Add CI

Shamelessly stolen from https://github.com/DigitalBrains1/prettyprinter-interp

.ci/all_check.py

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+#!/usr/bin/env python3
+"""
+Makes sure:
+ * All jobs are listed in the 'all' job
+ * Only existing tests are listed
+"""
+
+import sys
+import yaml
+
+CI_PATH = '.github/workflows/ci.yaml'
+ALL_TEST = 'all'
+
+
+def main():
+    ci_yaml_fp = open(CI_PATH, 'r')
+    ci_yaml_parsed = yaml.load(ci_yaml_fp, Loader=yaml.FullLoader)
+
+    all_jobs = set(ci_yaml_parsed['jobs'].keys()) - {ALL_TEST}
+    all_needs = set(ci_yaml_parsed['jobs'][ALL_TEST]['needs'])
+
+    if all_jobs - all_needs:
+        sys.exit(f'Not all jobs mentioned in {ALL_TEST}.needs: '
+                 f'{all_jobs - all_needs}')
+
+    if all_needs - all_jobs:
+        sys.exit(f'Non-existing jobs found in {ALL_TEST}.needs: '
+                 f'{all_needs - all_jobs}')
+
+
+if __name__ == '__main__':
+    main()

.ci/cabal.project.local

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+package docopt
+  ghc-options: -Werror

.ci/cabal.project.local-lower

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+package docopt
+  ghc-options: -Werror
+
+prefer-oldest: True
+
+constraints:
+  aeson >= 1.4.4.0,
+  contravariant >= 1.5.2

.ci/cabal.project.local-upper

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+package docopt
+  ghc-options: -Werror
+
+repository head.hackage.ghc.haskell.org
+   url: https://ghc.gitlab.haskell.org/head.hackage/
+   secure: True
+   key-threshold: 3
+   root-keys:
+       7541f32a4ccca4f97aea3b22f5e593ba2c0267546016b992dfadcd2fe944e55d
+       26021a13b401500c8eb2761ca95c61f2d625bfef951b939a8124ed12ecf07329
+       f76d08be13e9a61a377a85e2fb63f4c5435d40f8feb3e12eb05905edb8cdea89
+
+active-repositories: hackage.haskell.org, head.hackage.ghc.haskell.org
+
+-- HEAD.hackage standard allow-newer packages
+allow-newer:
+  Cabal,
+  base,
+  binary,
+  bytestring,
+  deepseq,
+  ghc,
+  ghc-bignum,
+  ghc-prim,
+  integer-gmp,
+  template-haskell,
+  text,
+  time
+
+-- Boot packages
+constraints:
+  base installed,
+  ghc installed,
+  ghc-bignum installed,
+  ghc-prim installed,
+  integer-gmp installed,
+  template-haskell installed

.github/workflows/ci.yaml

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+name: CI
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+concurrency:
+  group: ${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  # Cabal
+  cabal:
+    name: Cabal / GHC ${{ matrix.ghc }} ${{ matrix.project-variant }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        # TODO: "9.0.2", "9.2.8", "9.4.7", "9.6.3"
+        #       don't forget to update -upper!
+        ghc: ["8.0.2", "8.2.2", "8.4.4", "8.6.5", "8.8.4", "8.10.7", "9.0.2"]
+        project-variant: [""]
+        include:
+          - ghc: 8.0.2
+            project-variant: -lower
+          - ghc: 9.0.2
+            project-variant: -upper
+
+      fail-fast: false
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          show-progress: false
+
+      - name: Setup Haskell
+        uses: haskell-actions/setup@v2
+        id: setup-haskell
+        with:
+          ghc-version: ${{ matrix.ghc }}
+          cabal-update: false
+
+      - name: General Setup
+        run: |
+          cp .ci/cabal.project.local${{ matrix.project-variant}} \
+            cabal.project.local
+          # Print out some information for debugging purposes
+          ghc --version
+          cabal --version
+          cat cabal.project.local
+
+      - name: Setup CI
+        # This generates dist-newstyle/cache/plan.json with hashes for all
+        # dependencies, for cache invalidation.
+        run: |
+          cabal v2-update
+          cabal v2-build all --enable-tests --dry-run
+
+      - name: Restore cached dependencies
+        uses: actions/cache/restore@v3
+        id: cache
+        env:
+          key:
+            ${{ runner.os }}-ghc-${{ matrix.ghc }}-cabal-${{
+            steps.setup-haskell.outputs.cabal-version }}${{
+            matrix.project-variant }}
+        with:
+          path: ${{ steps.setup-haskell.outputs.cabal-store }}
+          key:
+            ${{ env.key }}-${{ hashFiles('cabal.project.local',
+            'dist-newstyle/cache/plan.json') }}
+          restore-keys: ${{ env.key }}-
+
+      - name: Install dependencies
+        run: cabal v2-build all --enable-tests --only-dependencies
+
+      # Cache dependencies already at this point, so that we do not have to
+      # rebuild them should the subsequent steps fail
+      - name: Save cached dependencies
+        uses: actions/cache/save@v4
+        # Trying to save over an existing cache gives distracting
+        # "Warning: Cache save failed." since they are immutable
+        if: steps.cache.outputs.cache-hit != 'true'
+        with:
+          path: ${{ steps.setup-haskell.outputs.cabal-store }}
+          key: ${{ steps.cache.outputs.cache-primary-key }}
+
+      - name: Build
+        run: cabal v2-build all
+
+      - name: Test
+        run: cabal v2-test --test-show-details=direct
+
+  # Mechanism copied from https://github.com/clash-lang/clash-compiler/
+  all:
+    name: All jobs finished
+    if: ${{ !cancelled() }}
+    needs:
+      - cabal
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          show-progress: false
+
+      - name: Check dependencies for failures
+        run: |
+          # Test all dependencies for success/failure
+          set -x
+          # True if at least one dependency succeeded
+          success="${{ contains(needs.*.result, 'success') }}"
+          # True if at least one dependency failed
+          fail="${{ contains(needs.*.result, 'failure') }}"
+          set +x
+
+          # Test whether success/fail variables contain sane values
+          if [[ "${success}" != "true" && "${success}" != "false" ]]; then exit 1; fi
+          if [[ "${fail}"    != "true" && "${fail}"    != "false" ]]; then exit 1; fi
+
+          # We want to fail if one or more dependencies fail. For safety, we introduce
+          # a second check: if no dependencies succeeded something weird is going on.
+          if [[ "${fail}" == "true" || "${success}" == "false" ]]; then
+            echo "One or more dependency failed, or no dependency succeeded."
+            exit 1
+          fi
+
+      # Currently, ubuntu-latest already has it installed, but keep it around in
+      # case they ever change that
+      #
+      # - name: Install dependencies
+      #   run: |
+      #     sudo apt-get update
+      #     sudo apt-get -y install python3-yaml
+
+      - name: Check that the 'all' job depends on all other jobs
+        run: .ci/all_check.py