Change to decide #thumb_method based on ActiveStorage version

Refs. railsadminteam#3255

Author: mshibuya

lib/rails_admin/config/fields/types/active_storage.rb

@@ -8,7 +8,7 @@ class ActiveStorage < RailsAdmin::Config::Fields::Types::FileUpload
           RailsAdmin::Config::Fields::Types.register(self)
 
           register_instance_option :thumb_method do
-            if Gem.loaded_specs.key?('ruby-vips')
+            if ::ActiveStorage::VERSION::MAJOR >= 6
               {resize_to_limit: [100, 100]}
             else
               {resize: '100x100>'}

lib/rails_admin/config/fields/types/multiple_active_storage.rb

@@ -9,7 +9,7 @@ class MultipleActiveStorage < RailsAdmin::Config::Fields::Types::MultipleFileUpl
 
           class ActiveStorageAttachment < RailsAdmin::Config::Fields::Types::MultipleFileUpload::AbstractAttachment
             register_instance_option :thumb_method do
-              if Gem.loaded_specs.key?('ruby-vips')
+              if ::ActiveStorage::VERSION::MAJOR >= 6
                 {resize_to_limit: [100, 100]}
               else
                 {resize: '100x100>'}

spec/rails_admin/config/fields/types/active_storage_spec.rb

@@ -10,6 +10,16 @@
     end.with(object: record)
   end
 
+  describe '#thumb_method' do
+    it 'returns corresponding value which is to be passed to image_processing(ActiveStorage >= 6.0) or mini_magick(ActiveStorage 5.2)' do
+      if ::ActiveStorage::VERSION::MAJOR >= 6
+        expect(field.thumb_method).to eq(resize_to_limit: [100, 100])
+      else
+        expect(field.thumb_method).to eq(resize: '100x100>')
+      end
+    end
+  end
+
   describe '#image?' do
     context 'when attachment is an image' do
       let(:record) { FactoryBot.create :field_test, active_storage_asset: {io: StringIO.new('dummy'), filename: "test.jpg", content_type: "image/jpeg"} }

spec/rails_admin/config/fields/types/multiple_active_storage_spec.rb

@@ -14,6 +14,19 @@
   end
 
   describe RailsAdmin::Config::Fields::Types::MultipleActiveStorage::ActiveStorageAttachment do
+    describe '#thumb_method' do
+      let(:record) { FactoryBot.create :field_test, active_storage_assets: [{io: StringIO.new('dummy'), filename: "test.txt", content_type: "text/plain"}] }
+      subject { field.attachments[0] }
+
+      it 'returns corresponding value which is to be passed to image_processing(ActiveStorage >= 6.0) or mini_magick(ActiveStorage 5.2)' do
+        if ::ActiveStorage::VERSION::MAJOR >= 6
+          expect(subject.thumb_method).to eq(resize_to_limit: [100, 100])
+        else
+          expect(subject.thumb_method).to eq(resize: '100x100>')
+        end
+      end
+    end
+
     describe '#pretty_value' do
       subject { field.pretty_value }