Modify keep_divergent_refs via RemoteMirror API

When the feature is enabled, this attribute can now be modified via the
API.

lib/api/entities/remote_mirror.rb

@@ -12,6 +12,9 @@ module API
       expose :last_successful_update_at
       expose :last_error
       expose :only_protected_branches
+      expose :keep_divergent_refs, if: -> (mirror, _options) do
+        ::Feature.enabled?(:keep_divergent_refs, mirror.project)
+      end
     end
   end
 end

lib/api/remote_mirrors.rb

@@ -33,9 +33,11 @@ module API
         requires :url, type: String, desc: 'The URL for a remote mirror'
         optional :enabled, type: Boolean, desc: 'Determines if the mirror is enabled'
         optional :only_protected_branches, type: Boolean, desc: 'Determines if only protected branches are mirrored'
+        optional :keep_divergent_refs, type: Boolean, desc: 'Determines if divergent refs are kept on the target'
       end
       post ':id/remote_mirrors' do
         create_params = declared_params(include_missing: false)
+        create_params.delete(:keep_divergent_refs) unless ::Feature.enabled?(:keep_divergent_refs, user_project)
 
         new_mirror = user_project.remote_mirrors.create(create_params)
 
@@ -53,12 +55,15 @@ module API
         requires :mirror_id, type: String, desc: 'The ID of a remote mirror'
         optional :enabled, type: Boolean, desc: 'Determines if the mirror is enabled'
         optional :only_protected_branches, type: Boolean, desc: 'Determines if only protected branches are mirrored'
+        optional :keep_divergent_refs, type: Boolean, desc: 'Determines if divergent refs are kept on the target'
       end
       put ':id/remote_mirrors/:mirror_id' do
         mirror = user_project.remote_mirrors.find(params[:mirror_id])
 
         mirror_params = declared_params(include_missing: false)
         mirror_params[:id] = mirror_params.delete(:mirror_id)
+        mirror_params.delete(:keep_divergent_refs) unless ::Feature.enabled?(:keep_divergent_refs, user_project)
+
         update_params = { remote_mirrors_attributes: mirror_params }
 
         result = ::Projects::UpdateService

spec/fixtures/api/schemas/remote_mirror.json

@@ -20,7 +20,8 @@
     "last_update_started_at": { "type": ["string", "null"] },
     "last_successful_update_at": { "type": ["string", "null"] },
     "last_error": { "type": ["string", "null"] },
-    "only_protected_branches": { "type": "boolean" }
+    "only_protected_branches": { "type": "boolean" },
+    "keep_divergent_refs": { "type": ["boolean", "null"] }
   },
   "additionalProperties": false
 }

spec/requests/api/remote_mirrors_spec.rb

@@ -91,6 +91,10 @@ describe API::RemoteMirrors do
     let(:route) { ->(id) { "/projects/#{project.id}/remote_mirrors/#{id}" } }
     let(:mirror) { project.remote_mirrors.first }
 
+    before do
+      stub_feature_flags(keep_divergent_refs: false)
+    end
+
     it 'requires `admin_remote_mirror` permission' do
       put api(route[mirror.id], developer)
 
@@ -102,12 +106,31 @@ describe API::RemoteMirrors do
 
       put api(route[mirror.id], user), params: {
         enabled: '0',
-        only_protected_branches: 'true'
+        only_protected_branches: 'true',
+        keep_divergent_refs: 'true'
       }
 
       expect(response).to have_gitlab_http_status(:success)
       expect(json_response['enabled']).to eq(false)
       expect(json_response['only_protected_branches']).to eq(true)
+
+      # Deleted due to lack of feature availability
+      expect(json_response['keep_divergent_refs']).to be_nil
+    end
+
+    context 'with the `keep_divergent_refs` feature enabled' do
+      before do
+        stub_feature_flags(keep_divergent_refs: { enabled: true, project: project })
+      end
+
+      it 'updates the `keep_divergent_refs` attribute' do
+        project.add_maintainer(user)
+
+        put api(route[mirror.id], user), params: { keep_divergent_refs: 'true' }
+
+        expect(response).to have_gitlab_http_status(:success)
+        expect(json_response['keep_divergent_refs']).to eq(true)
+      end
     end
 
     # TODO: Remove flag: https://gitlab.com/gitlab-org/gitlab/issues/38121