preview.yml

name: Preview image

# A throwaway image of any branch, for trying a change on an instance of
# one's own without a release: no version bump, no changelog entry, no
# release on GitHub and nothing on Docker Hub. Started by hand, from the
# Actions tab or with `gh workflow run preview.yml --ref <branch>`, it
# builds linux/amd64 and pushes to a private registry named in the
# repository's secrets, tagged preview-<branch> and preview-<branch>-<sha>.
#
# Secrets: PREVIEW_REGISTRY (the host to log in to), PREVIEW_IMAGE (the
# image name with the host, e.g. registry.example.org/me/legejo),
# PREVIEW_REGISTRY_USER and PREVIEW_REGISTRY_TOKEN.

on:
  workflow_dispatch:

jobs:
  preview:
    runs-on: ubuntu-24.04
    steps:
      - uses: actions/checkout@v4
      - uses: docker/setup-buildx-action@v3
      - uses: docker/login-action@v3
        with:
          registry: ${{ secrets.PREVIEW_REGISTRY }}
          username: ${{ secrets.PREVIEW_REGISTRY_USER }}
          password: ${{ secrets.PREVIEW_REGISTRY_TOKEN }}
      # The branch as a tag: lower case, slashes to dashes.
      - id: names
        run: |
          branch="${GITHUB_REF_NAME//\//-}"
          echo "branch=${branch,,}" >> "$GITHUB_OUTPUT"
          echo "sha=${GITHUB_SHA::7}" >> "$GITHUB_OUTPUT"
      - uses: docker/build-push-action@v6
        with:
          context: .
          platforms: linux/amd64
          push: true
          tags: |
            ${{ secrets.PREVIEW_IMAGE }}:preview-${{ steps.names.outputs.branch }}
            ${{ secrets.PREVIEW_IMAGE }}:preview-${{ steps.names.outputs.branch }}-${{ steps.names.outputs.sha }}
          # The same cache as the release build, so a preview of a branch
          # that differs little from the last release is quick.
          cache-from: type=gha,scope=linux/amd64
          cache-to: type=gha,scope=linux/amd64,mode=max
      - run: echo "Pushed preview-${{ steps.names.outputs.branch }}-${{ steps.names.outputs.sha }}"