Make hashed storage required for Design Management

As hashed storage is the default storage type since v10.0, and we
encourage people to migrate to hashed storage, design management now
has a hard requirement for hashed storage in order for us to handle
moving the design repository when the project repository moves on disk.

https://gitlab.com/gitlab-org/gitlab/issues/13428

doc/user/project/issues/design_management.md

@@ -33,6 +33,10 @@ to be enabled:
   project level, navigate to your project's **Settings > General**, expand **Visibility, project features, permissions**
   and enable **Git Large File Storage**.
 
+Design Management requires that projects are using
+[hashed storage](../../../administration/repository_storage_types.html#hashed-storage)
+(the default storage type since v10.0).
+
 ## Limitations
 
 - Files uploaded must have a file extension of either `png`, `jpg`, `jpeg`, `gif`, `bmp`, `tiff` or `ico`.

ee/app/models/ee/project.rb

@@ -630,13 +630,18 @@ module EE
       super.presence || build_feature_usage
     end
 
+    # LFS and hashed repository storage are required for using Design Management.
     def design_management_enabled?
-      # LFS is required for using Design Management
-      #
-      # Checking both feature availability on the license, as well as the feature
-      # flag, because we don't want to enable design_management by default on
-      # on prem installs yet.
       lfs_enabled? &&
+        # We will allow the hashed storage requirement to be disabled for
+        # a few releases until we are able to understand the impact of the
+        # hashed storage requirement for existing design management projects.
+        # See https://gitlab.com/gitlab-org/gitlab/issues/13428#note_238729038
+        (hashed_storage?(:repository) || ::Feature.disabled?(:design_management_require_hashed_storage, self, default_enabled: true)) &&
+        # Check both feature availability on the license, as well as the feature
+        # flag, because we don't want to enable design_management by default on
+        # on prem installs yet.
+        # See https://gitlab.com/gitlab-org/gitlab/issues/13709
         feature_available?(:design_management) &&
         ::Feature.enabled?(:design_management_flag, self, default_enabled: true)
     end

ee/changelogs/unreleased/13428-make-hashed-storage-a-requirement-for-design-management.yml

+---
+title: Hashed storage is now a requirement for Design Management
+merge_request: 19259
+author:
+type: changed

ee/spec/models/project_spec.rb

@@ -1900,27 +1900,29 @@ describe Project do
     end
   end
 
-  describe "#design_management_enabled?" do
+  describe '#design_management_enabled?' do
     let(:project) { build(:project) }
 
-    where(
-      feature_enabled: [false, true],
-      license_enabled: [false, true],
-      lfs_enabled: [false, true]
-    )
+    where(:feature_enabled, :license_enabled, :lfs_enabled, :hashed_storage_enabled, :hash_storage_required, :expectation) do
+      false | false | false | false | false | false
+      true  | false | false | false | false | false
+      true  | true  | false | false | false | false
+      true  | true  | true  | false | false | true
+      true  | true  | true  | false | true  | false
+      true  | true  | true  | true  | false | true
+      true  | true  | true  | true  | true  | true
+    end
 
     with_them do
       before do
         stub_licensed_features(design_management: license_enabled)
-        stub_feature_flags(design_management_flag: feature_enabled)
+        stub_feature_flags(design_management_flag: feature_enabled, design_management_require_hashed_storage: hash_storage_required)
         expect(project).to receive(:lfs_enabled?).and_return(lfs_enabled)
+        allow(project).to receive(:hashed_storage?).with(:repository).and_return(hashed_storage_enabled)
       end
 
-      # Design management is only available if all dependencies are enabled
-      let(:expected) { feature_enabled && license_enabled && lfs_enabled }
-
-      it "knows if design management is available" do
-        expect(project.design_management_enabled?).to be(expected)
+      it do
+        expect(project.design_management_enabled?).to be(expectation)
       end
     end
   end