feat(events): support event bus for rule (aws#4839)

* feat(cfnspec): update CloudFormation spec to 7.3.0

* feat(events): support event bus for rule

Adds an `eventBus` prop to the `Rule` construct.

packages/@aws-cdk/aws-events/lib/rule.ts

@@ -1,4 +1,5 @@
 import { App, Construct, Lazy, Resource, Stack, Token } from '@aws-cdk/core';
+import { IEventBus } from './event-bus';
 import { EventPattern } from './event-pattern';
 import { CfnEventBusPolicy, CfnRule } from './events.generated';
 import { IRule } from './rule-ref';
@@ -68,6 +69,13 @@ export interface RuleProps {
    * @default - No targets.
    */
   readonly targets?: IRuleTarget[];
+
+  /**
+   * The event bus to associate with this rule.
+   *
+   * @default - The default event bus.
+   */
+  readonly eventBus?: IEventBus;
 }
 
 /**
@@ -100,15 +108,22 @@ export class Rule extends Resource implements IRule {
     super(scope, id, {
       physicalName: props.ruleName,
     });
+
+    if (props.eventBus && props.schedule) {
+      throw new Error(`Cannot associate rule with 'eventBus' when using 'schedule'`);
+    }
+
     this.description = props.description;
+    this.scheduleExpression = props.schedule && props.schedule.expressionString;
 
     const resource = new CfnRule(this, 'Resource', {
       name: this.physicalName,
       description: this.description,
       state: props.enabled == null ? 'ENABLED' : (props.enabled ? 'ENABLED' : 'DISABLED'),
-      scheduleExpression: Lazy.stringValue({ produce: () => this.scheduleExpression }),
+      scheduleExpression: this.scheduleExpression,
       eventPattern: Lazy.anyValue({ produce: () => this._renderEventPattern() }),
       targets: Lazy.anyValue({ produce: () => this.renderTargets() }),
+      eventBusName: props.eventBus && props.eventBus.eventBusName,
     });
 
     this.ruleArn = this.getResourceArnAttribute(resource.attrArn, {
@@ -119,7 +134,6 @@ export class Rule extends Resource implements IRule {
     this.ruleName = this.getResourceNameAttribute(resource.ref);
 
     this.addEventPattern(props.eventPattern);
-    this.scheduleExpression = props.schedule && props.schedule.expressionString;
 
     for (const target of props.targets || []) {
       this.addTarget(target);
@@ -346,10 +360,10 @@ export class Rule extends Resource implements IRule {
 
   protected validate() {
     if (Object.keys(this.eventPattern).length === 0 && !this.scheduleExpression) {
-      return [ `Either 'eventPattern' or 'schedule' must be defined` ];
+      return [`Either 'eventPattern' or 'schedule' must be defined`];
     }
 
-    return [ ];
+    return [];
   }
 
   private renderTargets() {

packages/@aws-cdk/aws-events/test/test.rule.ts

@@ -4,7 +4,7 @@ import { ServicePrincipal } from '@aws-cdk/aws-iam';
 import cdk = require('@aws-cdk/core');
 import { CfnResource, Stack } from '@aws-cdk/core';
 import { Test } from 'nodeunit';
-import { EventField, IRule, IRuleTarget, RuleTargetConfig, RuleTargetInput, Schedule } from '../lib';
+import { EventBus, EventField, IRule, IRuleTarget, RuleTargetConfig, RuleTargetInput, Schedule } from '../lib';
 import { Rule } from '../lib/rule';
 
 // tslint:disable:object-literal-key-quotes
@@ -490,6 +490,43 @@ export = {
     test.done();
   },
 
+  'associate rule with event bus'(test: Test) {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const eventBus = new EventBus(stack, 'EventBus');
+
+    // WHEN
+    new Rule(stack, 'MyRule', {
+      eventPattern: {
+        detail: ['detail']
+      },
+      eventBus,
+    });
+
+    // THEN
+    expect(stack).to(haveResource('AWS::Events::Rule', {
+      EventBusName: {
+        Ref: 'EventBus7B8748AA'
+      }
+    }));
+
+    test.done();
+  },
+
+  'throws with eventBus and schedule'(test: Test) {
+    // GIVEN
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'MyStack');
+    const eventBus = new EventBus(stack, 'EventBus');
+
+    // THEN
+    test.throws(() => new Rule(stack, 'MyRule', {
+      schedule: Schedule.rate(cdk.Duration.minutes(10)),
+      eventBus,
+    }), /Cannot associate rule with 'eventBus' when using 'schedule'/);
+    test.done();
+  },
+
   'for cross-account targets': {
     'requires that the source stack specify a concrete account'(test: Test) {
       const app = new cdk.App();