Repository: webpack-contrib/mini-css-extract-plugin (js)

Issue:
Produces bloated runtime in webpack 5 when using `contenthash` or `chunkhash`
- Operating System: OSX 10.15.7
- Node Version: 12.20.1
- NPM Version: 6.14.10
- webpack Version: 5.17.0
- mini-css-extract-plugin Version: 1.3.4

### Expected Behavior

When using `filename: '[name].[contenthash].css'`, it produces a runtime chunk that only contains values for existing CSS files.

### Actual Behavior

Runtime is bloated with replacement maps that point to inexistent CSS files. For example, using this config:

```
  plugins: [new MiniCssExtractPlugin({
    filename: '[name].[id].[contenthash].css',
    chunkFilename: '[name].[id].[contenthash].css',
  })],
```

I got the following in the runtime:

```
/******/ __webpack_require__.miniCssF = (chunkId) => {
/******/ 	// return url for filenames based on template
/******/ 	return "" + ({"179":"main","303":"runtime~main"}[chunkId] || chunkId) + "." + chunkId + "." + {"179":"c539139b868f46f81e90","229":"31d6cfe0d16ae931b73c","851":"31d6cfe0d16ae931b73c"}[chunkId] + ".css";
/******/ };
```

However, only the file `main.179.c539139b868f46f81e90.css` exists (that is correct). The replacement function includes mapping for chunks that don't have CSS (eg: `"303":"runtime~main"` or `"229":"31d6cfe0d16ae931b73c"`). In the case of a big app this results in a bloated runtime.

Note that using `chunkhash` instead of `contenthash` does not solve the issue.

### How Do We Reproduce?

See https://github.com/scinos/mini-css-bug-contenthash for a reproduction repo.


Pull request:
fix: reduce runtime
<!--
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This PR contains a:

- [x] **bugfix**
- [ ] new **feature**
- [ ] **code refactor**
- [x] **test update** <!-- if bug or feature is checked, this should be too -->
- [ ] **typo fix**
- [ ] **metadata update**

### Motivation / Use-Case

fixes #681 fixes #680

### Breaking Changes

No

### Additional Info

Par of #1, we can reduce it more

Patch:
diff --git a/src/index.js b/src/index.js
index 6e791e5..b9a88d0 100644
--- a/src/index.js
+++ b/src/index.js
@@ -265,20 +265,25 @@ class MiniCssExtractPlugin {
 
       compilation.hooks.contentHash.tap(pluginName, (chunk) => {
         const { outputOptions, chunkGraph } = compilation;
-        const { hashFunction, hashDigest, hashDigestLength } = outputOptions;
-        const hash = createHash(hashFunction);
+        const modules = isWebpack4
+          ? Array.from(this.getChunkModules(chunk, chunkGraph)).filter(
+              (module) => module.type === MODULE_TYPE
+            )
+          : chunkGraph.getChunkModulesIterableBySourceType(chunk, MODULE_TYPE);
+
+        if (modules) {
+          const { hashFunction, hashDigest, hashDigestLength } = outputOptions;
+          const hash = createHash(hashFunction);
 
-        for (const m of this.getChunkModules(chunk, chunkGraph)) {
-          if (m.type === MODULE_TYPE) {
+          for (const m of modules) {
             m.updateHash(hash, { chunkGraph });
           }
-        }
-
-        const { contentHash } = chunk;
 
-        contentHash[MODULE_TYPE] = hash
-          .digest(hashDigest)
-          .substring(0, hashDigestLength);
+          // eslint-disable-next-line no-param-reassign
+          chunk.contentHash[MODULE_TYPE] = hash
+            .digest(hashDigest)
+            .substring(0, hashDigestLength);
+        }
       });
 
       const { mainTemplate } = compilation;
@@ -465,6 +470,7 @@ class MiniCssExtractPlugin {
           const CssLoadingRuntimeModule = require('./CssLoadingRuntimeModule');
 
           set.add(webpack.RuntimeGlobals.publicPath);
+
           compilation.addRuntimeModule(
             chunk,
             new webpack.runtime.GetChunkFilenameRuntimeModule(
@@ -483,6 +489,7 @@ class MiniCssExtractPlugin {
             new CssLoadingRuntimeModule(set, this.runtimeOptions)
           );
         };
+
         compilation.hooks.runtimeRequirementInTree
           .for(webpack.RuntimeGlobals.ensureChunkHandlers)
           .tap(pluginName, handler);


Test patch:
diff --git a/test/cases/runtime/async.js b/test/cases/runtime/async.js
new file mode 100644
index 0000000..96edba9
--- /dev/null
+++ b/test/cases/runtime/async.js
@@ -0,0 +1,2 @@
+// eslint-disable-next-line no-console
+console.log('HERE');
diff --git a/test/cases/runtime/expected/webpack-4/main.c4d90d38e7a606ae4d4c.css b/test/cases/runtime/expected/webpack-4/main.c4d90d38e7a606ae4d4c.css
new file mode 100644
index 0000000..cebc5c1
--- /dev/null
+++ b/test/cases/runtime/expected/webpack-4/main.c4d90d38e7a606ae4d4c.css
@@ -0,0 +1,4 @@
+body {
+  background: red;
+}
+
diff --git a/test/cases/runtime/expected/webpack-4/runtime~main.js b/test/cases/runtime/expected/webpack-4/runtime~main.js
new file mode 100644
index 0000000..27b6ee5
--- /dev/null
+++ b/test/cases/runtime/expected/webpack-4/runtime~main.js
@@ -0,0 +1,223 @@
+/******/ (function(modules) { // webpackBootstrap
+/******/ 	// install a JSONP callback for chunk loading
+/******/ 	function webpackJsonpCallback(data) {
+/******/ 		var chunkIds = data[0];
+/******/ 		var moreModules = data[1];
+/******/ 		var executeModules = data[2];
+/******/
+/******/ 		// add "moreModules" to the modules object,
+/******/ 		// then flag all "chunkIds" as loaded and fire callback
+/******/ 		var moduleId, chunkId, i = 0, resolves = [];
+/******/ 		for(;i < chunkIds.length; i++) {
+/******/ 			chunkId = chunkIds[i];
+/******/ 			if(Object.prototype.hasOwnProperty.call(installedChunks, chunkId) && installedChunks[chunkId]) {
+/******/ 				resolves.push(installedChunks[chunkId][0]);
+/******/ 			}
+/******/ 			installedChunks[chunkId] = 0;
+/******/ 		}
+/******/ 		for(moduleId in moreModules) {
+/******/ 			if(Object.prototype.hasOwnProperty.call(moreModules, moduleId)) {
+/******/ 				modules[moduleId] = moreModules[moduleId];
+/******/ 			}
+/******/ 		}
+/******/ 		if(parentJsonpFunction) parentJsonpFunction(data);
+/******/
+/******/ 		while(resolves.length) {
+/******/ 			resolves.shift()();
+/******/ 		}
+/******/
+/******/ 		// add entry modules from loaded chunk to deferred list
+/******/ 		deferredModules.push.apply(deferredModules, executeModules || []);
+/******/
+/******/ 		// run deferred modules when all chunks ready
+/******/ 		return checkDeferredModules();
+/******/ 	};
+/******/ 	function checkDeferredModules() {
+/******/ 		var result;
+/******/ 		for(var i = 0; i < deferredModules.length; i++) {
+/******/ 			var deferredModule = deferredModules[i];
+/******/ 			var fulfilled = true;
+/******/ 			for(var j = 1; j < deferredModule.length; j++) {
+/******/ 				var depId = deferredModule[j];
+/******/ 				if(installedChunks[depId] !== 0) fulfilled = false;
+/******/ 			}
+/******/ 			if(fulfilled) {
+/******/ 				deferredModules.splice(i--, 1);
+/******/ 				result = __webpack_require__(__webpack_require__.s = deferredModule[0]);
+/******/ 			}
+/******/ 		}
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+/******/ 		0: 0
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+/******/
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+/******/ 	function jsonpScriptSrc(chunkId) {
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+/******/ 		// Check if module is in cache
+/******/ 		if(installedModules[moduleId]) {
+/******/ 			return installedModules[moduleId].exports;
+/******/ 		}
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+/******/ 			l: false,
+/******/ 			exports: {}
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+/******/
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+/******/
+/******/ 	// This file contains only the entry chunk.
+/******/ 	// The chunk loading function for additional chunks
+/******/ 	__webpack_require__.e = function requireEnsure(chunkId) {
+/******/ 		var promises = [];
+/******/
+/******/
+/******/ 		// JSONP chunk loading for javascript
+/******/
+/******/ 		var installedChunkData = installedChunks[chunkId];
+/******/ 		if(installedChunkData !== 0) { // 0 means "already installed".
+/******/
+/******/ 			// a Promise means "currently loading".
+/******/ 			if(installedChunkData) {
+/******/ 				promises.push(installedChunkData[2]);
+/******/ 			} else {
+/******/ 				// setup Promise in chunk cache
+/******/ 				var promise = new Promise(function(resolve, reject) {
+/******/ 					installedChunkData = installedChunks[chunkId] = [resolve, reject];
+/******/ 				});
+/******/ 				promises.push(installedChunkData[2] = promise);
+/******/
+/******/ 				// start chunk loading
+/******/ 				var script = document.createElement('script');
+/******/ 				var onScriptComplete;
+/******/
+/******/ 				script.charset = 'utf-8';
+/******/ 				script.timeout = 120;
+/******/ 				if (__webpack_require__.nc) {
+/******/ 					script.setAttribute("nonce", __webpack_require__.nc);
+/******/ 				}
+/******/ 				script.src = jsonpScriptSrc(chunkId);
+/******/
+/******/ 				// create error before stack unwound to get useful stacktrace later
+/******/ 				var error = new Error();
+/******/ 				onScriptComplete = function (event) {
+/******/ 					// avoid mem leaks in IE.
+/******/ 					script.onerror = script.onload = null;
+/******/ 					clearTimeout(timeout);
+/******/ 					var chunk = installedChunks[chunkId];
+/******/ 					if(chunk !== 0) {
+/******/ 						if(chunk) {
+/******/ 							var errorType = event && (event.type === 'load' ? 'missing' : event.type);
+/******/ 							var realSrc = event && event.target && event.target.src;
+/******/ 							error.message = 'Loading chunk ' + chunkId + ' failed.\n(' + errorType + ': ' + realSrc + ')';
+/******/ 							error.name = 'ChunkLoadError';
+/******/ 							error.type = errorType;
+/******/ 							error.request = realSrc;
+/******/ 							chunk[1](error);
+/******/ 						}
+/******/ 						installedChunks[chunkId] = undefined;
+/******/ 					}
+/******/ 				};
+/******/ 				var timeout = setTimeout(function(){
+/******/ 					onScriptComplete({ type: 'timeout', target: script });
+/******/ 				}, 120000);
+/******/ 				script.onerror = script.onload = onScriptComplete;
+/******/ 				document.head.appendChild(script);
+/******/ 			}
+/******/ 		}
+/******/ 		return Promise.all(promises);
+/******/ 	};
+/******/
+/******/ 	// expose the modules object (__webpack_modules__)
+/******/ 	__webpack_require__.m = modules;
+/******/
+/******/ 	// expose the module cache
+/******/ 	__webpack_require__.c = installedModules;
+/******/
+/******/ 	// define getter function for harmony exports
+/******/ 	__webpack_require__.d = function(exports, name, getter) {
+/******/ 		if(!__webpack_require__.o(exports, name)) {
+/******/ 			Object.defineProperty(exports, name, { enumerable: true, get: getter });
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+/******/ 	__webpack_require__.r = function(exports) {
+/******/ 		if(typeof Symbol !== 'undefined' && Symbol.toStringTag) {
+/******/ 			Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
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+/******/ 		Object.defineProperty(exports, '__esModule', { value: true });
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+/******/ 	__webpack_require__.t = function(value, mode) {
+/******/ 		if(mode & 1) value = __webpack_require__(value);
+/******/ 		if(mode & 8) return value;
+/******/ 		if((mode & 4) && typeof value === 'object' && value && value.__esModule) return value;
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+/******/ 		__webpack_require__.r(ns);
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+/******/ 		if(mode & 2 && typeof value != 'string') for(var key in value) __webpack_require__.d(ns, key, function(key) { return value[key]; }.bind(null, key));
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+/******/ 			function getDefault() { return module['default']; } :
+/******/ 			function getModuleExports() { return module; };
+/******/ 		__webpack_require__.d(getter, 'a', getter);
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+/******/ ([]);
\ No newline at end of file
diff --git a/test/cases/runtime/expected/webpack-5/main.a7263f8f763dcf4051bc.css b/test/cases/runtime/expected/webpack-5/main.a7263f8f763dcf4051bc.css
new file mode 100644
index 0000000..cebc5c1
--- /dev/null
+++ b/test/cases/runtime/expected/webpack-5/main.a7263f8f763dcf4051bc.css
@@ -0,0 +1,4 @@
+body {
+  background: red;
+}
+
diff --git a/test/cases/runtime/expected/webpack-5/runtime~main.js b/test/cases/runtime/expected/webpack-5/runtime~main.js
new file mode 100644
index 0000000..13ea0c6
--- /dev/null
+++ b/test/cases/runtime/expected/webpack-5/runtime~main.js
@@ -0,0 +1,334 @@
+/******/ (() => { // webpackBootstrap
+/******/ 	"use strict";
+/******/ 	var __webpack_modules__ = ({});
+/************************************************************************/
+/******/ 	// The module cache
+/******/ 	var __webpack_module_cache__ = {};
+/******/ 	
+/******/ 	// The require function
+/******/ 	function __webpack_require__(moduleId) {
+/******/ 		// Check if module is in cache
+/******/ 		if(__webpack_module_cache__[moduleId]) {
+/******/ 			return __webpack_module_cache__[moduleId].exports;
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+/******/ 			// no module.id needed
+/******/ 			// no module.loaded needed
+/******/ 			exports: {}
+/******/ 		};
+/******/ 	
+/******/ 		// Execute the module function
+/******/ 		__webpack_modules__[moduleId](module, module.exports, __webpack_require__);
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+/******/ 		// Return the exports of the module
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+/******/ 	// expose the modules object (__webpack_modules__)
+/******/ 	__webpack_require__.m = __webpack_modules__;
+/******/ 	
+/******/ 	// the startup function
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+/******/ 	__webpack_require__.x = x => {}
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+/******/ 	(() => {
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+/******/ 			def['default'] = () => value;
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+/******/ 			Object.defineProperty(exports, '__esModule', { value: true });
+/******/ 		};
+/******/ 	})();
+/******/ 	
+/******/ 	/* webpack/runtime/publicPath */
+/******/ 	(() => {
+/******/ 		var scriptUrl;
+/******/ 		if (__webpack_require__.g.importScripts) scriptUrl = __webpack_require__.g.location + "";
+/******/ 		var document = __webpack_require__.g.document;
+/******/ 		if (!scriptUrl && document) {
+/******/ 			if (document.currentScript)
+/******/ 				scriptUrl = document.currentScript.src
+/******/ 			if (!scriptUrl) {
+/******/ 				var scripts = document.getElementsByTagName("script");
+/******/ 				if(scripts.length) scriptUrl = scripts[scripts.length - 1].src
+/******/ 			}
+/******/ 		}
+/******/ 		// When supporting browsers where an automatic publicPath is not supported you must specify an output.publicPath manually via configuration
+/******/ 		// or pass an empty string ("") and set the __webpack_public_path__ variable from your code to use your own logic.
+/******/ 		if (!scriptUrl) throw new Error("Automatic publicPath is not supported in this browser");
+/******/ 		scriptUrl = scriptUrl.replace(/#.*$/, "").replace(/\?.*$/, "").replace(/\/[^\/]+$/, "/");
+/******/ 		__webpack_require__.p = scriptUrl;
+/******/ 	})();
+/******/ 	
+/******/ 	/* webpack/runtime/jsonp chunk loading */
+/******/ 	(() => {
+/******/ 		// no baseURI
+/******/ 		
+/******/ 		// object to store loaded and loading chunks
+/******/ 		// undefined = chunk not loaded, null = chunk preloaded/prefetched
+/******/ 		// Promise = chunk loading, 0 = chunk loaded
+/******/ 		var installedChunks = {
+/******/ 			1: 0
+/******/ 		};
+/******/ 		
+/******/ 		var deferredModules = [
+/******/ 		
+/******/ 		];
+/******/ 		__webpack_require__.f.j = (chunkId, promises) => {
+/******/ 				// JSONP chunk loading for javascript
+/******/ 				var installedChunkData = __webpack_require__.o(installedChunks, chunkId) ? installedChunks[chunkId] : undefined;
+/******/ 				if(installedChunkData !== 0) { // 0 means "already installed".
+/******/ 		
+/******/ 					// a Promise means "currently loading".
+/******/ 					if(installedChunkData) {
+/******/ 						promises.push(installedChunkData[2]);
+/******/ 					} else {
+/******/ 						if(true) { // all chunks have JS
+/******/ 							// setup Promise in chunk cache
+/******/ 							var promise = new Promise((resolve, reject) => {
+/******/ 								installedChunkData = installedChunks[chunkId] = [resolve, reject];
+/******/ 							});
+/******/ 							promises.push(installedChunkData[2] = promise);
+/******/ 		
+/******/ 							// start chunk loading
+/******/ 							var url = __webpack_require__.p + __webpack_require__.u(chunkId);
+/******/ 							// create error before stack unwound to get useful stacktrace later
+/******/ 							var error = new Error();
+/******/ 							var loadingEnded = (event) => {
+/******/ 								if(__webpack_require__.o(installedChunks, chunkId)) {
+/******/ 									installedChunkData = installedChunks[chunkId];
+/******/ 									if(installedChunkData !== 0) installedChunks[chunkId] = undefined;
+/******/ 									if(installedChunkData) {
+/******/ 										var errorType = event && (event.type === 'load' ? 'missing' : event.type);
+/******/ 										var realSrc = event && event.target && event.target.src;
+/******/ 										error.message = 'Loading chunk ' + chunkId + ' failed.\n(' + errorType + ': ' + realSrc + ')';
+/******/ 										error.name = 'ChunkLoadError';
+/******/ 										error.type = errorType;
+/******/ 										error.request = realSrc;
+/******/ 										installedChunkData[1](error);
+/******/ 									}
+/******/ 								}
+/******/ 							};
+/******/ 							__webpack_require__.l(url, loadingEnded, "chunk-" + chunkId, chunkId);
+/******/ 						} else installedChunks[chunkId] = 0;
+/******/ 					}
+/******/ 				}
+/******/ 		};
+/******/ 		
+/******/ 		// no prefetching
+/******/ 		
+/******/ 		// no preloaded
+/******/ 		
+/******/ 		// no HMR
+/******/ 		
+/******/ 		// no HMR manifest
+/******/ 		
+/******/ 		var checkDeferredModules = x => {};
+/******/ 		
+/******/ 		// install a JSONP callback for chunk loading
+/******/ 		var webpackJsonpCallback = (parentChunkLoadingFunction, data) => {
+/******/ 			var [chunkIds, moreModules, runtime, executeModules] = data;
+/******/ 			// add "moreModules" to the modules object,
+/******/ 			// then flag all "chunkIds" as loaded and fire callback
+/******/ 			var moduleId, chunkId, i = 0, resolves = [];
+/******/ 			for(;i < chunkIds.length; i++) {
+/******/ 				chunkId = chunkIds[i];
+/******/ 				if(__webpack_require__.o(installedChunks, chunkId) && installedChunks[chunkId]) {
+/******/ 					resolves.push(installedChunks[chunkId][0]);
+/******/ 				}
+/******/ 				installedChunks[chunkId] = 0;
+/******/ 			}
+/******/ 			for(moduleId in moreModules) {
+/******/ 				if(__webpack_require__.o(moreModules, moduleId)) {
+/******/ 					__webpack_require__.m[moduleId] = moreModules[moduleId];
+/******/ 				}
+/******/ 			}
+/******/ 			if(runtime) runtime(__webpack_require__);
+/******/ 			if(parentChunkLoadingFunction) parentChunkLoadingFunction(data);
+/******/ 			while(resolves.length) {
+/******/ 				resolves.shift()();
+/******/ 			}
+/******/ 		
+/******/ 			// add entry modules from loaded chunk to deferred list
+/******/ 			if(executeModules) deferredModules.push.apply(deferredModules, executeModules);
+/******/ 		
+/******/ 			// run deferred modules when all chunks ready
+/******/ 			return checkDeferredModules();
+/******/ 		}
+/******/ 		
+/******/ 		var chunkLoadingGlobal = self["webpackChunk"] = self["webpackChunk"] || [];
+/******/ 		chunkLoadingGlobal.forEach(webpackJsonpCallback.bind(null, 0));
+/******/ 		chunkLoadingGlobal.push = webpackJsonpCallback.bind(null, chunkLoadingGlobal.push.bind(chunkLoadingGlobal));
+/******/ 		
+/******/ 		function checkDeferredModulesImpl() {
+/******/ 			var result;
+/******/ 			for(var i = 0; i < deferredModules.length; i++) {
+/******/ 				var deferredModule = deferredModules[i];
+/******/ 				var fulfilled = true;
+/******/ 				for(var j = 1; j < deferredModule.length; j++) {
+/******/ 					var depId = deferredModule[j];
+/******/ 					if(installedChunks[depId] !== 0) fulfilled = false;
+/******/ 				}
+/******/ 				if(fulfilled) {
+/******/ 					deferredModules.splice(i--, 1);
+/******/ 					result = __webpack_require__(__webpack_require__.s = deferredModule[0]);
+/******/ 				}
+/******/ 			}
+/******/ 			if(deferredModules.length === 0) {
+/******/ 				__webpack_require__.x();
+/******/ 				__webpack_require__.x = x => {};
+/******/ 			}
+/******/ 			return result;
+/******/ 		}
+/******/ 		var startup = __webpack_require__.x;
+/******/ 		__webpack_require__.x = () => {
+/******/ 			// reset startup function so it can be called again when more startup code is added
+/******/ 			__webpack_require__.x = startup || (x => {});
+/******/ 			return (checkDeferredModules = checkDeferredModulesImpl)();
+/******/ 		};
+/******/ 	})();
+/******/ 	
+/************************************************************************/
+/******/ 	// run startup
+/******/ 	__webpack_require__.x();
+/******/ })()
+;
\ No newline at end of file
diff --git a/test/cases/runtime/index.js b/test/cases/runtime/index.js
new file mode 100644
index 0000000..4d25dd7
--- /dev/null
+++ b/test/cases/runtime/index.js
@@ -0,0 +1,4 @@
+// eslint-disable-next-line import/no-unresolved
+import './style.css';
+
+import('./async.js');
diff --git a/test/cases/runtime/style.css b/test/cases/runtime/style.css
new file mode 100644
index 0000000..67ce83e
--- /dev/null
+++ b/test/cases/runtime/style.css
@@ -0,0 +1,3 @@
+body {
+  background: red;
+}
diff --git a/test/cases/runtime/webpack.config.js b/test/cases/runtime/webpack.config.js
new file mode 100644
index 0000000..d0ad3ee
--- /dev/null
+++ b/test/cases/runtime/webpack.config.js
@@ -0,0 +1,25 @@
+import Self from '../../../src';
+
+module.exports = {
+  entry: './index.js',
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [Self.loader, 'css-loader'],
+      },
+    ],
+  },
+  output: {
+    filename: `[name].js`,
+  },
+  plugins: [
+    new Self({
+      filename: `[name].[contenthash].css`,
+      chunkFilename: `[name].[contenthash].css`,
+    }),
+  ],
+  optimization: {
+    runtimeChunk: true,
+  },
+};