fix(source-map): fixes wrong source end offset (#296)

Author: leonidaz

packages/source-map/lib/sourceMap.ts

@@ -48,7 +48,12 @@ export class SourceMap<Data = unknown> {
 		return this.findMatchingOffsets(sourceOffset, 'sourceOffsets', filter);
 	}
 
-	*findMatchingOffsets(offset: number, fromRange: CodeRangeKey, filter?: (data: Data) => boolean) {
+	*findMatchingOffsets(
+		offset: number,
+		fromRange: CodeRangeKey,
+		filter?: (data: Data) => boolean,
+		preferEnd: boolean = false,
+	) {
 		const memo = this.getMemoBasedOnRange(fromRange);
 		if (memo.offsets.length === 0) {
 			return;
@@ -75,6 +80,7 @@ export class SourceMap<Data = unknown> {
 					mapping[toRange],
 					getLengths(mapping, fromRange),
 					getLengths(mapping, toRange),
+					preferEnd,
 				);
 				if (mapped !== undefined) {
 					yield [mapped, mapping] as const;
@@ -91,6 +97,7 @@ export class SourceMap<Data = unknown> {
 		filter?: (data: Data) => boolean,
 	): Generator<[mappedStart: number, mappedEnd: number, startMapping: Mapping<Data>, endMapping: Mapping<Data>]> {
 		const toRange: CodeRangeKey = fromRange === 'sourceOffsets' ? 'generatedOffsets' : 'sourceOffsets';
+		const preferEnd = toRange === 'sourceOffsets';
 		const mappedStarts: [number, Mapping<Data>][] = [];
 		let hadMatch = false;
 		for (const [mappedStart, mapping] of this.findMatchingOffsets(start, fromRange)) {
@@ -104,6 +111,7 @@ export class SourceMap<Data = unknown> {
 				mapping[toRange],
 				getLengths(mapping, fromRange),
 				getLengths(mapping, toRange),
+				preferEnd,
 			);
 			if (mappedEnd !== undefined) {
 				hadMatch = true;
@@ -112,7 +120,7 @@ export class SourceMap<Data = unknown> {
 		}
 		if (!hadMatch && fallbackToAnyMatch) {
 			for (const [mappedStart, mappingStart] of mappedStarts) {
-				for (const [mappedEnd, mappingEnd] of this.findMatchingOffsets(end, fromRange)) {
+				for (const [mappedEnd, mappingEnd] of this.findMatchingOffsets(end, fromRange, undefined, preferEnd)) {
 					if (filter && !filter(mappingEnd.data) || mappedEnd < mappedStart) {
 						continue;
 					}

packages/source-map/lib/translateOffset.ts

@@ -6,6 +6,7 @@ export function translateOffset(
 	toOffsets: number[],
 	fromLengths: number[],
 	toLengths: number[] = fromLengths,
+	preferEnd: boolean = false,
 ): number | undefined {
 	const isSorted = fromOffsets.every((value, index) => index === 0 || fromOffsets[index - 1] <= value);
 	if (!isSorted) {
@@ -15,7 +16,14 @@ export function translateOffset(
 			if (start >= fromOffset && start <= fromOffset + fromLength) {
 				const toLength = toLengths[i];
 				const toOffset = toOffsets[i];
-				let rangeOffset = Math.min(start - fromOffset, toLength);
+				let rangeOffset: number;
+				const relativePos = start - fromOffset;
+				if (preferEnd && toLength > fromLength && relativePos === fromLength) {
+					rangeOffset = toLength;
+				}
+				else {
+					rangeOffset = Math.min(relativePos, toLength);
+				}
 				return toOffset + rangeOffset;
 			}
 		}
@@ -36,7 +44,14 @@ export function translateOffset(
 		if (start >= fromOffset && start <= fromOffset + fromLength) {
 			const toLength = toLengths[mid];
 			const toOffset = toOffsets[mid];
-			let rangeOffset = Math.min(start - fromOffset, toLength);
+			let rangeOffset: number;
+			const relativePos = start - fromOffset;
+			if (preferEnd && toLength > fromLength && relativePos === fromLength) {
+				rangeOffset = toLength;
+			}
+			else {
+				rangeOffset = Math.min(relativePos, toLength);
+			}
 			return toOffset + rangeOffset;
 		}
 		else if (start < fromOffset) {

packages/source-map/tests/translateOffset.spec.ts

@@ -24,4 +24,10 @@ describe('translateOffset', () => {
 	test('start at the end of fromRange with shorter toLength', () => {
 		expect(translateOffset(10, [1], [11], [9], [7])).toEqual(18);
 	});
+	test('start at the end of fromRange with longer toLength and preferEnd true', () => {
+		expect(translateOffset(10, [1], [11], [9], [11], true)).toEqual(22);
+	});
+	test('start at the end of fromRange with longer toLength and preferEnd set to false by default', () => {
+		expect(translateOffset(10, [1], [11], [9], [11])).toEqual(20);
+	});
 });