Make repo optional and default to github name

.github/workflows/self-test-multistage-docker-build.yml

@@ -13,6 +13,37 @@ permissions:
   packages: write
 
 jobs:
+  test-build-auto-repo:
+    name: Automatic repository naming
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Auth to GH registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - uses: ./
+        id: build
+        with:
+          dockerfile: examples/Dockerfile
+          registry: ghcr.io
+          stages: env, configured
+          server-stage: server
+
+      - name: Print outputs
+        run: |
+          echo "Server: ${{ steps.build.outputs.server-tag }}"
+          echo "Testenv: ${{ steps.build.outputs.testenv-tag }}"
+          echo "Commit: ${{ steps.build.outputs.commit }}"
+
+      - name: Run image
+        run: docker run --rm ${{ steps.build.outputs.server-tag }}
+
+
   test-build-parallel-setting:
     name: Parallel via setting
     runs-on: ubuntu-latest

README.md

@@ -16,16 +16,27 @@ While the action allows many stages to be pushed to the registry for future re-u
 
 | Input | Required | Default | Description |
 |---|---|---|---|
-| `repository` | **yes** | | Repository name for pushed images |
-| `stages` | **yes** | | Comma-separarted list of build stages. Each of these will be an explicit cache target for subsequent builds |
 | `server-stage` | **yes** | | Name of stage for server |
-| `tag-latest-on-default` | no | `true` | Automatically create a `latest` tag when run on the default branch |
-| `testenv-stage` | no | | Name of stage for test environment |
+| `stages` | **yes** | | Comma-separarted list of build stages. Each of these will be an explicit cache target for subsequent builds |
+| `build-args` | no | | Comma-separated list of `--build-arg` flags. |
 | `context` | no | `.` | Build context |
 | `dockerfile` | no | `Dockerfile` | Path to the Dockerfile |
-| `quiet` | no | `true` | Should docker commands be passed `--quiet` |
 | `parallel` | no | `false` | Should stages be built in parallel (via BuildX) |
-| `build-args` | no | | Comma-separated list of `--build-arg` flags. |
+| `quiet` | no | `true` | Should docker commands be passed `--quiet` |
+| `repository` | no[^1] | | Repository name for pushed images |
+| `registry` | no[^1] | | Docker registry for automatically-named images |
+| `tag-latest-on-default` | no | `true` | Automatically create a `latest` tag when run on the default branch |
+| `testenv-stage` | no | | Name of stage for test environment |
+
+### `registry` and `repository`
+In versions `v1.7.x` and earlier, the `repository` input is used to control where the built images go.
+It should include the registry in the value (e.g. `ghcr.io`, `gcr.io`, etc.).
+
+As of `v1.8`, you can leave `repository` blank and instead provide only the `registry`.
+If you do so, the Github repository name will be used to produce the outputs.
+
+You **must** set either value, but not both.
+This limitation may be removed in a future version.
 
 ### Parallel builds
 The new `parallel` option, added in `v1.7`, defaults to off.
@@ -124,3 +135,5 @@ tl:dr: If it comes from one of the `outputs` of this action, go ahead and use it
 ## Known issues/Future features
 
 - Make a straightforward mechanism to do cleanup
+
+[^1]: You must provide either of these values, but do not provide both.

action.yml

@@ -21,8 +21,11 @@ inputs:
     description: Build in parallel
     required: false
     default: false
+  registry:
+    required: false
+    description: Registry to pull from and push to. Can be provided through `repository`
   repository:
-    required: true
+    required: false
     description: Repository that all of the images and tags will pull from and push to
   stages:
     required: true

src/helpers.ts

@@ -83,8 +83,29 @@ export function getAllStages(): string[] {
  * Takes the build stage and returns an untagged image name for it
  */
 function getUntaggedImageForStage(stage: string): string {
-  const repo = core.getInput('repository')
-  return `${repo}/${stage}`
+  const reg = core.getInput('registry')
+  let repo = core.getInput('repository')
+
+  if (reg === '' && repo === '') {
+    // Technically, this should be permissible. In practice, the default
+    // `docker push` going to Docker Hub when a registry isn't specified will
+    // break - so it's forbidden.
+    throw new Error('Registry and repository must not both be blank')
+  }
+
+  if (reg !== '' && repo !== '') {
+    // This is a temporary limitation - I'm not sure exactly what behavior is
+    // most desirable here. The main use-case of `registry` is to leave out
+    // `repository` so for now we're optimizing for that.
+    throw new Error('Use registry OR repository, but not both')
+  }
+
+  if (repo === '') {
+    repo = (github.context.repo.owner + '/' + github.context.repo.repo).toLowerCase()
+    return `${reg}/${repo}/${stage}`
+  } else {
+    return `${repo}/${stage}`
+  }
 }
 
 export function getTaggedImageForStage(stage: string, tag: string): string {