labeller.yaml

name: Labeller
on:
  pull_request_target:
    types:
      - auto_merge_disabled
      - auto_merge_enabled
      - opened
      - synchronize
      - reopened
  
permissions: {}

jobs:
  add_remove_labels:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write

    steps:
      - name: Harden Runner
        uses: step-security/harden-runner@17d0e2bd7d51742c71671bd19fa12bdc9d40a3d6 # v2.8.1
        with:
          disable-sudo: true
          egress-policy: block
          allowed-endpoints: >
            api.github.com:443

      - name: Add auto-merge label
        if: github.event.action == 'auto_merge_enabled'
        run: gh pr edit "$PR_URL" --add-label "auto-merge"
        env:
          PR_URL: ${{github.event.pull_request.html_url}}
          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}

      - name: Remove auto-merge label
        if: github.event.action == 'auto_merge_disabled'
        run: gh pr edit "$PR_URL" --remove-label "auto-merge"
        env:
          PR_URL: ${{github.event.pull_request.html_url}}
          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}

      - name: Set userscript-specific labels
        if: contains(fromJSON('["opened", "synchronize", "reopened"]'), github.event.action)
        env:
          GH_REPO: ${{github.repository}}
          PR_SHA: ${{github.sha}}
          PR_NUMBER: ${{github.event.number}}
          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
        run: |
          # Determine what userscripts are defined at the PR HEAD SHA. Each
          # userscript name is also the name of a label.
          scriptNames=$(
              gh api \
                  -H "Accept: application/vnd.github.object" \
                  -H "X-GitHub-Api-Version: 2022-11-28" \
                  "/repos/{owner}/{repo}/contents/scripts?ref=${PR_SHA}" \
                  --jq '.entries | map(select(.type == "dir")) | .[].name'
          )
          echo "Known userscripts: ${scriptNames//$'\n'/, }"
          if [ -z "${scriptNames}" ]; then exit; fi

          # utility functions to join arrrays with an arbitrary delimiter, and to print
          join() { local delim=$1 out; shift; printf -v out "%s$delim" "$@"; echo "${out%"${delim}"}"; }
          echoArr() { local msg=$1; shift; echo "$msg: $(join ', ' "$@")"; }

          # Determine the existing labels on this PR
          declare -A existingLabels=()
          for label in $(gh pr view "$PR_NUMBER" --json labels --jq '.labels[].name'); do
              existingLabels[$label]=1
          done
          echoArr 'Existing PR labels' "${!existingLabels[@]}"

          # Determine what scripts this PR touched, based on what files it changed
          declare -A touchedScripts=()
          for touched in $(
              gh api \
                  -H "Accept: application/vnd.github+json" \
                  -H "X-GitHub-Api-Version: 2022-11-28" \
                  "/repos/{owner}/{repo}/pulls/${PR_NUMBER}/files" \
                  --jq 'map(.filename | match("^scripts/([^/]+)/") | .captures[0].string) | unique | .[]'
          ); do
              touchedScripts[$touched]=1
          done
          echoArr 'Touched scripts' "${!touchedScripts[@]}"

          # if there are changes for a userscript, add the matching label. Otherwise, if
          # there is an existing label for a userscript the PR no longer touches, remove
          # it again.
          declare -A missingLabels=() surplusLabels=()
          for scriptName in $scriptNames; do
              if [[ ${touchedScripts["$scriptName"]} && ! ${existingLabels[$scriptName]} ]]; then
                  missingLabels[$scriptName]=1
              elif [[ ! ${touchedScripts["$scriptName"]} && ${existingLabels[$scriptName]} ]]; then
                  surplusLabels[$scriptName]=1
              fi
          done
          declare -a args=()
          if [ "${#missingLabels[*]}" -gt 0 ]; then
              echoArr 'Adding labels to PR' "${!missingLabels[@]}"
              args+=("--add-label" "$(join , "${!missingLabels[@]}")")
          fi
          if [ "${#surplusLabels[*]}" -gt 0 ]; then
              echoArr 'Removing labels from PR' "${!surplusLabels[@]}"
              args+=("--remove-label" "$(join , "${!surplusLabels[@]}")")
          fi
          if [ "${#args[*]}" -gt 0 ]; then
              gh pr edit "$PR_NUMBER" "${args[@]}"
          fi