add test and update changelog to show polymorphic slots extend

Author: joelhawksley

docs/CHANGELOG.md

@@ -22,12 +22,13 @@ nav_order: 6
 
     class SpecialButtonComponent < ButtonComponent
       renders_many :leading_items, types: {
-        svg: SvgComponent,
         checkbox: CheckboxComponent
       }
     end
     ```
 
+    Where `SpecialButtonComponent` will accept `with_leading_item_icon`, `with_leading_item_svg`, and `with_leading_item_checkbox`.
+
 ## 4.0.0.rc1
 
 Almost six years after releasing [v1.0.0](https://github.com/ViewComponent/view_component/releases/tag/v1.0.0), we're proud to ship the first release candidate of ViewComponent 4. This release marks a shift towards a Long Term Support model for the project, having reached significant feature maturity. While contributions are always welcome, we're unlikely to accept further breaking changes or major feature additions.

test/sandbox/app/components/polymorphic_slot_subclass_component.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class PolymorphicSlotSubclassComponent < PolymorphicSlotComponent
+  renders_one :header, types: {
+    my: lambda { |&block| content_tag(:div, class: "my", &block) },
+  }
+end

test/sandbox/test/slotable_test.rb

@@ -638,9 +638,12 @@ def test_component_delegation_slots_work_with_helpers
 
   def test_subclass_can_redefine_slot
     render_inline(SlotsSubclassComponent.new(classes: "mt-4")) do |component|
+      # overridden in subclass
       component.with_title do
         "This is my title!"
       end
+
+      # defined in parent class
       component.with_subtitle do
         "This is my subtitle!"
       end
@@ -650,6 +653,21 @@ def test_subclass_can_redefine_slot
     assert_selector(".subtitle", text: "This is my subtitle!")
   end
 
+  def test_subclass_can_redefine_polymorphic_slot_entirely
+    render_inline(PolymorphicSlotSubclassComponent.new) do |component|
+      # Overridden in subclass
+      component.with_header_my { "mine" }
+
+      # defined in parent class
+      component.with_foo_field(class_names: "custom-foo1")
+      component.with_item_bar(class_names: "custom-bar2")
+    end
+
+    assert_selector("div .my", text: "mine")
+    assert_selector("div .foo.custom-foo1")
+    assert_selector("div .bar.custom-bar2")
+  end
+
   def test_lambda_slot_content_can_be_provided_via_a_block
     render_inline LambdaSlotComponent.new do |component|
       component.with_header(classes: "some-class") do