Revert: Fix component registration race condition (#1972) (#1981)

## Summary

Reverts commit d1a8a1a which changed the default component loading
strategy from :sync to :defer.

This reverts the fix for the component registration race condition that
was introduced in #1972.

## Changes

- Reverts the defer loading strategy back to the original behavior
- Restores async loading support when available
- Updates tests to reflect the original expectations

<!-- Reviewable:start -->
- - -
This change is [<img src="https://reviewable.io/review_button.svg"
height="34" align="absmiddle"
alt="Reviewable"/>](https://reviewable.io/reviews/shakacode/react_on_rails/1981)
<!-- Reviewable:end -->

Author: justin808

lib/react_on_rails/configuration.rb

@@ -154,9 +154,9 @@ def check_component_registry_timeout
       raise ReactOnRails::Error, "component_registry_timeout must be a positive integer"
     end
 
-    # rubocop:disable Metrics/CyclomaticComplexity
+    # rubocop:disable Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
     def validate_generated_component_packs_loading_strategy
-      # rubocop:enable Metrics/CyclomaticComplexity
+      # rubocop:enable Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
 
       if defer_generated_component_packs
         if %i[async sync].include?(generated_component_packs_loading_strategy)
@@ -176,11 +176,12 @@ def validate_generated_component_packs_loading_strategy
         1. Use :defer or :sync loading strategy instead of :async
         2. Upgrade to Shakapacker v8.2.0 or above to enable async script loading
       MSG
-      if generated_component_packs_loading_strategy.nil?
-        # Use defer as the default to ensure generated component packs load and register
-        # components before main bundle executes, avoiding race conditions with async loading
-        self.generated_component_packs_loading_strategy = :defer
-      elsif generated_component_packs_loading_strategy == :async && !PackerUtils.supports_async_loading?
+      if PackerUtils.supports_async_loading?
+        self.generated_component_packs_loading_strategy ||= :async
+      elsif generated_component_packs_loading_strategy.nil?
+        Rails.logger.warn("**WARNING** #{msg}")
+        self.generated_component_packs_loading_strategy = :sync
+      elsif generated_component_packs_loading_strategy == :async
         raise ReactOnRails::Error, "**ERROR** #{msg}"
       end
 

spec/dummy/app/views/layouts/application.html.erb

@@ -9,10 +9,16 @@
 
   <%= yield :head %>
 
-  <%# Use defer: true to ensure proper script execution order.
-      When using generated component packs (auto_load_bundle), defer ensures
-      component registrations complete before React hydration begins. %>
-  <%= javascript_pack_tag('client-bundle', 'data-turbo-track': 'reload', defer: true) %>
+  <%# Conditionally use defer: true for pages with Redux shared stores (inline registration).
+      Modern apps should use async: true for optimal performance. See docs for details:
+      docs/building-features/streaming-server-rendering.md %>
+  <% if uses_redux_shared_store? %>
+    <%# defer: true required for Redux shared stores with inline component registration %>
+    <%= javascript_pack_tag('client-bundle', 'data-turbo-track': 'reload', defer: true) %>
+  <% else %>
+    <%# async: true is the recommended approach for modern apps (Shakapacker >= 8.2.0) %>
+    <%= javascript_pack_tag('client-bundle', 'data-turbo-track': 'reload', async: true) %>
+  <% end %>
 
   <%= csrf_meta_tags %>
 </head>

spec/dummy/config/initializers/react_on_rails.rb

@@ -42,6 +42,5 @@ def self.adjust_props_for_client_side_hydration(component_name, props)
   config.components_subdirectory = "startup"
   config.auto_load_bundle = true
   config.immediate_hydration = false
-  # Don't explicitly set generated_component_packs_loading_strategy - let it default to :defer
-  # which ensures generated component packs load and register components before main bundle executes
+  config.generated_component_packs_loading_strategy = :defer
 end

spec/react_on_rails/configuration_spec.rb

@@ -284,9 +284,9 @@ module ReactOnRails
             .with("8.2.0").and_return(true)
         end
 
-        it "defaults to :defer" do
+        it "defaults to :async" do
           ReactOnRails.configure {} # rubocop:disable Lint/EmptyBlock
-          expect(ReactOnRails.configuration.generated_component_packs_loading_strategy).to eq(:defer)
+          expect(ReactOnRails.configuration.generated_component_packs_loading_strategy).to eq(:async)
         end
 
         it "accepts :async value" do
@@ -332,9 +332,10 @@ module ReactOnRails
           allow(Rails.logger).to receive(:warn)
         end
 
-        it "defaults to :defer" do
+        it "defaults to :sync and logs a warning" do
           ReactOnRails.configure {} # rubocop:disable Lint/EmptyBlock
-          expect(ReactOnRails.configuration.generated_component_packs_loading_strategy).to eq(:defer)
+          expect(ReactOnRails.configuration.generated_component_packs_loading_strategy).to eq(:sync)
+          expect(Rails.logger).to have_received(:warn).with(/does not support async script loading/)
         end
 
         it "accepts :defer value" do