Merge pull request #16885 from overleaf/mj-scanops-tracking-info

Add comment and tracking information to ScanOps

GitOrigin-RevId: 475dab73d44529f793c7d07bc5ae6873f8e0b257

libraries/overleaf-editor-core/lib/file_data/comment_list.js

@@ -69,9 +69,12 @@ class CommentList {
 
   /**
    * @param {Range} range
-   * @param {{ commentIds: string[] }} opts
+   * @param {{ commentIds?: string[] }} opts
    */
   applyInsert(range, opts = { commentIds: [] }) {
+    if (!opts.commentIds) {
+      opts.commentIds = []
+    }
     for (const [commentId, comment] of this.comments) {
       comment.applyInsert(
         range.pos,
@@ -85,13 +88,21 @@ class CommentList {
    * @param {Range} range
    */
   applyDelete(range) {
-    for (const [commentId, comment] of this.comments) {
+    for (const [, comment] of this.comments) {
       comment.applyDelete(range)
-      if (comment.isEmpty()) {
-        this.delete(commentId)
-      }
     }
   }
+
+  /**
+   *
+   * @param {Range} range
+   * @returns {string[]}
+   */
+  idsCoveringRange(range) {
+    return Array.from(this.comments.entries())
+      .filter(([, comment]) => comment.ranges.some(r => r.contains(range)))
+      .map(([id]) => id)
+  }
 }
 
 module.exports = CommentList

libraries/overleaf-editor-core/lib/file_data/string_file_data.js

@@ -34,7 +34,11 @@ class StringFileData extends FileData {
    * @returns {StringFileData}
    */
   static fromRaw(raw) {
-    return new StringFileData(raw.content, raw.comments || [])
+    return new StringFileData(
+      raw.content,
+      raw.comments || [],
+      raw.trackedChanges || []
+    )
   }
 
   /**

libraries/overleaf-editor-core/lib/file_data/tracked_change.js

@@ -8,12 +8,19 @@ const TrackingProps = require('./tracking_props')
 
 class TrackedChange {
   /**
-   *
    * @param {Range} range
    * @param {TrackingProps} tracking
    */
   constructor(range, tracking) {
+    /**
+     * @readonly
+     * @type {Range}
+     */
     this.range = range
+    /**
+     * @readonly
+     * @type {TrackingProps}
+     */
     this.tracking = tracking
   }
 
@@ -60,17 +67,22 @@ class TrackedChange {
    * Merges another tracked change into this, updating the range and tracking
    * timestamp
    * @param {TrackedChange} other
-   * @returns {void}
+   * @returns {TrackedChange}
    */
   merge(other) {
     if (!this.canMerge(other)) {
       throw new Error('Cannot merge tracked changes')
     }
-    this.range = this.range.merge(other.range)
-    this.tracking.ts =
-      this.tracking.ts.getTime() > other.tracking.ts.getTime()
-        ? this.tracking.ts
-        : other.tracking.ts
+    return new TrackedChange(
+      this.range.merge(other.range),
+      new TrackingProps(
+        this.tracking.type,
+        this.tracking.userId,
+        this.tracking.ts.getTime() > other.tracking.ts.getTime()
+          ? this.tracking.ts
+          : other.tracking.ts
+      )
+    )
   }
 }
 

libraries/overleaf-editor-core/lib/file_data/tracked_change_list.js

@@ -46,6 +46,16 @@ class TrackedChangeList {
     return this.trackedChanges.filter(change => range.contains(change.range))
   }
 
+  /**
+   * Returns the tracking props for a given range.
+   * @param {Range} range
+   * @returns {TrackingProps | undefined}
+   */
+  propsAtRange(range) {
+    return this.trackedChanges.find(change => change.range.contains(range))
+      ?.tracking
+  }
+
   /**
    * Removes the tracked changes that are fully included in the range
    * @param {Range} range
@@ -80,7 +90,7 @@ class TrackedChangeList {
       const last = newTrackedChanges[newTrackedChanges.length - 1]
       const current = this.trackedChanges[i]
       if (last.canMerge(current)) {
-        last.merge(current)
+        newTrackedChanges[newTrackedChanges.length - 1] = last.merge(current)
       } else {
         newTrackedChanges.push(current)
       }
@@ -103,8 +113,12 @@ class TrackedChangeList {
         trackedChange.range.startIsAfter(cursor) ||
         cursor === trackedChange.range.start
       ) {
-        trackedChange.range = trackedChange.range.moveBy(insertedText.length)
-        newTrackedChanges.push(trackedChange)
+        newTrackedChanges.push(
+          new TrackedChange(
+            trackedChange.range.moveBy(insertedText.length),
+            trackedChange.tracking
+          )
+        )
       } else if (cursor === trackedChange.range.end) {
         // The insertion is at the end of the tracked change. So we don't need
         // to move it.
@@ -116,17 +130,15 @@ class TrackedChangeList {
           cursor,
           insertedText.length
         )
-        const firstPart = new TrackedChange(
-          firstRange,
-          trackedChange.tracking.clone()
-        )
-        newTrackedChanges.push(firstPart)
+        const firstPart = new TrackedChange(firstRange, trackedChange.tracking)
+        if (!firstPart.range.isEmpty()) {
+          newTrackedChanges.push(firstPart)
+        }
         // second part will be added at the end if it is a tracked insertion
-        const thirdPart = new TrackedChange(
-          thirdRange,
-          trackedChange.tracking.clone()
-        )
-        newTrackedChanges.push(thirdPart)
+        const thirdPart = new TrackedChange(thirdRange, trackedChange.tracking)
+        if (!thirdPart.range.isEmpty()) {
+          newTrackedChanges.push(thirdPart)
+        }
       } else {
         newTrackedChanges.push(trackedChange)
       }
@@ -157,11 +169,19 @@ class TrackedChangeList {
       if (deletedRange.contains(trackedChange.range)) {
         continue
       } else if (deletedRange.overlaps(trackedChange.range)) {
-        trackedChange.range = trackedChange.range.subtract(deletedRange)
-        newTrackedChanges.push(trackedChange)
+        const newRange = trackedChange.range.subtract(deletedRange)
+        if (!newRange.isEmpty()) {
+          newTrackedChanges.push(
+            new TrackedChange(newRange, trackedChange.tracking)
+          )
+        }
       } else if (trackedChange.range.startIsAfter(cursor)) {
-        trackedChange.range = trackedChange.range.moveBy(-length)
-        newTrackedChanges.push(trackedChange)
+        newTrackedChanges.push(
+          new TrackedChange(
+            trackedChange.range.moveBy(-length),
+            trackedChange.tracking
+          )
+        )
       } else {
         newTrackedChanges.push(trackedChange)
       }
@@ -188,28 +208,41 @@ class TrackedChangeList {
       } else if (retainedRange.overlaps(trackedChange.range)) {
         if (trackedChange.range.contains(retainedRange)) {
           const [leftRange, rightRange] = trackedChange.range.splitAt(cursor)
-          newTrackedChanges.push(
-            new TrackedChange(leftRange, trackedChange.tracking.clone())
-          )
-          newTrackedChanges.push(
-            new TrackedChange(
-              rightRange.moveBy(length).shrinkBy(length),
-              trackedChange.tracking.clone()
+          if (!leftRange.isEmpty()) {
+            newTrackedChanges.push(
+              new TrackedChange(leftRange, trackedChange.tracking)
             )
-          )
+          }
+          if (!rightRange.isEmpty() && rightRange.length > length) {
+            newTrackedChanges.push(
+              new TrackedChange(
+                rightRange.moveBy(length).shrinkBy(length),
+                trackedChange.tracking
+              )
+            )
+          }
         } else if (retainedRange.start <= trackedChange.range.start) {
           // overlaps to the left
           const [, reducedRange] = trackedChange.range.splitAt(
             retainedRange.end
           )
-          trackedChange.range = reducedRange
-          newTrackedChanges.push(trackedChange)
+          if (!reducedRange.isEmpty()) {
+            newTrackedChanges.push(
+              new TrackedChange(reducedRange, trackedChange.tracking)
+            )
+          }
         } else {
           // overlaps to the right
           const [reducedRange] = trackedChange.range.splitAt(cursor)
-          trackedChange.range = reducedRange
-          newTrackedChanges.push(trackedChange)
+          if (!reducedRange.isEmpty()) {
+            newTrackedChanges.push(
+              new TrackedChange(reducedRange, trackedChange.tracking)
+            )
+          }
         }
+      } else {
+        // keep the range
+        newTrackedChanges.push(trackedChange)
       }
     }
     if (opts.tracking?.type === 'delete' || opts.tracking?.type === 'insert') {

libraries/overleaf-editor-core/lib/file_data/tracking_props.js

@@ -1,6 +1,6 @@
 // @ts-check
 /**
- * @typedef {import("../types").TrackedChangeRawData} TrackedChangeRawData
+ * @typedef {import("../types").TrackingPropsRawData} TrackingPropsRawData
  */
 
 class TrackingProps {
@@ -22,6 +22,7 @@ class TrackingProps {
      */
     this.userId = userId
     /**
+     * @readonly
      * @type {Date}
      */
     this.ts = ts
@@ -29,13 +30,16 @@ class TrackingProps {
 
   /**
    *
-   * @param {TrackedChangeRawData['tracking']} raw
-   * @returns
+   * @param {TrackingPropsRawData} raw
+   * @returns {TrackingProps}
    */
   static fromRaw(raw) {
     return new TrackingProps(raw.type, raw.userId, new Date(raw.ts))
   }
 
+  /**
+   * @returns {TrackingPropsRawData}
+   */
   toRaw() {
     return {
       type: this.type,
@@ -44,8 +48,15 @@ class TrackingProps {
     }
   }
 
-  clone() {
-    return new TrackingProps(this.type, this.userId, this.ts)
+  equals(other) {
+    if (!(other instanceof TrackingProps)) {
+      return false
+    }
+    return (
+      this.type === other.type &&
+      this.userId === other.userId &&
+      this.ts.getTime() === other.ts.getTime()
+    )
   }
 }
 

libraries/overleaf-editor-core/lib/operation/edit_operation_builder.js

@@ -1,11 +1,14 @@
 // @ts-check
-/** @typedef {import('./edit_operation')} EditOperation */
+/**
+ * @typedef {import('./edit_operation')} EditOperation
+ * @typedef {import('../types').RawEditOperation} RawEditOperation
+ */
 const TextOperation = require('./text_operation')
 
 class EditOperationBuilder {
   /**
    *
-   * @param {object} raw
+   * @param {RawEditOperation} raw
    * @returns {EditOperation}
    */
   static fromJSON(raw) {

libraries/overleaf-editor-core/lib/operation/scan_op.js

@@ -5,9 +5,15 @@ const {
   InvalidInsertionError,
   UnprocessableError,
 } = require('../errors')
+const TrackingProps = require('../file_data/tracking_props')
 
-/** @typedef {{ result: string, inputCursor: number}} ApplyContext */
-/** @typedef {{ length: number, inputCursor: number, readonly inputLength: number}} LengthApplyContext */
+/**
+ * @typedef {{ length: number, inputCursor: number, readonly inputLength: number}} LengthApplyContext
+ * @typedef {import('../types').RawScanOp} RawScanOp
+ * @typedef {import('../types').RawInsertOp} RawInsertOp
+ * @typedef {import('../types').RawRetainOp} RawRetainOp
+ * @typedef {import('../types').RawRemoveOp} RawRemoveOp
+ */
 
 class ScanOp {
   constructor() {
@@ -16,16 +22,6 @@ class ScanOp {
     }
   }
 
-  /**
-   * Applies an operation to a string
-   * @param {string} input
-   * @param {ApplyContext} current
-   * @returns {ApplyContext}
-   */
-  apply(input, current) {
-    throw new Error('abstract method')
-  }
-
   /**
    * Applies an operation to a length
    * @param {LengthApplyContext} current
@@ -35,12 +31,15 @@ class ScanOp {
     throw new Error('abstract method')
   }
 
+  /**
+   * @returns {RawScanOp}
+   */
   toJSON() {
     throw new Error('abstract method')
   }
 
   /**
-   * @param {object} raw
+   * @param {RawScanOp} raw
    * @returns {ScanOp}
    */
   static fromJSON(raw) {
@@ -87,7 +86,13 @@ class ScanOp {
 }
 
 class InsertOp extends ScanOp {
-  constructor(insertion) {
+  /**
+   *
+   * @param {string} insertion
+   * @param {TrackingProps | undefined} tracking
+   * @param {string[] | undefined} commentIds
+   */
+  constructor(insertion, tracking = undefined, commentIds = undefined) {
     super()
     if (typeof insertion !== 'string') {
       throw new InvalidInsertionError('insertion must be a string')
@@ -95,12 +100,17 @@ class InsertOp extends ScanOp {
     if (containsNonBmpChars(insertion)) {
       throw new InvalidInsertionError('insertion contains non-BMP characters')
     }
+    /** @type {string} */
     this.insertion = insertion
+    /** @type {TrackingProps | undefined} */
+    this.tracking = tracking
+    /** @type {string[] | undefined} */
+    this.commentIds = commentIds
   }
 
   /**
    *
-   * @param {{i: string} | string} op
+   * @param {RawInsertOp} op
    * @returns {InsertOp}
    */
   static fromJSON(op) {
@@ -113,21 +123,11 @@ class InsertOp extends ScanOp {
         'insert operation must have a string property'
       )
     }
-    return new InsertOp(op.i)
-  }
-
-  /**
-   * @inheritdoc
-   * @param {string} input
-   * @param {ApplyContext} current
-   * @returns {ApplyContext}
-   *  */
-  apply(input, current) {
-    if (containsNonBmpChars(this.insertion)) {
-      throw new InvalidInsertionError(input, this.toJSON())
-    }
-    current.result += this.insertion
-    return current
+    return new InsertOp(
+      op.i,
+      op.tracking && TrackingProps.fromRaw(op.tracking),
+      op.commentIds
+    )
   }
 
   /**
@@ -145,24 +145,69 @@ class InsertOp extends ScanOp {
     if (!(other instanceof InsertOp)) {
       return false
     }
-    return this.insertion === other.insertion
+    if (this.insertion !== other.insertion) {
+      return false
+    }
+    if (this.tracking) {
+      if (!this.tracking.equals(other.tracking)) {
+        return false
+      }
+    } else if (other.tracking) {
+      return false
+    }
+
+    if (this.commentIds) {
+      return (
+        this.commentIds.length === other.commentIds?.length &&
+        this.commentIds.every(id => other.commentIds?.includes(id))
+      )
+    }
+    return !other.commentIds
   }
 
   canMergeWith(other) {
-    return other instanceof InsertOp
+    if (!(other instanceof InsertOp)) {
+      return false
+    }
+    if (this.tracking) {
+      if (!this.tracking.equals(other.tracking)) {
+        return false
+      }
+    } else if (other.tracking) {
+      return false
+    }
+    if (this.commentIds) {
+      return (
+        this.commentIds.length === other.commentIds?.length &&
+        this.commentIds.every(id => other.commentIds?.includes(id))
+      )
+    }
+    return !other.commentIds
   }
 
   mergeWith(other) {
-    if (!(other instanceof InsertOp)) {
+    if (!this.canMergeWith(other)) {
       throw new Error('Cannot merge with incompatible operation')
     }
     this.insertion += other.insertion
+    // We already have the same tracking info and commentIds
   }
 
+  /**
+   * @returns {RawInsertOp}
+   */
   toJSON() {
-    // TODO: Once we add metadata to the operation, generate an object rather
-    // than the compact representation.
-    return this.insertion
+    if (!this.tracking && !this.commentIds) {
+      return this.insertion
+    }
+    const obj = { i: this.insertion }
+    if (this.tracking) {
+      obj.tracking = this.tracking.toRaw()
+    }
+    if (this.commentIds) {
+      obj.commentIds = this.commentIds
+    }
+    return obj
   }
 
   toString() {
@@ -171,34 +216,19 @@ class InsertOp extends ScanOp {
 }
 
 class RetainOp extends ScanOp {
-  constructor(length) {
+  /**
+   * @param {number} length
+   * @param {TrackingProps | undefined} tracking
+   */
+  constructor(length, tracking = undefined) {
     super()
     if (length < 0) {
       throw new Error('length must be non-negative')
     }
+    /** @type {number} */
     this.length = length
-  }
-
-  /**
-   * @inheritdoc
-   * @param {string} input
-   * @param {ApplyContext} current
-   * @returns {ApplyContext}
-   *  */
-  apply(input, current) {
-    if (current.inputCursor + this.length > input.length) {
-      throw new ApplyError(
-        "Operation can't retain more chars than are left in the string.",
-        this.toJSON(),
-        input
-      )
-    }
-    current.result += input.slice(
-      current.inputCursor,
-      current.inputCursor + this.length
-    )
-    current.inputCursor += this.length
-    return current
+    /** @type {TrackingProps | undefined} */
+    this.tracking = tracking
   }
 
   /**
@@ -221,8 +251,8 @@ class RetainOp extends ScanOp {
 
   /**
    *
-   * @param {number | {r: number}} op
-   * @returns
+   * @param {RawRetainOp} op
+   * @returns {RetainOp}
    */
   static fromJSON(op) {
     if (typeof op === 'number') {
@@ -232,6 +262,9 @@ class RetainOp extends ScanOp {
     if (typeof op.r !== 'number') {
       throw new Error('retain operation must have a number property')
     }
+    if (op.tracking) {
+      return new RetainOp(op.r, TrackingProps.fromRaw(op.tracking))
+    }
     return new RetainOp(op.r)
   }
 
@@ -240,24 +273,40 @@ class RetainOp extends ScanOp {
     if (!(other instanceof RetainOp)) {
       return false
     }
-    return this.length === other.length
+    if (this.length !== other.length) {
+      return false
+    }
+    if (this.tracking) {
+      return this.tracking.equals(other.tracking)
+    }
+    return !other.tracking
   }
 
   canMergeWith(other) {
-    return other instanceof RetainOp
+    if (!(other instanceof RetainOp)) {
+      return false
+    }
+    if (this.tracking) {
+      return this.tracking.equals(other.tracking)
+    }
+    return !other.tracking
   }
 
   mergeWith(other) {
-    if (!(other instanceof RetainOp)) {
+    if (!this.canMergeWith(other)) {
       throw new Error('Cannot merge with incompatible operation')
     }
     this.length += other.length
   }
 
+  /**
+   * @returns {RawRetainOp}
+   */
   toJSON() {
-    // TODO: Once we add metadata to the operation, generate an object rather
-    // than the compact representation.
-    return this.length
+    if (!this.tracking) {
+      return this.length
+    }
+    return { r: this.length, tracking: this.tracking.toRaw() }
   }
 
   toString() {
@@ -271,20 +320,10 @@ class RemoveOp extends ScanOp {
     if (length < 0) {
       throw new Error('length must be non-negative')
     }
+    /** @type {number} */
     this.length = length
   }
 
-  /**
-   * @inheritdoc
-   * @param {string} _input
-   * @param {ApplyContext} current
-   * @returns {ApplyContext}
-   */
-  apply(_input, current) {
-    current.inputCursor += this.length
-    return current
-  }
-
   /**
    * @inheritdoc
    * @param {LengthApplyContext} current
@@ -297,7 +336,7 @@ class RemoveOp extends ScanOp {
 
   /**
    *
-   * @param {number} op
+   * @param {RawRemoveOp} op
    * @returns {RemoveOp}
    */
   static fromJSON(op) {
@@ -320,12 +359,15 @@ class RemoveOp extends ScanOp {
   }
 
   mergeWith(other) {
-    if (!(other instanceof RemoveOp)) {
+    if (!this.canMergeWith(other)) {
       throw new Error('Cannot merge with incompatible operation')
     }
     this.length += other.length
   }
 
+  /**
+   * @returns {RawRemoveOp}
+   */
   toJSON() {
     return -this.length
   }
@@ -335,20 +377,35 @@ class RemoveOp extends ScanOp {
   }
 }
 
+/**
+ * @param {RawScanOp} op
+ * @returns {op is RawRetainOp}
+ */
 function isRetain(op) {
   return (
     (typeof op === 'number' && op > 0) ||
-    (typeof op === 'object' && typeof op.r === 'number' && op.r > 0)
+    (typeof op === 'object' &&
+      'r' in op &&
+      typeof op.r === 'number' &&
+      op.r > 0)
   )
 }
 
+/**
+ * @param {RawScanOp} op
+ * @returns {op is RawInsertOp}
+ */
 function isInsert(op) {
   return (
     typeof op === 'string' ||
-    (typeof op === 'object' && typeof op.i === 'string')
+    (typeof op === 'object' && 'i' in op && typeof op.i === 'string')
   )
 }
 
+/**
+ * @param {RawScanOp} op
+ * @returns {op is RawRemoveOp}
+ */
 function isRemove(op) {
   return typeof op === 'number' && op < 0
 }

libraries/overleaf-editor-core/lib/operation/text_operation.js

@@ -12,7 +12,6 @@
 const containsNonBmpChars = require('../util').containsNonBmpChars
 const EditOperation = require('./edit_operation')
 const {
-  ScanOp,
   RetainOp,
   InsertOp,
   RemoveOp,
@@ -26,7 +25,13 @@ const {
   InvalidInsertionError,
   TooLongError,
 } = require('../errors')
-/** @typedef {import('../file_data/string_file_data')} StringFileData */
+const Range = require('../file_data/range')
+const TrackingProps = require('../file_data/tracking_props')
+/**
+ * @typedef {import('../file_data/string_file_data')} StringFileData
+ * @typedef {import('../types').RawTextOperation} RawTextOperation
+ * @typedef {import('../operation/scan_op').ScanOp} ScanOp
+ */
 
 /**
  * Create an empty text operation.
@@ -85,8 +90,10 @@ class TextOperation extends EditOperation {
   /**
    * Skip over a given number of characters.
    * @param {number | {r: number}} n
+   * @param {{tracking?: TrackingProps}} opts
+   * @returns {TextOperation}
    */
-  retain(n) {
+  retain(n, opts = {}) {
     if (n === 0) {
       return this
     }
@@ -95,6 +102,7 @@ class TextOperation extends EditOperation {
       throw new Error('retain expects an integer or a retain object')
     }
     const newOp = RetainOp.fromJSON(n)
+    newOp.tracking = opts.tracking
 
     if (newOp.length === 0) {
       return this
@@ -117,12 +125,16 @@ class TextOperation extends EditOperation {
   /**
    * Insert a string at the current position.
    * @param {string | {i: string}} insertValue
+   * @param {{tracking?: TrackingProps, commentIds?: string[]}} opts
+   * @returns {TextOperation}
    */
-  insert(insertValue) {
+  insert(insertValue, opts = {}) {
     if (!isInsert(insertValue)) {
       throw new Error('insert expects a string or an insert object')
     }
     const newOp = InsertOp.fromJSON(insertValue)
+    newOp.tracking = opts.tracking
+    newOp.commentIds = opts.commentIds
     if (newOp.insertion === '') {
       return this
     }
@@ -154,6 +166,7 @@ class TextOperation extends EditOperation {
   /**
    * Remove a string at the current position.
    * @param {number | string} n
+   * @returns {TextOperation}
    */
   remove(n) {
     if (typeof n === 'string') {
@@ -198,6 +211,7 @@ class TextOperation extends EditOperation {
 
   /**
    * @inheritdoc
+   * @returns {RawTextOperation}
    */
   toJSON() {
     return { textOperation: this.ops.map(op => op.toJSON()) }
@@ -205,16 +219,24 @@ class TextOperation extends EditOperation {
 
   /**
    * Converts a plain JS object into an operation and validates it.
+   * @param {RawTextOperation} obj
+   * @returns {TextOperation}
    */
   static fromJSON = function ({ textOperation: ops }) {
     const o = new TextOperation()
     for (const op of ops) {
       if (isRetain(op)) {
-        o.retain(op)
+        const retain = RetainOp.fromJSON(op)
+        o.retain(retain.length, { tracking: retain.tracking })
       } else if (isInsert(op)) {
-        o.insert(op)
+        const insert = InsertOp.fromJSON(op)
+        o.insert(insert.insertion, {
+          commentIds: insert.commentIds,
+          tracking: insert.tracking,
+        })
       } else if (isRemove(op)) {
-        o.remove(op)
+        const remove = RemoveOp.fromJSON(op)
+        o.remove(-remove.length)
       } else {
         throw new UnprocessableError('unknown operation: ' + JSON.stringify(op))
       }
@@ -248,10 +270,42 @@ class TextOperation extends EditOperation {
     }
 
     const ops = this.ops
-    const { inputCursor, result } = ops.reduce(
-      (intermediate, op) => op.apply(str, intermediate),
-      { result: '', inputCursor: 0 }
-    )
+    let inputCursor = 0
+    let result = ''
+    for (const op of ops) {
+      if (op instanceof RetainOp) {
+        if (inputCursor + op.length > str.length) {
+          throw new ApplyError(
+            "Operation can't retain more chars than are left in the string.",
+            op.toJSON(),
+            str
+          )
+        }
+        file.trackedChanges.applyRetain(result.length, op.length, {
+          tracking: op.tracking,
+        })
+        result += str.slice(inputCursor, inputCursor + op.length)
+        inputCursor += op.length
+      } else if (op instanceof InsertOp) {
+        if (containsNonBmpChars(op.insertion)) {
+          throw new InvalidInsertionError(str, op.toJSON())
+        }
+        file.trackedChanges.applyInsert(result.length, op.insertion, {
+          tracking: op.tracking,
+        })
+        file.comments.applyInsert(
+          new Range(result.length, op.insertion.length),
+          { commentIds: op.commentIds }
+        )
+        result += op.insertion
+      } else if (op instanceof RemoveOp) {
+        file.trackedChanges.applyDelete(result.length, op.length)
+        file.comments.applyDelete(new Range(result.length, op.length))
+        inputCursor += op.length
+      } else {
+        throw new UnprocessableError('Unknown ScanOp type during apply')
+      }
+    }
 
     if (inputCursor !== str.length) {
       throw new TextOperation.ApplyError(
@@ -311,14 +365,65 @@ class TextOperation extends EditOperation {
     for (let i = 0, l = ops.length; i < l; i++) {
       const op = ops[i]
       if (op instanceof RetainOp) {
-        inverse.retain(op.length)
-        strIndex += op.length
+        // Where we need to end up after the retains
+        const target = strIndex + op.length
+        // A previous retain could have overriden some tracking info. Now we
+        // need to restore it.
+        const previousRanges = previousState.trackedChanges.inRange(
+          new Range(strIndex, op.length)
+        )
+
+        let removeTrackingInfoIfNeeded
+        if (op.tracking) {
+          removeTrackingInfoIfNeeded = new TrackingProps(
+            'none',
+            op.tracking.userId,
+            op.tracking.ts
+          )
+        }
+
+        for (const trackedChange of previousRanges) {
+          if (strIndex < trackedChange.range.start) {
+            inverse.retain(trackedChange.range.start - strIndex, {
+              tracking: removeTrackingInfoIfNeeded,
+            })
+            strIndex = trackedChange.range.start
+          }
+          if (trackedChange.range.end < strIndex + op.length) {
+            inverse.retain(trackedChange.range.length, {
+              tracking: trackedChange.tracking,
+            })
+            strIndex = trackedChange.range.end
+          }
+          if (trackedChange.range.end !== strIndex) {
+            // No need to split the range at the end
+            const [left] = trackedChange.range.splitAt(strIndex)
+            inverse.retain(left.length, { tracking: trackedChange.tracking })
+            strIndex = left.end
+          }
+        }
+        if (strIndex < target) {
+          inverse.retain(target - strIndex, {
+            tracking: removeTrackingInfoIfNeeded,
+          })
+          strIndex = target
+        }
       } else if (op instanceof InsertOp) {
         inverse.remove(op.insertion.length)
       } else if (op instanceof RemoveOp) {
-        // remove op
-        inverse.insert(str.slice(strIndex, strIndex + op.length))
-        strIndex += op.length
+        const segments = calculateTrackingCommentSegments(
+          strIndex,
+          op.length,
+          previousState.comments,
+          previousState.trackedChanges
+        )
+        for (const segment of segments) {
+          inverse.insert(str.slice(strIndex, strIndex + segment.length), {
+            tracking: segment.tracking,
+            commentIds: segment.commentIds,
+          })
+          strIndex += segment.length
+        }
       } else {
         throw new UnprocessableError('unknown scanop during inversion')
       }
@@ -410,7 +515,10 @@ class TextOperation extends EditOperation {
       }
 
       if (op2 instanceof InsertOp) {
-        operation.insert(op2.insertion)
+        operation.insert(op2.insertion, {
+          tracking: op2.tracking,
+          commentIds: op2.commentIds,
+        })
         op2 = ops2[i2++]
         continue
       }
@@ -427,48 +535,70 @@ class TextOperation extends EditOperation {
       }
 
       if (op1 instanceof RetainOp && op2 instanceof RetainOp) {
+        // If both have tracking info, use the latter one. Otherwise use the
+        // tracking info from the former.
+        const tracking = op2.tracking ?? op1.tracking
         if (op1.length > op2.length) {
-          operation.retain(op2.length)
-          op1 = ScanOp.fromJSON(op1.length - op2.length)
+          operation.retain(op2.length, {
+            tracking,
+          })
+          op1 = new RetainOp(op1.length - op2.length, op1.tracking)
           op2 = ops2[i2++]
         } else if (op1.length === op2.length) {
-          operation.retain(op1.length)
+          operation.retain(op1.length, {
+            tracking,
+          })
           op1 = ops1[i1++]
           op2 = ops2[i2++]
         } else {
-          operation.retain(op1.length)
-          op2 = ScanOp.fromJSON(op2.length - op1.length)
+          operation.retain(op1.length, {
+            tracking,
+          })
+          op2 = new RetainOp(op2.length - op1.length, op2.tracking)
           op1 = ops1[i1++]
         }
       } else if (op1 instanceof InsertOp && op2 instanceof RemoveOp) {
         if (op1.insertion.length > op2.length) {
-          op1 = ScanOp.fromJSON(op1.insertion.slice(op2.length))
+          op1 = new InsertOp(
+            op1.insertion.slice(op2.length),
+            op1.tracking,
+            op1.commentIds
+          )
           op2 = ops2[i2++]
         } else if (op1.insertion.length === op2.length) {
           op1 = ops1[i1++]
           op2 = ops2[i2++]
         } else {
-          op2 = ScanOp.fromJSON(-op2.length + op1.insertion.length)
+          op2 = RemoveOp.fromJSON(op1.insertion.length - op2.length)
           op1 = ops1[i1++]
         }
       } else if (op1 instanceof InsertOp && op2 instanceof RetainOp) {
+        const opts = {
+          // Prefer the latter tracking info
+          tracking: op2.tracking ?? op1.tracking,
+          commentIds: op1.commentIds,
+        }
         if (op1.insertion.length > op2.length) {
-          operation.insert(op1.insertion.slice(0, op2.length))
-          op1 = ScanOp.fromJSON(op1.insertion.slice(op2.length))
+          operation.insert(op1.insertion.slice(0, op2.length), opts)
+          op1 = new InsertOp(
+            op1.insertion.slice(op2.length),
+            op1.tracking,
+            op1.commentIds
+          )
           op2 = ops2[i2++]
         } else if (op1.insertion.length === op2.length) {
-          operation.insert(op1.insertion)
+          operation.insert(op1.insertion, opts)
           op1 = ops1[i1++]
           op2 = ops2[i2++]
         } else {
-          operation.insert(op1.insertion)
-          op2 = ScanOp.fromJSON(op2.length - op1.insertion.length)
+          operation.insert(op1.insertion, opts)
+          op2 = new RetainOp(op2.length - op1.insertion.length, op2.tracking)
           op1 = ops1[i1++]
         }
       } else if (op1 instanceof RetainOp && op2 instanceof RemoveOp) {
         if (op1.length > op2.length) {
           operation.remove(-op2.length)
-          op1 = ScanOp.fromJSON(op1.length - op2.length)
+          op1 = new RetainOp(op1.length - op2.length, op1.tracking)
           op2 = ops2[i2++]
         } else if (op1.length === op2.length) {
           operation.remove(-op2.length)
@@ -476,7 +606,7 @@ class TextOperation extends EditOperation {
           op2 = ops2[i2++]
         } else {
           operation.remove(op1.length)
-          op2 = ScanOp.fromJSON(-op2.length + op1.length)
+          op2 = RemoveOp.fromJSON(op1.length - op2.length)
           op1 = ops1[i1++]
         }
       } else {
@@ -498,6 +628,7 @@ class TextOperation extends EditOperation {
    * heart of OT.
    * @param {TextOperation} operation1
    * @param {TextOperation} operation2
+   * @returns {[TextOperation, TextOperation]}
    */
   static transform(operation1, operation2) {
     if (operation1.baseLength !== operation2.baseLength) {
@@ -526,14 +657,20 @@ class TextOperation extends EditOperation {
       // => insert the string in the corresponding prime operation, skip it in
       // the other one. If both op1 and op2 are insert ops, prefer op1.
       if (op1 instanceof InsertOp) {
-        operation1prime.insert(op1.insertion)
+        operation1prime.insert(op1.insertion, {
+          tracking: op1.tracking,
+          commentIds: op1.commentIds,
+        })
         operation2prime.retain(op1.insertion.length)
         op1 = ops1[i1++]
         continue
       }
       if (op2 instanceof InsertOp) {
         operation1prime.retain(op2.insertion.length)
-        operation2prime.insert(op2.insertion)
+        operation2prime.insert(op2.insertion, {
+          tracking: op2.tracking,
+          commentIds: op2.commentIds,
+        })
         op2 = ops2[i2++]
         continue
       }
@@ -552,9 +689,21 @@ class TextOperation extends EditOperation {
       let minl
       if (op1 instanceof RetainOp && op2 instanceof RetainOp) {
         // Simple case: retain/retain
+
+        // If both have tracking info, we use the one from op1
+        /** @type {TrackingProps | undefined} */
+        let operation1primeTracking
+        /** @type {TrackingProps | undefined} */
+        let operation2primeTracking
+        if (op1.tracking) {
+          operation1primeTracking = op1.tracking
+        } else {
+          operation2primeTracking = op2.tracking
+        }
+
         if (op1.length > op2.length) {
           minl = op2.length
-          op1 = ScanOp.fromJSON(op1.length - op2.length)
+          op1 = new RetainOp(op1.length - op2.length, op1.tracking)
           op2 = ops2[i2++]
         } else if (op1.length === op2.length) {
           minl = op2.length
@@ -562,30 +711,30 @@ class TextOperation extends EditOperation {
           op2 = ops2[i2++]
         } else {
           minl = op1.length
-          op2 = ScanOp.fromJSON(op2.length - op1.length)
+          op2 = new RetainOp(op2.length - op1.length, op2.tracking)
           op1 = ops1[i1++]
         }
-        operation1prime.retain(minl)
-        operation2prime.retain(minl)
+        operation1prime.retain(minl, { tracking: operation1primeTracking })
+        operation2prime.retain(minl, { tracking: operation2primeTracking })
       } else if (op1 instanceof RemoveOp && op2 instanceof RemoveOp) {
         // Both operations remove the same string at the same position. We don't
         // need to produce any operations, we just skip over the remove ops and
         // handle the case that one operation removes more than the other.
         if (op1.length > op2.length) {
-          op1 = ScanOp.fromJSON(-op1.length - -op2.length)
+          op1 = RemoveOp.fromJSON(op2.length - op1.length)
           op2 = ops2[i2++]
         } else if (op1.length === op2.length) {
           op1 = ops1[i1++]
           op2 = ops2[i2++]
         } else {
-          op2 = ScanOp.fromJSON(-op2.length - -op1.length)
+          op2 = RemoveOp.fromJSON(op1.length - op2.length)
           op1 = ops1[i1++]
         }
         // next two cases: remove/retain and retain/remove
       } else if (op1 instanceof RemoveOp && op2 instanceof RetainOp) {
         if (op1.length > op2.length) {
           minl = op2.length
-          op1 = ScanOp.fromJSON(-op1.length + op2.length)
+          op1 = RemoveOp.fromJSON(op2.length - op1.length)
           op2 = ops2[i2++]
         } else if (op1.length === op2.length) {
           minl = op2.length
@@ -593,14 +742,14 @@ class TextOperation extends EditOperation {
           op2 = ops2[i2++]
         } else {
           minl = op1.length
-          op2 = ScanOp.fromJSON(op2.length + -op1.length)
+          op2 = new RetainOp(op2.length - op1.length, op2.tracking)
           op1 = ops1[i1++]
         }
         operation1prime.remove(minl)
       } else if (op1 instanceof RetainOp && op2 instanceof RemoveOp) {
         if (op1.length > op2.length) {
           minl = op2.length
-          op1 = ScanOp.fromJSON(op1.length + -op2.length)
+          op1 = new RetainOp(op1.length - op2.length, op1.tracking)
           op2 = ops2[i2++]
         } else if (op1.length === op2.length) {
           minl = op1.length
@@ -608,7 +757,7 @@ class TextOperation extends EditOperation {
           op2 = ops2[i2++]
         } else {
           minl = op1.length
-          op2 = ScanOp.fromJSON(-op2.length + op1.length)
+          op2 = RemoveOp.fromJSON(op1.length - op2.length)
           op1 = ops1[i1++]
         }
         operation2prime.remove(minl)
@@ -660,4 +809,77 @@ function getStartIndex(operation) {
   return 0
 }
 
+/**
+ * Constructs the segments defined as each overlapping range of tracked
+ * changes and comments. Each segment can have it's own tracking props and
+ * attached comment ids.
+ *
+ *                  The quick brown fox jumps over the lazy dog
+ * Tracked inserts            ----------               -----
+ * Tracked deletes      ------
+ * Comment 1               -------
+ * Comment 2                    ----
+ * Comment 3                           -----------------
+ *
+ * Approx. boundaries:  |  | | || |   |                |   |
+ *
+ * @param {number} cursor
+ * @param {number} length
+ * @param {import('../file_data/comment_list')} commentsList
+ * @param {import('../file_data/tracked_change_list')} trackedChangeList
+ * @returns {{length: number, commentIds?: string[], tracking?: TrackingProps}[]}
+ */
+function calculateTrackingCommentSegments(
+  cursor,
+  length,
+  commentsList,
+  trackedChangeList
+) {
+  const breaks = new Set()
+  const opStart = cursor
+  const opEnd = cursor + length
+  // Utility function to limit breaks to the boundary set by the operation range
+  function addBreak(rangeBoundary) {
+    if (rangeBoundary < opStart || rangeBoundary > opEnd) {
+      return
+    }
+    breaks.add(rangeBoundary)
+  }
+  // Add comment boundaries
+  for (const comment of commentsList.comments.values()) {
+    for (const range of comment.ranges) {
+      addBreak(range.end)
+      addBreak(range.start)
+    }
+  }
+  // Add tracked change boundaries
+  for (const trackedChange of trackedChangeList.trackedChanges) {
+    addBreak(trackedChange.range.start)
+    addBreak(trackedChange.range.end)
+  }
+  // Add operation boundaries
+  addBreak(opStart)
+  addBreak(opEnd)
+
+  // Sort the boundaries so that we can construct ranges between them
+  const sortedBreaks = Array.from(breaks).sort((a, b) => a - b)
+
+  const separateRanges = []
+  for (let i = 1; i < sortedBreaks.length; i++) {
+    const start = sortedBreaks[i - 1]
+    const end = sortedBreaks[i]
+    const currentRange = new Range(start, end - start)
+    // The comment ids that cover the current range is part of this sub-range
+    const commentIds = commentsList.idsCoveringRange(currentRange)
+    // The tracking info that covers the current range is part of this sub-range
+    const tracking = trackedChangeList.propsAtRange(currentRange)
+    separateRanges.push({
+      length: currentRange.length,
+      commentIds: commentIds.length > 0 ? commentIds : undefined,
+      tracking,
+    })
+  }
+  return separateRanges
+}
+
 module.exports = TextOperation

libraries/overleaf-editor-core/lib/types.ts

@@ -30,6 +30,32 @@ export type TrackingPropsRawData = {
 export type StringFileRawData = {
   content: string
   comments?: CommentRawData[]
+  trackedChanges?: TrackedChangeRawData[]
 }
 
 export type RawV2DocVersions = Record<string, { pathname: string; v: number }>
+
+export type RawInsertOp =
+  | {
+      i: string
+      commentIds?: string[]
+      tracking?: TrackingPropsRawData
+    }
+  | string
+
+export type RawRemoveOp = number
+export type RawRetainOp =
+  | {
+      r: number
+      commentIds?: string[]
+      tracking?: TrackingPropsRawData
+    }
+  | number
+
+export type RawScanOp = RawInsertOp | RawRemoveOp | RawRetainOp
+
+export type RawTextOperation = {
+  textOperation: RawScanOp[]
+}
+
+export type RawEditOperation = RawTextOperation

libraries/overleaf-editor-core/test/comments_list.test.js

@@ -413,7 +413,7 @@ describe('commentList', function () {
       })
     })
 
-    it('should delete entire comment', function () {
+    it('should leave comment without ranges', function () {
       const commentList = CommentList.fromRaw([
         {
           id: 'comm1',
@@ -436,6 +436,7 @@ describe('commentList', function () {
           ranges: [{ pos: 5, length: 10 }],
           resolved: false,
         },
+        { id: 'comm2', ranges: [], resolved: false },
         {
           id: 'comm3',
           ranges: [{ pos: 20, length: 15 }],

libraries/overleaf-editor-core/test/scan_op.test.js

@@ -7,6 +7,7 @@ const {
   RemoveOp,
 } = require('../lib/operation/scan_op')
 const { UnprocessableError, ApplyError } = require('../lib/errors')
+const TrackingProps = require('../lib/file_data/tracking_props')
 
 describe('ScanOp', function () {
   describe('fromJSON', function () {
@@ -41,7 +42,9 @@ describe('ScanOp', function () {
     })
 
     it('throws an error for invalid input', function () {
-      expect(() => ScanOp.fromJSON({})).to.throw(UnprocessableError)
+      expect(() => ScanOp.fromJSON(/** @type {any} */ ({}))).to.throw(
+        UnprocessableError
+      )
     })
 
     it('throws an error for zero', function () {
@@ -63,6 +66,27 @@ describe('RetainOp', function () {
     expect(op1.equals(op2)).to.be.false
   })
 
+  it('is not equal to another RetainOp with no tracking info', function () {
+    const op1 = new RetainOp(
+      4,
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    const op2 = new RetainOp(4)
+    expect(op1.equals(op2)).to.be.false
+  })
+
+  it('is not equal to another RetainOp with different tracking info', function () {
+    const op1 = new RetainOp(
+      4,
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    const op2 = new RetainOp(
+      4,
+      new TrackingProps('insert', 'user2', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    expect(op1.equals(op2)).to.be.false
+  })
+
   it('is not equal to an InsertOp', function () {
     const op1 = new RetainOp(1)
     const op2 = new InsertOp('a')
@@ -83,6 +107,43 @@ describe('RetainOp', function () {
     expect(op1.equals(new RetainOp(3))).to.be.true
   })
 
+  it('cannot merge with another RetainOp if tracking info is different', function () {
+    const op1 = new RetainOp(
+      4,
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    const op2 = new RetainOp(
+      4,
+      new TrackingProps('insert', 'user2', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    expect(op1.canMergeWith(op2)).to.be.false
+    expect(() => op1.mergeWith(op2)).to.throw(Error)
+  })
+
+  it('can merge with another RetainOp if tracking info is the same', function () {
+    const op1 = new RetainOp(
+      4,
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    const op2 = new RetainOp(
+      4,
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    op1.mergeWith(op2)
+    expect(
+      op1.equals(
+        new RetainOp(
+          8,
+          new TrackingProps(
+            'insert',
+            'user1',
+            new Date('2024-01-01T00:00:00.000Z')
+          )
+        )
+      )
+    ).to.be.true
+  })
+
   it('cannot merge with an InsertOp', function () {
     const op1 = new RetainOp(1)
     const op2 = new InsertOp('a')
@@ -112,16 +173,6 @@ describe('RetainOp', function () {
     expect(length).to.equal(13)
     expect(inputCursor).to.equal(13)
   })
-
-  it('adds from the input to the result when applied', function () {
-    const op = new RetainOp(3)
-    const { result, inputCursor } = op.apply('abcdefghi', {
-      result: 'xyz',
-      inputCursor: 3,
-    })
-    expect(result).to.equal('xyzdef')
-    expect(inputCursor).to.equal(6)
-  })
 })
 
 describe('InsertOp', function () {
@@ -137,6 +188,60 @@ describe('InsertOp', function () {
     expect(op1.equals(op2)).to.be.false
   })
 
+  it('is not equal to another InsertOp with no tracking info', function () {
+    const op1 = new InsertOp(
+      'a',
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    const op2 = new InsertOp('a')
+    expect(op1.equals(op2)).to.be.false
+  })
+
+  it('is not equal to another InsertOp with different tracking info', function () {
+    const op1 = new InsertOp(
+      'a',
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    const op2 = new InsertOp(
+      'a',
+      new TrackingProps('insert', 'user2', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    expect(op1.equals(op2)).to.be.false
+  })
+
+  it('is not equal to another InsertOp with no comment ids', function () {
+    const op1 = new InsertOp('a', undefined, ['1'])
+    const op2 = new InsertOp('a')
+    expect(op1.equals(op2)).to.be.false
+  })
+
+  it('is not equal to another InsertOp with tracking info', function () {
+    const op1 = new InsertOp('a', undefined)
+    const op2 = new InsertOp(
+      'a',
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    expect(op1.equals(op2)).to.be.false
+  })
+
+  it('is not equal to another InsertOp with comment ids', function () {
+    const op1 = new InsertOp('a')
+    const op2 = new InsertOp('a', undefined, ['1'])
+    expect(op1.equals(op2)).to.be.false
+  })
+
+  it('is not equal to another InsertOp with different comment ids', function () {
+    const op1 = new InsertOp('a', undefined, ['1'])
+    const op2 = new InsertOp('a', undefined, ['2'])
+    expect(op1.equals(op2)).to.be.false
+  })
+
+  it('is not equal to another InsertOp with overlapping comment ids', function () {
+    const op1 = new InsertOp('a', undefined, ['1'])
+    const op2 = new InsertOp('a', undefined, ['2', '1'])
+    expect(op1.equals(op2)).to.be.false
+  })
+
   it('is not equal to a RetainOp', function () {
     const op1 = new InsertOp('a')
     const op2 = new RetainOp(1)
@@ -157,6 +262,103 @@ describe('InsertOp', function () {
     expect(op1.equals(new InsertOp('ab'))).to.be.true
   })
 
+  it('cannot merge with another InsertOp if comment id info is different', function () {
+    const op1 = new InsertOp('a', undefined, ['1'])
+    const op2 = new InsertOp('b', undefined, ['1', '2'])
+    expect(op1.canMergeWith(op2)).to.be.false
+    expect(() => op1.mergeWith(op2)).to.throw(Error)
+  })
+
+  it('cannot merge with another InsertOp if comment id info is different while tracking info matches', function () {
+    const op1 = new InsertOp(
+      'a',
+      new TrackingProps(
+        'insert',
+        'user1',
+        new Date('2024-01-01T00:00:00.000Z')
+      ),
+      ['1', '2']
+    )
+    const op2 = new InsertOp(
+      'b',
+      new TrackingProps(
+        'insert',
+        'user1',
+        new Date('2024-01-01T00:00:00.000Z')
+      ),
+      ['3']
+    )
+    expect(op1.canMergeWith(op2)).to.be.false
+    expect(() => op1.mergeWith(op2)).to.throw(Error)
+  })
+
+  it('cannot merge with another InsertOp if comment id is present in other and tracking info matches', function () {
+    const op1 = new InsertOp(
+      'a',
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    const op2 = new InsertOp(
+      'b',
+      new TrackingProps(
+        'insert',
+        'user1',
+        new Date('2024-01-01T00:00:00.000Z')
+      ),
+      ['1']
+    )
+    expect(op1.canMergeWith(op2)).to.be.false
+    expect(() => op1.mergeWith(op2)).to.throw(Error)
+  })
+
+  it('cannot merge with another InsertOp if tracking info is different', function () {
+    const op1 = new InsertOp(
+      'a',
+      new TrackingProps('insert', 'user1', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    const op2 = new InsertOp(
+      'b',
+      new TrackingProps('insert', 'user2', new Date('2024-01-01T00:00:00.000Z'))
+    )
+    expect(op1.canMergeWith(op2)).to.be.false
+    expect(() => op1.mergeWith(op2)).to.throw(Error)
+  })
+
+  it('can merge with another InsertOp if tracking and comment info is the same', function () {
+    const op1 = new InsertOp(
+      'a',
+      new TrackingProps(
+        'insert',
+        'user1',
+        new Date('2024-01-01T00:00:00.000Z')
+      ),
+      ['1', '2']
+    )
+    const op2 = new InsertOp(
+      'b',
+      new TrackingProps(
+        'insert',
+        'user1',
+        new Date('2024-01-01T00:00:00.000Z')
+      ),
+      ['1', '2']
+    )
+    expect(op1.canMergeWith(op2)).to.be.true
+    op1.mergeWith(op2)
+    expect(
+      op1.equals(
+        new InsertOp(
+          'ab',
+          new TrackingProps(
+            'insert',
+            'user1',
+            new Date('2024-01-01T00:00:00.000Z')
+          ),
+          ['1', '2']
+        )
+      )
+    ).to.be.true
+  })
+
   it('cannot merge with a RetainOp', function () {
     const op1 = new InsertOp('a')
     const op2 = new RetainOp(1)
@@ -187,16 +389,6 @@ describe('InsertOp', function () {
     expect(inputCursor).to.equal(20)
   })
 
-  it('adds from the insertion to the result when applied', function () {
-    const op = new InsertOp('ghi')
-    const { result, inputCursor } = op.apply('abcdef', {
-      result: 'xyz',
-      inputCursor: 3,
-    })
-    expect(result).to.equal('xyzghi')
-    expect(inputCursor).to.equal(3)
-  })
-
   it('can apply a retain of the rest of the input', function () {
     const op = new RetainOp(10)
     const { length, inputCursor } = op.applyToLength({
@@ -282,14 +474,4 @@ describe('RemoveOp', function () {
     expect(length).to.equal(10)
     expect(inputCursor).to.equal(13)
   })
-
-  it('does not change the result and adds to the cursor when applied', function () {
-    const op = new RemoveOp(3)
-    const { result, inputCursor } = op.apply('abcdefghi', {
-      result: 'xyz',
-      inputCursor: 3,
-    })
-    expect(result).to.equal('xyz')
-    expect(inputCursor).to.equal(6)
-  })
 })

libraries/overleaf-editor-core/test/support/random.js

@@ -9,10 +9,10 @@ function randomInt(n) {
   return Math.floor(Math.random() * n)
 }
 
-function randomString(n) {
+function randomString(n, newLine = true) {
   let str = ''
   while (n--) {
-    if (Math.random() < 0.15) {
+    if (newLine && Math.random() < 0.15) {
       str += '\n'
     } else {
       const chr = randomInt(26) + 97
@@ -32,7 +32,35 @@ function randomTest(numTrials, test) {
   }
 }
 
+function randomSubset(arr) {
+  const n = randomInt(arr.length)
+  const subset = []
+  const indices = []
+  for (let i = 0; i < arr.length; i++) indices.push(i)
+  for (let i = 0; i < n; i++) {
+    const index = randomInt(indices.length)
+    subset.push(arr[indices[index]])
+    indices.splice(index, 1)
+  }
+  return subset
+}
+
+function randomComments(number) {
+  const ids = new Set()
+  const comments = []
+  while (comments.length < number) {
+    const id = randomString(10, false)
+    if (!ids.has(id)) {
+      comments.push({ id, ranges: [], resolved: false })
+      ids.add(id)
+    }
+  }
+  return { ids: Array.from(ids), comments }
+}
+
 exports.int = randomInt
 exports.string = randomString
 exports.element = randomElement
 exports.test = randomTest
+exports.comments = randomComments
+exports.subset = randomSubset

libraries/overleaf-editor-core/test/support/random_text_operation.js

@@ -1,12 +1,14 @@
+const TrackingProps = require('../../lib/file_data/tracking_props')
 const TextOperation = require('../../lib/operation/text_operation')
 const random = require('./random')
 
 /**
  *
  * @param {string} str
+ * @param {string[]} [commentIds]
  * @returns {TextOperation}
  */
-function randomTextOperation(str) {
+function randomTextOperation(str, commentIds) {
   const operation = new TextOperation()
   let left
   while (true) {
@@ -14,12 +16,33 @@ function randomTextOperation(str) {
     if (left === 0) break
     const r = Math.random()
     const l = 1 + random.int(Math.min(left - 1, 20))
+    const trackedChange =
+      Math.random() < 0.1
+        ? new TrackingProps(
+            random.element(['insert', 'delete', 'none']),
+            random.element(['user1', 'user2', 'user3']),
+            new Date(
+              random.element([
+                '2024-01-01T00:00:00.000Z',
+                '2023-01-01T00:00:00.000Z',
+                '2022-01-01T00:00:00.000Z',
+              ])
+            )
+          )
+        : undefined
     if (r < 0.2) {
-      operation.insert(random.string(l))
+      let operationCommentIds
+      if (commentIds?.length > 0 && Math.random() < 0.3) {
+        operationCommentIds = random.subset(commentIds)
+      }
+      operation.insert(random.string(l), {
+        tracking: trackedChange,
+        commentIds: operationCommentIds,
+      })
     } else if (r < 0.4) {
       operation.remove(l)
     } else {
-      operation.retain(l)
+      operation.retain(l, { tracking: trackedChange })
     }
   }
   if (Math.random() < 0.3) {

libraries/overleaf-editor-core/test/text_operation.test.js

@@ -14,6 +14,7 @@ const ot = require('..')
 const TextOperation = ot.TextOperation
 const StringFileData = require('../lib/file_data/string_file_data')
 const { RetainOp, InsertOp, RemoveOp } = require('../lib/operation/scan_op')
+const TrackingProps = require('../lib/file_data/tracking_props')
 
 describe('TextOperation', function () {
   const numTrials = 500
@@ -141,85 +142,27 @@ describe('TextOperation', function () {
     'applies (randomised)',
     random.test(numTrials, () => {
       const str = random.string(50)
-      const o = randomOperation(str)
+      const comments = random.comments(6)
+      const o = randomOperation(str, comments.ids)
       expect(str.length).to.equal(o.baseLength)
-      const file = new StringFileData(str)
+      const file = new StringFileData(str, comments.comments)
       o.apply(file)
       const result = file.getContent()
       expect(result.length).to.equal(o.targetLength)
     })
   )
 
-  it(
-    'inverts (randomised)',
-    random.test(numTrials, () => {
-      const str = random.string(50)
-      const o = randomOperation(str)
-      const p = o.invert(new StringFileData(str))
-      expect(o.baseLength).to.equal(p.targetLength)
-      expect(o.targetLength).to.equal(p.baseLength)
-      const file = new StringFileData(str)
-      o.apply(file)
-      p.apply(file)
-      const result = file.getContent()
-      expect(result).to.equal(str)
-    })
-  )
-
   it(
     'converts to/from JSON (randomised)',
     random.test(numTrials, () => {
       const doc = random.string(50)
-      const operation = randomOperation(doc)
+      const comments = random.comments(2)
+      const operation = randomOperation(doc, comments.ids)
       const roundTripOperation = TextOperation.fromJSON(operation.toJSON())
       expect(operation.equals(roundTripOperation)).to.be.true
     })
   )
 
-  it(
-    'composes (randomised)',
-    random.test(numTrials, () => {
-      // invariant: apply(str, compose(a, b)) === apply(apply(str, a), b)
-      const str = random.string(20)
-      const a = randomOperation(str)
-      const file = new StringFileData(str)
-      a.apply(file)
-      const afterA = file.getContent()
-      expect(afterA.length).to.equal(a.targetLength)
-      const b = randomOperation(afterA)
-      b.apply(file)
-      const afterB = file.getContent()
-      expect(afterB.length).to.equal(b.targetLength)
-      const ab = a.compose(b)
-      expect(ab.targetLength).to.equal(b.targetLength)
-      ab.apply(new StringFileData(str))
-      const afterAB = file.getContent()
-      expect(afterAB).to.equal(afterB)
-    })
-  )
-
-  it(
-    'transforms (randomised)',
-    random.test(numTrials, () => {
-      // invariant: compose(a, b') = compose(b, a')
-      // where (a', b') = transform(a, b)
-      const str = random.string(20)
-      const a = randomOperation(str)
-      const b = randomOperation(str)
-      const primes = TextOperation.transform(a, b)
-      const aPrime = primes[0]
-      const bPrime = primes[1]
-      const abPrime = a.compose(bPrime)
-      const baPrime = b.compose(aPrime)
-      const abFile = new StringFileData(str)
-      const baFile = new StringFileData(str)
-      abPrime.apply(abFile)
-      baPrime.apply(baFile)
-      expect(abPrime.equals(baPrime)).to.be.true
-      expect(abFile.getContent()).to.equal(baFile.getContent())
-    })
-  )
-
   it('throws when invalid operations are applied', function () {
     const operation = new TextOperation().retain(1)
     expect(() => {
@@ -261,4 +204,647 @@ describe('TextOperation', function () {
       /inserted text contains non BMP characters/
     )
   })
+
+  describe('invert', function () {
+    it(
+      'inverts (randomised)',
+      random.test(numTrials, () => {
+        const str = random.string(50)
+        const comments = random.comments(6)
+        const o = randomOperation(str, comments.ids)
+        const originalFile = new StringFileData(str, comments.comments)
+        const p = o.invert(originalFile)
+        expect(o.baseLength).to.equal(p.targetLength)
+        expect(o.targetLength).to.equal(p.baseLength)
+        const file = new StringFileData(str, comments.comments)
+        o.apply(file)
+        p.apply(file)
+        const result = file.toRaw()
+        expect(result).to.deep.equal(originalFile.toRaw())
+      })
+    )
+
+    it('re-inserts removed range and comment when inverting', function () {
+      expectInverseToLeadToInitialState(
+        new StringFileData(
+          'foo bar baz',
+          [{ id: 'comment1', ranges: [{ pos: 4, length: 3 }] }],
+          [
+            {
+              range: { pos: 4, length: 3 },
+              tracking: {
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'insert',
+                userId: 'user1',
+              },
+            },
+          ]
+        ),
+        new TextOperation().retain(4).remove(4).retain(3)
+      )
+    })
+
+    it('deletes inserted range and comment when inverting', function () {
+      expectInverseToLeadToInitialState(
+        new StringFileData('foo baz', [
+          { id: 'comment1', ranges: [], resolved: false },
+        ]),
+        new TextOperation()
+          .retain(4)
+          .insert('bar', {
+            commentIds: ['comment1'],
+            tracking: TrackingProps.fromRaw({
+              ts: '2024-01-01T00:00:00.000Z',
+              type: 'insert',
+              userId: 'user1',
+            }),
+          })
+          .insert(' ')
+          .retain(3)
+      )
+    })
+
+    it('removes a tracked delete', function () {
+      expectInverseToLeadToInitialState(
+        new StringFileData('foo bar baz'),
+        new TextOperation()
+          .retain(4)
+          .retain(4, {
+            tracking: TrackingProps.fromRaw({
+              ts: '2023-01-01T00:00:00.000Z',
+              type: 'delete',
+              userId: 'user1',
+            }),
+          })
+          .retain(3)
+      )
+    })
+
+    it('restores comments that were removed', function () {
+      expectInverseToLeadToInitialState(
+        new StringFileData('foo bar baz', [
+          {
+            id: 'comment1',
+            ranges: [{ pos: 4, length: 3 }],
+            resolved: false,
+          },
+        ]),
+        new TextOperation().retain(4).remove(4).retain(3)
+      )
+    })
+
+    it('re-inserting removed part of comment restores original comment range', function () {
+      expectInverseToLeadToInitialState(
+        new StringFileData('foo bar baz', [
+          {
+            id: 'comment1',
+            ranges: [{ pos: 0, length: 11 }],
+            resolved: false,
+          },
+        ]),
+        new TextOperation().retain(4).remove(4).retain(3)
+      )
+    })
+
+    it('re-inserting removed part of tracked change restores tracked change range', function () {
+      expectInverseToLeadToInitialState(
+        new StringFileData('foo bar baz', undefined, [
+          {
+            range: { pos: 0, length: 11 },
+            tracking: {
+              ts: '2023-01-01T00:00:00.000Z',
+              type: 'delete',
+              userId: 'user1',
+            },
+          },
+        ]),
+        new TextOperation().retain(4).remove(4).retain(3)
+      )
+    })
+  })
+
+  describe('compose', function () {
+    it(
+      'composes (randomised)',
+      random.test(numTrials, () => {
+        // invariant: apply(str, compose(a, b)) === apply(apply(str, a), b)
+        const str = random.string(20)
+        const comments = random.comments(6)
+        const a = randomOperation(str, comments.ids)
+        const file = new StringFileData(str, comments.comments)
+        a.apply(file)
+        const afterA = file.toRaw()
+        expect(afterA.content.length).to.equal(a.targetLength)
+        const b = randomOperation(afterA.content, comments.ids)
+        b.apply(file)
+        const afterB = file.toRaw()
+        expect(afterB.content.length).to.equal(b.targetLength)
+        const ab = a.compose(b)
+        expect(ab.targetLength).to.equal(b.targetLength)
+        ab.apply(new StringFileData(str, comments.comments))
+        const afterAB = file.toRaw()
+        expect(afterAB).to.deep.equal(afterB)
+      })
+    )
+
+    it('composes two operations with comments', function () {
+      expect(
+        compose(
+          new StringFileData('foo baz', [
+            { id: 'comment1', ranges: [], resolved: false },
+          ]),
+          new TextOperation()
+            .retain(4)
+            .insert('bar', {
+              commentIds: ['comment1'],
+              tracking: TrackingProps.fromRaw({
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'insert',
+                userId: 'user1',
+              }),
+            })
+            .insert(' ')
+            .retain(3),
+          new TextOperation().retain(4).remove(4).retain(3)
+        )
+      ).to.deep.equal({
+        content: 'foo baz',
+        comments: [{ id: 'comment1', ranges: [], resolved: false }],
+      })
+    })
+
+    it('prioritizes tracked changes info from the latter operation', function () {
+      expect(
+        compose(
+          new StringFileData('foo bar baz'),
+          new TextOperation()
+            .retain(4)
+            .retain(4, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2023-01-01T00:00:00.000Z',
+                type: 'delete',
+                userId: 'user1',
+              }),
+            })
+            .retain(3),
+          new TextOperation()
+            .retain(4)
+            .retain(4, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'delete',
+                userId: 'user2',
+              }),
+            })
+            .retain(3)
+        )
+      ).to.deep.equal({
+        content: 'foo bar baz',
+        trackedChanges: [
+          {
+            range: { pos: 4, length: 4 },
+            tracking: {
+              ts: '2024-01-01T00:00:00.000Z',
+              type: 'delete',
+              userId: 'user2',
+            },
+          },
+        ],
+      })
+    })
+
+    it('does not remove tracked change if not overriden by operation 2', function () {
+      expect(
+        compose(
+          new StringFileData('foo bar baz'),
+          new TextOperation()
+            .retain(4)
+            .retain(4, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2023-01-01T00:00:00.000Z',
+                type: 'delete',
+                userId: 'user1',
+              }),
+            })
+            .retain(3),
+          new TextOperation().retain(11)
+        )
+      ).to.deep.equal({
+        content: 'foo bar baz',
+        trackedChanges: [
+          {
+            range: { pos: 4, length: 4 },
+            tracking: {
+              ts: '2023-01-01T00:00:00.000Z',
+              type: 'delete',
+              userId: 'user1',
+            },
+          },
+        ],
+      })
+    })
+
+    it('adds comment ranges from both operations', function () {
+      expect(
+        compose(
+          new StringFileData('foo bar baz', [
+            {
+              id: 'comment1',
+              ranges: [{ pos: 4, length: 3 }],
+              resolved: false,
+            },
+            {
+              id: 'comment2',
+              ranges: [{ pos: 8, length: 3 }],
+              resolved: false,
+            },
+          ]),
+          new TextOperation()
+            .retain(5)
+            .insert('aa', {
+              commentIds: ['comment1'],
+            })
+            .retain(6),
+          new TextOperation()
+            .retain(11)
+            .insert('bb', { commentIds: ['comment2'] })
+            .retain(2)
+        )
+      ).to.deep.equal({
+        content: 'foo baaar bbbaz',
+        comments: [
+          { id: 'comment1', ranges: [{ pos: 4, length: 5 }], resolved: false },
+          { id: 'comment2', ranges: [{ pos: 10, length: 5 }], resolved: false },
+        ],
+      })
+    })
+
+    it('it removes the tracking range from a tracked delete if operation 2 resolves it', function () {
+      expect(
+        compose(
+          new StringFileData('foo bar baz'),
+          new TextOperation()
+            .retain(4)
+            .retain(4, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2023-01-01T00:00:00.000Z',
+                type: 'delete',
+                userId: 'user1',
+              }),
+            })
+            .retain(3),
+          new TextOperation()
+            .retain(4)
+            .retain(4, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'none',
+                userId: 'user2',
+              }),
+            })
+            .retain(3)
+        )
+      ).to.deep.equal({
+        content: 'foo bar baz',
+      })
+    })
+  })
+
+  describe('transform', function () {
+    it(
+      'transforms (randomised)',
+      random.test(numTrials, () => {
+        // invariant: compose(a, b') = compose(b, a')
+        // where (a', b') = transform(a, b)
+        const str = random.string(20)
+        const comments = random.comments(6)
+        const a = randomOperation(str, comments.ids)
+        const b = randomOperation(str, comments.ids)
+        const primes = TextOperation.transform(a, b)
+        const aPrime = primes[0]
+        const bPrime = primes[1]
+        const abPrime = a.compose(bPrime)
+        const baPrime = b.compose(aPrime)
+        const abFile = new StringFileData(str, comments.comments)
+        const baFile = new StringFileData(str, comments.comments)
+        abPrime.apply(abFile)
+        baPrime.apply(baFile)
+        expect(abPrime.equals(baPrime)).to.be.true
+        expect(abFile.toRaw()).to.deep.equal(baFile.toRaw())
+      })
+    )
+
+    it('adds a tracked change from operation 1', function () {
+      expect(
+        transform(
+          new StringFileData('foo baz'),
+          new TextOperation()
+            .retain(4)
+            .insert('bar', {
+              tracking: TrackingProps.fromRaw({
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'insert',
+                userId: 'user1',
+              }),
+            })
+            .insert(' ')
+            .retain(3),
+          new TextOperation().retain(7).insert(' qux')
+        )
+      ).to.deep.equal({
+        content: 'foo bar baz qux',
+        trackedChanges: [
+          {
+            range: { pos: 4, length: 3 },
+            tracking: {
+              ts: '2024-01-01T00:00:00.000Z',
+              type: 'insert',
+              userId: 'user1',
+            },
+          },
+        ],
+      })
+    })
+
+    it('prioritizes tracked change from the first operation', function () {
+      expect(
+        transform(
+          new StringFileData('foo bar baz'),
+          new TextOperation()
+            .retain(4)
+            .retain(4, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2023-01-01T00:00:00.000Z',
+                type: 'delete',
+                userId: 'user1',
+              }),
+            })
+            .retain(3),
+          new TextOperation()
+            .retain(4)
+            .retain(4, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'delete',
+                userId: 'user2',
+              }),
+            })
+            .retain(3)
+        )
+      ).to.deep.equal({
+        content: 'foo bar baz',
+        trackedChanges: [
+          {
+            range: { pos: 4, length: 4 },
+            tracking: {
+              ts: '2023-01-01T00:00:00.000Z',
+              type: 'delete',
+              userId: 'user1',
+            },
+          },
+        ],
+      })
+    })
+
+    it('splits a tracked change in two to resolve conflicts', function () {
+      expect(
+        transform(
+          new StringFileData('foo bar baz'),
+          new TextOperation()
+            .retain(4)
+            .retain(4, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2023-01-01T00:00:00.000Z',
+                type: 'delete',
+                userId: 'user1',
+              }),
+            })
+            .retain(3),
+          new TextOperation()
+            .retain(4)
+            .retain(5, {
+              tracking: TrackingProps.fromRaw({
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'delete',
+                userId: 'user2',
+              }),
+            })
+            .retain(2)
+        )
+      ).to.deep.equal({
+        content: 'foo bar baz',
+        trackedChanges: [
+          {
+            range: { pos: 4, length: 4 },
+            tracking: {
+              ts: '2023-01-01T00:00:00.000Z',
+              type: 'delete',
+              userId: 'user1',
+            },
+          },
+          {
+            range: { pos: 8, length: 1 },
+            tracking: {
+              ts: '2024-01-01T00:00:00.000Z',
+              type: 'delete',
+              userId: 'user2',
+            },
+          },
+        ],
+      })
+    })
+
+    it('inserts a tracked change from operation 2 after a tracked change from operation 1', function () {
+      expect(
+        transform(
+          new StringFileData('aaabbbccc'),
+          new TextOperation()
+            .retain(3)
+            .insert('xxx', {
+              tracking: TrackingProps.fromRaw({
+                ts: '2023-01-01T00:00:00.000Z',
+                type: 'insert',
+                userId: 'user1',
+              }),
+            })
+            .retain(6),
+          new TextOperation()
+            .retain(3)
+            .insert('yyy', {
+              tracking: TrackingProps.fromRaw({
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'insert',
+                userId: 'user2',
+              }),
+            })
+            .retain(6)
+        )
+      ).to.deep.equal({
+        content: 'aaaxxxyyybbbccc',
+        trackedChanges: [
+          {
+            range: { pos: 3, length: 3 },
+            tracking: {
+              ts: '2023-01-01T00:00:00.000Z',
+              type: 'insert',
+              userId: 'user1',
+            },
+          },
+          {
+            range: { pos: 6, length: 3 },
+            tracking: {
+              ts: '2024-01-01T00:00:00.000Z',
+              type: 'insert',
+              userId: 'user2',
+            },
+          },
+        ],
+      })
+    })
+
+    it('preserves a comment even if it is completely removed in one operation', function () {
+      expect(
+        transform(
+          new StringFileData('foo bar baz', [
+            {
+              id: 'comment1',
+              ranges: [{ pos: 4, length: 3 }],
+              resolved: false,
+            },
+          ]),
+          new TextOperation().retain(4).remove(4).retain(3),
+          new TextOperation()
+            .retain(7)
+            .insert('qux ', {
+              commentIds: ['comment1'],
+            })
+            .retain(4)
+        )
+      ).to.deep.equal({
+        content: 'foo qux baz',
+        comments: [
+          { id: 'comment1', ranges: [{ pos: 4, length: 4 }], resolved: false },
+        ],
+      })
+    })
+
+    it('extends a comment to both ranges if both operations add text in it', function () {
+      expect(
+        transform(
+          new StringFileData('foo bar baz', [
+            {
+              id: 'comment1',
+              ranges: [{ pos: 4, length: 3 }],
+              resolved: false,
+            },
+          ]),
+          new TextOperation()
+            .retain(4)
+            .insert('qux ', {
+              commentIds: ['comment1'],
+            })
+            .retain(7),
+          new TextOperation()
+            .retain(4)
+            .insert('corge ', { commentIds: ['comment1'] })
+            .retain(7)
+        )
+      ).to.deep.equal({
+        content: 'foo qux corge bar baz',
+        comments: [
+          { id: 'comment1', ranges: [{ pos: 4, length: 13 }], resolved: false },
+        ],
+      })
+    })
+
+    it('adds a tracked change from both operations at different places', function () {
+      expect(
+        transform(
+          new StringFileData('foo bar baz'),
+          new TextOperation()
+            .retain(4)
+            .insert('qux ', {
+              tracking: TrackingProps.fromRaw({
+                ts: '2023-01-01T00:00:00.000Z',
+                type: 'insert',
+                userId: 'user1',
+              }),
+            })
+            .retain(7),
+          new TextOperation()
+            .retain(8)
+            .insert('corge ', {
+              tracking: TrackingProps.fromRaw({
+                ts: '2024-01-01T00:00:00.000Z',
+                type: 'insert',
+                userId: 'user2',
+              }),
+            })
+            .retain(3)
+        )
+      ).to.deep.equal({
+        content: 'foo qux bar corge baz',
+        trackedChanges: [
+          {
+            range: { pos: 4, length: 4 },
+            tracking: {
+              ts: '2023-01-01T00:00:00.000Z',
+              type: 'insert',
+              userId: 'user1',
+            },
+          },
+          {
+            range: { pos: 12, length: 6 },
+            tracking: {
+              ts: '2024-01-01T00:00:00.000Z',
+              type: 'insert',
+              userId: 'user2',
+            },
+          },
+        ],
+      })
+    })
+  })
 })
+
+function expectInverseToLeadToInitialState(fileData, operation) {
+  const initialState = fileData
+  const result = initialState.toRaw()
+  const invertedOperation = operation.invert(initialState)
+  operation.apply(initialState)
+  invertedOperation.apply(initialState)
+  const invertedResult = initialState.toRaw()
+  expect(invertedResult).to.deep.equal(result)
+}
+
+function compose(fileData, op1, op2) {
+  const copy = StringFileData.fromRaw(fileData.toRaw())
+  op1.apply(fileData)
+  op2.apply(fileData)
+  const result1 = fileData.toRaw()
+
+  const composed = op1.compose(op2)
+  composed.apply(copy)
+  const result2 = copy.toRaw()
+
+  expect(result1).to.deep.equal(result2)
+  return fileData.toRaw()
+}
+
+function transform(fileData, a, b) {
+  const initialState = fileData
+  const aFileData = StringFileData.fromRaw(initialState.toRaw())
+  const bFileData = StringFileData.fromRaw(initialState.toRaw())
+
+  const [aPrime, bPrime] = TextOperation.transform(a, b)
+  a.apply(aFileData)
+  bPrime.apply(aFileData)
+  b.apply(bFileData)
+  aPrime.apply(bFileData)
+
+  const resultA = aFileData.toRaw()
+  const resultB = bFileData.toRaw()
+  expect(resultA).to.deep.equal(resultB)
+
+  return aFileData.toRaw()
+}

libraries/overleaf-editor-core/test/tracked_change_list.test.js

@@ -841,5 +841,44 @@ describe('TrackedChangeList', function () {
       expect(trackedChanges.trackedChanges.length).to.equal(0)
       expect(trackedChanges.toRaw()).to.deep.equal([])
     })
+
+    it('should append a new tracked change when retaining a range from another user with tracking info', function () {
+      const trackedChanges = TrackedChangeList.fromRaw([
+        {
+          range: { pos: 4, length: 4 },
+          tracking: {
+            type: 'delete',
+            userId: 'user1',
+            ts: '2023-01-01T00:00:00.000Z',
+          },
+        },
+      ])
+      trackedChanges.applyRetain(8, 1, {
+        tracking: TrackingProps.fromRaw({
+          type: 'delete',
+          userId: 'user2',
+          ts: '2024-01-01T00:00:00.000Z',
+        }),
+      })
+      expect(trackedChanges.trackedChanges.length).to.equal(2)
+      expect(trackedChanges.toRaw()).to.deep.equal([
+        {
+          range: { pos: 4, length: 4 },
+          tracking: {
+            type: 'delete',
+            userId: 'user1',
+            ts: '2023-01-01T00:00:00.000Z',
+          },
+        },
+        {
+          range: { pos: 8, length: 1 },
+          tracking: {
+            type: 'delete',
+            userId: 'user2',
+            ts: '2024-01-01T00:00:00.000Z',
+          },
+        },
+      ])
+    })
   })
 })