Improve approximation of coarse sourcemap segments (#5985)

* add test

* Improve approximation of coarse sourcemap segments

* tweak test

Author: TrickyPi

src/utils/collapseSourcemaps.ts

@@ -122,11 +122,22 @@ class Link {
 
 		while (searchStart <= searchEnd) {
 			const m = (searchStart + searchEnd) >> 1;
-			const segment = segments[m];
+			let segment = segments[m];
 
 			// If a sourcemap does not have sufficient resolution to contain a
-			// necessary mapping, e.g. because it only contains line information, we
-			// use the best approximation we could find
+			// necessary mapping, e.g. because it only contains line information or
+			// the column is not precise (e.g. the sourcemap is generated by esbuild, segment[0] may be shorter than the location of the first letter),
+			// we approximate by finding the closest segment whose segment[0] is less than the given column
+			if (segment[0] !== column && searchStart === searchEnd) {
+				let approximatedSegmentIndex = 0;
+				for (let index = 0; index < segments.length; index++) {
+					if (segments[index][0] > column) {
+						break;
+					}
+					approximatedSegmentIndex = index;
+				}
+				segment = segments[approximatedSegmentIndex];
+			}
 			if (segment[0] === column || searchStart === searchEnd) {
 				if (segment.length == 1) return null;
 				const source = this.sources[segment[1]];

src/utils/getOriginalLocation.ts

@@ -15,14 +15,18 @@ export function getOriginalLocation(
 				(segment): segment is [number, number, number, number] => segment.length > 1
 			);
 			const lastSegment = filteredLine[filteredLine.length - 1];
-			for (const segment of filteredLine) {
+			let previousSegment = filteredLine[0];
+			for (let segment of filteredLine) {
 				if (segment[0] >= location.column || segment === lastSegment) {
+					const notMatched = segment[0] !== location.column;
+					segment = notMatched ? previousSegment : segment;
 					location = {
 						column: segment[3],
 						line: segment[2] + 1
 					};
 					continue traceSourcemap;
 				}
+				previousSegment = segment;
 			}
 		}
 		throw new Error("Can't resolve original location of error.");

test/sourcemaps/samples/combined-sourcemap-2/_config.js

@@ -0,0 +1,82 @@
+const assert = require('node:assert');
+const { encode } = require('@jridgewell/sourcemap-codec');
+const terser = require('terser');
+const { SourceMapConsumer } = require('source-map');
+const getLocation = require('../../getLocation');
+
+const originalCode = `
+export function App() {
+  return <div>{'.'}</div>;
+}
+`;
+
+module.exports = defineTest({
+	description: 'get correct combined sourcemap in transforming',
+	formats: ['es'],
+	options: {
+		external: ['react/jsx-runtime'],
+		plugins: [
+			{
+				resolveId(id) {
+					return id;
+				},
+				load() {
+					return {
+						code: originalCode
+					};
+				}
+			},
+			{
+				async transform(code) {
+					return {
+						code: `import { jsx } from "react/jsx-runtime";
+export function App() {
+  return /* @__PURE__ */ jsx("div", { children: "." });
+}
+`,
+						map: {
+							mappings: encode([
+								[[0, 0, 2, 9]],
+								[
+									[0, 0, 1, 7],
+									[16, 0, 1, 16],
+									[22, 0, 1, 22]
+								],
+								[
+									// coarse segment
+									[0, 0, 2, 2],
+									[9, 0, 2, 9],
+									[29, 0, 2, 10],
+									[38, 0, 2, 15],
+									[53, 0, 2, 19]
+								],
+								[[0, 0, 3, 0]],
+								[]
+							]),
+							sourcesContent: [code]
+						}
+					};
+				}
+			},
+			{
+				transform(code) {
+					return terser.minify(code, {
+						sourceMap: true
+					});
+				}
+			},
+			{
+				async transform(code) {
+					const generatedLoc = getLocation(code, code.indexOf('return'));
+					const map = this.getCombinedSourcemap();
+					const smc = await new SourceMapConsumer(map);
+					const originalLoc = smc.originalPositionFor(generatedLoc);
+					const expectedOriginalLoc = getLocation(originalCode, originalCode.indexOf('return'));
+					assert.equal(originalLoc.line, expectedOriginalLoc.line);
+					assert.equal(originalLoc.column, expectedOriginalLoc.column);
+				}
+			}
+		]
+	},
+	async test() {}
+});

test/sourcemaps/samples/warning-with-coarse-sourcemap/_config.js

@@ -0,0 +1,77 @@
+const { encode } = require('@jridgewell/sourcemap-codec');
+const terser = require('terser');
+const path = require('node:path');
+const ID_MAIN = path.join(__dirname, 'main.js');
+
+const originalCode = `
+console.log(
+  this + 2
+)
+`;
+
+module.exports = defineTest({
+	description: 'get correct mapping location with coarse sourcemap',
+	formats: ['es'],
+	options: {
+		plugins: [
+			{
+				resolveId() {
+					return ID_MAIN;
+				},
+				load() {
+					return {
+						code: originalCode
+					};
+				}
+			},
+			{
+				transform(code) {
+					return {
+						code,
+						map: {
+							mappings: encode([
+								[],
+								[
+									[0, 0, 1, 0],
+									[8, 0, 1, 8]
+								],
+								[
+									// coarse segment
+									[0, 0, 2, 2],
+									[9, 0, 2, 9]
+								],
+								[[0, 0, 3, 0]],
+								[]
+							]),
+							sourcesContent: [code]
+						}
+					};
+				}
+			},
+			{
+				transform(code) {
+					return terser.minify(code, {
+						sourceMap: true
+					});
+				}
+			}
+		]
+	},
+	warnings: [
+		{
+			code: 'THIS_IS_UNDEFINED',
+			message:
+				"main.js (3:2): The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten",
+			url: 'https://rollupjs.org/troubleshooting/#error-this-is-undefined',
+			id: ID_MAIN,
+			pos: 12,
+			loc: {
+				column: 2,
+				file: ID_MAIN,
+				line: 3
+			},
+			frame: ' 1:\n' + '2: console.log(\n' + '3:   this + 2\n' + '     ^\n' + '4: )'
+		}
+	],
+	async test() {}
+});