When there's not enough Danger in your life

#TLDR: Peril

Peril is a hosted instance of Danger. So instead of running on CI, it will run on a server somewhere and can respond instantly to webhooks. This gives Danger the ability to respond instantly to PR changes, and to run on more than just PRs.

A lot of the information on Peril can be found on the Artsy blog: here

Today Peril is self-hosted via heroku. There is a walkthrough on the Peril repo: here. It’s still a pretty fast moving project ever 6 months into deployment so expect to maybe fix your own problem occasionally.

#Dangerfile implications

Two tricky problems in Peril today:

  • Async is weird.
  • Can’t do relative imports.

Today Peril runs by inline execution of a JavaScript script. This has a serious draw-back in that async behavior doesn’t work how you think it does. Here are some patterns for handling that.

  • Ignore Async. - A Dangerfile is a script, the non-blocking aspect of the node API can be ignored. E.g. use path.xSync instead of path.x

  • Scheduling - The Dangerfile DSL includes a function called schedule, this can handle either a promise or a function with a callback arg. For example using async/await:

import { schedule, danger } from "danger"

/// [... a bunch of functions]

schedule(async () => {
  const packageDiff = await danger.git.JSONDiffForFile("package.json")

In this case, the closure is queued up and Danger waits until all schedule functions/promises are finished before continuing, so make sure to not cause it to lock.

#Plugin implications

A plugin that runs on Peril will also have to handle the above if it uses async code. For some examples of this, see danger-plugin-spellcheck.

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