TypeScript SDK: Config Decoding to Type Bug

[rawkode]

Hello!

• Vote on this issue by adding a 👍 reaction
• To contribute a fix for this issue, leave a comment (and link to your pull request, if you've opened one already)

Issue details

Pulumi doesn't error if the decoded config, from a stack.yaml, doesn't reflect the types being coerced to.

Steps to reproduce

# Stack.yaml
config:
  config-and-secrets:name: rawkode
  config-and-secrets:user:
    name: David Flanagan
    age: hello
    handles: rawkode

# index.ts
import * as pulumi from "@pulumi/pulumi";

interface MyConfig {
  name: string;
  age: number;
  handles: string[];
}

const config = new pulumi.Config();

const myConfig: MyConfig = config.requireObject<MyConfig>("user");

export const user = myConfig;

Expected: Error because YAML doesn't decode into interface type
Actual: Decodes fine:

Outputs:
    user: {
        age    : "hello"
        handles: "rawkode"
        name   : "David Flanagan"
    }

[pgavlin]

IIRC interface types have no runtime representation--they're only used by the TypeScript compiler--so I don't think that there's any way for us to actually check this when decoding. I agree that this is surprising, but I'm not sure how we can do better without some pretty substantial changes.