webpack/lib/performance/UnusedDefinesPlugin.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Alexander Akait @alexander-akait
*/

"use strict";

const { VALUE_DEP_PREFIX, getDeclaredKeys } = require("../DefinePlugin");
const UnusedDefinesWarning = require("../errors/UnusedDefinesWarning");

/** @import { PerformanceOptions } from "../../declarations/WebpackOptions" */
/** @import Compiler from "../Compiler" */
/** @import { NormalModuleBuildInfo } from "../NormalModule" */

const PLUGIN_NAME = "UnusedDefinesPlugin";

class UnusedDefinesPlugin {
	/**
	 * Creates an instance of UnusedDefinesPlugin.
	 * @param {PerformanceOptions} options the plugin options
	 */
	constructor(options) {
		/** @type {PerformanceOptions["hints"]} */
		this.hints = options.hints;
	}

	/**
	 * Applies the plugin by registering its hooks on the compiler.
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		const hints = this.hints;

		compiler.hooks.compilation.tap(PLUGIN_NAME, (compilation) => {
			compilation.hooks.afterSeal.tap(PLUGIN_NAME, () => {
				const declared = getDeclaredKeys(compilation);

				if (declared === undefined || declared.size === 0) return;
				// Nothing was parsed, so no key could be substituted — an empty build is
				// not evidence that a key is unused.
				if (compilation.modules.size === 0) return;

				/** @type {Set<string>} */
				const used = new Set();

				for (const module of compilation.modules) {
					const buildInfo =
						/** @type {NormalModuleBuildInfo} */
						(module.buildInfo);

					if (!buildInfo || !buildInfo.valueDependencies) continue;

					// Survives the persistent cache: `valueDependencies` is serialized
					// with the module, so a restored module answers without rebuilding.
					for (const name of buildInfo.valueDependencies.keys()) {
						if (name.startsWith(VALUE_DEP_PREFIX)) {
							used.add(name.slice(VALUE_DEP_PREFIX.length));
						}
					}
				}

				const unused = [];

				for (const key of declared) {
					if (!used.has(key)) unused.push(key);
				}

				if (unused.length === 0) return;

				unused.sort();

				const warning = new UnusedDefinesWarning(unused);

				if (hints === "error") {
					compilation.errors.push(warning);
				} else if (hints === "stats") {
					compilation.hints.push(warning);
				} else {
					compilation.warnings.push(warning);
				}
			});
		});
	}
}

module.exports = UnusedDefinesPlugin;