if KO_DOCKER_REPO is set, skip login and propagate it

.github/workflows/use-action.yaml

@@ -22,18 +22,30 @@ jobs:
       - uses: imjasonh/setup-ko@main
       - run: ko publish --bare ./
 
-      # Install an old release.
-      - uses: imjasonh/setup-ko@main
+      - name: Install old release
+        uses: imjasonh/setup-ko@main
         with:
           version: v0.8.0
       - name: Check installed version
         run: ko version | grep 0.8.0
 
-      # Install from tip
-      - uses: imjasonh/setup-ko@main
+      - name: Install from tip
+        uses: imjasonh/setup-ko@main
         with:
           version: tip
       - name: Check installed version (tip)
         run: |
           sudo rm /usr/local/bin/ko # Uninstall previous versions.
           ko version
+
+      # If KO_DOCKER_REPO is set during setup, it's set for future steps.
+      - name: Pre-set KO_DOCKER_REPO
+        uses: imjasonh/setup-ko@main
+        env:
+          KO_DOCKER_REPO: already-set
+      - name: Check pre-set KO_DOCKER_REPO
+        run: |
+          if [[ ${KO_DOCKER_REPO} -ne "already-set"]]; then
+            echo "${KO_DOCKER_REPO} != already-set"
+            exit 1
+          fi

README.md

@@ -30,8 +30,8 @@ _That's it!_ This workflow will build and publish your code to [GitHub Container
 By default, the action sets `KO_DOCKER_REPO=ghcr.io/[owner]/[repo]`.
 See [documentation for `ko`](https://github.com/google/ko#configuration) to learn more about configuring `ko`.
 
-:warning: **Note:** The action _sets_ `KO_DOCKER_REPO` for all subsequent steps.
-If you define `KO_DOCKER_REPO` as a workflow-wide environment variable, its value will be modified after the action runs.
+By default the action sets `KO_DOCKER_REPO` for all subsequent steps.
+Instead, if the `env` is already set when the action runs, it will skip logging in to ghcr.io and propagate `KO_DOCKER_REPO` for subsequent steps.
 
 The action works on Linux and macOS [runners](https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners), and _should_ work for Windows runners when `ko` releases include Windows binaries (next `ko` release🤞! see [google/ko#339](https://github.com/google/ko/pull/339))
 

action.yml

@@ -41,9 +41,15 @@ runs:
         curl -fsL https://github.com/google/ko/releases/download/${tag}/ko_${tag:1}_${os}_x86_64.tar.gz | sudo tar xzf - -C /usr/local/bin ko
       fi
 
-      # NB: username doesn't seem to matter.
-      echo "${{ github.token }}" | ko login ghcr.io --username "dummy" --password-stdin
+      if [[ ! -z ${KO_DOCKER_REPO} ]]; then
+        echo "KO_DOCKER_REPO is already set"
+        echo "Skipping login to ghcr.io and passing KO_DOCKER_REPO=${KO_DOCKER_REPO} on to future steps"
+        echo "KO_DOCKER_REPO=${KO_DOCKER_REPO}" >> $GITHUB_ENV
+      else
+        # NB: username doesn't seem to matter.
+        echo "${{ github.token }}" | ko login ghcr.io --username "dummy" --password-stdin
 
-      # Set KO_DOCKER_REPO for future steps.
-      echo "KO_DOCKER_REPO=ghcr.io/${{ github.repository }}"
-      echo "KO_DOCKER_REPO=ghcr.io/${{ github.repository }}" >> $GITHUB_ENV
+        # Set KO_DOCKER_REPO for future steps.
+        echo "KO_DOCKER_REPO=ghcr.io/${{ github.repository }}"
+        echo "KO_DOCKER_REPO=ghcr.io/${{ github.repository }}" >> $GITHUB_ENV
+      fi