feat(coverage-istanbul): transform coverage using source map

e2e/test-coverage/fixtures/rstest.config.ts

@@ -1,6 +1,7 @@
 import { defineConfig } from '@rstest/core';
 
 export default defineConfig({
+  exclude: ['test/sourcemapMapping.test.ts'],
   setupFiles: ['./rstest.setup.ts'],
   coverage: {
     reporters: ['text'],

e2e/test-coverage/fixtures/rstest.enable.config.ts

@@ -1,9 +1,11 @@
 import { defineConfig } from '@rstest/core';
 
 export default defineConfig({
+  exclude: ['test/sourcemapMapping.test.ts'],
   coverage: {
     enabled: true,
     provider: 'istanbul',
+    exclude: ['src/sourcemap.ts'],
   },
   setupFiles: ['./rstest.setup.ts'],
 });

e2e/test-coverage/fixtures/rstest.globThresholds.config.ts

@@ -1,6 +1,7 @@
 import { defineConfig } from '@rstest/core';
 
 export default defineConfig({
+  exclude: ['test/sourcemapMapping.test.ts'],
   coverage: {
     enabled: true,
     provider: 'istanbul',

e2e/test-coverage/fixtures/rstest.perFileThresholds.config.ts

@@ -1,6 +1,7 @@
 import { defineConfig } from '@rstest/core';
 
 export default defineConfig({
+  exclude: ['test/sourcemapMapping.test.ts'],
   coverage: {
     enabled: true,
     provider: 'istanbul',

e2e/test-coverage/fixtures/rstest.reportsDirectory.config.ts

@@ -1,6 +1,7 @@
 import { defineConfig } from '@rstest/core';
 
 export default defineConfig({
+  exclude: ['test/sourcemapMapping.test.ts'],
   coverage: {
     enabled: true,
     provider: 'istanbul',

e2e/test-coverage/fixtures/rstest.skipFull.config.ts

@@ -1,6 +1,7 @@
 import { defineConfig } from '@rstest/core';
 
 export default defineConfig({
+  exclude: ['test/sourcemapMapping.test.ts'],
   coverage: {
     enabled: true,
     provider: 'istanbul',

e2e/test-coverage/fixtures/rstest.sourcemap.config.ts

@@ -0,0 +1,12 @@
+import { defineConfig } from '@rstest/core';
+
+export default defineConfig({
+  include: ['test/sourcemapMapping.test.ts'],
+  coverage: {
+    enabled: true,
+    provider: 'istanbul',
+    include: ['test-temp-sourcemap-dist/sourcemap.js'],
+    clean: true,
+    reporters: ['text'],
+  },
+});

e2e/test-coverage/fixtures/rstest.thresholds.config.ts

@@ -1,6 +1,7 @@
 import { defineConfig } from '@rstest/core';
 
 export default defineConfig({
+  exclude: ['test/sourcemapMapping.test.ts'],
   coverage: {
     enabled: true,
     provider: 'istanbul',

e2e/test-coverage/fixtures/src/sourcemap.ts

@@ -0,0 +1,18 @@
+// Use enum to ensure the compiled JS has different line mapping from the original TS source.
+export enum Status {
+  Active = 'active',
+  Inactive = 'inactive',
+}
+
+export class Calculator {
+  public base = 10;
+
+  constructor(public factor: number) {}
+
+  add(val: number) {
+    if (val > 0) {
+      return this.base + val * this.factor;
+    }
+    return this.base;
+  }
+}

e2e/test-coverage/fixtures/test/sourcemapMapping.test.ts

@@ -0,0 +1,9 @@
+import { expect, test } from '@rstest/core';
+// @ts-expect-error
+import { Calculator, Status } from '../test-temp-sourcemap-dist/sourcemap.js';
+
+test('calculator', () => {
+  const calc = new Calculator(2);
+  expect(calc.add(5)).toBe(20);
+  expect(Status.Active).toBe('active');
+});

e2e/test-coverage/sourcemap.test.ts

@@ -0,0 +1,77 @@
+import { join } from 'node:path';
+import { describe, expect, it } from '@rstest/core';
+import { x } from 'tinyexec';
+import { runRstestCli } from '../scripts';
+
+describe('test coverage-istanbul sourcemap', () => {
+  it('should map coverage back to source files using sourcemaps', async () => {
+    const fixturePath = join(__dirname, 'fixtures');
+
+    // 1. Execute tsc in the test case to generate JS files with sourcemaps
+    const tsc = x(
+      'npx',
+      [
+        'tsc',
+        '--sourceMap',
+        '--module',
+        'esnext',
+        '--target',
+        'esnext',
+        '--moduleResolution',
+        'node',
+        '--outDir',
+        'test-temp-sourcemap-dist',
+        'src/sourcemap.ts',
+      ],
+      {
+        nodeOptions: {
+          cwd: fixturePath,
+        },
+      },
+    );
+    await tsc;
+
+    if (tsc.process?.exitCode !== 0) {
+      throw new Error(
+        `tsc compilation failed with exit code: ${tsc.process?.exitCode}`,
+      );
+    }
+
+    // 2. Run rstest with configuration including the compiled JS file
+    const { expectExecSuccess, expectLog, cli } = await runRstestCli({
+      command: 'rstest',
+      args: [
+        'run',
+        '-c',
+        'rstest.sourcemap.config.ts',
+        'test/sourcemapMapping.test.ts',
+      ],
+      options: {
+        nodeOptions: {
+          cwd: fixturePath,
+        },
+      },
+    });
+
+    await expectExecSuccess();
+
+    const logs = cli.stdout.split('\n').filter(Boolean);
+
+    // 3. Verify that the coverage report shows the original .ts file instead of the compiled .js file
+    expectLog('sourcemap.ts', logs);
+
+    const sourcemapLog = logs
+      .find((log) => log.includes('sourcemap.ts'))
+      ?.replaceAll(' ', '');
+
+    expect(sourcemapLog).toMatchInlineSnapshot(
+      `"sourcemap.ts|87.5|75|100|87.5|16"`,
+    );
+
+    const allFilesLog = logs
+      .find((log) => log.includes('All files'))
+      ?.replaceAll(' ', '');
+
+    expect(allFilesLog).toMatchInlineSnapshot(`"Allfiles|87.5|75|100|87.5|"`);
+  });
+});

packages/coverage-istanbul/package.json

@@ -24,20 +24,22 @@
     "@rstest/core": "workspace:~"
   },
   "dependencies": {
-    "swc-plugin-coverage-instrument": "0.0.32",
     "istanbul-lib-coverage": "^3.2.2",
     "istanbul-lib-report": "^3.0.1",
-    "istanbul-reports": "^3.2.0"
+    "istanbul-lib-source-maps": "^5.0.6",
+    "istanbul-reports": "^3.2.0",
+    "swc-plugin-coverage-instrument": "0.0.32"
   },
   "devDependencies": {
-    "@rstest/tsconfig": "workspace:*",
-    "@rstest/core": "workspace:*",
     "@rslib/core": "^0.19.0",
-    "@types/node": "^22.16.5",
-    "typescript": "^5.9.3",
+    "@rstest/core": "workspace:*",
+    "@rstest/tsconfig": "workspace:*",
     "@types/istanbul-lib-coverage": "^2.0.6",
     "@types/istanbul-lib-report": "^3.0.3",
-    "@types/istanbul-reports": "^3.0.4"
+    "@types/istanbul-lib-source-maps": "^4.0.4",
+    "@types/istanbul-reports": "^3.0.4",
+    "@types/node": "^22.16.5",
+    "typescript": "^5.9.3"
   },
   "keywords": [
     "rstest",

packages/coverage-istanbul/src/provider.ts

@@ -6,7 +6,11 @@ import type { CoverageMap, FileCoverageData } from 'istanbul-lib-coverage';
 import istanbulLibCoverage from 'istanbul-lib-coverage';
 import { createContext } from 'istanbul-lib-report';
 import reports from 'istanbul-reports';
-import { readInitialCoverage } from './utils';
+import {
+  readInitialCoverage,
+  registerSourceMapURL,
+  transformCoverage,
+} from './utils';
 
 const { createCoverageMap } = istanbulLibCoverage;
 
@@ -17,6 +21,8 @@ declare global {
 
 export class CoverageProvider implements RstestCoverageProvider {
   private coverageMap: ReturnType<typeof createCoverageMap> | null = null;
+  // Cache to avoid redundant readFile calls in generateCoverageForUntestedFiles and generateReports.
+  private sourcemapUrlCache = new Map<string, string | undefined>();
 
   constructor(private options: NormalizedCoverageOptions) {}
 
@@ -47,6 +53,7 @@ export class CoverageProvider implements RstestCoverageProvider {
             content,
             file,
           );
+          registerSourceMapURL(file, code, this.sourcemapUrlCache);
           return readInitialCoverage(code);
         } catch (e) {
           console.error(
@@ -87,7 +94,10 @@ export class CoverageProvider implements RstestCoverageProvider {
     try {
       const context = createContext({
         dir: this.options.reportsDirectory,
-        coverageMap: createCoverageMap(coverageMap.toJSON()),
+        coverageMap: await transformCoverage(
+          coverageMap,
+          this.sourcemapUrlCache,
+        ),
       });
       const reportersList = this.options.reporters;
       for (const reporter of reportersList) {

packages/coverage-istanbul/src/utils.ts

@@ -1,5 +1,6 @@
 import { runInNewContext } from 'node:vm';
-import type { FileCoverageData } from 'istanbul-lib-coverage';
+import type { CoverageMap, FileCoverageData } from 'istanbul-lib-coverage';
+import type { MapStore } from 'istanbul-lib-source-maps';
 
 // ATTENTION: when swc-plugin-coverage-instrument version changed, magic value should be updated too
 // https://github.com/kwonoj/swc-plugin-coverage-instrument/blob/63e9d5e16dbe61073c62af4b7dfed3c1779cbafa/spec/util/constants.ts#L1-L2
@@ -55,3 +56,94 @@ export function readInitialCoverage(
 
   return coverageData;
 }
+
+// https://github.com/webpack/webpack/blob/99c36fab8e8b21885f02cca76c253f51b97997eb/lib/util/extractSourceMap.js#L53
+
+// Matches only the last occurrence of sourceMappingURL
+const innerRegex = /\s*[#@]\s*sourceMappingURL\s*=\s*([^\s'"]*)\s*/;
+
+const sourceMappingURLRegex = new RegExp(
+  '(?:' +
+    '/\\*' +
+    '(?:\\s*\r?\n(?://)?)?' +
+    `(?:${innerRegex.source})` +
+    '\\s*' +
+    '\\*/' +
+    '|' +
+    `//(?:${innerRegex.source})` +
+    ')' +
+    '\\s*',
+);
+
+/**
+ * Extract source mapping URL from code comments
+ * @param {string} code source code content
+ * @returns {string | undefined} source mapping information
+ */
+function getSourceMappingURL(code: string): string | undefined {
+  const lines = code.split(/^/m);
+  let match: RegExpMatchArray | null | undefined = null;
+
+  for (let i = lines.length - 1; i >= 0; i--) {
+    match = lines[i]?.match(sourceMappingURLRegex);
+    if (match) {
+      break;
+    }
+  }
+
+  const sourceMappingURL = match ? match[1] || match[2] || '' : '';
+
+  return sourceMappingURL ? decodeURI(sourceMappingURL) : sourceMappingURL;
+}
+
+export function registerSourceMapURL(
+  filename: string,
+  code: string,
+  sourcemapUrlCache: Map<string, string | undefined>,
+): void {
+  // process js/cjs/mjs file only
+  if (!filename.endsWith('js')) return;
+
+  const url = getSourceMappingURL(code);
+  sourcemapUrlCache.set(filename, url);
+}
+
+export async function transformCoverage(
+  coverageMap: CoverageMap,
+  sourcemapUrlCache: Map<string, string | undefined>,
+): Promise<CoverageMap> {
+  await Promise.all(
+    coverageMap
+      .files()
+      // process js/cjs/mjs file only
+      .filter((filename) => filename.endsWith('js'))
+      .map(async (filename) => {
+        let url = sourcemapUrlCache.get(filename);
+        if (!url) {
+          const { readFile } = await import('node:fs/promises');
+          url = await readFile(filename, 'utf8').then(
+            (content) => getSourceMappingURL(content),
+            () => undefined,
+          );
+        }
+        sourcemapUrlCache.set(filename, url);
+      }),
+  );
+
+  // Call createSourceMapStore as needed
+  let store: MapStore | undefined;
+  for (const [filename, url] of sourcemapUrlCache) {
+    if (url) {
+      if (!store) {
+        const { createSourceMapStore } = await import(
+          'istanbul-lib-source-maps'
+        );
+        store = createSourceMapStore();
+      }
+      store.registerURL(filename, url);
+    }
+  }
+  if (store) return store.transformCoverage(coverageMap);
+
+  return coverageMap;
+}