From 7ade5561f86399764aaa5a6ad359ffc9f8a204fe Mon Sep 17 00:00:00 2001
From: Maarten Jacobs <maarten@defacto.nl>
Date: Sun, 24 May 2026 10:52:43 +0200
Subject: [PATCH] Build and publish images via GitHub Actions

Adds a workflow that auto-detects every version directory containing a
Dockerfile, builds it on every PR (to catch Dockerfile regressions
before merge), and publishes to Docker Hub on merge to master.

Removes the manual Docker Desktop ceremony from the README and
documents the two repo secrets the workflow needs (DOCKERHUB_USERNAME
and DOCKERHUB_TOKEN).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 .github/workflows/publish.yml | 61 +++++++++++++++++++++++++++++++++++
 README.md                     | 26 +++++++++------
 2 files changed, 77 insertions(+), 10 deletions(-)
 create mode 100644 .github/workflows/publish.yml

diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
new file mode 100644
index 0000000..be84bbd
--- /dev/null
+++ b/.github/workflows/publish.yml
@@ -0,0 +1,61 @@
+name: Build and publish
+
+# Builds each version directory as `defactosoftware/elixir:<dir-name>` and
+# publishes to Docker Hub on merge to master. PR runs build-only (no push) so
+# Dockerfile regressions surface before merge.
+on:
+  push:
+    branches: [master]
+    paths:
+      - "*/Dockerfile"
+      - ".github/workflows/publish.yml"
+  pull_request:
+    paths:
+      - "*/Dockerfile"
+      - ".github/workflows/publish.yml"
+  workflow_dispatch:
+
+jobs:
+  detect-versions:
+    runs-on: ubuntu-latest
+    outputs:
+      versions: ${{ steps.set.outputs.versions }}
+    steps:
+      - uses: actions/checkout@v4
+      - id: set
+        run: |
+          versions=$(find . -mindepth 2 -maxdepth 2 -name Dockerfile \
+            | sed -E 's|^\./([^/]+)/Dockerfile$|\1|' \
+            | sort \
+            | jq -R -s -c 'split("\n") | map(select(length > 0))')
+          echo "versions=$versions" >> "$GITHUB_OUTPUT"
+          echo "Detected: $versions"
+
+  build:
+    needs: detect-versions
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        version: ${{ fromJson(needs.detect-versions.outputs.versions) }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Docker Hub
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: ./${{ matrix.version }}
+          platforms: linux/amd64
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: defactosoftware/elixir:${{ matrix.version }}
+          cache-from: type=gha,scope=${{ matrix.version }}
+          cache-to: type=gha,scope=${{ matrix.version }},mode=max
diff --git a/README.md b/README.md
index cc08523..45ee856 100644
--- a/README.md
+++ b/README.md
@@ -12,21 +12,27 @@ Included:
 - Some build tools (for dependencies that require compilation steps)
 <br>
 
-*There is currently no GitHub Action to automatically build the images, so building and publishing has to be done manually through Docker Desktop or CLI for now.*
-<br>
-<br>
+### Adding a new version
+
+1. Create a new directory named after the Elixir version (e.g. `1.20.0-rc.6/`) containing a `Dockerfile`.
+2. Open a PR — the `Build and publish` workflow builds the image to verify the Dockerfile compiles.
+3. On merge to `master`, the workflow pushes the image to Docker Hub as `defactosoftware/elixir:<version>`.
+
+### Required Docker Hub secrets
 
-### To Build (Docker Desktop)
+The publish workflow needs two repository secrets configured in **Settings → Secrets and variables → Actions**:
 
-*First, install/setup Docker Desktop and login.*
+- `DOCKERHUB_USERNAME` — a Docker Hub account with push access to `defactosoftware/elixir`
+- `DOCKERHUB_TOKEN` — a Docker Hub access token (create one at https://hub.docker.com/settings/security)
+
+### Building locally
+
+If you need to build the image on your machine (e.g. to test ahead of pushing):
 
 ```
 cd VERSION
 docker build --platform=linux/amd64 -t defactosoftware/elixir:VERSION .
+docker push defactosoftware/elixir:VERSION   # optional
 ```
-<br>
-
-### To Publish (Docker Desktop)
 
-- Find the built image under **images**
-- Click the *three-dot* menu and select **Push to Docker Hub**
+Docker Desktop, Colima, OrbStack and Podman all work — anything that provides a `docker` CLI with buildx.