Raise ArgumentError when conflicting slots are defined. (#1455)

* Raise `ArgumentError` when conflicting slots are defined.

* Update lib/view_component/slotable_v2.rb

Co-authored-by: Blake Williams <blakewilliams@github.com>

Co-authored-by: Blake Williams <blakewilliams@github.com>

Author: joelhawksley

docs/CHANGELOG.md

@@ -9,6 +9,19 @@ title: Changelog
 
 ## main
 
+* Raise `ArgumentError` when conflicting Slots are defined.
+
+    Before this change it was possible to define Slots with conflicting names, for example:
+
+    ```ruby
+    class MyComponent < ViewComponent::Base
+      renders_one :item
+      renders_many :items
+    end
+    ```
+
+    *Joel Hawksley*
+
 ## 2.64.0
 
 * Add `warn_on_deprecated_slot_setter` flag to opt-in to deprecation warning.

lib/view_component/slotable_v2.rb

@@ -80,6 +80,7 @@ def warn_on_deprecated_slot_setter
       #   <% end %>
       def renders_one(slot_name, callable = nil)
         validate_singular_slot_name(slot_name)
+        validate_plural_slot_name(ActiveSupport::Inflector.pluralize(slot_name).to_sym)
 
         define_method :"with_#{slot_name}" do |*args, &block|
           set_slot(slot_name, nil, *args, &block)
@@ -147,9 +148,9 @@ def renders_one(slot_name, callable = nil)
       #     <% end %>
       #   <% end %>
       def renders_many(slot_name, callable = nil)
-        validate_plural_slot_name(slot_name)
-
         singular_name = ActiveSupport::Inflector.singularize(slot_name)
+        validate_plural_slot_name(slot_name)
+        validate_singular_slot_name(ActiveSupport::Inflector.singularize(slot_name).to_sym)
 
         # Define setter for singular names
         # for example `renders_many :items` allows fetching all tabs with

test/sandbox/test/slotable_v2_test.rb

@@ -588,4 +588,26 @@ def test_lambda_slot_content_can_be_provided_via_a_block
 
     assert_selector("h1.some-class", text: "This is a header!")
   end
+
+  def test_raises_error_on_conflicting_slot_names
+    error = assert_raises ArgumentError do
+      Class.new(ViewComponent::Base) do
+        renders_one :conflicting_item
+        renders_many :conflicting_items
+      end
+    end
+
+    assert_includes error.message, "conflicting_item slot multiple times"
+  end
+
+  def test_raises_error_on_conflicting_slot_names_in_reverse_order
+    error = assert_raises ArgumentError do
+      Class.new(ViewComponent::Base) do
+        renders_many :conflicting_items
+        renders_one :conflicting_item
+      end
+    end
+
+    assert_includes error.message, "conflicting_items slot multiple times"
+  end
 end