fix(reporters): make sure to handle empty files in v8 coverage

CHANGELOG.md

@@ -9,6 +9,7 @@
 
 - `[jest-console]` `console.dir` now respects the second argument correctly ([#10638](https://github.com/facebook/jest/pull/10638))
 - `[expect]` [**BREAKING**] Revise `expect.not.objectContaining()` to be the inverse of `expect.objectContaining()`, as documented. ([#10708](https://github.com/facebook/jest/pull/10708))
+- `[jest-reporter]` Handle empty files when reporting code coverage with V8
 - `[jest-resolve]` Replace read-pkg-up with escalade package ([#10781](https://github.com/facebook/jest/pull/10781))
 - `[jest-runtime]` [**BREAKING**] Do not inject `global` variable into module wrapper ([#10644](https://github.com/facebook/jest/pull/10644))
 - `[jest-runtime]` [**BREAKING**] remove long-deprecated `jest.addMatchers`, `jest.resetModuleRegistry`, and `jest.runTimersToTime` ([#9853](https://github.com/facebook/jest/pull/9853))

e2e/__tests__/__snapshots__/v8Coverage.test.ts.snap

@@ -1,6 +1,15 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`prints coverage 1`] = `
+exports[`prints coverage with empty sourcemaps 1`] = `
+"----------|---------|----------|---------|---------|-------------------
+File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
+----------|---------|----------|---------|---------|-------------------
+All files |     100 |      100 |     100 |     100 |                   
+ types.ts |     100 |      100 |     100 |     100 |                   
+----------|---------|----------|---------|---------|-------------------"
+`;
+
+exports[`prints coverage with missing sourcemaps 1`] = `
 "  console.log
     42
 

e2e/__tests__/v8Coverage.test.ts

@@ -10,7 +10,7 @@ import runJest from '../runJest';
 
 const DIR = path.resolve(__dirname, '../v8-coverage');
 
-test('prints coverage', () => {
+test('prints coverage with missing sourcemaps', () => {
   const sourcemapDir = path.join(DIR, 'no-sourcemap');
 
   const {stdout, exitCode} = runJest(
@@ -22,3 +22,16 @@ test('prints coverage', () => {
   expect(exitCode).toBe(0);
   expect(stdout).toMatchSnapshot();
 });
+
+test('prints coverage with empty sourcemaps', () => {
+  const sourcemapDir = path.join(DIR, 'empty-sourcemap');
+
+  const {stdout, exitCode} = runJest(
+    sourcemapDir,
+    ['--coverage', '--coverage-provider', 'v8'],
+    {stripAnsi: true},
+  );
+
+  expect(exitCode).toBe(0);
+  expect(stdout).toMatchSnapshot();
+});

e2e/v8-coverage/empty-sourcemap/babel.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  presets: ['@babel/preset-env', '@babel/preset-typescript'],
+};

e2e/v8-coverage/empty-sourcemap/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "empty-sourcemap",
+  "version": "1.0.0",
+  "jest": {
+    "testEnvironment": "node"
+  }
+}

e2e/v8-coverage/empty-sourcemap/test.ts

@@ -0,0 +1,5 @@
+import * as types from './types';
+
+test('dummy-test', () => {
+  expect(types).toEqual({default: {}});
+});

e2e/v8-coverage/empty-sourcemap/types.ts

@@ -0,0 +1,2 @@
+export interface obj {}
+

packages/jest-reporters/src/CoverageReporter.ts

@@ -37,7 +37,7 @@ import type {
 // This is fixed in a newer versions of source-map, but our dependencies are still stuck on old versions
 interface FixedRawSourceMap extends Omit<RawSourceMap, 'version'> {
   version: number;
-  file: string;
+  file?: string;
 }
 
 const FAIL_COLOR = chalk.bold.red;
@@ -442,8 +442,7 @@ export default class CoverageReporter extends BaseReporter {
           let sourcemapContent: FixedRawSourceMap | undefined = undefined;
 
           if (
-            fileTransform &&
-            fileTransform.sourceMapPath &&
+            fileTransform?.sourceMapPath &&
             fs.existsSync(fileTransform.sourceMapPath)
           ) {
             sourcemapContent = JSON.parse(
@@ -458,7 +457,9 @@ export default class CoverageReporter extends BaseReporter {
               ? {
                   originalSource: fileTransform.originalCode,
                   source: fileTransform.code,
-                  sourceMap: {sourcemap: sourcemapContent},
+                  sourceMap: {
+                    sourcemap: {file: res.url, ...sourcemapContent},
+                  },
                 }
               : {source: fs.readFileSync(res.url, 'utf8')},
           );