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

@@ -15028,6 +15028,44 @@ 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'])
+    proc = self.run_process(shared.get_npm_cmd('vite') + ['build'], stderr=PIPE, stdout=PIPE)
+    # vite should not need to externalize any node modules. When it does,
+    # it means the input contains require() which is invalid in ESM.
+    self.assertNotContained('externalized for browser compatibility', proc.stdout + proc.stderr)
+
   def test_rlimit(self):
     self.do_other_test('test_rlimit.c', cflags=['-O1'])