Define __esModule interop flag when requiring ES module from CommonJS

packages/core/integration-tests/test/integration/scope-hoisting/commonjs/interop-require-es-module/a.js

@@ -0,0 +1 @@
+module.exports = require('./b');

packages/core/integration-tests/test/integration/scope-hoisting/commonjs/interop-require-es-module/b.js

@@ -0,0 +1 @@
+export default 2;

packages/core/integration-tests/test/scope-hoisting.js

@@ -1203,5 +1203,18 @@ describe('scope hoisting', function() {
       let output = await run(b);
       assert.deepEqual(output, 42);
     });
+
+    it('should insert __esModule interop flag when importing from an ES module', async function() {
+      let b = await bundle(
+        path.join(
+          __dirname,
+          '/integration/scope-hoisting/commonjs/interop-require-es-module/a.js'
+        )
+      );
+
+      let output = await run(b);
+      assert.equal(output.__esModule, true);
+      assert.equal(output.default, 2);
+    });
   });
 });

packages/core/parcel-bundler/src/Asset.js

@@ -9,6 +9,7 @@ const syncPromise = require('./utils/syncPromise');
 const logger = require('@parcel/logger');
 const Resolver = require('./Resolver');
 const objectHash = require('./utils/objectHash');
+const t = require('babel-types');
 
 /**
  * An Asset represents a file in the dependency tree. Assets can have multiple
@@ -204,7 +205,7 @@ class Asset {
     if (!this.id) {
       this.id =
         this.options.production || this.options.scopeHoist
-          ? md5(this.relativeName, 'base64').slice(0, 4)
+          ? t.toIdentifier(md5(this.relativeName, 'base64')).slice(0, 4)
           : this.relativeName;
     }
 

packages/core/parcel-bundler/src/builtins/helpers.js

@@ -4,6 +4,10 @@ function $parcel$interopDefault(a) {
     : {d: a};
 }
 
+function $parcel$defineInteropFlag(a) {
+  Object.defineProperty(a, '__esModule', {value: true});
+}
+
 function $parcel$exportWildcard(dest, source) {
   Object.keys(source).forEach(function(key) {
     if(key === "default" || key === "__esModule") {

packages/core/parcel-bundler/src/scope-hoisting/concat.js

@@ -9,6 +9,7 @@ const {getName, getIdentifier} = require('./utils');
 
 const EXPORTS_RE = /^\$([^$]+)\$exports$/;
 
+const ESMODULE_TEMPLATE = template(`$parcel$defineInteropFlag(EXPORTS);`);
 const DEFAULT_INTEROP_TEMPLATE = template(
   'var NAME = $parcel$interopDefault(MODULE)'
 );
@@ -142,10 +143,11 @@ module.exports = (packager, ast) => {
           );
         }
 
+        let asset = assets.get(id.value);
         let mod = packager.resolveModule(id.value, source.value);
 
         if (!mod) {
-          if (assets.get(id.value).dependencies.get(source.value).optional) {
+          if (asset.dependencies.get(source.value).optional) {
             path.replaceWith(
               THROW_TEMPLATE({MODULE: t.stringLiteral(source.value)})
             );
@@ -161,6 +163,29 @@ module.exports = (packager, ast) => {
             if (!isUnusedValue(path)) {
               let name = getName(mod, 'exports');
               node = t.identifier(replacements.get(name) || name);
+
+              // Insert __esModule interop flag if the required module is an ES6 module with a default export.
+              // This ensures that code generated by Babel and other tools works properly.
+              if (
+                asset.cacheData.isCommonJS &&
+                mod.cacheData.isES6Module &&
+                mod.cacheData.exports.default
+              ) {
+                let binding = path.scope.getBinding(name);
+                if (binding && !binding.path.getData('hasESModuleFlag')) {
+                  if (binding.path.node.init) {
+                    binding.path
+                      .getStatementParent()
+                      .insertAfter(ESMODULE_TEMPLATE({EXPORTS: name}));
+                  }
+
+                  for (let path of binding.constantViolations) {
+                    path.insertAfter(ESMODULE_TEMPLATE({EXPORTS: name}));
+                  }
+
+                  binding.path.setData('hasESModuleFlag', true);
+                }
+              }
             }
 
             // We need to wrap the module in a function when a require