Returning certain values asynchronously causes Deno to fail to resolve promise

[manterfield]

Disclaimer: I could totally be doing something stupid here, but I can't see what.

Code that reproduces the issue for me:

// mod.ts

import { SlackAPI } from "https://deno.land/x/deno_slack_api@2.1.1/mod.ts";

const getClientAsync = async () => {
  // This return style always fails
  return SlackAPI("foo");
};

const getClientNestedAsync = async () => {
  // Nesting it in an object succeeds
  return { c: SlackAPI("foo") };
};

const getClient = () => {
  // Returning from a non-async function succeeds
  return SlackAPI("foo");
};

const run = async () => {
  console.log("Running");
  SlackAPI("foo");
  console.log("Got inline client");

  getClient();
  console.log("Got client from func");

  await getClientNestedAsync();
  console.log("Got client from nested async func");

  await getClientAsync();
  console.log("Got client from async func");
};

if (import.meta.main) {
  await run();
}

Run this with: deno run --allow-all mod.ts
Deno version: deno 1.44.4+86010be

If I run the above code, I get this output:

Running
Got inline client
Got client from func
Got client from nested async func
error: Top-level await promise never resolved
  await run();
  ^
    at <anonymous> (file:///Users/tm/Code/scratch/denobug/mod.ts:31:3)

I can swap the order of the getClient calls around - it always fails at the call to the async, non-nested return.

I first saw this behaviour in a worker, where it doesn't even show the error. It just seems to... stop. No error, nothing to show it has crashed - I have a lot going on in my worker though so can't rule out suppression.

I've also tested the returned client in all cases, and in all cases the client is functional/can make calls as expected. I've tried every odd variation I can think of, including assigning the client to a variable, using it first, then returning.

It seems that no matter what, if that specific value is returned from an async function, it crashes Deno and can not be caught.

[marvinhagemeister]

Smaller reproduction case:

import { SlackAPI } from "https://deno.land/x/deno_slack_api@2.1.1/mod.ts";
await SlackAPI("foo");

Error:

error: Top-level await promise never resolved
await SlackAPI("foo");
^
    at <anonymous> (file:///Users/marvinh/dev/test/deno-slack/main.ts:3:1)

[manterfield]

@marvinhagemeister Having dug into the Slack code more and taught myself a bit more about Proxies and nested promises, I'm not sure this is an issue with Deno.

The Slack code returns a Proxy with a getter. Deno checks if this is thenable, which is caught by the getter which in turn will eventually return a proxied function (so it appears as if it's a promise).

I suppose Deno could potentially help with making it clear what just happened, but I wonder if this is expected behaviour other than that.

[manterfield]

Slack code that's relevant is here: https://github.com/slackapi/deno-slack-api/blob/26fcdd6645c96998a0d3870d325edf476ae83716/src/api-proxy.ts#L46-L57

Just so you can judge if this is Deno acting properly in the face of that.