jest: Use babel-jest instead of a custom implementation (#1183)

We were previously just reimplementing parts of it, and not using
the latest recommended Babel settings (such as still setting
`retainLines: true` when sourcemaps are supported natively).

There isn't currently a way to set the babel-jest `createTransformer()`
options via Jest configuration/globals, so we instead have to resort
to using an environment variable. This has the limitation of only
supporting Babel options that are serializable (virtually all commonly
used configuration options are), with any others being silently omitted.
However this was already the case when using `globals` anyway.

See:
https://github.com/facebook/jest/blob/v23.6.0/packages/babel-jest/README.md
https://github.com/facebook/jest/blob/v23.6.0/packages/babel-jest/src/index.js

Fixes #851.

packages/jest/package.json

@@ -22,14 +22,11 @@
     "yarn": ">=1.2.1"
   },
   "dependencies": {
-    "@babel/core": "^7.1.2",
-    "@babel/plugin-transform-modules-commonjs": "^7.1.0",
-    "@neutrinojs/compile-loader": "9.0.0-0",
     "@neutrinojs/loader-merge": "9.0.0-0",
-    "babel-plugin-jest-hoist": "^23.2.0",
+    "babel-core": "^7.0.0-bridge",
+    "babel-jest": "^23.6.0",
     "deepmerge": "^1.5.2",
-    "eslint-plugin-jest": "^21.25.0",
-    "lodash.omit": "^4.5.0"
+    "eslint-plugin-jest": "^21.25.0"
   },
   "peerDependencies": {
     "jest": "^23.0.0",

packages/jest/src/index.js

@@ -1,7 +1,5 @@
 const loaderMerge = require('@neutrinojs/loader-merge');
-const compileLoader = require('@neutrinojs/compile-loader');
 const merge = require('deepmerge');
-const omit = require('lodash.omit');
 const { basename, isAbsolute, join, relative } = require('path');
 const { media, style } = require('neutrino/extensions');
 
@@ -20,43 +18,12 @@ module.exports = (neutrino, options = {}) => {
   });
 
   neutrino.register('jest', (neutrino) => {
-    const usingBabel = neutrino.config.module.rules.has('compile');
+    const compileRule = neutrino.config.module.rules.get('compile');
+    const babelOptions = compileRule ? compileRule.use('babel').get('options') : {};
+    // Any parts of the babel config that are not serializable will be omitted, however
+    // that also occurs when passing to the custom transformer using `globals` instead.
+    process.env.JEST_BABEL_OPTIONS = JSON.stringify(babelOptions);
 
-    if (usingBabel) {
-      neutrino.config.module
-        .rule('compile')
-        .use('babel')
-        .tap(options => compileLoader.merge(options, {
-          plugins: [
-            // Once babel-preset-jest has better Babel 7 support we should
-            // switch back to it (or even use babel-jest, which will allow
-            // simplifying the transformer too):
-            // https://github.com/facebook/jest/issues/6126
-            // For now this plugin is taken from here (we don't need
-            // object-rest-spread since node >=8.3):
-            // https://github.com/facebook/jest/blob/v22.4.2/packages/babel-preset-jest/index.js#L11-L12
-            require.resolve('babel-plugin-jest-hoist'),
-            // Since the tests will be run by node which doesn't yet support
-            // ES2015 modules
-            require.resolve('@babel/plugin-transform-modules-commonjs')
-          ]
-        }));
-    }
-
-    const babelOptions = usingBabel
-      ? compileLoader.merge(
-        omit(
-          neutrino.config.module.rule('compile').use('babel').get('options'),
-          ['cacheDirectory']
-        ),
-        {
-          retainLines: true,
-          plugins: [
-            require.resolve('@babel/plugin-transform-modules-commonjs')
-          ]
-        }
-      )
-      : {};
     const getFinalPath = path => {
       if (isAbsolute(path)) {
         return path;
@@ -109,9 +76,6 @@ module.exports = (neutrino, options = {}) => {
         // property name where a Regex object will cause issues. e.g.:
         // https://github.com/neutrinojs/neutrino/issues/638.
         [extensionsToNames(extensions)]: require.resolve('./transformer')
-      },
-      globals: {
-        BABEL_OPTIONS: babelOptions
       }
     }, options);
   });

packages/jest/src/transformer.js

@@ -1,13 +1,5 @@
-const { transform } = require('@babel/core');
+const { createTransformer } = require('babel-jest');
 
-module.exports = {
-  // This is inspired by:
-  // https://github.com/facebook/jest/blob/v22.4.2/packages/babel-jest/src/index.js#L105-L147
-  // And is required due to:
-  // https://github.com/facebook/jest/issues/1468
-  // TODO: See if it would be easier to wrap the higher-level babel-jest instead.
-  process(src, filename, config) {
-    // Babel 7 returns null if the file was ignored.
-    return transform(src, { filename, ...config.globals.BABEL_OPTIONS }) || src;
-  }
-};
+const babelOptions = JSON.parse(process.env.JEST_BABEL_OPTIONS);
+
+module.exports = createTransformer(babelOptions);

yarn.lock

@@ -1536,6 +1536,11 @@ babel-core@^6.0.0, babel-core@^6.26.0:
     slash "^1.0.0"
     source-map "^0.5.7"
 
+babel-core@^7.0.0-bridge:
+  version "7.0.0-bridge.0"
+  resolved "https://registry.yarnpkg.com/babel-core/-/babel-core-7.0.0-bridge.0.tgz#95a492ddd90f9b4e9a4a1da14eb335b87b634ece"
+  integrity sha512-poPX9mZH/5CSanm50Q+1toVci6pv5KSRv/5TWCwtzQS5XEwn40BcCrgIeMFWP9CKKIniKXNxoIOnOq4VVlGXhg==
+
 babel-eslint@^10.0.1:
   version "10.0.1"
   resolved "https://registry.yarnpkg.com/babel-eslint/-/babel-eslint-10.0.1.tgz#919681dc099614cd7d31d45c8908695092a1faed"