Replace fast-diff within Delta

.eslintignore

@@ -5,5 +5,6 @@ build-types
 node_modules
 packages/block-serialization-spec-parser/parser.js
 packages/react-native-editor/bundle
+packages/sync/src/quill-delta
 vendor
 !.*.js

.prettierignore

@@ -5,5 +5,6 @@ build-types
 packages/block-serialization-spec-parser/parser.js
 packages/edit-site/lib
 packages/react-native-editor/bundle
+packages/sync/src/quill-delta
 packages/url/src/test/fixtures
 vendor

packages/core-data/package.json

@@ -55,7 +55,6 @@
 		"fast-deep-equal": "^3.1.3",
 		"lib0": "^0.2.99",
 		"memize": "^2.1.0",
-		"quill-delta": "5.1.0",
 		"uuid": "^9.0.1"
 	},
 	"peerDependencies": {

packages/core-data/src/utils/crdt-blocks.ts

@@ -4,22 +4,16 @@
 import { v4 as uuidv4 } from 'uuid';
 import * as math from 'lib0/math';
 import * as fun from 'lib0/function';
-import Delta from 'quill-delta';
 
 /**
  * WordPress dependencies
  */
 import { RichTextData } from '@wordpress/rich-text';
-import { Y } from '@wordpress/sync';
+import { Y, Delta } from '@wordpress/sync';
 
 // @ts-expect-error - This is a TypeScript file, and @wordpress/blocks doesn't have a tsconfig.json?
 import { getBlockTypes } from '@wordpress/blocks';
 
-/**
- * Internal dependencies
- */
-import type { WPBlockSelection } from '../types';
-
 interface BlockAttributes {
 	[ key: string ]: unknown;
 }
@@ -190,13 +184,13 @@ function createNewYBlock( block: Block ): YBlock {
  *
  * @param yblocks        The blocks in the local Y.Doc.
  * @param incomingBlocks Gutenberg blocks being synced.
- * @param lastSelection
+ * @param cursorPosition The position of the cursor after the change occurs.
  * @param _origin        The origin of the sync, either 'syncProvider' or 'gutenberg'.
  */
 export function mergeCrdtBlocks(
 	yblocks: Y.Array< YBlock >, // yblocks represent the blocks in the local Y.Doc
 	incomingBlocks: Block[], // incomingBlocks represent JSON blocks being synced, either from a peer or from the local editor
-	lastSelection: WPBlockSelection | null, // Last cursor position, used for hinting the diff algorithm
+	cursorPosition: number | null,
 	_origin: string // eslint-disable-line @typescript-eslint/no-unused-vars
 ): void {
 	// Ensure we are working with serializable block data.
@@ -313,7 +307,7 @@ export function mergeCrdtBlocks(
 								mergeRichTextUpdate(
 									blockYText,
 									attributeValue,
-									lastSelection
+									cursorPosition
 								);
 							} else {
 								currentAttributes.set(
@@ -346,7 +340,7 @@ export function mergeCrdtBlocks(
 					mergeCrdtBlocks(
 						yInnerBlocks,
 						value ?? [],
-						lastSelection,
+						cursorPosition,
 						_origin
 					);
 					break;
@@ -465,14 +459,14 @@ let localDoc: Y.Doc | null = null;
  * Given a Y.Text object and an updated string value, diff the new value and
  * apply the delta to the Y.Text.
  *
- * @param blockYText    The Y.Text to update.
- * @param updatedValue  The updated value.
- * @param lastSelection The last cursor position before this update, used to hint the diff algorithm.
+ * @param blockYText     The Y.Text to update.
+ * @param updatedValue   The updated value.
+ * @param cursorPosition The position of the cursor after the change occurs.
  */
 function mergeRichTextUpdate(
 	blockYText: Y.Text,
 	updatedValue: string,
-	lastSelection: WPBlockSelection | null
+	cursorPosition: number | null
 ): void {
 	const doc = blockYText.doc;
 
@@ -492,10 +486,9 @@ function mergeRichTextUpdate(
 
 	const currentValueAsDelta = new Delta( blockYText.toDelta() );
 	const updatedValueAsDelta = new Delta( localYText.toDelta() );
-
-	const deltaDiff = currentValueAsDelta.diff(
+	const deltaDiff = currentValueAsDelta.diffWithCursor(
 		updatedValueAsDelta,
-		lastSelection?.offset
+		cursorPosition
 	);
 
 	blockYText.applyDelta( deltaDiff.ops );

packages/core-data/src/utils/crdt.ts

@@ -17,15 +17,13 @@ import { type CRDTDoc, CRDT_RECORD_MAP_KEY, Y } from '@wordpress/sync';
 import { mergeCrdtBlocks, type Block, type YBlock } from './crdt-blocks';
 import { type Post } from '../entity-types/post';
 import { type Type } from '../entity-types';
-import type { WPBlockSelection, WPSelection } from '../types';
+import type { WPSelection } from '../types';
 
 type PostChanges = Partial< Post > & {
 	blocks?: Block[];
 	selection?: WPSelection;
 };
 
-let lastSelection: WPBlockSelection | null = null;
-
 /**
  * Given a set of local changes to a post record, apply those changes to the
  * local Y.Doc.
@@ -76,12 +74,17 @@ export function applyPostChangesToCRDTDoc(
 				// Block[] from local changes.
 				const newBlocks = ( newValue as PostChanges[ 'blocks' ] ) ?? [];
 
+				// Block changes from typing are bundled with a 'selection' update.
+				// Pass the resulting cursor position to the mergeCrdtBlocks function.
+				const cursorPosition =
+					changes.selection?.selectionStart?.offset ?? null;
+
 				// Merge blocks does not need `setValue` because it is operating on a
 				// Yjs type that is already in the Y.Doc.
 				mergeCrdtBlocks(
 					currentBlocks,
 					newBlocks,
-					lastSelection,
+					cursorPosition,
 					origin
 				);
 				break;
@@ -177,11 +180,6 @@ export function applyPostChangesToCRDTDoc(
 			}
 		}
 	} );
-
-	// Update the lastSelection for CRDT use
-	if ( 'selection' in changes ) {
-		lastSelection = changes.selection?.selectionStart ?? null;
-	}
 }
 
 /**