- fix handling of insertions when there is nothing left in the lines

  array.
- add some more test cases

src/node/easysync_tests.js

@@ -218,16 +218,28 @@ const runTests = () => {
   ], ['banana\n', 'cabbage\n', 'duffle\n']);
 
   // #2836 regressions
-  runMutationTest(8, ['\n'], [
+  runMutationTest(8, ['\n', 'foo\n', '\n'], [
+    ['remove', 1, 1, '\n'],
+    ['skip', 4, 1, false],
+    ['remove', 1, 1, '\n'],
+    ['insert', 'c'],
+  ], ['foo\n', 'c']);
+  runMutationTest(9, ['\n', 'foo\n', '\n'], [
+    ['remove', 1, 1, '\n'],
+    ['skip', 3, 0, false],
+    ['remove', 2, 2, '\n\n'],
+    ['insert', 'c'],
+  ], ['fooc']);
+  runMutationTest(10, ['\n'], [
     ['remove', 1, 1, '\n'],
     ['insert', 'c', 0],
-  ], ['c']);
-  runMutationTest(9, ['\n'], [
+  ], ['c']); // TODO find out if c must have a newline because of unknown constraints
+  runMutationTest(11, ['\n'], [
     ['remove', 1, 1, '\n'],
     ['insert', 'a'],
     ['insert', 'c\n', 1],
   ], ['ac\n']);
-  runMutationTest(10, ['\n'], [
+  runMutationTest(12, ['\n'], [
     ['remove', 1, 1, '\n'],
     ['insert', 'a\n', 1],
     ['insert', 'c'],

src/static/js/Changeset.js

@@ -758,9 +758,14 @@ exports.textLinesMutator = (lines) => {
           curSplice[1] += L - 1;
           const sline = curSplice.length - 1;
           removed = curSplice[sline].substring(curCol) + removed;
-          curSplice[sline] = curSplice[sline].substring(0, curCol) +
-              lines_get(curSplice[0] + curSplice[1]);
-          curSplice[1] += 1;
+          cosnt line = lines_get(curSplice[0] + curSplice[1]);
+          // if no line follows the splice
+          if (!line) {
+            curSplice[sline] = curSplice[sline].substring(0, curCol);
+          } else {
+            curSplice[sline] = curSplice[sline].substring(0, curCol) + line;
+            curSplice[1] += 1;
+          }
         }
       } else {
         removed = nextKLinesText(L);
@@ -813,21 +818,46 @@ exports.textLinesMutator = (lines) => {
           const sline = curSplice.length - 1;
           const theLine = curSplice[sline];
           const lineCol = curCol;
+          // insert the first new line
           curSplice[sline] = theLine.substring(0, lineCol) + newLines[0];
           curLine++;
           newLines.splice(0, 1);
+          // insert the remaining new lines
           Array.prototype.push.apply(curSplice, newLines);
           curLine += newLines.length;
-          curSplice.push(theLine.substring(lineCol));
-          curCol = 0;
+          // insert the remaining chars from the "old" line (e.g. the line we were in
+          // when we started to insert new lines)
+          // if nothing is left we don't push an empty string
+          if (theLine.substring(lineCol)) {
+            curSplice.push(theLine.substring(lineCol));
+          }
+          curCol = 0; // TODO(doc) why is this not set to the length of last line?
         } else {
           Array.prototype.push.apply(curSplice, newLines);
           curLine += newLines.length;
         }
       } else {
-        const sline = putCurLineInSplice();
-        if (!curSplice[sline]) {
-          console.error('curSplice[sline] not populated, actual curSplice contents is ', curSplice, '. Possibly related to https://github.com/ether/etherpad-lite/issues/2802');
+        // there are no additional lines
+        if (lines_get(curSplice[0] + curSplice[1]) === undefined) {
+          // find out if there is a line in splice that is not finished processing
+          // if yes, we can add our text to it
+          if (isCurLineInSplice()) {
+            var sline = curSplice.length - 1;
+            curSplice[sline] = curSplice[sline].substring(0, curCol) + text + curSplice[sline].substring(curCol);
+            curCol += text.length;
+          }
+          // if no, we need to add the text in a new line
+          else {
+            Array.prototype.push.apply(curSplice, [text]);
+            curCol += text.length;
+          }
+        } else {
+          // although the line is put into splice, curLine is not increased, because
+          // there may be more chars in the line (newline is not reached)
+          const sline = putCurLineInSplice();
+          if (!curSplice[sline]) {
+            console.error('curSplice[sline] not populated, actual curSplice contents is ', curSplice, '. Possibly related to https://github.com/ether/etherpad-lite/issues/2802');
+          }
         }
         curSplice[sline] = curSplice[sline].substring(0, curCol) + text +
             curSplice[sline].substring(curCol);