migrate to GitHub actions for haskell-libraries ci

.github/workflows/ci.yml

@@ -0,0 +1,48 @@
+name: Run tests and push shell closures
+on:
+  pull_request:
+    branches:
+      - "trunk"
+  push:
+    branches:
+      - "trunk"
+
+  # We also provide a way to run this manually, if needed.
+  workflow_dispatch:
+
+jobs:
+  ci:
+    strategy:
+      matrix:
+        runner:
+          - os: macos-14 # macos sonoma on m1; 3 vcpu, 7 GB memory
+            base-nixpkgs-channel: nixpkgs-23.11-darwin
+          - os: ubuntu-22.04 # linux x86_64; 4 vcpu, 16 GB memory
+            base-nixpkgs-channel: nixos-23.11
+        ghc:
+          - ghc-8-10
+          - ghc-9-2
+          - ghc-9-4
+    runs-on: ${{ matrix.runner.os }}
+    steps:
+      - name: Install Nix
+        uses: cachix/install-nix-action@v26
+        with:
+          nix_path: nixpkgs=channel:${{ matrix.runner.base-nixpkgs-channel }}
+          extra_nix_config: |
+            extra-substituters = https://nri.cachix.org https://nix-script.cachix.org
+            trusted-public-keys = nri.cachix.org-1:9/BMj3Obc+uio3O5rYGT+egHzkBzDunAzlZZfhCGj6o= nix-script.cachix.org-1:czo3tF6XERpkDdMd6m84XjmgeHQXNeIooSt7b0560+c= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+
+      - name: Install cachix
+        run: nix-env -f '<nixpkgs>' -iA cachix
+
+      - name: Check out repository code
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Run tests and push shell closures
+        run: cachix watch-exec nri -- nix-shell shell-${{ matrix.ghc }}.nix --run "./run-tests.sh"
+        env:
+          CACHIX_SIGNING_KEY: ${{ secrets.CACHIX_SIGNING_KEY }}
+          PGPORT: "8088"

README.md

@@ -30,13 +30,13 @@ We use [Ormolu][ormolu] for code formatting.
 
 Documentation comments use the [Haddock][haddock] format to ensure they are rendered correctly on package websites.
 
-### Testing compilation against GHC 8.10
+### Testing compilation
 
-Our default `shell.nix` sets up an environment around GHC version 8.10. CI also runs tests against GHC 9.0. To test using this version locally:
+Our default `shell.nix` sets up an environment around the most recent version of GHC that we support. CI also runs tests against a couple of older versions of GHC. To test using any of these versions locally:
 
 ```sh
-cachix use nri-open-source       # set up cache so the next step goes faster
-nix-shell shell-ghc-9-0.nix
+cachix use nri              # set up cache so the next step goes faster
+nix-shell shell-ghc-X-Y.nix # where X and Y correspond to any of the shells at the root of this repo
 ```
 
 This starts a special shell in which you can run any of the commands above.