From 064baf31ad70f5bacc600d126c0e45e146c5b65e Mon Sep 17 00:00:00 2001
From: Eric Mc Sween <5454374+emcsween@users.noreply.github.com>
Date: Fri, 7 Feb 2025 08:34:03 -0500
Subject: [PATCH] Merge pull request #23478 from overleaf/em-doc-hash-diff

Fix doc hash on delete + insert combination

GitOrigin-RevId: ecea5f8ab01f24a9064be88611256b502500d91f
---
 .../app/js/UpdateCompressor.js                |  9 +++++++-
 .../UpdateCompressor/UpdateCompressorTests.js | 21 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/services/project-history/app/js/UpdateCompressor.js b/services/project-history/app/js/UpdateCompressor.js
index 9010348598..b548b7529e 100644
--- a/services/project-history/app/js/UpdateCompressor.js
+++ b/services/project-history/app/js/UpdateCompressor.js
@@ -397,9 +397,16 @@ function _concatTwoUpdates(firstUpdate, secondUpdate) {
           // Make sure that commentIds metadata is propagated to inserts
           op.commentIds = secondOp.commentIds
         }
-        return mergeUpdatesWithOp(firstUpdate, secondUpdate, op)
+        const update = mergeUpdatesWithOp(firstUpdate, secondUpdate, op)
+        // Set the doc hash only on the last update
+        delete update.meta.doc_hash
+        return update
       }
     )
+    const docHash = secondUpdate.meta.doc_hash
+    if (docHash != null && diffUpdates.length > 0) {
+      diffUpdates[diffUpdates.length - 1].meta.doc_hash = docHash
+    }
 
     // Doing a diff like this loses track of the doc lengths for each
     // update, so recalculate them
diff --git a/services/project-history/test/unit/js/UpdateCompressor/UpdateCompressorTests.js b/services/project-history/test/unit/js/UpdateCompressor/UpdateCompressorTests.js
index 04d5163476..c8d50b16f4 100644
--- a/services/project-history/test/unit/js/UpdateCompressor/UpdateCompressorTests.js
+++ b/services/project-history/test/unit/js/UpdateCompressor/UpdateCompressorTests.js
@@ -1565,6 +1565,27 @@ describe('UpdateCompressor', function () {
           },
         ])
       })
+
+      it('special case for delete + insert triggering diff', function () {
+        const meta = { ts: this.ts1, user_id: this.user_id, doc_length: 10 }
+        expect(
+          this.UpdateCompressor.compressUpdates([
+            { op: { p: 3, d: 'foo' }, meta, v: 42 },
+            {
+              op: { p: 3, i: 'bar' },
+              meta: { ...meta, doc_hash: 'hash1' },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          { op: { p: 3, d: 'foo' }, meta, v: 43 },
+          {
+            op: { p: 3, i: 'bar' },
+            meta: { ...meta, doc_length: 7, doc_hash: 'hash1' },
+            v: 43,
+          },
+        ])
+      })
     })
   })
 })