Exercise cache digest dependency discovery in the boot benchmark

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 6
 
 ## main
 
+* Measure cache digest precomputation in the boot benchmark by disabling class reloading in the benchmark app and having each generated component render another.
+
+    *Joel Hawksley*
+
 * Add a CI performance check that fails a pull request when any benchmark scenario's component/partial render-time ratio, or ViewComponent's share of app boot time, regresses by more than 5% against the base branch on Rails 8.1 or Rails main.
 
     *Joel Hawksley*

performance/boot.rb

@@ -32,6 +32,7 @@
 class BootApp < Rails::Application
   config.root = ARGV.fetch(0)
   config.load_defaults Rails::VERSION::STRING.to_f
+  config.cache_classes = true
   config.eager_load = true
   config.secret_key_base = "performance"
   config.logger = Logger.new(nil)

performance/measure.rb

@@ -121,7 +121,17 @@ class BenchmarksController < ActionController::Base
   components = File.join(root, "app", "components")
   FileUtils.mkdir_p(components)
 
+  # Each component renders another, so boot also discovers cache digest dependencies.
+  render_call = lambda do |i|
+    case i % 3
+    when 0 then "render Sidecar#{i}Component.new(name: 'x')"
+    when 1 then "render(Inline#{i}Component.new) { 'x' }"
+    else "render Slots#{i}Component.new"
+    end
+  end
+
   Integer(ENV.fetch("BOOT_COMPONENTS", 300)).times do |i|
+    rendered = render_call.call(i.zero? ? 1 : (i - 1) / 2)
     case i % 3
     when 0
       File.write(File.join(components, "sidecar#{i}_component.rb"), <<~RUBY)
@@ -131,11 +141,11 @@ def initialize(name:)
           end
         end
       RUBY
-      File.write(File.join(components, "sidecar#{i}_component.html.erb"), "<p><%= @name %></p>\n")
+      File.write(File.join(components, "sidecar#{i}_component.html.erb"), "<p><%= @name %></p><%= #{rendered} %>\n")
     when 1
       File.write(File.join(components, "inline#{i}_component.rb"), <<~RUBY)
         class Inline#{i}Component < ViewComponent::Base
-          erb_template "<p><%= content %></p>"
+          erb_template "<p><%= content %></p><%= #{rendered} %>"
         end
       RUBY
     else
@@ -145,7 +155,7 @@ class Slots#{i}Component < ViewComponent::Base
           renders_many :items
         end
       RUBY
-      File.write(File.join(components, "slots#{i}_component.html.erb"), "<%= header %><% items.each do |item| %><%= item %><% end %>\n")
+      File.write(File.join(components, "slots#{i}_component.html.erb"), "<%= header %><% items.each do |item| %><%= item %><% end %><%= #{rendered} %>\n")
     end
   end