From f6235ce7a0f1123f76e17bb5963a631a3434d428 Mon Sep 17 00:00:00 2001
From: webzwo0i <webzwo0i@c3d2.de>
Date: Sun, 31 Oct 2021 00:17:48 +0200
Subject: [PATCH] textLinesMutator: Fix insertions with newlines at the end of
 a line

In such cases the remaining part of the old line is directly pushed to
the splice but we need to ensure it is not an empty string.
Before this commit an empty string was pushed to the splice.
---
 src/static/js/Changeset.js                     | 5 +++--
 src/tests/frontend/specs/easysync-mutations.js | 5 +++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/static/js/Changeset.js b/src/static/js/Changeset.js
index 95958c12c83..f14433a7dd5 100644
--- a/src/static/js/Changeset.js
+++ b/src/static/js/Changeset.js
@@ -977,8 +977,9 @@ class TextLinesMutator {
         this._curLine += newLines.length;
         // insert the remaining chars from the "old" line (e.g. the line we were in
         // when we started to insert new lines)
-        this._curSplice.push(theLine.substring(lineCol));
-        this._curCol = 0; // TODO(doc) why is this not set to the length of last line?
+        const remaining = theLine.substring(lineCol);
+        if (remaining !== '') this._curSplice.push(remaining);
+        this._curCol = 0;
       } else {
         this._curSplice.push(...newLines);
         this._curLine += newLines.length;
diff --git a/src/tests/frontend/specs/easysync-mutations.js b/src/tests/frontend/specs/easysync-mutations.js
index 2ecf1bb0116..cf988c3b7bc 100644
--- a/src/tests/frontend/specs/easysync-mutations.js
+++ b/src/tests/frontend/specs/easysync-mutations.js
@@ -179,6 +179,11 @@ describe('easysync-mutations', function () {
     ['insert', 'c'],
   ], ['fun\n', 'c']);
 
+  runMutationTest(14, ['\n'], [
+    ['remove', 1, 1, '\n'],
+    ['insert', 'a'],
+    ['insert', 'c\n', 1],
+  ], ['ac\n']);
   it('mutatorHasMore', async function () {
     const lines = ['1\n', '2\n', '3\n', '4\n'];
     let mu;