Support nil activestorage objects

lib/file_validators/validators/file_size_validator.rb

@@ -60,6 +60,8 @@ def check_options(klass, options)
       def value_byte_size(value)
         if value.respond_to?(:byte_size)
           value.byte_size
+        elsif value.respond_to?(:attached?)
+          value.size if value.attached?
         else
           value.size
         end

spec/lib/file_validators/validators/file_size_validator_spec.rb

@@ -208,4 +208,15 @@ def build_validator(options)
       expect { build_validator in: 5.kilobytes }.to raise_error(ArgumentError)
     end
   end
+
+  ##
+  # trying to call #size on an ActiveStorage attachment
+  # causes errors when it is not defined e.g.
+  # "Module::DelegationError: size delegated to attachment, but attachment is nil"
+  context 'on ActiveStorage attachment' do
+    before { build_validator greater_than: 5.kilobytes }
+
+    it { is_expected.not_to allow_file_size_on_nil_activesupport_file(6.kilobytes, @validator,
+                                          message: "Avatar file size must be greater than #{@storage_units[5120]}") }
+  end
 end

spec/support/matchers/allow_file_size_on_nil_activesupport_file.rb

@@ -0,0 +1,16 @@
+RSpec::Matchers.define :allow_file_size_on_nil_activesupport_file do |size, validator, message|
+  match do |model|
+    value = double
+    allow(value).to(receive(:size).and_raise(Module::DelegationError, "size delegated to attachment, but attachment is nil"))
+    allow(value).to(receive(:attached?).and_return(false))
+
+    allow_any_instance_of(model).to receive(:read_attribute_for_validation).and_return(value)
+    dummy = model.new
+    validator.validate(dummy)
+    if message.present?
+      dummy.errors.full_messages.exclude?(message[:message])
+    else
+      dummy.errors.empty?
+    end
+  end
+end