fix(toolkit): ignore hidden files for 'cdk init' (#1766)

Don't block 'cdk init' on the presence of files start with '.'.

In particular, don't care about the presence of a '.git' directory.

Fixes #1758.

packages/aws-cdk/lib/init.ts

@@ -208,7 +208,7 @@ async function initializeProject(template: InitTemplate, language: string, canUs
 
 async function assertIsEmptyDirectory() {
   const files = await fs.readdir(process.cwd());
-  if (files.length !== 0) {
+  if (files.filter(f => !f.startsWith('.')).length !== 0) {
     throw new Error('`cdk init` cannot be run in a non-empty directory!');
   }
 }

packages/aws-cdk/test/test.init.ts

@@ -45,6 +45,18 @@ export = {
     test.equal(true, await fs.pathExists('package.json'));
     test.equal(true, await fs.pathExists('bin'));
 
+    test.done();
+  },
+
+  async 'git directory does not throw off the initer!'(test: Test) {
+    fs.mkdirSync('.git');
+
+    await cliInit('app', 'typescript', false);
+
+    // Check that package.json and bin/ got created in the current directory
+    test.equal(true, await fs.pathExists('package.json'));
+    test.equal(true, await fs.pathExists('bin'));
+
     test.done();
   }
 };