Fix using_swc? to properly parse YAML and default to babel

Change using_swc? helper to parse shakapacker.yml with YAML.safe_load_file
instead of raw string matching, which incorrectly interpreted commented
lines as active configuration.

Changes:
- Add require "yaml" to base_generator.rb
- Parse YAML to read javascript_compiler from default section
- Return true only when javascript_compiler is explicitly set to "swc"
- Default to false (babel) when file is missing or key is absent
- Add error handling for YAML parsing failures
- Update template comment to reflect babel as default

This ensures commented configuration lines don't affect compiler detection
and provides more predictable behavior.

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

Co-Authored-By: Claude <[email protected]>

Author: justin808

lib/generators/react_on_rails/base_generator.rb

@@ -2,6 +2,7 @@
 
 require "rails/generators"
 require "fileutils"
+require "yaml"
 require_relative "generator_messages"
 require_relative "generator_helper"
 module ReactOnRails
@@ -232,13 +233,21 @@ def add_dev_dependencies
 
       def using_swc?
         # Check shakapacker.yml for javascript_compiler setting
-        # Shakapacker 9.3.0 defaults to SWC if not specified
+        # Parse YAML to properly handle comments and get actual configured value
         shakapacker_config_path = File.join(destination_root, "config", "shakapacker.yml")
-        return true unless File.exist?(shakapacker_config_path)
-
-        config_content = File.read(shakapacker_config_path)
-        # Return true (SWC) unless explicitly set to babel
-        !config_content.include?("javascript_compiler: babel")
+        return false unless File.exist?(shakapacker_config_path)
+
+        begin
+          config = YAML.safe_load_file(shakapacker_config_path)
+          # Check default section for javascript_compiler setting
+          javascript_compiler = config.dig("default", "javascript_compiler")
+          # Return true only if explicitly set to "swc"
+          javascript_compiler == "swc"
+        rescue StandardError => e
+          # If YAML parsing fails, default to babel (false)
+          puts "Warning: Could not parse shakapacker.yml: #{e.message}"
+          false
+        end
       end
 
       def install_js_dependencies

lib/generators/react_on_rails/templates/base/base/config/shakapacker.yml

@@ -58,9 +58,9 @@ default: &default
 
   # Compiler to use for JavaScript: 'babel' or 'swc'
   # SWC is faster but Babel has more plugins and wider ecosystem support
-  # Shakapacker 9.3.0+ defaults to 'swc' if not specified
-  # Uncomment to use Babel instead:
-  # javascript_compiler: babel
+  # React on Rails defaults to Babel if not specified for wider compatibility
+  # Uncomment and set to 'swc' for faster compilation:
+  # javascript_compiler: swc
 
   # Setting the asset host here will override Rails.application.config.asset_host.
   # Here, you can set different asset_host per environment. Note that