How to get the PR (Pull Request) number

I just started using Pulumi and I checked a lot of docs, a lot of repos and just can't find how can I get the PR (Pull Request) number to be used.

I know that Pulumi generates an Environment variable/output/config named ci.pr.number.

I would like to use that number to create an Azure Resource Group like rg-{appname}-{environment}-{pr number}. For example, rg-myapp-dev-022.

Last attempt was this one:

var config = new Pulumi.Config();
var prNumber = config.Require("ci.pr.number");

Thanks in advance!

PS: I am using GitHub Actions to run Pulumi.

If you want to use the PR number in your Pulumi program at runtime, you'll need to read it from the GitHub Actions runtime environment somehow; Pulumi doesn't write it to your stack configuration. GitHub Actions exposes a Context API that makes this fairly straightforward, assuming you have access to make a small addition to the workflow itself. Here's an example of a PR workflow containing a step that pulls the PR number into an environment variable (PR_NUMBER) and then uses it in a couple of scripts, first Bash, then Node.js:

name: My Workflow
on:
  pull_request:
    branches:
      - master
jobs:
  build:
    name: Do Things
    runs-on: ubuntu-18.04
    steps:
      - name: Install Node
        uses: actions/setup-node@v1
        with:
          node-version: '14.x'

      - name: Check out branch
        uses: actions/checkout@v2

      - name: Read the PR number
        env:
          PR_NUMBER: ${{ github.event.number }}
        run: |
          echo "From Bash: ${PR_NUMBER}"
          node -e "console.log('From Node:', process.env.PR_NUMBER);"

I don't have a way to verify the relevant C# handy, but it looks like you should be able to do this with System.Environment.GetEnvironmentVariable("PR_NUMBER").

https://docs.microsoft.com/en-us/dotnet/api/system.environment.getenvironmentvariable