {
+		for ( const change of differ.getMarkersToAdd() ) {
 			this._convertMarkerAdd( change.name, change.range, conversionApi );
 		}
 
@@ -246,9 +230,7 @@ export class DowncastDispatcher extends /* #__PURE__ */ EmitterMixin() {
 
 		this._convertInsert( range, conversionApi );
 
-		// Sort markers in reverse DOM order for deterministic downcast output.
-		// See the analogous sort in `convertChanges()` for a detailed rationale and examples.
-		for ( const [ name, range ] of Array.from( markers ).sort( compareMarkersForDowncast ) ) {
+		for ( const [ name, range ] of markers ) {
 			this._convertMarkerAdd( name, range, conversionApi );
 		}
 

packages/ckeditor5-engine/src/conversion/downcasthelpers.ts

@@ -1335,24 +1335,16 @@ export function insertUIElement( elementCreator: DowncastMarkerElementCreatorFun
 		const mapper = conversionApi.mapper;
 		const viewWriter = conversionApi.writer;
 
-		viewWriter.setCustomProperty( 'markerBoundaryType', 'start', viewStartElement );
-		viewWriter.setCustomProperty( 'markerBoundaryType', 'end', viewEndElement );
+		// Add "opening" element.
+		viewWriter.insert( mapper.toViewPosition( markerRange.start ), viewStartElement );
+		conversionApi.mapper.bindElementToMarker( viewStartElement, data.markerName );
 
-		// Add "end" element only if range is not collapsed.
+		// Add "closing" element only if range is not collapsed.
 		if ( !markerRange.isCollapsed ) {
 			viewWriter.insert( mapper.toViewPosition( markerRange.end ), viewEndElement );
 			conversionApi.mapper.bindElementToMarker( viewEndElement, data.markerName );
 		}
 
-		// Jump over end UI elements to find a proper position for "start" element.
-		// It should be after all marker "end" UI elements as markers conversion should be triggered in reverse DOM order.
-		const startViewPosition = mapper.toViewPosition( markerRange.start ).getLastMatchingPosition( ( { item } ) =>
-			item.is( 'uiElement' ) && item.getCustomProperty( 'markerBoundaryType' ) === 'end'
-		);
-
-		viewWriter.insert( startViewPosition, viewStartElement );
-		conversionApi.mapper.bindElementToMarker( viewStartElement, data.markerName );
-
 		evt.stop();
 	};
 }