Add max_pinned_statuses to instances serializer and api response (#29441)

spec/requests/api/v2/instance_spec.rb

@@ -18,6 +18,7 @@ describe 'Instances' do
         expect(body_as_json)
           .to be_present
           .and include(title: 'Mastodon')
+          .and include_configuration_limits
       end
     end
 
@@ -31,7 +32,26 @@ describe 'Instances' do
         expect(body_as_json)
           .to be_present
           .and include(title: 'Mastodon')
+          .and include_configuration_limits
       end
     end
+
+    def include_configuration_limits
+      include(
+        configuration: include(
+          accounts: include(
+            max_featured_tags: FeaturedTag::LIMIT,
+            max_pinned_statuses: StatusPinValidator::PIN_LIMIT
+          ),
+          statuses: include(
+            max_characters: StatusLengthValidator::MAX_CHARS,
+            max_media_attachments: 4 # TODO, move to constant somewhere
+          ),
+          polls: include(
+            max_options: PollValidator::MAX_OPTIONS
+          )
+        )
+      )
+    end
   end
 end

spec/serializers/rest/instance_serializer_spec.rb

@@ -10,11 +10,22 @@ describe REST::InstanceSerializer do
     it 'returns recent usage data' do
       expect(serialization['usage']).to eq({ 'users' => { 'active_month' => 0 } })
     end
+  end
 
+  describe 'configuration' do
     it 'returns the VAPID public key' do
       expect(serialization['configuration']['vapid']).to eq({
         'public_key' => Rails.configuration.x.vapid_public_key,
       })
     end
+
+    it 'returns the max pinned statuses limit' do
+      expect(serialization.deep_symbolize_keys)
+        .to include(
+          configuration: include(
+            accounts: include(max_pinned_statuses: StatusPinValidator::PIN_LIMIT)
+          )
+        )
+    end
   end
 end