feat(docker): Support dangling Docker images

Docker images that were overwritten by a new one
with the same name and tag do not have a name or
tag. Docker images that were pulled by digest do
not have a tag. Support the former by falling back
on their ID and the latter by using their name.

These changes prevent the action from crashing on
such images. Continue using both the name and tag
for images that have them so that they are
retained upon restoring the cache.

.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>;