Show proper image ID on registry page

CHANGELOG

@@ -19,6 +19,7 @@ v 8.9.0 (unreleased)
   - Don't show 'Leave Project' to group members
   - Fix wiki page events' webhook to point to the wiki repository
   - Don't show tags for revert and cherry-pick operations
+  - Show image ID on registry page
   - Fix issue todo not remove when leave project !4150 (Long Nguyen)
   - Allow customisable text on the 'nearly there' page after a user signs up
   - Bump recaptcha gem to 3.0.0 to remove deprecated stoken support

app/views/projects/container_registry/_tag.html.haml

@@ -3,9 +3,9 @@
     = escape_once(tag.name)
     = clipboard_button(clipboard_text: "docker pull #{tag.path}")
   %td
-    - if layer = tag.layers.first
-      %span.has-tooltip{ title: "#{layer.revision}" }
-        = layer.short_revision
+    - if tag.revision
+      %span.has-tooltip{ title: "#{tag.revision}" }
+        = tag.short_revision
     - else
       \-
   %td

lib/container_registry/tag.rb

@@ -3,6 +3,7 @@ module ContainerRegistry
     attr_reader :repository, :name
     delegate :registry, :client, to: :repository
+    delegate :revision, :short_revision, to: :config_blob, allow_nil: true
     def initialize(repository, name)
       @repository, @name = repository, name

spec/features/container_registry_spec.rb

@@ -26,7 +26,8 @@ describe "Container Registry" do
     end
     context 'when there are tags' do
-      it { expect(page).to have_content(tag_name)}
+      it { expect(page).to have_content(tag_name) }
+      it { expect(page).to have_content('d7a513a66') }
     end
   end

spec/fixtures/container_registry/tag_manifest.json

-{"schemaVersion":2,"mediaType":"application/vnd.docker.distribution.manifest.v2+json","config":{"mediaType":"application/octet-stream","size":1145,"digest":"sha256:d7a513a663c1a6dcdba9ed832ca53c02ac2af0c333322cd6ca92936d1d9917ac"},"layers":[{"mediaType":"application/vnd.docker.image.rootfs.diff.tar.gzip","size":2319870,"digest":"sha256:420890c9e918b6668faaedd9000e220190f2493b0693ee563ebd7b4cc754a57d"}]}
+{
+  "schemaVersion": 2,
+  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
+  "config": {
+    "mediaType": "application/octet-stream",
+    "size": 1145,
+    "digest": "sha256:d7a513a663c1a6dcdba9ed832ca53c02ac2af0c333322cd6ca92936d1d9917ac"
+  },
+  "layers": [
+    {
+      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
+      "size": 2319870,
+      "digest": "sha256:420890c9e918b6668faaedd9000e220190f2493b0693ee563ebd7b4cc754a57d"
+    }
+  ]
+}