webpack/lib/performance/LegacyJavascriptPlugin.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 LegacyJavascriptWarning = require("../errors/LegacyJavascriptWarning");
const { compareStrings } = require("../util/comparators");
const { WINDOWS_PATH_SEPARATOR_REGEXP } = require("../util/identifier");
const getModuleSize = require("./getModuleSize");
const getSourceModules = require("./getSourceModules");

/** @import { Environment, PerformanceOptions } from "../../declarations/WebpackOptions" */
/** @import Compiler from "../Compiler" */
/** @import { LegacyPackageDetails } from "../errors/LegacyJavascriptWarning" */

const PLUGIN_NAME = "LegacyJavascriptPlugin";

// Packages that exist to emulate syntax. `core-js` is absent on purpose: it
// polyfills APIs, which `output.environment` says nothing about.
const EMULATING_PACKAGES = ["regenerator-runtime", "@babel/runtime"];

// The syntax the report leans on: each is what one of those packages exists to
// lower, so a target with all of them needs none of the lowering.
/** @type {(keyof Environment)[]} */
const NATIVE_FEATURES = [
	"arrowFunction",
	"asyncFunction",
	"const",
	"destructuring",
	"forOf",
	"generator",
	"templateLiteral"
];

/**
 * The emulating package a module belongs to, if it is in one.
 * @param {string} resource the module's path
 * @returns {string | undefined} the package, or undefined when it is not one
 */
const emulatingPackage = (resource) => {
	// Separators normalized so one check serves both platforms, and matched
	// against the path so an alias or re-export is still recognized.
	const path = resource.replace(WINDOWS_PATH_SEPARATOR_REGEXP, "/");

	for (const name of EMULATING_PACKAGES) {
		if (path.includes(`node_modules/${name}/`)) return name;
	}

	return undefined;
};

class LegacyJavascriptPlugin {
	/**
	 * Creates an instance of LegacyJavascriptPlugin.
	 * @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;

		if (!hints) return;

		compiler.hooks.compilation.tap(PLUGIN_NAME, (compilation) => {
			// `afterSeal` is past the hash, which folds every message into it — a
			// hint reported earlier would change the build's identity.
			compilation.hooks.afterSeal.tap(PLUGIN_NAME, () => {
				const environment = compilation.outputOptions.environment;

				// Reported only when the target has every one of them: emulating a
				// feature the target is missing is the polyfill doing its job.
				for (const feature of NATIVE_FEATURES) {
					if (!environment[feature]) return;
				}

				/** @type {Map<string, LegacyPackageDetails>} */
				const found = new Map();
				let totalSize = 0;

				for (const module of compilation.modules) {
					for (const inner of getSourceModules(module)) {
						const resource = inner.nameForCondition();

						if (!resource) continue;

						const name = emulatingPackage(resource);

						if (!name) continue;

						const size = getModuleSize(inner);
						const details = found.get(name);

						totalSize += size;

						if (details === undefined) {
							found.set(name, { name, modules: 1, size });
						} else {
							details.modules++;
							details.size += size;
						}
					}
				}

				if (found.size === 0) return;

				// Ties break by name: module order is not stable across runs.
				const packages = [...found.values()].sort(
					(a, b) => b.size - a.size || compareStrings(a.name, b.name)
				);

				const warning = new LegacyJavascriptWarning(
					packages,
					totalSize,
					NATIVE_FEATURES
				);

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

module.exports = LegacyJavascriptPlugin;