Fix second 500 error with NULL restricted visibility levels

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/30313 fixed one
500 error when `application_settings.restricted_visibility_levels` is
NULL, but https://gitlab.com/gitlab-org/gitlab/-/merge_requests/22522
introduced the public visiblity check in two places.

To fix this problem and reduce code duplication, move this check into
`Gitlab::VisibilityLevel`, where NULL values of
`restricted_visibility_levels` was already handled.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/215638

app/controllers/application_controller.rb

@@ -497,7 +497,7 @@ class ApplicationController < ActionController::Base
   end
 
   def public_visibility_restricted?
-    Gitlab::CurrentSettings.restricted_visibility_levels.include? Gitlab::VisibilityLevel::PUBLIC
+    Gitlab::VisibilityLevel.public_visibility_restricted?
   end
 
   def set_usage_stats_consent_flag

app/helpers/explore_helper.rb

@@ -52,7 +52,7 @@ module ExploreHelper
   end
 
   def public_visibility_restricted?
-    Gitlab::CurrentSettings.restricted_visibility_levels&.include? Gitlab::VisibilityLevel::PUBLIC
+    Gitlab::VisibilityLevel.public_visibility_restricted?
   end
 
   private

changelogs/unreleased/sh-clean-up-public-visiblity-level-check.yml

+---
+title: Fix second 500 error with NULL restricted visibility levels
+merge_request: 30414
+author:
+type: fixed

lib/gitlab/visibility_level.rb

@@ -82,15 +82,23 @@ module Gitlab
       end
 
       def non_restricted_level?(level)
+        !restricted_level?(level)
+      end
+
+      def restricted_level?(level)
         restricted_levels = Gitlab::CurrentSettings.restricted_visibility_levels
 
         if restricted_levels.nil?
-          true
+          false
         else
-          !restricted_levels.include?(level)
+          restricted_levels.include?(level)
         end
       end
 
+      def public_visibility_restricted?
+        restricted_level?(PUBLIC)
+      end
+
       def valid_level?(level)
         options.value?(level)
       end

spec/helpers/explore_helper_spec.rb

@@ -19,23 +19,10 @@ describe ExploreHelper do
   end
 
   describe '#public_visibility_restricted?' do
-    using RSpec::Parameterized::TableSyntax
+    it 'delegates to Gitlab::VisibilityLevel' do
+      expect(Gitlab::VisibilityLevel).to receive(:public_visibility_restricted?).and_call_original
 
-    where(:visibility_levels, :expected_status) do
-      nil | nil
-      [Gitlab::VisibilityLevel::PRIVATE] | false
-      [Gitlab::VisibilityLevel::PRIVATE, Gitlab::VisibilityLevel::INTERNAL] | false
-      [Gitlab::VisibilityLevel::PUBLIC] | true
-    end
-
-    with_them do
-      before do
-        stub_application_setting(restricted_visibility_levels: visibility_levels)
-      end
-
-      it 'returns the expected status' do
-        expect(helper.public_visibility_restricted?).to eq(expected_status)
-      end
+      helper.public_visibility_restricted?
     end
   end
 end

spec/lib/gitlab/visibility_level_spec.rb

@@ -96,6 +96,30 @@ describe Gitlab::VisibilityLevel do
     end
   end
 
+  describe '.restricted_level?, .non_restricted_level?, and .public_level_restricted?' do
+    using RSpec::Parameterized::TableSyntax
+
+    where(:visibility_levels, :expected_status) do
+      nil | false
+      [Gitlab::VisibilityLevel::PRIVATE] | false
+      [Gitlab::VisibilityLevel::PRIVATE, Gitlab::VisibilityLevel::INTERNAL] | false
+      [Gitlab::VisibilityLevel::PUBLIC] | true
+      [Gitlab::VisibilityLevel::PUBLIC, Gitlab::VisibilityLevel::INTERNAL] | true
+    end
+
+    with_them do
+      before do
+        stub_application_setting(restricted_visibility_levels: visibility_levels)
+      end
+
+      it 'returns the expected status' do
+        expect(described_class.restricted_level?(Gitlab::VisibilityLevel::PUBLIC)).to eq(expected_status)
+        expect(described_class.non_restricted_level?(Gitlab::VisibilityLevel::PUBLIC)).to eq(!expected_status)
+        expect(described_class.public_visibility_restricted?).to eq(expected_status)
+      end
+    end
+  end
+
   describe '#visibility_level_decreased?' do
     let(:project) { create(:project, :internal) }