haskell.yml

name: Haskell CI

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

# INFO: The following configuration block ensures that only one build runs per branch,
# which may be desirable for projects with a costly build process.
# Remove this block from the CI workflow to let each CI job run to completion.
concurrency:
  group: build-${{ github.ref }}
  cancel-in-progress: true

# INFO: The caching strategy was created following this post https://github.com/commercialhaskell/stack/issues/5754#issuecomment-1696156869
env:
  #-- increment this if you think cache of GHC installation needs cold rebuild
  MANUAL_CACHE_RESET_COMPILER: v0
  #-- increment this if you think cache of .stack-work needs cold rebuild
  MANUAL_CACHE_RESET_PRODUCTS: v0
  #-- increment this to force-rebuild the cache of dependency packages
  MANUAL_CACHE_RESET_TESTDEPS: v0
  #-- should never be needed, as stackage snapshots are immutable
  # MANUAL_CACHE_RESET_SNAPSHOT: v0

jobs:
  build-haskell:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        versions:
          - { lts: "22.27", ghc: "9.6.5" }

    steps:
      - name: Cache GHC installation
        uses: actions/cache@v4
        id: ghcup
        env:
          MANUAL_RESET: ${{ env.MANUAL_CACHE_RESET_COMPILER }}
        with:
          path: |
            ~/.ghcup/bin/*
            ~/.ghcup/cache/*
            ~/.ghcup/config.yaml
            ~/.ghcup/ghc/${{ matrix.versions.ghc }}
          key: CI-ghcup-${{ env.MANUAL_RESET }}--${{ matrix.versions.ghc }}

      - uses: haskell-actions/setup@v2
        if: steps.ghcup.outputs.cache-hit != 'true'
        with:
          ghc-version: ${{ matrix.versions.ghc }}
          enable-stack: true
          stack-version: 'latest'
          cabal-update: false

      - name: Cache Pantry (Stackage package index)
        id: pantry
        uses: actions/cache@v4
        with:
          path: ~/.stack/pantry
          key: CI-pantry-${{ matrix.versions.lts }}
  
      - name: Recompute Stackage package index
        if: steps.pantry.outputs.cache-hit != 'true'
        run: stack update # populates ~/.stack/pantry

      - name: Cache Haskell dependencies
        uses: actions/cache@v4
        env:
          MANUAL_RESET: ${{ env.MANUAL_CACHE_RESET_TESTDEPS }}
        with:
          #-- NOTE no, shouldn't cache the entire ~/.stack -- that'd be bad. just these 2:
          path: |
            ~/.stack/stack.sqlite3
            ~/.stack/snapshots
          #-- NOTE the caching key structure:
          #--   * fixed ID string -- to indicate scope & purpose, descriptive;
          #--   * manual reset -- on top level, stupid simple manual override;
          #--   * resolver version -- helps maintain sleek size of the cache;
          #--   * lockfile hashsum -- as invalidation trigger of the correct granularity.
          #-- Since this cache only stores built *dependency packages* (not project code!),
          #-- we should invalidate/reupload it on each change to the dependency forest (≈lockfile).
          #--
          #-- All this decides when cache gets REBUILT (invalidated & recreated):
          key: CI-testdeps-${{ env.MANUAL_RESET }}--${{ matrix.versions.lts }}--${{ hashFiles('stack-${{ matrix.versions.ghc }}.yaml.lock') }}
          #-- All this adds fallbacks to UNPACK stale cache copies, prefix-matched:
          restore-keys: |
            CI-testdeps-${{ env.MANUAL_RESET }}--${{ matrix.versions.lts }}--
            CI-testdeps-${{ env.MANUAL_RESET }}--

      - name: Clone project
        uses: actions/checkout@v2

      - name: Cache per-branch Haskell project buildstate
        uses: actions/cache@v4
        env:
          MANUAL_RESET: ${{ env.MANUAL_CACHE_RESET_PRODUCTS }}
        with:
          #-- I wasn't able to find the non absolute path and I decided to set the full path. This is britle
          path: /home/runner/work/gogol/gogol/.stack-work
          key: CI-builddir-${{ env.MANUAL_RESET }}--${{ matrix.versions.ghc }}--${{ github.head_ref }}

      - name: Install dependencies
        run: stack build --system-ghc --stack-yaml stack-${{ matrix.versions.ghc }}.yaml --only-dependencies

      - name: Run tests
        run: stack test --system-ghc --stack-yaml stack-${{ matrix.versions.ghc }}.yaml

      - name: Build
        run: stack build --system-ghc --stack-yaml stack-${{ matrix.versions.ghc }}.yaml