Fix presence matcher against an AM record

When using the presence matcher against an ActiveModel record, check to
ensure that the model is using the Attributes API and has explicitly
declared the attribute to be a string before attempting to set the
attribute to an empty string. Otherwise, the attribute may be getting
treated as an object in some point in the validation process, and
therefore setting it to an empty string would create problems.

lib/shoulda/matchers/active_model/validate_presence_of_matcher.rb

@@ -310,11 +310,13 @@ def belongs_to_association_being_validated?
         end
 
         def attribute_accepts_string_values?
-          !association? && (
-            !attribute_type.respond_to?(:coder) ||
-            !attribute_type.coder ||
-            attribute_type.coder.object_class == String
-          )
+          if association?
+            false
+          elsif attribute_serializer
+            attribute_serializer.object_class == String
+          else
+            attribute_type.try(:type) == :string
+          end
         end
 
         def association?
@@ -339,6 +341,14 @@ def association_reflection
           model.try(:reflect_on_association, @attribute)
         end
 
+        def attribute_serializer
+          if attribute_type.respond_to?(:coder)
+            attribute_type.coder
+          else
+            nil
+          end
+        end
+
         def attribute_type
           RailsShim.attribute_type_for(model, @attribute)
         end

lib/shoulda/matchers/rails_shim.rb

@@ -157,7 +157,7 @@ def secure_password_module
         end
 
         def attribute_type_for(model, attribute_name)
-          if model.respond_to?(:attribute_types)
+          if supports_full_attributes_api?(model)
             model.attribute_types[attribute_name.to_s]
           else
             LegacyAttributeType.new(model, attribute_name)
@@ -188,6 +188,11 @@ def simply_generate_validation_message(
           I18n.translate(primary_translation_key, translate_options)
         end
 
+        def supports_full_attributes_api?(model)
+          defined?(::ActiveModel::Attributes) &&
+            model.respond_to?(:attribute_types)
+        end
+
         class LegacyAttributeType
           def initialize(model, attribute_name)
             @model = model

spec/unit/shoulda/matchers/active_model/validate_presence_of_matcher_spec.rb

@@ -109,10 +109,17 @@
         expect(record).to matcher
       end
 
+      blank_value =
+        if active_model_supports_full_attributes_api?
+          ''
+        else
+          nil
+        end
+
       message = <<-MESSAGE
 Expected Example to validate that :attr cannot be empty/falsy, but this
 could not be proved.
-  After setting :attr to ‹""›, the matcher expected the Example to be
+  After setting :attr to ‹#{blank_value.inspect}›, the matcher expected the Example to be
   invalid, but it was valid instead.
       MESSAGE
 
@@ -178,6 +185,28 @@
           end
         end
       end
+
+      context 'when the attribute has not been configured with a type' do
+        context 'and it is assumed to be something other than a string' do
+          it 'still works' do
+            record = active_model_object_validating_presence_of(:user) do
+              attribute :user
+
+              validate :validate_user_has_email, if: :user
+
+              private
+
+              def validate_user_has_email
+                if !user.email
+                  errors.add(:base, 'user does not have an email')
+                end
+              end
+            end
+
+            expect(record).to validate_presence_of(:user)
+          end
+        end
+      end
     end
 
     def model_creator
@@ -196,7 +225,7 @@ def model_creator
       message = <<-MESSAGE
 Expected Example to validate that :attr cannot be empty/falsy, but this
 could not be proved.
-  After setting :attr to ‹""›, the matcher expected the Example to be
+  After setting :attr to ‹nil›, the matcher expected the Example to be
   invalid, but it was valid instead.
       MESSAGE
 
@@ -735,10 +764,17 @@ def record_belonging_to(
         expect(validating_presence(strict: false)).to matcher.strict
       end
 
+      blank_value =
+        if active_model_supports_full_attributes_api?
+          ''
+        else
+          nil
+        end
+
       message = <<-MESSAGE
 Expected Example to validate that :attr cannot be empty/falsy, raising a
 validation exception on failure, but this could not be proved.
-  After setting :attr to ‹""›, the matcher expected the Example to be
+  After setting :attr to ‹#{blank_value.inspect}›, the matcher expected the Example to be
   invalid and to raise a validation exception, but the record produced
   validation errors instead.
       MESSAGE
@@ -827,14 +863,23 @@ def foo=(value)
 
           assertion = -> { expect(record).not_to matcher.allow_nil }
 
-          expect(&assertion).to fail_with_message(<<-MESSAGE)
+          if active_model_supports_full_attributes_api?
+            expect(&assertion).to fail_with_message(<<-MESSAGE)
 Expected Example not to validate that :attr cannot be empty/falsy, but
 this could not be proved.
   After setting :attr to ‹""›, the matcher expected the Example to be
   valid, but it was invalid instead, producing these validation errors:
 
   * attr: ["can't be blank"]
-          MESSAGE
+            MESSAGE
+          else
+            expect(&assertion).to fail_with_message(<<-MESSAGE)
+Expected Example not to validate that :attr cannot be empty/falsy, but
+this could not be proved.
+  After setting :attr to ‹nil›, the matcher expected the Example to be
+  invalid, but it was valid instead.
+            MESSAGE
+          end
         end
       end
 
@@ -867,27 +912,52 @@ def foo=(value)
     end
 
     context 'when validating a model without a presence validator' do
-      it 'does not match in the positive' do
-        record = without_validating_presence
+      if active_model_supports_full_attributes_api?
+        it 'does not match in the positive' do
+          record = without_validating_presence
 
-        assertion = lambda do
-          expect(record).to matcher.allow_nil
-        end
+          assertion = lambda do
+            expect(record).to matcher.allow_nil
+          end
 
-        message = <<-MESSAGE
+          message = <<-MESSAGE
 Expected Example to validate that :attr cannot be empty/falsy, but this
 could not be proved.
   After setting :attr to ‹""›, the matcher expected the Example to be
   invalid, but it was valid instead.
-        MESSAGE
+          MESSAGE
 
-        expect(&assertion).to fail_with_message(message)
-      end
+          expect(&assertion).to fail_with_message(message)
+        end
 
-      it 'matches in the negative' do
-        record = without_validating_presence
+        it 'matches in the negative' do
+          record = without_validating_presence
 
-        expect(record).not_to matcher.allow_nil
+          expect(record).not_to matcher.allow_nil
+        end
+      else
+        it 'matches in the positive' do
+          record = without_validating_presence
+
+          expect(record).to matcher.allow_nil
+        end
+
+        it 'does not match in the negative' do
+          record = without_validating_presence
+
+          assertion = lambda do
+            expect(record).not_to matcher.allow_nil
+          end
+
+          message = <<-MESSAGE
+Expected Example not to validate that :attr cannot be empty/falsy, but
+this could not be proved.
+  After setting :attr to ‹nil›, the matcher expected the Example to be
+  invalid, but it was valid instead.
+          MESSAGE
+
+          expect(&assertion).to fail_with_message(message)
+        end
       end
     end
   end