Fix stale content cache when slots are accessed before render_in

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 6
 
 ## main
 
+* Fix stale content cache when slots are accessed before `render_in`.
+
+    *Jared Armstrong*
+
 * Add rubocop-view_component to resources.
 
     *Andy Waite*

lib/view_component/base.rb

@@ -131,6 +131,7 @@ def render_in(view_context, &block)
       end
 
       @__vc_content_evaluated = false
+      remove_instance_variable(:@__vc_content) if defined?(@__vc_content)
       @__vc_render_in_block = block
       @view_context.instance_variable_set(:@virtual_path, virtual_path)
 

test/sandbox/app/components/slot_with_content_block_component.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class SlotWithContentBlockComponent < ViewComponent::Base
+  renders_one :header
+
+  def call
+    out = +""
+    out << content_tag(:div, header, class: "header") if header?
+    out << content_tag(:div, content, class: "body") if content?
+    out.html_safe
+  end
+end

test/sandbox/test/slotable_test.rb

@@ -822,6 +822,23 @@ def test_slot_name_methods_are_not_shared_accross_components
     assert_not_equal SlotsComponent.instance_method(:title).owner, SlotNameOverrideComponent::OtherComponent.instance_method(:title).owner
   end
 
+  def test_slot_predicate_before_render_does_not_poison_content_cache
+    component = SlotWithContentBlockComponent.new
+    component.with_header { "My Header" }
+
+    # Accessing a slot predicate before render_in triggers content evaluation
+    # via __vc_get_slot. Without the fix, this caches a nil @__vc_content that
+    # persists through render_in, causing the content block to be silently ignored.
+    assert component.header?
+
+    render_inline(component) do
+      "Body content from block"
+    end
+
+    assert_selector(".header", text: "My Header")
+    assert_selector(".body", text: "Body content from block")
+  end
+
   def test_allows_marking_slot_as_last
     render_inline(LastItemComponent.new) do |component|
       component.with_item("animal")