From 5f1c964eb255469e80499c93c22517ab9e58a860 Mon Sep 17 00:00:00 2001
From: reivilibre <38398653+reivilibre@users.noreply.github.com>
Date: Tue, 10 Aug 2021 14:29:22 +0100
Subject: [PATCH] Add a GitHub Action CI check to ensure Dockerfile changes
 actually work (#248)

---
 .github/workflows/docker_check.yml | 48 ++++++++++++++++++++++++++++++
 changelog.d/248.docker             |  1 +
 2 files changed, 49 insertions(+)
 create mode 100644 .github/workflows/docker_check.yml
 create mode 100644 changelog.d/248.docker

diff --git a/.github/workflows/docker_check.yml b/.github/workflows/docker_check.yml
new file mode 100644
index 00000000..af04002a
--- /dev/null
+++ b/.github/workflows/docker_check.yml
@@ -0,0 +1,48 @@
+# GitHub actions workflow which builds the docker images.
+# This is useful as it will run in PRs that change the Dockerfile, and can be
+# an early source of warnings that the Dockerfile isn't right.
+# This check also triggers when this file itself is modified.
+
+name: Check Docker image can be built successfully
+
+on:
+  push:
+    paths:
+      - 'docker/Dockerfile'
+      - '.github/workflows/docker_check.yml'
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up QEMU
+        id: qemu
+        uses: docker/setup-qemu-action@v1
+        with:
+          platforms: arm64
+
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Inspect builder
+        run: docker buildx inspect
+
+      # we explicitly check out the repository (and use `context: .` in buildx)
+      # because we need to preserve the git metadata so that setuptools_scm
+      # (as part of Sygnal's setup.py) can deduce the package version.
+      # See: https://github.com/marketplace/actions/build-and-push-docker-images#path-context
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Build all platforms
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: false
+          labels: "gitsha1=${{ github.sha }}"
+          file: "docker/Dockerfile"
+          platforms: linux/amd64,linux/arm64
diff --git a/changelog.d/248.docker b/changelog.d/248.docker
new file mode 100644
index 00000000..aaa23983
--- /dev/null
+++ b/changelog.d/248.docker
@@ -0,0 +1 @@
+CI now checks that the Docker image still builds after the Dockerfile is modified.