Merge pull request #34993 from overleaf/mj-compose-associativity-tests

[overleaf-editor-core] Ignore timestamps in associativity tests

GitOrigin-RevId: eed120881fc66fd804759f25565a2e5664f3776c

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

@@ -444,10 +444,71 @@ describe('TextOperation', function () {
           c: c.toJSON(),
         })
 
-        expect(ab_c_file.toRaw()).to.deep.equal(a_bc_file.toRaw(), fuzzingError)
+        // See 'compose associativity does not handle timestamps' test below
+        // for why we ignore timestamps here.
+        expect(stripTrackedChangeTimestamps(ab_c_file.toRaw())).to.deep.equal(
+          stripTrackedChangeTimestamps(a_bc_file.toRaw()),
+          fuzzingError
+        )
       })
     )
 
+    it('compose associativity does not handle timestamps', function () {
+      const str = 'AB'
+      const comments = []
+
+      // a tracks both chars as a delete @2023
+      const a = TextOperation.fromJSON({
+        textOperation: [
+          {
+            r: 2,
+            tracking: {
+              type: 'delete',
+              userId: 'user1',
+              ts: '2023-01-01T00:00:00.000Z',
+            },
+          },
+        ],
+      })
+      // b re-tracks the first char as a delete @2022 (same user), leaving the
+      // second char as an untracked retain (still @2023 from a, and adjacent)
+      const b = TextOperation.fromJSON({
+        textOperation: [
+          {
+            r: 1,
+            tracking: {
+              type: 'delete',
+              userId: 'user1',
+              ts: '2022-01-01T00:00:00.000Z',
+            },
+          },
+          1,
+        ],
+      })
+      // c inserts between the two chars, breaking their adjacency
+      const c = TextOperation.fromJSON({ textOperation: [1, 'X', 1] })
+
+      const ab_c = a.compose(b).compose(c)
+      const a_bc = a.compose(b.compose(c))
+
+      const ab_c_file = new StringFileData(str, comments)
+      ab_c.apply(ab_c_file)
+
+      const a_bc_file = new StringFileData(str, comments)
+      a_bc.apply(a_bc_file)
+
+      // The two composition orders diverge, but only on the tracked-change
+      // timestamp: (a∘b)∘c merges char 1 down to @2022 before c splits it,
+      // while a∘(b∘c) leaves char 1 at @2023.
+      //
+      // If we fix the associativity for timestamps, feel free to update the
+      // assertions below
+      expect(ab_c_file.toRaw()).to.not.deep.equal(a_bc_file.toRaw())
+      expect(stripTrackedChangeTimestamps(ab_c_file.toRaw())).to.deep.equal(
+        stripTrackedChangeTimestamps(a_bc_file.toRaw())
+      )
+    })
+
     it('composes two operations with comments', function () {
       expect(
         compose(
@@ -1026,3 +1087,19 @@ function transform(fileData, a, b) {
 
   return aFileData.toRaw()
 }
+
+/**
+ * @param {import('../../lib/types').StringFileRawData} raw
+ */
+function stripTrackedChangeTimestamps(raw) {
+  if (!raw.trackedChanges) {
+    return raw
+  }
+  return {
+    ...raw,
+    trackedChanges: raw.trackedChanges.map(change => {
+      const { ts, ...tracking } = change.tracking
+      return { ...change, tracking }
+    }),
+  }
+}