Merge pull request #2375 from ViewComponent/2344-around-render

Add around_render lifecycle method for wrapping component rendering

Author: joelhawksley

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 6
 
 ## main
 
+* Add `around_render` lifecyle method for wrapping component rendering in custom instrumentation, etc.
+
+    *Joel Hawksley*, *Blake Williams*
+
 ## 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.

docs/guide/lifecycle.md

@@ -21,3 +21,21 @@ class ExampleComponent < ViewComponent::Base
   end
 end
 ```
+
+## `#around_render`
+
+Since 4.0.0.rc2
+{: .label }
+
+Define an `around_render` method to be called around the rendering of a component:
+
+```ruby
+# app/components/example_component.rb
+class ExampleComponent < ViewComponent::Base
+  def around_render
+    MyIntrumenter.instrument do
+      yield
+    end
+  end
+end
+```

docs/how-it-works.md

@@ -42,4 +42,4 @@ First, ViewComponent calls the `before_render` method, which gives ViewComponent
 
 Second, ViewComponent calls `render?`, returning early with an empty string if `render?` returns false.
 
-ViewComponent then renders the component template.
+ViewComponent then renders the component template, wrapped in a call to the `around_render` method.

lib/view_component/base.rb

@@ -143,7 +143,10 @@ def render_in(view_context, &block)
         @output_buffer.with_buffer do
           @view_context.instance_variable_set(:@virtual_path, virtual_path)
 
-          rendered_template = render_template_for(@__vc_requested_details).to_s
+          rendered_template =
+            around_render do
+              render_template_for(@__vc_requested_details).to_s
+            end
 
           # Avoid allocating new string when output_preamble and output_postamble are blank
           value = if output_preamble.blank? && output_postamble.blank?
@@ -228,6 +231,14 @@ def before_render
       # noop
     end
 
+    # Called around rendering the component. Override to wrap the rendering of a
+    # component in custom instrumentation, etc.
+    #
+    # @return [void]
+    def around_render
+      yield
+    end
+
     # Override to determine whether the ViewComponent should render.
     #
     # @return [Boolean]

test/sandbox/app/components/around_render_component.rb

@@ -0,0 +1,11 @@
+class AroundRenderComponent < ViewComponent::Base
+  def call
+    "Hi!".html_safe
+  end
+
+  def around_render
+    Instrumenter.tick do
+      yield
+    end
+  end
+end

test/sandbox/app/models/instrumenter.rb

@@ -0,0 +1,8 @@
+class Instrumenter
+  cattr_accessor :count, instance_reader: false, instance_writer: false, instance_accessor: false, default: 0
+
+  def self.tick
+    Instrumenter.count = Instrumenter.count + 1
+    yield
+  end
+end

test/sandbox/test/rendering_test.rb

@@ -1311,4 +1311,14 @@ def test_supports_components_with_unnamed_splatted_arguments
     assert_selector("*[data-name='#{orders.first.name}']", text: orders.first.name)
     assert_selector("*[data-name='#{orders.last.name}']", text: orders.last.name)
   end
+
+  def test_around_render
+    assert_equal(0, Instrumenter.count)
+
+    render_inline(AroundRenderComponent.new)
+
+    assert_equal(1, Instrumenter.count)
+
+    assert_text("Hi!")
+  end
 end