correct plugin exsit validation

Author: Barak Igal

src/index.js

@@ -3,9 +3,10 @@
 import { validate } from 'schema-utils';
 
 import schema from './plugin-options.json';
-import { MODULE_TYPE, compareModulesByIdentifier } from './utils';
+import { MODULE_TYPE, compareModulesByIdentifier, provideLoaderContext } from './utils';
 
-const pluginName = 'mini-css-extract-plugin';
+export const pluginName = 'mini-css-extract-plugin';
+export const pluginSymbol = Symbol(pluginName);
 
 const REGEXP_CHUNKHASH = /\[chunkhash(?::(\d+))?\]/i;
 const REGEXP_CONTENTHASH = /\[contenthash(?::(\d+))?\]/i;
@@ -384,6 +385,11 @@ class MiniCssExtractPlugin {
     const CssModule = MiniCssExtractPlugin.getCssModule(webpack);
     const CssDependency = MiniCssExtractPlugin.getCssDependency(webpack);
 
+    provideLoaderContext(compiler, `${pluginName} loader context`, (loaderContext)=>{
+      // eslint-disable-next-line no-param-reassign
+      loaderContext[pluginSymbol] = true;
+    }, false)
+
     compiler.hooks.thisCompilation.tap(pluginName, (compilation) => {
       class CssModuleFactory {
         // eslint-disable-next-line class-methods-use-this

src/loader.js

@@ -3,12 +3,10 @@ import path from 'path';
 import loaderUtils from 'loader-utils';
 import { validate } from 'schema-utils';
 
-import { findModuleById, evalModuleCode } from './utils';
+import { findModuleById, evalModuleCode, provideLoaderContext } from './utils';
 import schema from './loader-options.json';
 
-import MiniCssExtractPlugin from './index';
-
-const pluginName = 'mini-css-extract-plugin';
+import MiniCssExtractPlugin, {pluginName, pluginSymbol} from './index';
 
 function hotLoader(content, context) {
   const accept = context.locals
@@ -39,6 +37,12 @@ export function pitch(request) {
     baseDataPath: 'options',
   });
 
+  if (!this[pluginSymbol]) {
+    throw new Error(
+      "You forgot to add 'mini-css-extract-plugin' plugin (i.e. `{ plugins: [new MiniCssExtractPlugin()] }`), please read https://github.com/webpack-contrib/mini-css-extract-plugin#getting-started"
+    );
+  }
+
   const loaders = this.loaders.slice(this.loaderIndex + 1);
 
   this.addDependency(this.resourcePath);
@@ -104,33 +108,18 @@ export function pitch(request) {
 
   new LimitChunkCountPlugin({ maxChunks: 1 }).apply(childCompiler);
 
-  const NormalModule = webpack.NormalModule
-    ? webpack.NormalModule
-    : // eslint-disable-next-line global-require
-      require('webpack/lib/NormalModule');
-
-  childCompiler.hooks.thisCompilation.tap(
-    `${pluginName} loader`,
-    (compilation) => {
-      const normalModuleHook =
-        typeof NormalModule.getCompilationHooks !== 'undefined'
-          ? NormalModule.getCompilationHooks(compilation).loader
-          : compilation.hooks.normalModuleLoader;
-
-      normalModuleHook.tap(`${pluginName} loader`, (loaderContext, module) => {
-        if (module.request === request) {
-          // eslint-disable-next-line no-param-reassign
-          module.loaders = loaders.map((loader) => {
-            return {
-              loader: loader.path,
-              options: loader.options,
-              ident: loader.ident,
-            };
-          });
-        }
+  provideLoaderContext(childCompiler, `${pluginName} loader`, (_, module) => {
+    if (module.request === request) {
+      // eslint-disable-next-line no-param-reassign
+      module.loaders = loaders.map((loader) => {
+        return {
+          loader: loader.path,
+          options: loader.options,
+          ident: loader.ident,
+        };
       });
     }
-  );
+  });
 
   let source;
 
@@ -203,12 +192,6 @@ export function pitch(request) {
         const count = identifierCountMap.get(dependency.identifier) || 0;
         const CssDependency = MiniCssExtractPlugin.getCssDependency(webpack);
 
-        if (!CssDependency) {
-          throw new Error(
-            "You forgot to add 'mini-css-extract-plugin' plugin (i.e. `{ plugins: [new MiniCssExtractPlugin()] }`), please read https://github.com/webpack-contrib/mini-css-extract-plugin#getting-started"
-          );
-        }
-
         this._module.addDependency(
           (lastDep = new CssDependency(dependency, dependency.context, count))
         );

src/utils.js

@@ -49,7 +49,27 @@ function compareModulesByIdentifier(a, b) {
   return compareIds(a.identifier(), b.identifier());
 }
 
+function provideLoaderContext(compiler, name, handler, thisCompilation = true){
+  const NormalModule = compiler.webpack && compiler.webpack.NormalModule
+  ? compiler.webpack.NormalModule
+  : // eslint-disable-next-line global-require
+    require('webpack/lib/NormalModule');
+
+  compiler.hooks[thisCompilation ? 'thisCompilation': 'compilation'].tap(
+    name,
+    (compilation) => {
+      const normalModuleHook =
+        typeof NormalModule.getCompilationHooks !== 'undefined'
+          ? NormalModule.getCompilationHooks(compilation).loader
+          : compilation.hooks.normalModuleLoader;
+
+      normalModuleHook.tap(name, (loaderContext, module) => handler(loaderContext, module, compilation));
+    }
+  );
+}
+
 export {
+  provideLoaderContext,
   MODULE_TYPE,
   findModuleById,
   evalModuleCode,