refactor: L2 constructs should not use TypeScript unions (awslint:pro…

…ps-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

@@ -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}`);
+ }
+ }
+});