Only output the wrapper if the block yields content

This change allows the wrappers to not output their rendered HTML when
when the block yields no content.

e.g. when defining an optional component :

  ba.wrapper tag: :div, class: 'form-helper -message -hint' do |bb|
    bb.optional :hint, wrap_with: { tag: :p }
  end

and that component is not used in a template :

  <%= form.input :name %>

Then the HTML output still contains the wrapper output :

  <div class="form-helper -message -help"></div>

If this behaviour is not desired, then the output of the empty tags can
be disabled via the `remove_empty` option.

  ba.wrapper tag: :div, class: 'form-helper -message -hint', remove_empty: true do |bb|
    bb.optional :hint, wrap_with: { tag: :p }
  end

The above config will not output any wrapper HTML.

lib/simple_form/wrappers/many.rb

@@ -50,6 +50,7 @@ module SimpleForm
 
       def wrap(input, options, content)
         return content if options[namespace] == false
+        return if defaults[:optional] && content.empty?
 
         tag = (namespace && options[:"#{namespace}_tag"]) || @defaults[:tag]
         return content unless tag

test/form_builder/hint_test.rb

@@ -141,4 +141,29 @@ class HintTest < ActionView::TestCase
       assert_select 'div.omg_hint', "can&#39;t be blank"
     end
   end
+
+  test 'optional hint displays when given' do
+    swap_wrapper :default, self.custom_wrapper_with_optional_div do
+      with_form_for @user, :name, hint: "can't be blank"
+      assert_select 'section.custom_wrapper div.no_output_wrapper p.omg_hint', "can&#39;t be blank"
+      assert_select 'p.omg_hint'
+    end
+  end
+
+  test 'optional hint displays empty wrapper when no hint given' do
+    swap_wrapper :default, self.custom_wrapper_with_optional_div do
+      with_form_for @user, :name
+      assert_select 'section.custom_wrapper div.no_output_wrapper'
+      assert_no_select 'p.omg_hint'
+    end
+  end
+
+  test 'optional hint displays no wrapper or hint when no hint and override is given' do
+    swap_wrapper :default, self.custom_wrapper_with_optional_div_and_override do
+      with_form_for @user, :name
+      assert_no_select 'section.custom_wrapper div.no_output_wrapper'
+      assert_no_select 'div.no_output_wrapper'
+      assert_no_select 'p.omg_hint'
+    end
+  end
 end

test/support/misc_helpers.rb

@@ -68,6 +68,22 @@ module MiscHelpers
     end
   end
 
+  def custom_wrapper_with_optional_div
+    SimpleForm.build tag: :section, class: "custom_wrapper" do |b|
+      b.wrapper tag: :div, class: 'no_output_wrapper' do |ba|
+        ba.optional :hint, wrap_with: { tag: :p, class: 'omg_hint' }
+      end
+    end
+  end
+
+  def custom_wrapper_with_optional_div_and_override
+    SimpleForm.build tag: :section, class: "custom_wrapper" do |b|
+      b.wrapper tag: :div, class: 'no_output_wrapper', optional: true do |ba|
+        ba.optional :hint, wrap_with: { tag: :p, class: 'omg_hint' }
+      end
+    end
+  end
+
   def custom_wrapper_with_input_class
     SimpleForm.build tag: :div, class: "custom_wrapper" do |b|
       b.use :label