Hi, I'm trying to log a message during a stack transformation. Here's a dummy Pulumi program:

"use strict";
const pulumi = require("@pulumi/pulumi");
const aws = require("@pulumi/aws");

pulumi.runtime.registerStackTransformation((args) => {
  pulumi.log.warn("dummy", args.resource);
  return undefined;
});

const bucket = new aws.s3.BucketV2("mybucket");

However, when I do

pulumi preview

(just to test it out), I get an error:

Previewing update (dev):
     Type                 Name         Plan       Info
 +   pulumi:pulumi:Stack  test-js-dev  create     1 error

Diagnostics:
  pulumi:pulumi:Stack (test-js-dev):
    error: Running program '/home/xxx/index.js' failed with an unhandled exception:
    TypeError: Cannot read properties of undefined (reading 'promise')
        at log (/home/xxx/node_modules/@pulumi/log/index.ts:103:48)
        at Object.warn (/home/xxx/node_modules/@pulumi/log/index.ts:70:16)
        at /home/xxx/index.js:6:14
        at new Resource (/home/xxx/node_modules/@pulumi/resource.ts:410:26)
        at new CustomResource (/home/xxx/node_modules/@pulumi/resource.ts:976:9)
        at new BucketV2 (/home/xxx/node_modules/@pulumi/s3/bucketV2.ts:295:9)
        at Object.<anonymous> (/home/xxx/index.js:10:16)
        at Module._compile (node:internal/modules/cjs/loader:1369:14)
        at Object.Module._extensions..js (node:internal/modules/cjs/loader:1427:10)
        at Module.load (node:internal/modules/cjs/loader:1206:32)

Am I doing anything wrong or should I consider this a bug? The same thing works in Python without a problem.

Are you sure it's the stack transformation that's at fault? Other than the

return undefined

(which is technically wrong since that's a void function), your code is good. You could try using

console.log

to see if the problem is in

pulumi.log

, but I think that's unlikely. What is on line 103 of index.ts? Is there an object called promise whose value is undefined?

Yeah I’m pretty sure there’s a problem in the log function. See the issue I opened - https://github.com/pulumi/pulumi/issues/16654. Anyway thanks for the note about return, will take a look.

Yes it's fine, JS doesn't complain about returning values from void functions. After all, it's JS, so it's completely untyped, even void doesn't mean anything :)

The thing is, the function that's returning

undefined

actually can return is as per the link a provided. It can return

ResourceTransformationResult | undefined

.

I'm looking at different code, I guess. I see

* parents walking from the resource up to the stack.

. In my editor, the intellisense is showing only that it's a void function. Odd.

Look again where I return undefined 🙂