Remove immediate_hydration validation (will be handled in PR 1997)

Focus this PR solely on validating that :async loading strategy requires Pro.
immediate_hydration will be completely removed in PR 1997, so no need to
validate it here.

Changes:
- Remove immediate_hydration from Pro-only feature validation
- Simplify validate_pro_only_features to only check :async loading strategy
- Remove immediate_hydration checks from doctor.rb
- Update tests to only test :async Pro validation
- Simplify error messages to focus on :async requirement

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

lib/react_on_rails/configuration.rb

@@ -150,26 +150,18 @@ def setup_config_values
     def validate_pro_only_features
       return if defined?(ReactOnRailsPro)
 
-      pro_only_features = []
-
-      pro_only_features << "config.immediate_hydration = true" if immediate_hydration == true
-
       # generated_component_packs_loading_strategy itself is NOT Pro-only
       # However, :async loading specifically requires React on Rails Pro
-      if generated_component_packs_loading_strategy == :async
-        pro_only_features << "config.generated_component_packs_loading_strategy = :async"
-      end
-
-      return if pro_only_features.empty?
+      return unless generated_component_packs_loading_strategy == :async
 
       msg = <<~MSG
-        **ERROR** ReactOnRails: You are using Pro-only features without React on Rails Pro:
+        **ERROR** ReactOnRails: You are using a Pro-only feature without React on Rails Pro:
 
-        #{pro_only_features.map { |f| "  - #{f}" }.join("\n")}
+          - config.generated_component_packs_loading_strategy = :async
 
-        These features are only available with a React on Rails Pro license.
+        Async loading is only available with a React on Rails Pro license.
         Please either:
-        1. Remove these settings from your config/initializers/react_on_rails.rb
+        1. Change to :defer or :sync loading strategy in your config/initializers/react_on_rails.rb
         2. Purchase a React on Rails Pro license at https://www.shakacode.com/react-on-rails-pro
 
         For more information, see: https://www.shakacode.com/react-on-rails/docs/

lib/react_on_rails/doctor.rb

@@ -1146,7 +1146,6 @@ def safe_display_config_value(label, config, method_name)
       end
     end
 
-    # rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexity
     def check_async_usage
       # When Pro is installed, async is fully supported and is the default behavior
       # No need to check for async usage in this case
@@ -1171,24 +1170,13 @@ def check_async_usage
       return if async_issues.empty?
 
       # Report errors if async usage is found without Pro
-      # Note: immediate_hydration alone is not sufficient - Pro is required for safe async usage
-      immediate_hydration_enabled = check_immediate_hydration_enabled?
-
-      if immediate_hydration_enabled
-        checker.add_warning("⚠️  Using :async without React on Rails Pro may cause race conditions")
-        async_issues.each { |issue| checker.add_warning("  #{issue}") }
-        checker.add_info("  💡 immediate_hydration is enabled but Pro gem is not installed")
-        checker.add_info("  💡 For production-safe async loading, upgrade to React on Rails Pro")
-      else
-        checker.add_error("🚫 :async usage detected without proper configuration")
-        async_issues.each { |issue| checker.add_error("  #{issue}") }
-        checker.add_info("  💡 :async can cause race conditions. Options:")
-        checker.add_info("    1. Upgrade to React on Rails Pro (recommended for :async support)")
-        checker.add_info("    2. Change to :defer or :sync loading strategy")
-        checker.add_info("  📖 https://www.shakacode.com/react-on-rails/docs/guides/configuration/")
-      end
+      checker.add_error("🚫 :async usage detected without React on Rails Pro")
+      async_issues.each { |issue| checker.add_error("  #{issue}") }
+      checker.add_info("  💡 :async can cause race conditions. Options:")
+      checker.add_info("    1. Upgrade to React on Rails Pro (recommended for :async support)")
+      checker.add_info("    2. Change to :defer or :sync loading strategy")
+      checker.add_info("  📖 https://www.shakacode.com/react-on-rails/docs/guides/configuration/")
     end
-    # rubocop:enable Metrics/AbcSize, Metrics/CyclomaticComplexity
 
     def scan_view_files_for_async_pack_tag
       files_with_async = []
@@ -1223,16 +1211,6 @@ def config_has_async_loading_strategy?
     rescue StandardError
       false
     end
-
-    def check_immediate_hydration_enabled?
-      # Check if immediate_hydration is enabled in configuration
-      return false unless defined?(ReactOnRails)
-
-      config = ReactOnRails.configuration
-      config.immediate_hydration == true
-    rescue StandardError
-      false
-    end
   end
   # rubocop:enable Metrics/ClassLength
 end

spec/lib/react_on_rails/doctor_spec.rb

@@ -224,13 +224,13 @@
           allow(File).to receive(:read).with("app/views/layouts/application.html.erb")
                                        .and_return('<%= javascript_pack_tag "application", :async %>')
           allow(File).to receive(:exist?).with("config/initializers/react_on_rails.rb").and_return(false)
-          allow(doctor).to receive_messages(relativize_path: "app/views/layouts/application.html.erb",
-                                            check_immediate_hydration_enabled?: false)
+          allow(doctor).to receive(:relativize_path).with("app/views/layouts/application.html.erb")
+                                                    .and_return("app/views/layouts/application.html.erb")
         end
 
         it "reports an error" do
           doctor.send(:check_async_usage)
-          expect(checker).to have_received(:add_error).with("🚫 :async usage detected without proper configuration")
+          expect(checker).to have_received(:add_error).with("🚫 :async usage detected without React on Rails Pro")
           expect(checker).to have_received(:add_error)
             .with("  javascript_pack_tag with :async found in view files:")
         end
@@ -241,39 +241,21 @@
           allow(File).to receive(:exist?).with("config/initializers/react_on_rails.rb").and_return(true)
           allow(File).to receive(:read).with("config/initializers/react_on_rails.rb")
                                        .and_return("config.generated_component_packs_loading_strategy = :async")
-          allow(doctor).to receive(:check_immediate_hydration_enabled?).and_return(false)
         end
 
         it "reports an error" do
           doctor.send(:check_async_usage)
-          expect(checker).to have_received(:add_error).with("🚫 :async usage detected without proper configuration")
+          expect(checker).to have_received(:add_error).with("🚫 :async usage detected without React on Rails Pro")
           expect(checker).to have_received(:add_error)
             .with("  config.generated_component_packs_loading_strategy = :async in initializer")
         end
       end
 
-      context "when immediate_hydration is enabled but Pro is not installed" do
-        before do
-          allow(File).to receive(:exist?).with("config/initializers/react_on_rails.rb").and_return(true)
-          allow(File).to receive(:read).with("config/initializers/react_on_rails.rb")
-                                       .and_return("config.generated_component_packs_loading_strategy = :async")
-          allow(doctor).to receive(:check_immediate_hydration_enabled?).and_return(true)
-        end
-
-        it "reports a warning instead of error" do
-          doctor.send(:check_async_usage)
-          expect(checker).to have_received(:add_warning)
-            .with("⚠️  Using :async without React on Rails Pro may cause race conditions")
-          expect(checker).not_to have_received(:add_error)
-        end
-      end
-
       context "when no async usage is detected" do
         before do
           allow(File).to receive(:exist?).with("config/initializers/react_on_rails.rb").and_return(true)
           allow(File).to receive(:read).with("config/initializers/react_on_rails.rb")
                                        .and_return("config.generated_component_packs_loading_strategy = :defer")
-          allow(doctor).to receive(:check_immediate_hydration_enabled?).and_return(false)
         end
 
         it "does not report any issues" do
@@ -362,28 +344,4 @@
       end
     end
   end
-
-  describe "#check_immediate_hydration_enabled?" do
-    context "when immediate_hydration is enabled" do
-      before do
-        config = instance_double(ReactOnRails::Configuration, immediate_hydration: true)
-        allow(ReactOnRails).to receive(:configuration).and_return(config)
-      end
-
-      it "returns true" do
-        expect(doctor.send(:check_immediate_hydration_enabled?)).to be true
-      end
-    end
-
-    context "when immediate_hydration is disabled" do
-      before do
-        config = instance_double(ReactOnRails::Configuration, immediate_hydration: false)
-        allow(ReactOnRails).to receive(:configuration).and_return(config)
-      end
-
-      it "returns false" do
-        expect(doctor.send(:check_immediate_hydration_enabled?)).to be false
-      end
-    end
-  end
 end

spec/react_on_rails/configuration_spec.rb

@@ -406,7 +406,7 @@ module ReactOnRails
             ReactOnRails.configure do |config|
               config.generated_component_packs_loading_strategy = :async
             end
-          end.to raise_error(ReactOnRails::Error, /Pro-only features without React on Rails Pro/)
+          end.to raise_error(ReactOnRails::Error, /Pro-only feature without React on Rails Pro/)
         end
       end
     end
@@ -467,7 +467,7 @@ module ReactOnRails
       end
     end
 
-    describe "Pro-only feature validation" do
+    describe "Pro-only feature validation for :async loading strategy" do
       context "when ReactOnRailsPro is not defined" do
         before do
           # Ensure ReactOnRailsPro is not defined
@@ -476,36 +476,14 @@ module ReactOnRails
           allow(ReactOnRails::PackerUtils).to receive(:supports_async_loading?).and_return(true)
         end
 
-        context "when immediate_hydration is set to true" do
-          it "raises error in non-production environments" do
-            allow(Rails.env).to receive(:production?).and_return(false)
-            expect do
-              ReactOnRails.configure do |config|
-                config.immediate_hydration = true
-              end
-            end.to raise_error(ReactOnRails::Error, /Pro-only features without React on Rails Pro/)
-          end
-
-          it "logs error in production but does not raise" do
-            allow(Rails.env).to receive(:production?).and_return(true)
-            allow(Rails.logger).to receive(:error)
-            expect do
-              ReactOnRails.configure do |config|
-                config.immediate_hydration = true
-              end
-            end.not_to raise_error
-            expect(Rails.logger).to have_received(:error).with(/Pro-only features/)
-          end
-        end
-
         context "when generated_component_packs_loading_strategy is set to :async" do
           it "raises error in non-production environments" do
             allow(Rails.env).to receive(:production?).and_return(false)
             expect do
               ReactOnRails.configure do |config|
                 config.generated_component_packs_loading_strategy = :async
               end
-            end.to raise_error(ReactOnRails::Error, /Pro-only features without React on Rails Pro/)
+            end.to raise_error(ReactOnRails::Error, /Pro-only feature without React on Rails Pro/)
           end
 
           it "logs error in production but does not raise" do
@@ -516,7 +494,7 @@ module ReactOnRails
                 config.generated_component_packs_loading_strategy = :async
               end
             end.not_to raise_error
-            expect(Rails.logger).to have_received(:error).with(/Pro-only features/)
+            expect(Rails.logger).to have_received(:error).with(/Pro-only feature/)
           end
         end
 
@@ -538,28 +516,6 @@ module ReactOnRails
           end
         end
 
-        context "when both Pro-only features are set" do
-          it "lists both features in error message" do
-            allow(Rails.env).to receive(:production?).and_return(false)
-            expect do
-              ReactOnRails.configure do |config|
-                config.immediate_hydration = true
-                config.generated_component_packs_loading_strategy = :async
-              end
-            end.to raise_error(ReactOnRails::Error, /immediate_hydration.*generated_component_packs_loading_strategy/m)
-          end
-        end
-
-        context "when immediate_hydration is set to false" do
-          it "does not raise error" do
-            expect do
-              ReactOnRails.configure do |config|
-                config.immediate_hydration = false
-              end
-            end.not_to raise_error
-          end
-        end
-
         context "when no Pro-only features are set" do
           it "does not raise error" do
             expect do
@@ -576,15 +532,7 @@ module ReactOnRails
           allow(ReactOnRails::PackerUtils).to receive(:supports_async_loading?).and_return(true)
         end
 
-        it "allows immediate_hydration = true" do
-          expect do
-            ReactOnRails.configure do |config|
-              config.immediate_hydration = true
-            end
-          end.not_to raise_error
-        end
-
-        it "allows generated_component_packs_loading_strategy to be set" do
+        it "allows generated_component_packs_loading_strategy = :async" do
           expect do
             ReactOnRails.configure do |config|
               config.generated_component_packs_loading_strategy = :async