fix(coverage): respect source maps of pre-transpiled sources (#5367)

Author: AriPerkkio

eslint.config.js

@@ -15,6 +15,8 @@ export default antfu(
       'test/workspaces/results.json',
       'test/reporters/fixtures/with-syntax-error.test.js',
       'test/network-imports/public/slash@3.0.0.js',
+      'test/coverage-test/src/transpiled.js',
+      'test/coverage-test/src/original.ts',
       'examples/**/mockServiceWorker.js',
       'examples/sveltekit/.svelte-kit',
     ],

packages/coverage-v8/src/provider.ts

@@ -323,14 +323,18 @@ export class V8CoverageProvider extends BaseCoverageProvider implements Coverage
       }
     }
 
+    const sources = [url]
+    if (map.sources && map.sources[0] && !url.endsWith(map.sources[0]))
+      sources[0] = new URL(map.sources[0], url).href
+
     return {
       originalSource: sourcesContent,
       source: code || sourcesContent,
       sourceMap: {
         sourcemap: excludeGeneratedCode(code, {
           ...map,
           version: 3,
-          sources: [url],
+          sources,
           sourcesContent: [sourcesContent],
         }),
       },

test/coverage-test/coverage-report-tests/__snapshots__/custom.report.test.ts.snap

@@ -29,6 +29,7 @@ exports[`custom json report 1`] = `
     "<process-cwd>/src/index.mts",
     "<process-cwd>/src/multi-environment.ts",
     "<process-cwd>/src/multi-suite.ts",
+    "<process-cwd>/src/transpiled.js",
     "<process-cwd>/src/utils.ts",
   ],
 }

test/coverage-test/coverage-report-tests/__snapshots__/istanbul.report.test.ts.snap

@@ -0,0 +1,21 @@
+export const hello = (arg?: unknown) => {
+  if (arg) {
+    // Uncovered
+    noop();
+  }
+
+  // Covered
+  noop();
+
+  if (arg === 3) {
+    // Uncovered
+    noop();
+  }
+
+  if (arg === undefined) {
+    // Covered
+    noop();
+  }
+};
+
+function noop() {}

test/coverage-test/coverage-report-tests/__snapshots__/v8.report.test.ts.snap

@@ -0,0 +1 @@
+export * from './original'

test/coverage-test/src/original.ts

@@ -76,3 +76,10 @@ test('virtual file imports', () => {
 test('decorators', () => {
   new DecoratorsTester().method('cover line')
 })
+
+// Istanbul fails to follow source maps on windows
+test.skipIf(globalThis.process?.env.COVERAGE_PROVIDER === 'istanbul')('pre-transpiled code with source maps to original', async () => {
+  const transpiled = await import('../src/transpiled.js')
+
+  transpiled.hello()
+})