From 7863ad329f42c67e847ab0b4c7b5a6e26a9e6940 Mon Sep 17 00:00:00 2001
From: shivlaks <32604953+shivlaks@users.noreply.github.com>
Date: Sun, 12 May 2019 23:55:45 -0700
Subject: [PATCH] refactor: L2 constructs should not use TypeScript unions
 (awslint:props-no-unions) (#2430) (#2509)

Adds a new awslint:props-no-unions rule which valides that props for L2 constructs do not use TypeScript unions. This is in accordance with the new AWS Construct Library guidelines.
---
 tools/awslint/lib/rules/construct.ts | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/tools/awslint/lib/rules/construct.ts b/tools/awslint/lib/rules/construct.ts
index fbb624d3c2a97..d1b50276dde9c 100644
--- a/tools/awslint/lib/rules/construct.ts
+++ b/tools/awslint/lib/rules/construct.ts
@@ -80,7 +80,7 @@ export class ConstructReflection {
     }
 
     if (!found.isInterfaceType()) {
-      throw new Error(`Expecrting props struct ${this.propsFqn} to be an interface`);
+      throw new Error(`Expecting props struct ${this.propsFqn} to be an interface`);
     }
 
     return found;
@@ -196,3 +196,19 @@ constructLinter.add({
     e.assert(!e.ctx.sys.tryFindFqn(baseFqn), baseFqn);
   }
 });
+
+constructLinter.add({
+  code: 'props-no-unions',
+  message: 'props should not use TypeScript unions',
+  eval: e => {
+    if (!e.ctx.propsType) { return; }
+    if (!e.ctx.hasPropsArgument) { return; }
+
+    // this rule only applies to L2 constructs
+    if (e.ctx.classType.name.startsWith('Cfn')) { return; }
+
+    for (const property of e.ctx.propsType.ownProperties) {
+      e.assert(!property.type.unionOfTypes, `${e.ctx.propsFqn}.${property.name}`);
+    }
+  }
+});
\ No newline at end of file