Add bundler integration tests verifying EXPORT_ES6 output has no require()

Add two tests that verify EXPORT_ES6 output is valid ESM and works with
bundlers:

- test_webpack_esm_output_clean: Compiles with EXPORT_ES6 and default
  environment (web+node), then builds with webpack. On main, webpack
  hard-fails because it cannot resolve 'node:module' (used by emscripten's
  createRequire polyfill). This breaks any webpack/Next.js/Nuxt project.

- test_vite_esm_output_clean: Compiles with EXPORT_ES6 and default
  environment, then builds with vite. On main, vite externalizes
  'node:module' for browser compatibility, emitting a warning. The
  resulting bundle contains code referencing unavailable node modules.

These tests are expected to fail on main and pass after eliminating
require() from EXPORT_ES6 output.

Author: Bartek Wrona

test/test_other.py

@@ -14991,6 +14991,43 @@ def test_rollup(self):
     shutil.copy('hello.wasm', 'dist/')
     self.assertContained('Hello, world!', self.run_js('dist/bundle.mjs'))
 
+  @crossplatform
+  @requires_dev_dependency('webpack')
+  def test_webpack_esm_output_clean(self):
+    """Verify webpack can build EXPORT_ES6 output without errors.
+
+    When emscripten generates require() in EXPORT_ES6 output (via
+    createRequire from 'node:module'), webpack fails with:
+      UnhandledSchemeError: Reading from "node:module" is not handled by plugins
+    This breaks any webpack/Next.js/Nuxt project using emscripten's ESM output.
+    """
+    copytree(test_file('webpack_es6'), '.')
+    # Compile with default environment (web+node). On main, this generates
+    # 'import { createRequire } from "node:module"' and require() calls for
+    # node support, which webpack cannot resolve for web targets.
+    self.run_process([EMCC, test_file('hello_world.c'), '-sEXPORT_ES6', '-sEXIT_RUNTIME',
+                      '-sMODULARIZE', '-o', 'src/hello.mjs'])
+    self.run_process(shared.get_npm_cmd('webpack') + ['--mode=development', '--no-devtool'])
+
+  @crossplatform
+  @requires_dev_dependency('vite')
+  def test_vite_esm_output_clean(self):
+    """Verify vite bundles EXPORT_ES6 output without require() or externalizing.
+
+    When emscripten generates require() in EXPORT_ES6 output, vite externalizes
+    the node modules for browser compatibility, emitting a warning. The resulting
+    bundle contains code that references modules unavailable in browsers.
+    """
+    copytree(test_file('vite'), '.')
+    # Compile with default environment (web+node). On main, this generates
+    # require() calls for node support which vite externalizes but leaves
+    # as require() in the bundle output.
+    self.run_process([EMCC, test_file('hello_world.c'), '-sEXPORT_ES6', '-sEXIT_RUNTIME',
+                      '-sMODULARIZE', '-o', 'hello.mjs'])
+    # vite.config.js turns externalization warnings into errors, so vite
+    # will fail with non-zero exit code if require() appears in ESM output.
+    self.run_process(shared.get_npm_cmd('vite') + ['build'])
+
   def test_rlimit(self):
     self.do_other_test('test_rlimit.c', cflags=['-O1'])
 

test/vite/vite.config.js

@@ -1,3 +1,15 @@
 export default {
   base: './',
+  build: {
+    rollupOptions: {
+      onwarn(warning, defaultHandler) {
+        // Treat externalized-for-browser-compatibility warnings as errors.
+        // This catches require() in ESM output that vite silently externalizes.
+        if (warning.message && warning.message.includes('externalized for browser compatibility')) {
+          throw new Error(warning.message);
+        }
+        defaultHandler(warning);
+      },
+    },
+  },
 }