Fixes bug in diffing algorithm. (microsoft#157702)

Author: hediet

src/vs/editor/browser/widget/workerBasedDocumentDiffProvider.ts

@@ -22,7 +22,7 @@ export class WorkerBasedDocumentDiffProvider implements IDocumentDiffProvider {
 		}
 
 		// Convert from space efficient JSON data to rich objects.
-		return {
+		const diff: IDocumentDiff = {
 			identical: result.identical,
 			quitEarly: result.quitEarly,
 			changes: result.changes.map(
@@ -40,5 +40,6 @@ export class WorkerBasedDocumentDiffProvider implements IDocumentDiffProvider {
 					)
 			),
 		};
+		return diff;
 	}
 }

src/vs/editor/common/diff/algorithms/myersDiffAlgorithm.ts

@@ -106,14 +106,14 @@ class FastInt32Array {
 	set(idx: number, value: number): void {
 		if (idx < 0) {
 			idx = -idx - 1;
-			if (idx > this.negativeArr.length) {
+			if (idx >= this.negativeArr.length) {
 				const arr = this.negativeArr;
 				this.negativeArr = new Int32Array(arr.length * 2);
 				this.negativeArr.set(arr);
 			}
 			this.negativeArr[idx] = value;
 		} else {
-			if (idx > this.positiveArr.length) {
+			if (idx >= this.positiveArr.length) {
 				const arr = this.positiveArr;
 				this.positiveArr = new Int32Array(arr.length * 2);
 				this.positiveArr.set(arr);

src/vs/editor/common/diff/standardLinesDiffComputer.ts

@@ -80,13 +80,14 @@ export class StandardLinesDiffComputer implements ILinesDiffComputer {
 		const targetSlice = new Slice(modifiedLines, diff.seq2Range);
 
 		const diffs = this.detailedDiffingAlgorithm.compute(sourceSlice, targetSlice);
-		return diffs.map(
+		const result = diffs.map(
 			(d) =>
 				new RangeMapping(
 					sourceSlice.translateRange(d.seq1Range).delta(diff.seq1Range.start),
 					targetSlice.translateRange(d.seq2Range).delta(diff.seq2Range.start)
 				)
 		);
+		return result;
 	}
 }