fix: output warning when built-in CSS support enabled (#1520)

README.md

@@ -1696,6 +1696,8 @@ module.exports = {
   module: {
     rules: [
       {
+        // If you enable `experiments.css` or `experiments.futureDefaults`, please uncomment line below
+        // type: "javascript/auto",
         test: /\.(sa|sc|c)ss$/i,
         use: [
           devMode ? "style-loader" : MiniCssExtractPlugin.loader,

src/index.js

@@ -31,9 +31,27 @@ import {
 
 export default async function loader(content, map, meta) {
   const rawOptions = this.getOptions(schema);
-  const plugins = [];
   const callback = this.async();
 
+  if (
+    this._compiler &&
+    this._compiler.options &&
+    this._compiler.options.experiments &&
+    this._compiler.options.experiments.css &&
+    this._module &&
+    this._module.type === "css"
+  ) {
+    this.emitWarning(
+      new Error(
+        'You can\'t use `experiments.css` (`experiments.futureDefaults` enable built-in CSS support by default) and `css-loader` together, please set `experiments.css` to `false` or set `{ type: "javascript/auto" }` for rules with `css-loader` in your webpack config (now css-loader does nothing).'
+      )
+    );
+
+    callback(null, content, map, meta);
+
+    return;
+  }
+
   let options;
 
   try {
@@ -44,6 +62,7 @@ export default async function loader(content, map, meta) {
     return;
   }
 
+  const plugins = [];
   const replacements = [];
   const exports = [];