feat(core): include jsii runtime version in analytics

Add the jsii runtime version to the library version reporting
under "jsii-runtime". jsii runtime clients populate the JSII_AGENT
environment variable with this information (see aws/jsii#325).

If JSII_AGENT is not defined, we assume this is a node.js runtime
and include the node.js version.

Fixes #1258

packages/@aws-cdk/cdk/lib/app.ts

@@ -133,6 +133,9 @@ export class App extends Root {
       }
     }
 
+    // add jsii runtime version
+    libraries['jsii-runtime'] = getJsiiAgentVersion();
+
     return { libraries };
   }
 
@@ -205,3 +208,15 @@ function findNpmPackage(fileName: string): { name: string, version: string, priv
     return s;
   }
 }
+
+function getJsiiAgentVersion() {
+  let jsiiAgent = process.env.JSII_AGENT;
+
+  // if JSII_AGENT is not specified, we will assume this is a node.js runtime
+  // and plug in our node.js version
+  if (!jsiiAgent) {
+    jsiiAgent = `node.js/${process.version}`;
+  }
+
+  return jsiiAgent;
+}

packages/@aws-cdk/cdk/test/test.app.ts

@@ -17,6 +17,7 @@ function withApp(context: { [key: string]: any } | undefined, block: (app: App)
   }
 
   const app = new App();
+
   block(app);
 
   app.run();
@@ -266,6 +267,36 @@ export = {
 
     test.done();
   },
+
+  'runtime library versions'(test: Test) {
+    const response = withApp({}, app => {
+      const stack = new Stack(app, 'stack1');
+      new Resource(stack, 'MyResource', { type: 'Resource::Type' });
+    });
+
+    const libs = response.runtime.libraries;
+
+    const version = require('../package.json').version;
+    test.deepEqual(libs['@aws-cdk/cdk'], version);
+    test.deepEqual(libs['@aws-cdk/cx-api'], version);
+    test.deepEqual(libs['jsii-runtime'], `node.js/${process.version}`);
+    test.done();
+  },
+
+  'jsii-runtime version loaded from JSII_AGENT'(test: Test) {
+    process.env.JSII_AGENT = 'Java/1.2.3.4';
+
+    const response = withApp({}, app => {
+      const stack = new Stack(app, 'stack1');
+      new Resource(stack, 'MyResource', { type: 'Resource::Type' });
+    });
+
+    const libs = response.runtime.libraries;
+    test.deepEqual(libs['jsii-runtime'], `Java/1.2.3.4`);
+
+    delete process.env.JSII_AGENT;
+    test.done();
+  }
 };
 
 class MyConstruct extends Construct {