validate_presence_of(:active_storage_field) throws exception

lib/shoulda/matchers/active_model/validate_presence_of_matcher.rb

@@ -236,6 +236,8 @@ def disallows_original_or_typecast_value?(value)
         def disallowed_values
           if collection?
             [Array.new]
+          elsif attachment?
+            [nil]
           else
             values = []
 
@@ -341,6 +343,11 @@ def association_reflection
             model.reflect_on_association(@attribute)
         end
 
+        def attachment?
+          model.respond_to?(:reflect_on_association) &&
+            model_has_associations?(["#{@attribute}_attachment", "#{@attribute}_attachments"])
+        end
+
         def attribute_type
           if model.respond_to?(:attribute_types)
             model.attribute_types[@attribute.to_s]
@@ -349,6 +356,10 @@ def attribute_type
           end
         end
 
+        def model_has_associations?(associations)
+          associations.any? { |association| !!model.reflect_on_association(association) }
+        end
+
         def presence_validation_exists_on_attribute?
           model._validators.include?(@attribute)
         end

spec/support/unit/helpers/active_record_versions.rb

@@ -44,5 +44,9 @@ def active_record_supports_optional_for_associations?
     def active_record_supports_expression_indexes?
       active_record_version >= 5
     end
+
+    def active_record_supports_validate_presence_on_active_storage?
+      active_record_version >= '6.0.0.beta1'
+    end
   end
 end

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

@@ -204,6 +204,88 @@ def model_creator
     end
   end
 
+  if active_record_supports_validate_presence_on_active_storage?
+    context 'a has_one_attached association with a presence validation' do
+      it 'requires the attribute to be set' do
+        expect(has_one_attached_child(presence: true)).to validate_presence_of(:child)
+      end
+
+      it_supports(
+        'ignoring_interference_by_writer',
+        tests: {
+          accept_if_qualified_but_changing_value_does_not_interfere: {
+            changing_values_with: :nil_to_blank
+          },
+          reject_if_qualified_but_changing_value_interferes: {
+            model_name: 'Example',
+            attribute_name: :attr,
+            changing_values_with: :never_falsy,
+            expected_message: <<-MESSAGE
+Expected Example to validate that :attr cannot be empty/falsy, but this
+could not be proved.
+  After setting :attr to ‹nil› -- which was read back as ‹"dummy value"›
+  -- the matcher expected the Example to be invalid, but it was valid
+  instead.
+
+  As indicated in the message above, :attr seems to be changing certain
+  values as they are set, and this could have something to do with why
+  this test is failing. If you've overridden the writer method for this
+  attribute, then you may need to change it to make this test pass, or
+  do something else entirely.
+            MESSAGE
+          }
+        }
+      )
+    end
+
+    context 'a has_one_attached association without a presence validation' do
+      it 'requires the attribute to be set' do
+        expect(has_one_attached_child(presence: false)).
+          not_to validate_presence_of(:child)
+      end
+    end
+
+    context 'a has_many_attached association with a presence validation' do
+      it 'requires the attribute to be set' do
+        expect(has_many_attached_children(presence: true)).to validate_presence_of(:children)
+      end
+
+      it_supports(
+        'ignoring_interference_by_writer',
+        tests: {
+          accept_if_qualified_but_changing_value_does_not_interfere: {
+            changing_values_with: :nil_to_blank
+          },
+          reject_if_qualified_but_changing_value_interferes: {
+            model_name: 'Example',
+            attribute_name: :attr,
+            changing_values_with: :never_falsy,
+            expected_message: <<-MESSAGE
+Expected Example to validate that :attr cannot be empty/falsy, but this
+could not be proved.
+  After setting :attr to ‹nil› -- which was read back as ‹"dummy value"›
+  -- the matcher expected the Example to be invalid, but it was valid
+  instead.
+
+  As indicated in the message above, :attr seems to be changing certain
+  values as they are set, and this could have something to do with why
+  this test is failing. If you've overridden the writer method for this
+  attribute, then you may need to change it to make this test pass, or
+  do something else entirely.
+            MESSAGE
+          }
+        }
+      )
+    end
+
+    context 'a has_many_attached association without a presence validation' do
+      it 'does not require the attribute to be set' do
+        expect(has_many_attached_children(presence: false)).
+          not_to validate_presence_of(:children)
+      end
+    end
+  end
+
   context 'a has_many association with a presence validation' do
     it 'requires the attribute to be set' do
       expect(has_many_children(presence: true)).to validate_presence_of(:children)
@@ -960,6 +1042,26 @@ def has_many_children(options = {})
     end.new
   end
 
+  def has_one_attached_child(options = {})
+    define_model :child
+    define_model :parent do
+      has_one_attached :child
+      if options[:presence]
+        validates_presence_of :child
+      end
+    end.new
+  end
+
+  def has_many_attached_children(options = {})
+    define_model :child
+    define_model :parent do
+      has_many_attached :children
+      if options[:presence]
+        validates_presence_of :children
+      end
+    end.new
+  end
+
   def active_resource_model
     define_active_resource_class :foo, attr: :string do
       validates_presence_of :attr