From ec278082f8fca8073fcfe365a7f873d98acac1b2 Mon Sep 17 00:00:00 2001
From: Henning Dieterichs <hdieterichs@microsoft.com>
Date: Fri, 2 Jun 2023 15:54:26 +0200
Subject: [PATCH] Fixes line range mapping construction bug.

---
 .../common/diff/standardLinesDiffComputer.ts  | 20 ++++++++------
 .../node/diffing/lineRangeMapping.test.ts     | 27 ++++++++++++++++---
 2 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/src/vs/editor/common/diff/standardLinesDiffComputer.ts b/src/vs/editor/common/diff/standardLinesDiffComputer.ts
index 47e7c76da35..c502bf4f0eb 100644
--- a/src/vs/editor/common/diff/standardLinesDiffComputer.ts
+++ b/src/vs/editor/common/diff/standardLinesDiffComputer.ts
@@ -280,19 +280,23 @@ export function getLineRangeMapping(rangeMapping: RangeMapping, originalLines: s
 
 	// rangeMapping describes the edit that replaces `rangeMapping.originalRange` with `newText := getText(modifiedLines, rangeMapping.modifiedRange)`.
 
-	// original: xxx[ \n <- this line is not modified
-	// modified: xxx[ \n
-	if (rangeMapping.modifiedRange.startColumn - 1 >= modifiedLines[rangeMapping.modifiedRange.startLineNumber - 1].length
-		&& rangeMapping.originalRange.startColumn - 1 >= originalLines[rangeMapping.originalRange.startLineNumber - 1].length) {
-		lineStartDelta = 1; // +1 is always possible, as startLineNumber < endLineNumber + 1
-	}
-
 	// original: ]xxx \n <- this line is not modified
 	// modified: ]xx  \n
 	if (rangeMapping.modifiedRange.endColumn === 1 && rangeMapping.originalRange.endColumn === 1
 		&& rangeMapping.originalRange.startLineNumber + lineStartDelta <= rangeMapping.originalRange.endLineNumber
 		&& rangeMapping.modifiedRange.startLineNumber + lineStartDelta <= rangeMapping.modifiedRange.endLineNumber) {
-		lineEndDelta = -1; // We can only do this if the range is not empty yet
+		// We can only do this if the range is not empty yet
+		lineEndDelta = -1;
+	}
+
+	// original: xxx[ \n <- this line is not modified
+	// modified: xxx[ \n
+	if (rangeMapping.modifiedRange.startColumn - 1 >= modifiedLines[rangeMapping.modifiedRange.startLineNumber - 1].length
+		&& rangeMapping.originalRange.startColumn - 1 >= originalLines[rangeMapping.originalRange.startLineNumber - 1].length
+		&& rangeMapping.originalRange.startLineNumber <= rangeMapping.originalRange.endLineNumber + lineEndDelta
+		&& rangeMapping.modifiedRange.startLineNumber <= rangeMapping.modifiedRange.endLineNumber + lineEndDelta) {
+		// We can only do this if the range is not empty yet
+		lineStartDelta = 1;
 	}
 
 	const originalLineRange = new LineRange(
diff --git a/src/vs/editor/test/node/diffing/lineRangeMapping.test.ts b/src/vs/editor/test/node/diffing/lineRangeMapping.test.ts
index 9b2fd2181a0..5cda2c94794 100644
--- a/src/vs/editor/test/node/diffing/lineRangeMapping.test.ts
+++ b/src/vs/editor/test/node/diffing/lineRangeMapping.test.ts
@@ -9,8 +9,7 @@ import { RangeMapping } from 'vs/editor/common/diff/linesDiffComputer';
 import { getLineRangeMapping } from 'vs/editor/common/diff/standardLinesDiffComputer';
 
 suite('lineRangeMapping', () => {
-	test('lineRangeMapping', () => {
-		// {[2,1 -> 3,1]->[2,1 -> 2,1]}
+	test('1', () => {
 		assert.deepStrictEqual(
 			getLineRangeMapping(
 				new RangeMapping(
@@ -27,7 +26,29 @@ suite('lineRangeMapping', () => {
 					''
 				]
 			).toString(),
-			"{[3,4)->[3,3)}"
+			"{[2,3)->[2,2)}"
+		);
+	});
+
+	test('2', () => {
+		assert.deepStrictEqual(
+			getLineRangeMapping(
+				new RangeMapping(
+					new Range(2, 1, 2, 1),
+					new Range(2, 1, 4, 1),
+				),
+				[
+					'',
+					'',
+				],
+				[
+					'',
+					'',
+					'',
+					'',
+				]
+			).toString(),
+			"{[2,2)->[2,4)}"
 		);
 	});
 });