Enable babel on symlinked node_modules with package.source field

src/transforms/babel.js

@@ -89,9 +89,18 @@ async function getBabelConfig(asset) {
     return asset.babelConfig;
   }
 
-  let babelrc = await getBabelRc(asset);
-  let envConfig = await getEnvConfig(asset, !!babelrc);
-  let jsxConfig = getJSXConfig(asset, !!babelrc);
+  // Consider the module source code rather than precompiled if the resolver
+  // used the `source` field, or it is not in node_modules.
+  let isSource =
+    !!(asset.package && asset.package.source) ||
+    !asset.name.includes(NODE_MODULES);
+
+  // Try to resolve a .babelrc file. If one is found, consider the module source code.
+  let babelrc = await getBabelRc(asset, isSource);
+  isSource = isSource || !!babelrc;
+
+  let envConfig = await getEnvConfig(asset, isSource);
+  let jsxConfig = getJSXConfig(asset, isSource);
 
   // Merge the babel-preset-env config and the babelrc if needed
   if (babelrc && !shouldIgnoreBabelrc(asset.name, babelrc)) {
@@ -162,8 +171,9 @@ function getPluginName(p) {
  * Finds a .babelrc for an asset. By default, .babelrc files inside node_modules are not used.
  * However, there are some exceptions:
  *   - if `browserify.transforms` includes "babelify" in package.json (for legacy module compat)
+ *   - the `source` field in package.json is used by the resolver
  */
-async function getBabelRc(asset) {
+async function getBabelRc(asset, isSource) {
   // Support legacy browserify packages
   let browserify = asset.package && asset.package.browserify;
   if (browserify && Array.isArray(browserify.transform)) {
@@ -182,7 +192,7 @@ async function getBabelRc(asset) {
   }
 
   // If this asset is not in node_modules, always use the .babelrc
-  if (!asset.name.includes(NODE_MODULES)) {
+  if (isSource) {
     return await findBabelRc(asset);
   }
 
@@ -224,7 +234,7 @@ async function getEnvConfig(asset, isSourceModule) {
 
   // If this is the app module, the source and target will be the same, so just compile everything.
   // Otherwise, load the source engines and generate a babel-present-env config.
-  if (asset.name.includes(NODE_MODULES) && !isSourceModule) {
+  if (!isSourceModule) {
     let sourceEngines = await getTargetEngines(asset, false);
     let sourceEnv = (await getEnvPlugins(sourceEngines, false)) || targetEnv;
 
@@ -264,7 +274,7 @@ async function getEnvPlugins(targets, useBuiltIns = false) {
  */
 function getJSXConfig(asset, isSourceModule) {
   // Don't enable JSX in node_modules
-  if (asset.name.includes(NODE_MODULES) && !isSourceModule) {
+  if (!isSourceModule) {
     return null;
   }
 

test/integration/babel-node-modules-source-unlinked/.eslintrc.json

@@ -0,0 +1,6 @@
+{
+  "extends": "../.eslintrc.json",
+  "parserOptions": {
+    "sourceType": "module"
+  }
+}

test/integration/babel-node-modules-source-unlinked/index.js

@@ -0,0 +1,4 @@
+import Foo from 'foo';
+
+export {Foo};
+export class Bar {}

test/integration/babel-node-modules-source-unlinked/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "parcel-test-browser-browserslist",
+  "browserslist": ["last 2 Chrome versions", "IE >= 11"]
+}

test/integration/babel-node-modules-source/.eslintrc.json

@@ -0,0 +1,6 @@
+{
+  "extends": "../.eslintrc.json",
+  "parserOptions": {
+    "sourceType": "module"
+  }
+}

test/integration/babel-node-modules-source/index.js

@@ -0,0 +1,4 @@
+import Foo from 'foo';
+
+export {Foo};
+export class Bar {}

test/integration/babel-node-modules-source/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "parcel-test-browser-browserslist",
+  "browserslist": ["last 2 Chrome versions", "IE >= 11"]
+}

test/integration/babel-node-modules-source/packages/foo/index.js

@@ -0,0 +1 @@
+export default class Foo {}

test/integration/babel-node-modules-source/packages/foo/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "foo",
+  "source": true
+}

test/javascript.js

@@ -723,6 +723,24 @@ describe('javascript', function() {
     assert(!file.includes('class Bar {}'));
   });
 
+  it('should compile node_modules when symlinked with a source field in package.json', async function() {
+    await bundle(__dirname + '/integration/babel-node-modules-source/index.js');
+
+    let file = fs.readFileSync(__dirname + '/dist/index.js', 'utf8');
+    assert(!file.includes('class Foo {}'));
+    assert(!file.includes('class Bar {}'));
+  });
+
+  it('should not compile node_modules with a source field in package.json when not symlinked', async function() {
+    await bundle(
+      __dirname + '/integration/babel-node-modules-source-unlinked/index.js'
+    );
+
+    let file = fs.readFileSync(__dirname + '/dist/index.js', 'utf8');
+    assert(file.includes('class Foo {}'));
+    assert(!file.includes('class Bar {}'));
+  });
+
   it('should support compiling JSX', async function() {
     await bundle(__dirname + '/integration/jsx/index.jsx');