rust-cache-bust.yml

name: Rust Cache Bust

# The shared cargo build directory is cached as an extra `cache-directories`
# entry, and rust-cache prunes only workspace target dirs, never extra ones. So
# that entry is cached wholesale and accumulates artifacts for dependencies and
# profiles that no longer exist. Left alone it grows against the repository's
# 10GB Actions cache allowance and evicts entries that are still wanted.
#
# Dropping it on a schedule keeps that bounded. The next warm run rebuilds it
# from scratch, so the only cost is one cold Rust compile.
on:
  schedule:
    # 1st and 15th, so roughly fortnightly. Ahead of the Monday 06:00 warm run
    # rather than alongside it, and the warm workflow is dispatched below in any
    # case so a fresh cache does not wait for the next merge.
    - cron: "0 5 1,15 * *"
  workflow_dispatch:

permissions:
  actions: write

concurrency:
  group: rust-cache-bust
  cancel-in-progress: false

jobs:
  bust:
    name: Drop Rust caches
    runs-on: ubuntu-latest
    timeout-minutes: 10
    steps:
      - name: Delete Rust caches
        env:
          GH_TOKEN: ${{ github.token }}
          REPO: ${{ github.repository }}
        run: |
          set -euo pipefail
          # rust-cache prefixes every key it writes with `prefix-key`, which is
          # left at its default. Matching on that keeps Turbo and any other
          # cache in this repository untouched.
          ids="$(gh api --paginate "/repos/$REPO/actions/caches?per_page=100" \
            --jq '.actions_caches[] | select(.key | startswith("v0-rust")) | .id')"

          if [ -z "$ids" ]; then
            echo "No Rust caches to drop."
            echo "No Rust caches to drop." >> "$GITHUB_STEP_SUMMARY"
            exit 0
          fi

          count=0
          while read -r id; do
            [ -n "$id" ] || continue
            gh api -X DELETE "/repos/$REPO/actions/caches/$id"
            count=$((count + 1))
          done <<< "$ids"

          echo "Dropped $count Rust cache entries."
          echo "Dropped $count Rust cache entries." >> "$GITHUB_STEP_SUMMARY"

      - name: Request a fresh warm run
        env:
          GH_TOKEN: ${{ github.token }}
          REPO: ${{ github.repository }}
        run: |
          set -euo pipefail
          # Rebuild immediately rather than leaving every branch cold until the
          # next merge or the Monday schedule.
          gh workflow run turbo-cache-warm.yml --repo "$REPO" --ref main
          echo "Dispatched Turbo Cache Warm on main." >> "$GITHUB_STEP_SUMMARY"