# Checks pkgs/by-name (see pkgs/by-name/README.md)
# using the nixpkgs-check-by-name tool (see https://github.com/NixOS/nixpkgs-check-by-name)
#
# When you make changes to this workflow, also update pkgs/test/check-by-name/run-local.sh adequately
name: Check pkgs/by-name

on:
  # Using pull_request_target instead of pull_request avoids having to approve first time contributors
  pull_request_target:
    # This workflow depends on the base branch of the PR,
    # but changing the base branch is not included in the default trigger events,
    # which would be `opened`, `synchronize` or `reopened`.
    # Instead it causes an `edited` event, so we need to add it explicitly here
    # While `edited` is also triggered when the PR title/body is changed,
    # this PR action is fairly quick, and PR's don't get edited that often,
    # so it shouldn't be a problem
    types: [opened, synchronize, reopened, edited]

permissions:
  # We need this permission to cancel the workflow run if there's a merge conflict
  actions: write

jobs:
  check:
    # This needs to be x86_64-linux, because we depend on the tooling being pre-built in the GitHub releases
    runs-on: ubuntu-latest
    # This should take 1 minute at most, but let's be generous.
    # The default of 6 hours is definitely too long
    timeout-minutes: 10
    steps:
      # This step has to be in this file,
      # because it's needed to determine which revision of the repository to fetch,
      # and we can only use other files from the repository once it's fetched.
      - name: Resolving the merge commit
        env:
          GH_TOKEN: ${{ github.token }}
        run: |
          # This checks for mergeability of a pull request as recommended in
          # https://docs.github.com/en/rest/guides/using-the-rest-api-to-interact-with-your-git-database?apiVersion=2022-11-28#checking-mergeability-of-pull-requests

          # Retry the API query this many times
          retryCount=3
          # Start with 5 seconds, but double every retry
          retryInterval=5
          while true; do
            echo "Checking whether the pull request can be merged"
            prInfo=$(gh api \
              -H "Accept: application/vnd.github+json" \
              -H "X-GitHub-Api-Version: 2022-11-28" \
              /repos/"$GITHUB_REPOSITORY"/pulls/${{ github.event.pull_request.number }})
            mergeable=$(jq -r .mergeable <<< "$prInfo")
            mergedSha=$(jq -r .merge_commit_sha <<< "$prInfo")

            if [[ "$mergeable" == "null" ]]; then
              if (( retryCount == 0 )); then
                echo "Not retrying anymore, probably GitHub is having internal issues"
                exit 1
              else
                (( retryCount -= 1 )) || true

                # null indicates that GitHub is still computing whether it's mergeable
                # Wait a couple seconds before trying again
                echo "GitHub is still computing whether this PR can be merged, waiting $retryInterval seconds before trying again ($retryCount retries left)"
                sleep "$retryInterval"

                (( retryInterval *= 2 )) || true
              fi
            else
              break
            fi
          done

          if [[ "$mergeable" == "true" ]]; then
            echo "The PR can be merged, checking the merge commit $mergedSha"
          else
            echo "The PR cannot be merged, it has a merge conflict, cancelling the workflow.."
            gh api \
              --method POST \
              -H "Accept: application/vnd.github+json" \
              -H "X-GitHub-Api-Version: 2022-11-28" \
              /repos/"$GITHUB_REPOSITORY"/actions/runs/"$GITHUB_RUN_ID"/cancel
            sleep 60
            # If it's still not canceled after a minute, something probably went wrong, just exit
            exit 1
          fi
          echo "mergedSha=$mergedSha" >> "$GITHUB_ENV"
      - uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
        with:
          # pull_request_target checks out the base branch by default
          ref: ${{ env.mergedSha }}
          # Fetches the merge commit and its parents
          fetch-depth: 2
      - name: Checking out base branch
        run: |
          base=$(mktemp -d)
          git worktree add "$base" "$(git rev-parse HEAD^1)"
          echo "base=$base" >> "$GITHUB_ENV"
      - uses: cachix/install-nix-action@8887e596b4ee1134dae06b98d573bd674693f47c # v26
      - name: Fetching the pinned tool
        # Update the pinned version using pkgs/test/check-by-name/update-pinned-tool.sh
        run: |
          # The pinned version of the tooling to use
          toolVersion=$(<pkgs/test/check-by-name/pinned-version.txt)
          # Fetch the x86_64-linux-specific release artifact containing the Gzipped NAR of the pre-built tool
          toolPath=$(curl -sSfL https://github.com/NixOS/nixpkgs-check-by-name/releases/download/"$toolVersion"/x86_64-linux.nar.gz \
            | gzip -cd | nix-store --import | tail -1)
          # Adds a result symlink as a GC root
          nix-store --realise "$toolPath" --add-root result
      - name: Running nixpkgs-check-by-name
        run: |
          if result/bin/nixpkgs-check-by-name --base "$base" .; then
            exit 0
          else
            exitCode=$?
            echo "To run locally: ./maintainers/scripts/check-by-name.sh $GITHUB_BASE_REF https://github.com/$GITHUB_REPOSITORY.git"
            exit "$exitCode"
          fi
