Add ARM64 emulated CI check

Author: AlistairB

.github/workflows/ci.yml

@@ -1,9 +1,12 @@
-name: Validate
+name: Validate Docker
 
 on:
   pull_request:
     branches:
       - master
+    paths:
+      - '**/Dockerfile'
+      - '.github/workflows/**'
 
 jobs:
   build-smoke-test:
@@ -47,3 +50,52 @@ jobs:
     - uses: hadolint/[email protected]
       with:
         recursive: true
+
+  emulated-architecture-tests:
+    timeout-minutes: 60
+    runs-on: ubuntu-latest
+    name: ${{ matrix.arch }}-${{ matrix.ghc }}-${{ matrix.deb }}
+    strategy:
+      fail-fast: false
+      matrix:
+        ghc: ['8.10.7', '9.0.2', '9.2.1']
+        deb: ['buster']
+        arch: ['aarch64']
+        include:
+          - ghc: '8.10.7'
+            ghc_minor: '8.10'
+          - ghc: '9.0.2'
+            ghc_minor: '9.0'
+          - ghc: '9.2.1'
+            ghc_minor: '9.2'
+          - arch: aarch64
+            docker_platform: arm64
+    steps:
+      - uses: actions/checkout@v2
+      - name: docker build [ ${{ matrix.arch }} ${{ matrix.ghc }}]
+        uses: uraimo/run-on-arch-action@e9117b926d001f8683802c315b5a134f8c5da3d3
+        with:
+          arch: ${{ matrix.arch }}
+          distro: ${{ matrix.deb }}
+          githubToken: ${{ github.token }}
+          install: |
+            apt-get update
+            apt-get install -y curl
+            curl -fsSL https://get.docker.com | sh
+          run: |
+            docker build --pull \
+              --platform "linux/${{ matrix.docker_platform }}" \
+              -t haskell:${{ matrix.ghc }}-${{ matrix.deb }} \
+              ${{ matrix.ghc_minor }}/${{ matrix.deb }}
+            echo 'testing..'
+            docker run \
+              --platform "linux/${{ matrix.docker_platform }}" \
+              -t haskell:${{ matrix.ghc }}-${{ matrix.deb }} \
+              bash -c "cabal update && cabal install --lib hashable"
+            docker run \
+              --platform "linux/${{ matrix.docker_platform }}" \
+              -t haskell:${{ matrix.ghc }}-${{ matrix.deb }} \
+              bash -c "echo | ghci"
+
+# Running the official tests does not work as we need to hardcode the plaform due to the emulated nature.
+# This solution is fairly hacky, but gets us most of benefit of the official tests.