Switch from Babel to SWC for faster JavaScript transpilation (#677)

This commit migrates the project from Babel to SWC (Speedy Web Compiler)
following the Shakapacker documentation.

* Add loose: false to SWC config for Stimulus compatibility

Override Shakapacker's default loose: true setting with loose: false
to ensure spec-compliant class transforms that work with Stimulus.

Without this, Stimulus controllers fail silently even with
keepClassNames: true.

Author: justin808

config/shakapacker.yml

@@ -8,7 +8,7 @@ default: &default
   cache_path: tmp/shakapacker
   webpack_compile_output: true
   nested_entries: true
-  javascript_transpiler: babel
+  javascript_transpiler: swc
 
   # Additional paths webpack should lookup modules
   # ['app/assets', 'engine/foo/app/assets']

config/swc.config.js

@@ -0,0 +1,23 @@
+const { env } = require('shakapacker');
+
+const customConfig = {
+  options: {
+    jsc: {
+      // Preserve class names for Stimulus controller discovery
+      keepClassNames: true,
+      // Use spec-compliant transforms (override Shakapacker's loose: true default)
+      // This is required for Stimulus controllers to work correctly
+      loose: false,
+      transform: {
+        react: {
+          // Use automatic runtime (React 17+) - no need to import React
+          runtime: 'automatic',
+          // Enable React Fast Refresh in development
+          refresh: env.isDevelopment && env.runningWebpackDevServer,
+        },
+      },
+    },
+  },
+};
+
+module.exports = customConfig;

package.json

@@ -45,6 +45,8 @@
     "@rails/actioncable": "7.0.5",
     "@rescript/core": "^0.5.0",
     "@rescript/react": "^0.11.0",
+    "@swc/core": "^1.13.5",
+    "ajv": "^8.17.1",
     "autoprefixer": "^10.4.14",
     "axios": "^0.21.1",
     "babel-loader": "^9.1.2",
@@ -96,6 +98,7 @@
     "shakapacker": "9.0.0-beta.8",
     "stimulus": "^3.0.1",
     "style-loader": "^3.3.1",
+    "swc-loader": "^0.2.6",
     "tailwindcss": "^3.3.3",
     "terser-webpack-plugin": "5",
     "turbolinks": "^5.2.0",