Hide rules when approval feature is unavailable

This means existing unapproved rules would have no effect on MR
merging process.

ee/app/models/approval_state.rb

@@ -31,6 +31,8 @@ class ApprovalState
 
   def wrapped_approval_rules
     strong_memoize(:wrapped_approval_rules) do
+      next [] unless project.feature_available?(:merge_request_approvers)
+
       result = use_fallback? ? [fallback_rule] : regular_rules
       result += code_owner_rules
       result

ee/spec/models/approval_state_spec.rb

@@ -17,6 +17,11 @@ describe ApprovalState do
     end
   end
 
+  def disable_feature
+    allow(subject.project).to receive(:feature_available?).and_call_original
+    allow(subject.project).to receive(:feature_available?).with(:merge_request_approvers).and_return(false)
+  end
+
   let(:merge_request) { create(:merge_request) }
   let(:project) { merge_request.target_project }
   let(:approver1) { create(:user) }
@@ -108,6 +113,14 @@ describe ApprovalState do
         expect(subject.wrapped_approval_rules).to all(be_an(ApprovalWrappedRule))
         expect(subject.wrapped_approval_rules.size).to eq(2)
       end
+
+      context 'when approval feature is unavailable' do
+        it 'returns empty array' do
+          disable_feature
+
+          expect(subject.wrapped_approval_rules).to eq([])
+        end
+      end
     end
 
     describe '#approval_needed?' do
@@ -150,6 +163,14 @@ describe ApprovalState do
           expect(subject.approval_needed?).to eq(false)
         end
       end
+
+      context 'when approval feature is unavailable' do
+        it 'returns false' do
+          disable_feature
+
+          expect(subject.approval_needed?).to eq(false)
+        end
+      end
     end
 
     describe '#approved?' do
@@ -216,6 +237,15 @@ describe ApprovalState do
 
         it_behaves_like 'when rules are present'
       end
+
+      context 'when approval feature is unavailable' do
+        it 'returns true' do
+          disable_feature
+          create_rule(users: [create(:user)], approvals_required: 1)
+
+          expect(subject.approved?).to eq(true)
+        end
+      end
     end
 
     describe '#any_approver_allowed?' do
@@ -261,6 +291,14 @@ describe ApprovalState do
       it 'sums approvals_left from rules' do
         expect(subject.approvals_left).to eq(12)
       end
+
+      context 'when approval feature is unavailable' do
+        it 'returns 0' do
+          disable_feature
+
+          expect(subject.approvals_left).to eq(0)
+        end
+      end
     end
 
     describe '#approval_rules_left' do
@@ -268,12 +306,21 @@ describe ApprovalState do
         create_rule(approvals_required: 1, users: [create(:user)])
       end
 
-      it 'counts approval_rules left' do
-        create_unapproved_rule
-        create_unapproved_rule
+      before do
+        2.times { create_unapproved_rule }
+      end
 
+      it 'counts approval_rules left' do
         expect(subject.approval_rules_left.size).to eq(2)
       end
+
+      context 'when approval feature is unavailable' do
+        it 'returns empty array' do
+          disable_feature
+
+          expect(subject.approval_rules_left).to eq([])
+        end
+      end
     end
 
     describe '#approvers' do