src/vs/workbench/contrib/mergeEditor/browser/model/mapping.ts/DocumentLineRangeMap/outputLineCount
class DocumentLineRangeMap:	public get outputLineCount(): number {
		const last = lastOrDefault(this.lineRangeMappings);
		const diff = last ? last.outputRange.endLineNumberExclusive - last.inputRange.endLineNumberExclusive : 0;
		return this.inputLineCount + diff;
	}