Fix rspack configuration not applying to all environments

react_on_rails/lib/generators/react_on_rails/base_generator.rb

@@ -298,21 +298,22 @@ def configure_rspack_in_shakapacker
 
         puts Rainbow("🔧 Configuring Shakapacker for Rspack...").yellow
 
-        # Parse YAML config properly to avoid fragile regex manipulation
-        # Support both old and new Psych versions
-        config = begin
-          YAML.load_file(shakapacker_config_path, aliases: true)
-        rescue ArgumentError
-          # Older Psych versions don't support the aliases parameter
-          YAML.load_file(shakapacker_config_path)
-        end
-        # Update default section
-        config["default"] ||= {}
-        config["default"]["assets_bundler"] = "rspack"
-        config["default"]["webpack_loader"] = "swc"
+        # Use regex replacement to preserve file structure (comments, anchors, aliases)
+        # This replaces ALL occurrences of assets_bundler, not just in default section
+        # Using gsub_file (Thor method) for consistency with Rails generator patterns
+        gsub_file(
+          shakapacker_config_path,
+          /^(\s*assets_bundler:\s*)["']?webpack["']?(\s*(?:#.*)?)$/,
+          '\1rspack\2'
+        )
+
+        # Update webpack_loader to swc (rspack works best with SWC)
+        gsub_file(
+          shakapacker_config_path,
+          /^(\s*webpack_loader:\s*)["']?babel["']?(\s*(?:#.*)?)$/,
+          '\1swc\2'
+        )
 
-        # Write back as YAML
-        File.write(shakapacker_config_path, YAML.dump(config))
         puts Rainbow("✅ Updated shakapacker.yml for Rspack").green
       end
     end

react_on_rails/lib/generators/react_on_rails/templates/base/base/bin/switch-bundler

@@ -2,7 +2,6 @@
 # frozen_string_literal: true
 
 require "fileutils"
-require "yaml"
 require "json"
 
 # Script to switch between webpack and rspack bundlers
@@ -48,16 +47,25 @@ class BundlerSwitcher
     abort "❌ #{@shakapacker_config} not found" unless File.exist?(@shakapacker_config)
 
     puts "📝 Updating #{@shakapacker_config}..."
-    config = YAML.load_file(@shakapacker_config)
-
-    config["default"] ||= {}
-    config["default"]["assets_bundler"] = @target_bundler
-
-    # Update webpack_loader based on bundler
-    # Rspack works best with SWC, webpack typically uses babel
-    config["default"]["webpack_loader"] = @target_bundler == "rspack" ? "swc" : "babel"
-
-    File.write(@shakapacker_config, YAML.dump(config))
+    content = File.read(@shakapacker_config)
+
+    # Use regex replacement to preserve file structure (comments, anchors, aliases)
+    # This replaces ALL occurrences of assets_bundler, not just in default section
+    old_bundler = @target_bundler == "rspack" ? "webpack" : "rspack"
+    new_content = content.gsub(
+      /^(\s*assets_bundler:\s*)["']?#{old_bundler}["']?(\s*(?:#.*)?)$/,
+      "\\1#{@target_bundler}\\2"
+    )
+
+    # Update webpack_loader based on bundler (rspack works best with SWC)
+    new_loader = @target_bundler == "rspack" ? "swc" : "babel"
+    old_loader = @target_bundler == "rspack" ? "babel" : "swc"
+    new_content = new_content.gsub(
+      /^(\s*webpack_loader:\s*)["']?#{old_loader}["']?(\s*(?:#.*)?)$/,
+      "\\1#{new_loader}\\2"
+    )
+
+    File.write(@shakapacker_config, new_content)
     puts "✅ Updated assets_bundler to '#{@target_bundler}'"
   end