fix(lambda-nodejs): parcel in Docker fails on Windows

This is because the operations of [`path`](https://nodejs.org/api/path.html) are
OS specific. But for the container working directory and inside the container we
never want to use Windows style paths.

Fixes #8107

packages/@aws-cdk/aws-lambda-nodejs/lib/builder.ts

@@ -111,11 +111,11 @@ export class Builder {
         '-v', `${this.options.projectRoot}:${containerProjectRoot}`,
         '-v', `${path.resolve(this.options.outDir)}:${containerOutDir}`,
         ...(this.options.cacheDir ? ['-v', `${path.resolve(this.options.cacheDir)}:${containerCacheDir}`] : []),
-        '-w', path.dirname(containerEntryPath),
+        '-w', path.dirname(containerEntryPath).replace(/\\/g, '/'), // Always use POSIX paths in the container
         'parcel-bundler',
       ];
       const parcelArgs = [
-        'parcel', 'build', containerEntryPath,
+        'parcel', 'build', containerEntryPath.replace(/\\/g, '/'), // Always use POSIX paths in the container
         '--out-dir', containerOutDir,
         '--out-file', 'index.js',
         '--global', this.options.global,

packages/@aws-cdk/aws-lambda-nodejs/test/builder.test.ts

@@ -20,6 +20,10 @@ jest.mock('child_process', () => ({
   }),
 }));
 
+beforeEach(() => {
+  jest.clearAllMocks();
+});
+
 test('calls docker with the correct args', () => {
   const builder = new Builder({
     entry: '/project/folder/entry.ts',
@@ -58,6 +62,24 @@ test('calls docker with the correct args', () => {
   ]);
 });
 
+test('with Windows paths', () => {
+  const builder = new Builder({
+    entry: 'C:\\my-project\\lib\\entry.ts',
+    global: 'handler',
+    outDir: '/out-dir',
+    cacheDir: '/cache-dir',
+    nodeDockerTag: 'lts-alpine',
+    nodeVersion: '12',
+    projectRoot: 'C:\\my-project',
+  });
+  builder.build();
+
+  // docker run
+  expect(spawnSync).toHaveBeenCalledWith('docker', expect.arrayContaining([
+    'parcel', 'build', expect.stringContaining('/lib/entry.ts'),
+  ]));
+});
+
 test('throws in case of error', () => {
   const builder = new Builder({
     entry: '/project/folder/error',