Add tests for rendering parents from inline templates (i.e. #call met…

…hods); add helpful #render_parent_to_string method

docs/api.md

@@ -114,6 +114,19 @@ double render if they emit the result.
 parent template considering the current variant and emits the result without
 double-rendering.
 
+### `#render_parent_to_string`
+
+Renders the parent component to a string and returns it. This method is meant
+to be used inside custom #call methods when a string result is desired, eg.
+
+```ruby
+def call
+  "<div>#{render_parent_to_string}</div>"
+end
+```
+
+When rendering the parent inside an .erb template, use `#render_parent` instead.
+
 ### `#request` → [ActionDispatch::Request]
 
 The current request. Use sparingly as doing so introduces coupling that

docs/guide/templates.md

@@ -143,19 +143,31 @@ class MyComponent < ViewComponent::Base
 end
 ```
 
-To render a parent component's template from a `#call` method, call `super`.
+Finally, `#render_parent` also works inside `#call` methods:
+
+```ruby
+class MyComponent < ViewComponent::Base
+  def call
+    content_tag("div") do
+      render_parent
+    end
+  end
+end
+```
+
+When composing `#call` methods, keep in mind that `#render_parent` does not return a string. If a string is desired, call `#render_parent_to_string` instead. For example:
 
 ```ruby
 class MyComponent < ViewComponent::Base
   # "phone" variant
   def call_phone
-    "<div>#{super}</div>"
+    content_tag("div") do
+      "<div>#{render_parent_to_string}</div>"
+    end
   end
 end
 ```
 
-`super` will attempt to call the `#call_phone` method on the parent class. If the parent class doesn't support the "phone" variant, Ruby will raise a `NoMethodError`. Consider using a template and `#render_parent` to handle superclass variants automatically.
-
 ## Trailing whitespace
 
 Code editors commonly add a trailing newline character to source files in keeping with the Unix standard. Including trailing whitespace in component templates can result in unwanted whitespace in the HTML, eg. if the component is rendered before the period at the end of a sentence.

lib/view_component/base.rb

@@ -140,6 +140,20 @@ def render_parent
       end
     end
 
+    # Renders the parent component to a string and returns it. This method is meant
+    # to be used inside custom #call methods when a string result is desired, eg.
+    #
+    # ```ruby
+    # def call
+    #   "<div>#{render_parent_to_string}</div>"
+    # end
+    # ```
+    #
+    # When rendering the parent inside an .erb template, use `#render_parent` instead.
+    def render_parent_to_string
+      capture { render_parent }
+    end
+
     # Optional content to be returned after the rendered template.
     #
     # @return [String]

test/sandbox/app/components/inline_level1_component.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class InlineLevel1Component < ViewComponent::Base
+  def call
+    content_tag(:div, class: "level1-component")
+  end
+end

test/sandbox/app/components/inline_level2_component.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class InlineLevel2Component < Level2Component
+  def call
+    "<div level2-component base>#{render_parent_to_string}</div>"
+  end
+
+  def call_variant
+    "<div level2-component variant>#{render_parent_to_string}</div>"
+  end
+end

test/sandbox/app/components/inline_level3_component.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class InlineLevel3Component < Level2Component
+  def call
+    content_tag(:div, class: "level3-component base") do
+      render_parent
+    end
+  end
+
+  def call_variant
+    content_tag(:div, class: "level3-component variant") do
+      render_parent
+    end
+  end
+end

test/sandbox/test/rendering_test.rb

@@ -991,6 +991,28 @@ def test_child_components_fall_back_to_default_variant
     assert_selector ".level3-component.base .level2-component.base .level1-component"
   end
 
+  def test_child_components_can_render_parent_with_inline_templates
+    render_inline(InlineLevel3Component.new)
+
+    assert_selector(".level3-component.base .level2-component.base .level1-component")
+  end
+
+  def test_variant_propagates_to_parent_with_inline_templates
+    with_variant :variant do
+      render_inline(InlineLevel3Component.new)
+    end
+
+    assert_selector ".level3-component.variant .level2-component.variant .level1-component"
+  end
+
+  def test_child_components_fall_back_to_default_variant_with_inline_templates
+    with_variant :non_existent_variant do
+      render_inline(InlineLevel3Component.new)
+    end
+
+    assert_selector ".level3-component.base .level2-component.base .level1-component"
+  end
+
   def test_component_renders_without_trailing_whitespace
     template = File.read(Rails.root.join("app/components/trailing_whitespace_component.html.erb"))
     assert template =~ /\s+\z/, "Template does not contain any trailing whitespace"