feat(docker): Support dangling Docker images

.github/workflows/test.yaml

@@ -87,14 +87,15 @@ jobs:
         uses: ./
         with:
           key: docker-cache-test-${{ matrix.os }}-${{ github.run_id }}-${{ github.run_attempt }}
-      - name: Build an empty test Docker image.
+      - name: Build one tagged and one dangling empty test Docker image.
         run: |
           if [[ "${{ matrix.os }}" =~ 'windows' ]]; then
             DOCKERFILE='Dockerfile.windows'
           else
             DOCKERFILE='Dockerfile'
           fi
-          docker build --tag empty . --file "$DOCKERFILE"
+          docker build --tag empty . --file "$DOCKERFILE" # Dangling image
+          docker build --tag empty --no-cache . --file "$DOCKERFILE" # Tagged image
         shell: bash
   restore-cache:
     name: Restore Cache
@@ -115,10 +116,15 @@ jobs:
         uses: ./
         with:
           key: docker-cache-test-${{ matrix.os }}-${{github.run_id }}-${{ github.run_attempt }}
-      - name: Verify Docker loaded empty image from cache.
+      - name: Verify Docker loaded both empty images from cache.
         run: |
-          description="$(docker inspect --format '{{ index .Config.Labels "description" }}' empty)"
-          [[ $description == 'empty image' ]]
+          function emptyImageExists() {
+            id="$(docker images --quiet --filter "label=description=empty image" "$@")"
+            [[ -n "$id" ]]
+          }
+          emptyImageExists empty
+          emptyImageExists --filter "dangling=true"
+
         shell: bash
       - name: Delete test cache if permitted (i.e., workflow not triggered from fork).
         if: always()

src/docker.test.ts

@@ -50,6 +50,11 @@ const assertCalledInOrder = <T extends FunctionLike>(
 };
 
 describe("Docker images", (): void => {
+  const LIST_COMMAND =
+    "docker image list --format '" +
+    '{{ if ne .Repository "<none>" }}{{ .Repository }}' +
+    `{{ if ne .Tag "<none>" }}:{{ .Tag }}{{ end }}{{ else }}{{ .ID }}{{ end }}'`;
+
   const assertLoadDockerImages = (key: string, cacheHit: boolean): void => {
     expect(core.getInput).lastCalledWith("key", { required: true });
     expect(cache.restoreCache).lastCalledWith([docker.DOCKER_IMAGES_PATH], key);
@@ -64,9 +69,7 @@ describe("Docker images", (): void => {
         `docker load --input ${docker.DOCKER_IMAGES_PATH}`,
       );
     } else {
-      expect(util.execBashCommand).lastCalledWith(
-        'docker image list --format "{{ .Repository }}:{{ .Tag }}"',
-      );
+      expect(util.execBashCommand).lastCalledWith(LIST_COMMAND);
     }
     expect(util.execBashCommand).toHaveBeenCalledTimes(1);
   };
@@ -106,10 +109,7 @@ describe("Docker images", (): void => {
             1,
             "Listing Docker images.",
           );
-          expect(util.execBashCommand).nthCalledWith<[string]>(
-            1,
-            'docker image list --format "{{ .Repository }}:{{ .Tag }}"',
-          );
+          expect(util.execBashCommand).nthCalledWith<[string]>(1, LIST_COMMAND);
         }
       }
     }

src/docker.ts

@@ -7,7 +7,9 @@ const CACHE_HIT = "cache-hit";
 const DOCKER_IMAGES_LIST = "docker-images-list";
 const DOCKER_IMAGES_PATH = "~/.docker-images.tar";
 const LIST_COMMAND =
-  'docker image list --format "{{ .Repository }}:{{ .Tag }}"';
+  "docker image list --format '" +
+  '{{ if ne .Repository "<none>" }}{{ .Repository }}' +
+  `{{ if ne .Tag "<none>" }}:{{ .Tag }}{{ end }}{{ else }}{{ .ID }}{{ end }}'`;
 
 const loadDockerImages = async (): Promise<void> => {
   const requestedKey = getInput("key", { required: true });

src/integration.test.ts

@@ -31,7 +31,9 @@ const getKey = (paths: string[], primaryKey: string): string =>
 describe("Integration Test", (): void => {
   const EXEC_OPTIONS = { shell: "/usr/bin/bash" };
   const LIST_COMMAND =
-    'docker image list --format "{{ .Repository }}:{{ .Tag }}"';
+    "docker image list --format '" +
+    '{{ if ne .Repository "<none>" }}{{ .Repository }}' +
+    `{{ if ne .Tag "<none>" }}:{{ .Tag }}{{ end }}{{ else }}{{ .ID }}{{ end }}'`;
 
   let loadCommand: string;
   let inMemoryCache: Map<string, string>;