avoid allocation of meta info for dependencies when unused

lib/ModuleGraph.js

@@ -655,6 +655,14 @@ class ModuleGraph {
 		return meta;
 	}
 
+	/**
+	 * @param {any} thing any thing
+	 * @returns {Object} metadata
+	 */
+	getMetaIfExisting(thing) {
+		return this._metaMap.get(thing);
+	}
+
 	// TODO remove in webpack 6
 	/**
 	 * @param {Module} module the module

lib/dependencies/HarmonyImportSpecifierDependency.js

@@ -66,7 +66,10 @@ class HarmonyImportSpecifierDependency extends HarmonyImportDependency {
 	 * @returns {string[]} the imported ids
 	 */
 	getIds(moduleGraph) {
-		return moduleGraph.getMeta(this)[idsSymbol] || this.ids;
+		const meta = moduleGraph.getMetaIfExisting(this);
+		if (meta === undefined) return this.ids;
+		const ids = meta[idsSymbol];
+		return ids !== undefined ? ids : this.ids;
 	}
 
 	/**

types.d.ts

@@ -5713,6 +5713,7 @@ declare class ModuleGraph {
 	isAsync(module: Module): boolean;
 	setAsync(module: Module): void;
 	getMeta(thing?: any): Object;
+	getMetaIfExisting(thing?: any): Object;
 	static getModuleGraphForModule(
 		module: Module,
 		deprecateMessage: string,