Throw exception if we can't find an updatable version

github_actions/lib/dependabot/github_actions/file_parser.rb

@@ -35,6 +35,9 @@ def parse
           dependency_set += workfile_file_dependencies(file)
         end
 
+        dependencies_without_version = dependency_set.dependencies.select { |dep| dep.version.nil? }
+        raise UpdateNotPossible, dependencies_without_version.map(&:name) unless dependencies_without_version.empty?
+
         dependency_set.dependencies
       end
 

github_actions/spec/dependabot/github_actions/file_parser_spec.rb

@@ -560,5 +560,24 @@ def mock_service_pack_request(nwo)
         end
       end
     end
+
+    context "with an unresolvable version" do
+      let(:workflow_file_fixture_name) { "unresolved_version.yml" }
+      let(:service_pack_url) do
+        "https://github.com/taiki-e/install-action.git/info/refs" \
+          "?service=git-upload-pack"
+      end
+
+      before do
+        mock_service_pack_request("taiki-e/install-action")
+      end
+
+      it "raises an UpdateNotPossible error" do
+        expect { parser.parse }.to raise_error(
+          Dependabot::UpdateNotPossible,
+          "The following dependencies could not be updated: taiki-e/install-action"
+        )
+      end
+    end
   end
 end

github_actions/spec/fixtures/workflow_files/unresolved_version.yml

@@ -0,0 +1,7 @@
+on: [push]
+
+name: Integration
+jobs:
+  chore:
+    steps:
+    - uses: taiki-e/install-action@nextest