From e074e1c1ad7c84870ef3c6fdd3d5950b3d45ffba Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=F0=9F=91=A8=F0=9F=8F=BC=E2=80=8D=F0=9F=92=BB=20Romain=20M?=
 =?UTF-8?q?arcadier-Muller?= <rmuller@amazon.com>
Date: Fri, 7 Jun 2019 15:43:49 +0200
Subject: [PATCH] feat(lambda): Expose $LATEST function version

Sometimes, one wants to create an `Alias` to the `$LATEST` version of a
`Function`, but this requires access to an `IVersion` representing that.
This features adds a `latestVersion` property to `IFunction` that offers
simple access to `$LATEST`. Prior to this, each user needing to access
this would have had to roll theiw own implementation of `IVersion`,
which is rather cumbersome.

Fixes #2776
---
 .../@aws-cdk/aws-lambda/lib/function-base.ts  | 24 ++++++++++++++
 packages/@aws-cdk/aws-lambda/lib/function.ts  |  2 +-
 .../@aws-cdk/aws-lambda/test/test.alias.ts    | 33 +++++++++++++++++++
 3 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/packages/@aws-cdk/aws-lambda/lib/function-base.ts b/packages/@aws-cdk/aws-lambda/lib/function-base.ts
index d569ff8cc9d26..a2979ae2ffcee 100644
--- a/packages/@aws-cdk/aws-lambda/lib/function-base.ts
+++ b/packages/@aws-cdk/aws-lambda/lib/function-base.ts
@@ -4,6 +4,7 @@ import iam = require('@aws-cdk/aws-iam');
 import { IResource, Resource } from '@aws-cdk/cdk';
 import { IEventSource } from './event-source';
 import { EventSourceMapping, EventSourceMappingOptions } from './event-source-mapping';
+import { IVersion } from './lambda-version';
 import { CfnPermission } from './lambda.generated';
 import { Permission } from './permission';
 
@@ -40,6 +41,11 @@ export interface IFunction extends IResource, ec2.IConnectable, iam.IGrantable {
    */
   readonly isBoundToVpc: boolean;
 
+  /**
+   * The `$LATEST` version of this function.
+   */
+  readonly latestVersion: IVersion;
+
   /**
    * Adds an event source that maps to this AWS Lambda function.
    * @param id construct ID
@@ -139,6 +145,11 @@ export abstract class FunctionBase extends Resource implements IFunction  {
    */
   public abstract readonly role?: iam.IRole;
 
+  /**
+   * The $LATEST version of this function.
+   */
+  public readonly latestVersion: IVersion = new LatestVersion(this);
+
   /**
    * Whether the addPermission() call adds any permissions
    *
@@ -277,3 +288,16 @@ export abstract class FunctionBase extends Resource implements IFunction  {
       'Supported: AccountPrincipal, ServicePrincipal');
   }
 }
+
+/**
+ * The $LATEST version of a function, useful when attempting to create aliases.
+ */
+class LatestVersion extends Resource implements IVersion {
+  public readonly lambda: IFunction;
+  public readonly version = '$LATEST';
+
+  constructor(lambda: FunctionBase) {
+    super(lambda, '$LATEST');
+    this.lambda = lambda;
+  }
+}
diff --git a/packages/@aws-cdk/aws-lambda/lib/function.ts b/packages/@aws-cdk/aws-lambda/lib/function.ts
index e7aa0cee86089..6beb1fb72febe 100644
--- a/packages/@aws-cdk/aws-lambda/lib/function.ts
+++ b/packages/@aws-cdk/aws-lambda/lib/function.ts
@@ -241,7 +241,7 @@ export class Function extends FunctionBase {
 
   /**
    * Creates a Lambda function object which represents a function not defined
-   * within this stack.
+   * within this stwack.
    *
    *    Lambda.import(this, 'MyImportedFunction', { lambdaArn: new LambdaArn('arn:aws:...') });
    *
diff --git a/packages/@aws-cdk/aws-lambda/test/test.alias.ts b/packages/@aws-cdk/aws-lambda/test/test.alias.ts
index f3208e37f0d39..f4e404308098f 100644
--- a/packages/@aws-cdk/aws-lambda/test/test.alias.ts
+++ b/packages/@aws-cdk/aws-lambda/test/test.alias.ts
@@ -40,6 +40,39 @@ export = {
     test.done();
   },
 
+  'can create an alias to $LATEST'(test: Test): void {
+    const stack = new Stack();
+    const fn = new lambda.Function(stack, 'MyLambda', {
+      code: new lambda.InlineCode('hello()'),
+      handler: 'index.hello',
+      runtime: lambda.Runtime.NodeJS810,
+    });
+
+    new lambda.Alias(stack, 'Alias', {
+      aliasName: 'latest',
+      version: fn.latestVersion,
+    });
+
+    expect(stack).to(beASupersetOfTemplate({
+      MyLambdaVersion16CDE3C40: {
+        Type: "AWS::Lambda::Version",
+        Properties: {
+          FunctionName: { Ref: "MyLambdaCCE802FB" }
+        }
+        },
+        Alias325C5727: {
+        Type: "AWS::Lambda::Alias",
+        Properties: {
+          FunctionName: { Ref: "MyLambdaCCE802FB" },
+          FunctionVersion: '$LATEST',
+          Name: "latest"
+        }
+        }
+    }));
+
+    test.done();
+  },
+
   'can use newVersion to create a new Version'(test: Test) {
     const stack = new Stack();
     const fn = new lambda.Function(stack, 'MyLambda', {