Hotfix PostCSS loader incompatibility

We were seeing

    Invalid options object. PostCSS Loader has been initialized using an options object that does not match the API schema.

        options has an unknown property 'config'. These properties are valid:
        object { postcssOptions?, execute?, sourceMap? }

This patch seems to fix it
rails/webpacker#2784 at least until we can
upgrade properly.

Author: koppen

config/webpack/environment.js

@@ -1,3 +1,23 @@
 const { environment } = require('@rails/webpacker')
 
+function hotfixPostcssLoaderConfig (subloader) {
+  const subloaderName = subloader.loader
+  if (subloaderName === 'postcss-loader') {
+    if (subloader.options.postcssOptions) {
+      console.log(
+        '\x1b[31m%s\x1b[0m',
+        'Remove postcssOptions workaround in config/webpack/environment.js'
+      )
+    } else {
+      subloader.options.postcssOptions = subloader.options.config;
+      delete subloader.options.config;
+    }
+  }
+}
+
+environment.loaders.keys().forEach(loaderName => {
+  const loader = environment.loaders.get(loaderName);
+  loader.use.forEach(hotfixPostcssLoaderConfig);
+});
+
 module.exports = environment