Add support for JS coverage

Summary:
Changelog: [Internal]
Adding babel-istanbul-plugin to instrument bundle code with coverage reporting.
Metro will transform source code only when coverage flag is set up globally in jest.
Coverage map is then provided by runner as part of test result.

Differential Revision: D80716433

Author: andrewdacenko

private/react-native-fantom/config/metro-babel-transformer.flow.js

@@ -26,6 +26,23 @@ const transform: BabelTransformer['transform'] = (
       ...(args.plugins ?? []),
       // $FlowExpectedError[untyped-import]
       require('./babel-plugins/inject-debugger-statements-in-tests'),
+      ...(args.options.customTransformOptions?.collectCoverage != null
+        ? [
+            [
+              require.resolve('babel-plugin-istanbul'),
+              {
+                include: [
+                  '**/packages/react-native/Libraries/**/*.js',
+                  '**/packages/react-native/src/**/*.js',
+                ],
+                exclude: [
+                  '**/packages/react-native/Libraries/Renderer/implementations/**',
+                  '**/__tests__/**',
+                ],
+              },
+            ],
+          ]
+        : []),
     ],
   };
   return MetroBabelTransformer.transform(processedArgs);

private/react-native-fantom/package.json

@@ -10,5 +10,8 @@
   "peerDependencies": {
     "jest": "^29.7.0",
     "jest-snapshot": "^29.7.0"
+  },
+  "devDependencies": {
+    "babel-plugin-istanbul": "^6.1.1"
   }
 }

private/react-native-fantom/runner/bundling.js

@@ -15,6 +15,9 @@ import path from 'path';
 
 type BundleOptions = {
   ...RunBuildOptions,
+  customTransformOptions: ?{
+    collectCoverage: boolean,
+  },
   out: $NonMaybeType<RunBuildOptions['out']>,
   testPath: string,
 };
@@ -94,6 +97,7 @@ function getBundleBaseURL({
   dev,
   sourceMap,
   sourceMapUrl,
+  customTransformOptions,
 }: BundleOptions): URL {
   const requestPath = path.relative(PROJECT_ROOT, entry).replace(/\.js$/, '');
   const port = getMetroPort();
@@ -120,6 +124,15 @@ function getBundleBaseURL({
     baseURL.searchParams.append('sourceMapUrl', sourceMapUrl);
   }
 
+  if (customTransformOptions != null) {
+    Object.keys(customTransformOptions).forEach(key => {
+      const value = customTransformOptions[key];
+      if (value != null) {
+        baseURL.searchParams.append(`transform.${key}`, JSON.stringify(value));
+      }
+    });
+  }
+
   return baseURL;
 }
 

private/react-native-fantom/runner/global-setup/build.js

@@ -78,6 +78,7 @@ async function warmUpMetro(isOptimizedMode: boolean): Promise<void> {
     platform: 'android',
     minify: isOptimizedMode,
     dev: !isOptimizedMode,
+    customTransformOptions: undefined,
   });
 
   try {

private/react-native-fantom/runner/runner.js

@@ -9,6 +9,7 @@
  */
 
 import type {
+  CoverageMap,
   FailureDetail,
   TestCaseResult,
   TestSuiteResult,
@@ -193,6 +194,7 @@ function generateBytecodeBundle({
 module.exports = async function runTest(
   globalConfig: {
     updateSnapshot: 'all' | 'new' | 'none',
+    collectCoverage: boolean,
     ...
   },
   config: {
@@ -205,6 +207,7 @@ module.exports = async function runTest(
   runtime: {...},
   testPath: string,
 ): mixed {
+  let coverageMap: CoverageMap | void;
   const snapshotResolver = await buildSnapshotResolver(config);
   const snapshotPath = snapshotResolver.resolveSnapshotPath(testPath);
   const snapshotState = new SnapshotState(snapshotPath, {
@@ -339,6 +342,9 @@ module.exports = async function runTest(
       dev: !testConfig.isJsOptimized,
       sourceMap: true,
       sourceMapUrl: sourceMapPath,
+      customTransformOptions: {
+        collectCoverage: globalConfig.collectCoverage,
+      },
     };
 
     await createBundle({
@@ -456,6 +462,8 @@ module.exports = async function runTest(
     }
 
     testResultsByConfig.push(testResults);
+
+    coverageMap = processedResult.coverageMap;
   }
 
   const endTime = Date.now();
@@ -481,6 +489,7 @@ module.exports = async function runTest(
       globalConfig,
       testPath,
     ),
+    coverage: coverageMap,
     leaks: false,
     openHandles: [],
     perfStats: {

private/react-native-fantom/runtime/setup.js

@@ -36,9 +36,12 @@ export type FailureDetail = {
   cause?: FailureDetail,
 };
 
+export opaque type CoverageMap = mixed;
+
 export type TestSuiteResult =
   | {
       testResults: Array<TestCaseResult>,
+      coverageMap?: CoverageMap,
     }
   | {
       error: FailureDetail,
@@ -465,6 +468,7 @@ global.$$RunTests$$ = () => {
   } else {
     reportTestSuiteResult({
       testResults: runTest(),
+      coverageMap: global.__coverage__,
     });
   }
 };