Fixes microsoft#182329 (microsoft#183206)

Author: hediet

src/vs/workbench/contrib/mergeEditor/browser/model/mapping.ts

@@ -240,14 +240,23 @@ export class DetailedLineRangeMapping extends LineRangeMapping {
 
 		assertFn(() => {
 			for (const map of this.rangeMappings) {
-				const inputRangesValid =
-					inputRange.startLineNumber <= map.inputRange.startLineNumber
-					&& map.inputRange.endLineNumber <= inputRange.endLineNumberExclusive
-					&& (map.inputRange.endLineNumber !== inputRange.endLineNumberExclusive || map.inputRange.endColumn === 1);
-
-				const outputRangesValid = outputRange.startLineNumber <= map.outputRange.startLineNumber
-					&& map.outputRange.endLineNumber <= outputRange.endLineNumberExclusive
-					&& (map.outputRange.endLineNumber !== outputRange.endLineNumberExclusive || map.outputRange.endColumn === 1);
+				let inputRangesValid = inputRange.startLineNumber - 1 <= map.inputRange.startLineNumber
+					&& map.inputRange.endLineNumber <= inputRange.endLineNumberExclusive;
+				if (inputRangesValid && map.inputRange.startLineNumber === inputRange.startLineNumber - 1) {
+					inputRangesValid = map.inputRange.endColumn >= inputTextModel.getLineMaxColumn(map.inputRange.startLineNumber);
+				}
+				if (inputRangesValid && map.inputRange.endLineNumber === inputRange.endLineNumberExclusive) {
+					inputRangesValid = map.inputRange.endColumn === 1;
+				}
+
+				let outputRangesValid = outputRange.startLineNumber - 1 <= map.outputRange.startLineNumber
+					&& map.outputRange.endLineNumber <= outputRange.endLineNumberExclusive;
+				if (outputRangesValid && map.outputRange.startLineNumber === outputRange.startLineNumber - 1) {
+					outputRangesValid = map.outputRange.endColumn >= outputTextModel.getLineMaxColumn(map.outputRange.startLineNumber);
+				}
+				if (outputRangesValid && map.outputRange.endLineNumber === outputRange.endLineNumberExclusive) {
+					outputRangesValid = map.outputRange.endColumn === 1;
+				}
 
 				if (!inputRangesValid || !outputRangesValid) {
 					return false;

src/vs/workbench/contrib/mergeEditor/browser/model/modifiedBaseRange.ts

@@ -206,7 +206,7 @@ function editsToLineRangeEdit(range: LineRange, sortedEdits: RangeEdit[], textMo
 	let currentPosition = startsLineBefore
 		? new Position(
 			range.startLineNumber - 1,
-			Constants.MAX_SAFE_SMALL_INTEGER
+			textModel.getLineMaxColumn(range.startLineNumber - 1)
 		)
 		: new Position(range.startLineNumber, 1);