fix(@ngtools/webpack): barrel files fail on windows

Fixes #12035

packages/ngtools/webpack/src/entry_resolver.ts

@@ -5,8 +5,8 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-import * as fs from 'fs';
-import { join } from 'path';
+
+import { Path, join } from '@angular-devkit/core';
 import * as ts from 'typescript';
 import { TypeScriptFileRefactor } from './refactor';
 
@@ -54,9 +54,10 @@ function _recursiveSymbolExportLookup(refactor: TypeScriptFileRefactor,
     for (const specifier of binding.elements) {
       if (specifier.name.text == symbolName) {
         // If it's a directory, load its index and recursively lookup.
-        if (fs.statSync(module).isDirectory()) {
-          const indexModule = join(module, 'index.ts');
-          if (fs.existsSync(indexModule)) {
+        // If it's a file it will return false
+        if (host.directoryExists && host.directoryExists(module)) {
+          const indexModule = join(module as Path, 'index.ts');
+          if (host.fileExists(indexModule)) {
             const indexRefactor = new TypeScriptFileRefactor(indexModule, host, program);
             const maybeModule = _recursiveSymbolExportLookup(
               indexRefactor, symbolName, host, program);

tests/legacy-cli/e2e/tests/build/barrel-file.ts

@@ -0,0 +1,8 @@
+import { replaceInFile, writeFile } from '../../utils/fs';
+import { ng } from '../../utils/process';
+
+export default async function() {
+  await writeFile('src/app/index.ts', `export { AppModule } from './app.module';`);
+  await replaceInFile('src/main.ts', './app/app.module', './app');
+  await ng('build');
+}