src/vs/workbench/contrib/mergeEditor/browser/model/mapping.ts/DocumentLineRangeMap/project
class DocumentLineRangeMap:	public project(lineNumber: number): LineRangeMapping {
		const lastBefore = findLast(this.lineRangeMappings, r => r.inputRange.startLineNumber <= lineNumber);
		if (!lastBefore) {
			return new LineRangeMapping(
				new LineRange(lineNumber, 1),
				new LineRange(lineNumber, 1)
			);
		}

		if (lastBefore.inputRange.contains(lineNumber)) {
			return lastBefore;
		}
		const containingRange = new LineRange(lineNumber, 1);
		const mappedRange = new LineRange(
			lineNumber +
			lastBefore.outputRange.endLineNumberExclusive -
			lastBefore.inputRange.endLineNumberExclusive,
			1
		);
		return new LineRangeMapping(containingRange, mappedRange);
	}