evanw/node-source-map-support

Node 12 "async" annotations are lost when using this package

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#243 opened on May 28, 2019

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bughelp wanted

Description

Node 12 added some limited support for async stack traces. I'm impressed that this package supports them, but it removes a useful annotation from them:

Given this file:

function p() {
  return new Promise(resolve => setTimeout(resolve, 0))
}

async function f() {
  await p()
  throw Error("")
}

async function main() {
  await f()
}

main()
  .catch(console.error)

The stack traces without registering source-map-support is:

Error
    at f (/private/tmp/async-stack-traces/index.js:9:9)
    at async main (/private/tmp/async-stack-traces/index.js:13:3)

With source-map-support registered is:

Error:
    at f (/private/tmp/async-stack-traces/index.js:9:9)
    at main (/private/tmp/async-stack-traces/index.js:13:3)

I think the async annotation there is useful, as this stack trace is not the actual one as seen by v8, but an augmented one. This augmentation doesn't always work, and it would be surprising to the user if they look like normal stack traces.

Contributor guide

Tech stack
javascriptnodejs
Domain
backendobservability
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Node.js async stack tracessource map mapping concept
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the source map support source code, specifically the hook for async stack traces. Look at how it processes stack frames and see if it filters out the 'async' annotation. Check for any existing discussion or comments in the issue about preserving the annotation. The fix likely involves modifying the stack trace parsing to retain the async keyword.