Prepare the HTML attribute hash for Rails 6.0.3

Rails 6.0.3 doesn't appear to like receiving HTML attribute lists (like
classes) as arrays. This has been improved from Rails 6.1.0 but to
maintain backward-compatibility we're joining the arrays.

This is taken care of by the Attributes class.

Refs #256

lib/govuk_design_system_formbuilder/elements/check_boxes/collection_check_box.rb

@@ -31,7 +31,7 @@ def options
           {
             id: field_id(link_errors: @link_errors),
             class: %(#{brand}-checkboxes__input),
-            aria: { describedby: [hint_id] }
+            aria: { describedby: hint_id }
           }
         end
 

lib/govuk_design_system_formbuilder/elements/radios/collection_radio_button.rb

@@ -35,7 +35,7 @@ def radio
         def options
           {
             id: field_id(link_errors: @link_errors),
-            aria: { describedby: [hint_id] },
+            aria: { describedby: hint_id },
             class: %(#{brand}-radios__input)
           }
         end

lib/govuk_design_system_formbuilder/traits/html_attributes.rb

@@ -1,45 +1,50 @@
 module GOVUKDesignSystemFormBuilder
   module Traits
     module HTMLAttributes
-      class Parser
-        # target any element where the content is a string that represents a
-        # list of things separated by a space, e.g.,
-        #
-        # <span class="red spots">xyz</span>
-        #
-        # could be respresented as
-        #
-        # = span(class: %w(red spots)) { "xyz" }
-        TARGETS = [%i(class), %i(aria describedby)].freeze
-
-        def initialize(attributes)
-          @attributes = parse(attributes)
+      # Attributes eases working with default and custom attributes by
+      # * deeply merging them so both the default (required) attributes are
+      #   present
+      # * joins the arrays into strings to maintain Rails 6.0.3 compatibility
+      class Attributes
+        def initialize(defaults, custom)
+          @merged = defaults.deeper_merge(deep_split_values(custom))
         end
 
         def to_h
-          @attributes
+          deep_join_values(@merged)
         end
 
       private
 
-        def parse(attributes)
-          attributes.tap do |a|
-            a[:class]              = a[:class].split              if has_class_string?(a)
-            a[:aria][:describedby] = a[:aria][:describedby].split if has_aria_describedby_string?(attributes)
+        def deep_split_values(hash)
+          hash.each.with_object({}) do |(key, value), result|
+            result[key] = case value
+                          when Hash
+                            deep_split_values(value)
+                          when String
+                            value.split
+                          else
+                            value
+                          end
           end
         end
 
-        def has_class_string?(attributes)
-          attributes.key?(:class) && attributes[:class].is_a?(String)
-        end
-
-        def has_aria_describedby_string?(attributes)
-          attributes.dig(:aria, :describedby)&.is_a?(String)
+        def deep_join_values(hash)
+          hash.each.with_object({}) do |(key, value), result|
+            result[key] = case value
+                          when Hash
+                            deep_join_values(value)
+                          when Array
+                            value.uniq.join(' ').presence
+                          else
+                            value
+                          end
+          end
         end
       end
 
       def attributes(html_attributes = {})
-        options.deeper_merge(Parser.new(html_attributes).to_h)
+        Attributes.new(options, html_attributes).to_h
       end
     end
   end

spec/govuk_design_system_formbuilder/builder/radios/collection_spec.rb

@@ -148,7 +148,7 @@
           end
         end
 
-        specify 'radio buttons without hints shouldn not have aria-describedby attributes' do
+        specify 'radio buttons without hints should not have aria-describedby attributes' do
           colours_without_descriptions.each do |cwd|
             "person-favourite_colour-#{cwd.id}-hint".tap do |association|
               expect(subject).not_to have_tag('input', with: { "aria-describedby" => association })