update-nightly.yml

# GitHub Actions CI job to update the Rust toolchain nightly versions used in `rust.yml` every 2 weeks.
# 
# Note: This particularly affects the fuzzing CI jobs that have to pin a nightly
#       release in order to not invalidate their caches on a daily basis.

name: Update Rust Nightly Version

on:
  schedule:
    - cron: '0 0 */14 * *'  # Every 2 weeks
  workflow_dispatch:        # Allows to trigger this CI job via GitHub UI

jobs:
  update-nightly:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@v4

      - name: Install the latest Rust nightly
        uses: dtolnay/rust-toolchain@nightly

      - name: Get the latest Rust nightly version
        run: |
          # Fetch the Rust version, e.g., rustc 1.81.0-nightly (eeb90cda1 2024-09-04)
          RUSTC_VERSION=$(rustc --version)
          echo "Rustc Version: $RUSTC_VERSION"

          # Extract the nightly version date (2024-09-04)
          LATEST_NIGHTLY=$(echo $RUSTC_VERSION | grep -Po '\d{4}-\d{2}-\d{2}')
          echo "LATEST_NIGHTLY=$LATEST_NIGHTLY" >> $GITHUB_ENV

      - name: Create new branch
        run: |
          git checkout -b update-rust-nightly-$LATEST_NIGHTLY
  
      - name: Update nightly version in CI workflow
        run: |
          FILE=".github/workflows/rust.yml"
          sed -i "s/toolchain: nightly-[0-9]\{4\}-[0-9]\{2\}-[0-9]\{2\}/toolchain: nightly-$LATEST_NIGHTLY/" $FILE

      - name: Commit changes
        run: |
          git config --local user.email "github-actions[bot]@users.noreply.github.com"
          git config --local user.name "github-actions[bot]"
          git add .github/workflows/rust.yml
          git commit -m "Update Rust nightly version to $LATEST_NIGHTLY"
  
      - name: Push changes to new branch
        run: |
          git push origin update-rust-nightly-$LATEST_NIGHTLY
  
      - name: Create Pull Request
        uses: peter-evans/create-pull-request@v7
        with:
          token: ${{ secrets.GITHUB_TOKEN }}
          branch: update-rust-nightly-$LATEST_NIGHTLY
          title: "CI: Update Rust nightly version to $LATEST_NIGHTLY"
          body: "This PR updates the Rust nightly version to $LATEST_NIGHTLY."
          base: main