fix: tree-shaking unused RawModule (#19671)

Author: colinaaa

lib/Dependency.js

@@ -85,9 +85,11 @@ const memoize = require("./util/memoize");
 
 const TRANSITIVE = Symbol("transitive");
 
-const getIgnoredModule = memoize(
-	() => new RawModule("/* (ignored) */", "ignored", "(ignored)")
-);
+const getIgnoredModule = memoize(() => {
+	const module = new RawModule("/* (ignored) */", "ignored", "(ignored)");
+	module.factoryMeta = { sideEffectFree: true };
+	return module;
+});
 
 class Dependency {
 	constructor() {

lib/IgnorePlugin.js

@@ -80,11 +80,14 @@ class IgnorePlugin {
 					resolveData.dependencies.length > 0 &&
 					resolveData.dependencies[0] instanceof EntryDependency
 				) {
-					resolveData.ignoredModule = new RawModule(
+					const module = new RawModule(
 						"",
 						"ignored-entry-module",
 						"(ignored-entry-module)"
 					);
+					module.factoryMeta = { sideEffectFree: true };
+
+					resolveData.ignoredModule = module;
 				}
 
 				return result;

lib/RawModule.js

@@ -24,6 +24,8 @@ const makeSerializable = require("./util/makeSerializable");
 /** @typedef {import("./Module").NeedBuildCallback} NeedBuildCallback */
 /** @typedef {import("./Module").NeedBuildContext} NeedBuildContext */
 /** @typedef {import("./Module").ReadOnlyRuntimeRequirements} ReadOnlyRuntimeRequirements */
+/** @typedef {import("./ModuleGraph")} ModuleGraph */
+/** @typedef {import("./ModuleGraphConnection").ConnectionState} ConnectionState */
 /** @typedef {import("./RequestShortener")} RequestShortener */
 /** @typedef {import("./ResolverFactory").ResolverWithOptions} ResolverWithOptions */
 /** @typedef {import("./RuntimeTemplate")} RuntimeTemplate */
@@ -105,6 +107,18 @@ class RawModule extends Module {
 		callback();
 	}
 
+	/**
+	 * @param {ModuleGraph} moduleGraph the module graph
+	 * @returns {ConnectionState} how this module should be connected to referencing modules when consumed for side-effects only
+	 */
+	getSideEffectsConnectionState(moduleGraph) {
+		if (this.factoryMeta !== undefined) {
+			if (this.factoryMeta.sideEffectFree) return false;
+			if (this.factoryMeta.sideEffectFree === false) return true;
+		}
+		return true;
+	}
+
 	/**
 	 * @param {CodeGenerationContext} context context for code generation
 	 * @returns {CodeGenerationResult} result

lib/dependencies/ModuleDependency.js

@@ -61,11 +61,13 @@ class ModuleDependency extends Dependency {
 	 * @returns {Module} ignored module
 	 */
 	createIgnoredModule(context) {
-		return new RawModule(
+		const module = new RawModule(
 			"/* (ignored) */",
 			`ignored|${context}|${this.request}`,
 			`${this.request} (ignored)`
 		);
+		module.factoryMeta = { sideEffectFree: true };
+		return module;
 	}
 
 	/**

test/configCases/ignore/side-effects/ignored-module.js

@@ -0,0 +1 @@
+module.exports = "ignored";

test/configCases/ignore/side-effects/locales/a.js

@@ -0,0 +1 @@
+export default "a";

test/configCases/ignore/side-effects/locales/b.js

@@ -0,0 +1 @@
+export default "b";

test/configCases/ignore/side-effects/test.js

@@ -0,0 +1,15 @@
+"use strict";
+
+import "ignored-module";
+import "./ignored-module";
+
+it("should remove all ignored modules", async function() {
+	// Current module + module with runtime code to load context modules
+	expect(Object.keys(__webpack_modules__)).toHaveLength(2);
+
+	const x = "a";
+	const locale = (await import("./locales/" + x)).default;
+
+	expect(locale).toBe("a");
+	expect(Object.keys(__webpack_modules__)).toHaveLength(3);
+});

test/configCases/ignore/side-effects/webpack.config.js

@@ -0,0 +1,18 @@
+"use strict";
+
+const webpack = require("../../../../");
+
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	entry: "./test.js",
+	resolve: {
+		alias: {
+			"ignored-module": false,
+			"./ignored-module": false
+		}
+	},
+	plugins: [new webpack.IgnorePlugin({ resourceRegExp: /(b\.js|b)$/ })],
+	optimization: {
+		sideEffects: true
+	}
+};