webpack/lib/optimize/MangleExportsPlugin.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 Tobias Koppers @sokra
*/

"use strict";

const { UsageState } = require("../ExportsInfo");
const {
	numberToIdentifier,
	NUMBER_OF_IDENTIFIER_START_CHARS,
	NUMBER_OF_IDENTIFIER_CONTINUATION_CHARS
} = require("../Template");
const { assignDeterministicIds } = require("../ids/IdHelpers");
const { compareSelect, compareStringsNumeric } = require("../util/comparators");

/** @typedef {import("../Compiler")} Compiler */
/** @typedef {import("../ExportsInfo")} ExportsInfo */
/** @typedef {import("../ExportsInfo").ExportInfo} ExportInfo */

/**
 * @param {ExportsInfo} exportsInfo exports info
 * @returns {boolean} mangle is possible
 */
const canMangle = exportsInfo => {
	if (exportsInfo.otherExportsInfo.getUsed(undefined) !== UsageState.Unused)
		return false;
	let hasSomethingToMangle = false;
	for (const exportInfo of exportsInfo.exports) {
		if (exportInfo.canMangle === true) {
			hasSomethingToMangle = true;
		}
	}
	return hasSomethingToMangle;
};

// Sort by name
const comparator = compareSelect(e => e.name, compareStringsNumeric);
/**
 * @param {boolean} deterministic use deterministic names
 * @param {ExportsInfo} exportsInfo exports info
 * @param {boolean | undefined} isNamespace is namespace object
 * @returns {void}
 */
const mangleExportsInfo = (deterministic, exportsInfo, isNamespace) => {
	if (!canMangle(exportsInfo)) return;
	const usedNames = new Set();
	/** @type {ExportInfo[]} */
	const mangleableExports = [];

	// Avoid to renamed exports that are not provided when
	// 1. it's not a namespace export: non-provided exports can be found in prototype chain
	// 2. there are other provided exports and deterministic mode is chosen:
	//    non-provided exports would break the determinism
	let avoidMangleNonProvided = !isNamespace;
	if (!avoidMangleNonProvided && deterministic) {
		for (const exportInfo of exportsInfo.ownedExports) {
			if (exportInfo.provided !== false) {
				avoidMangleNonProvided = true;
				break;
			}
		}
	}
	for (const exportInfo of exportsInfo.ownedExports) {
		const name = exportInfo.name;
		if (!exportInfo.hasUsedName()) {
			if (
				// Can the export be mangled?
				exportInfo.canMangle !== true ||
				// Never rename 1 char exports
				(name.length === 1 && /^[a-zA-Z0-9_$]/.test(name)) ||
				// Don't rename 2 char exports in deterministic mode
				(deterministic &&
					name.length === 2 &&
					/^[a-zA-Z_$][a-zA-Z0-9_$]|^[1-9][0-9]/.test(name)) ||
				// Don't rename exports that are not provided
				(avoidMangleNonProvided && exportInfo.provided !== true)
			) {
				exportInfo.setUsedName(name);
				usedNames.add(name);
			} else {
				mangleableExports.push(exportInfo);
			}
		}
		if (exportInfo.exportsInfoOwned) {
			const used = exportInfo.getUsed(undefined);
			if (
				used === UsageState.OnlyPropertiesUsed ||
				used === UsageState.Unused
			) {
				mangleExportsInfo(
					deterministic,
					/** @type {ExportsInfo} */ (exportInfo.exportsInfo),
					false
				);
			}
		}
	}
	if (deterministic) {
		assignDeterministicIds(
			mangleableExports,
			e => e.name,
			comparator,
			(e, id) => {
				const name = numberToIdentifier(id);
				const size = usedNames.size;
				usedNames.add(name);
				if (size === usedNames.size) return false;
				e.setUsedName(name);
				return true;
			},
			[
				NUMBER_OF_IDENTIFIER_START_CHARS,
				NUMBER_OF_IDENTIFIER_START_CHARS *
					NUMBER_OF_IDENTIFIER_CONTINUATION_CHARS
			],
			NUMBER_OF_IDENTIFIER_CONTINUATION_CHARS,
			usedNames.size
		);
	} else {
		const usedExports = [];
		const unusedExports = [];
		for (const exportInfo of mangleableExports) {
			if (exportInfo.getUsed(undefined) === UsageState.Unused) {
				unusedExports.push(exportInfo);
			} else {
				usedExports.push(exportInfo);
			}
		}
		usedExports.sort(comparator);
		unusedExports.sort(comparator);
		let i = 0;
		for (const list of [usedExports, unusedExports]) {
			for (const exportInfo of list) {
				let name;
				do {
					name = numberToIdentifier(i++);
				} while (usedNames.has(name));
				exportInfo.setUsedName(name);
			}
		}
	}
};

const PLUGIN_NAME = "MangleExportsPlugin";

class MangleExportsPlugin {
	/**
	 * @param {boolean} deterministic use deterministic names
	 */
	constructor(deterministic) {
		this._deterministic = deterministic;
	}

	/**
	 * Apply the plugin
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		const { _deterministic: deterministic } = this;
		compiler.hooks.compilation.tap(PLUGIN_NAME, compilation => {
			const moduleGraph = compilation.moduleGraph;
			compilation.hooks.optimizeCodeGeneration.tap(PLUGIN_NAME, modules => {
				if (compilation.moduleMemCaches) {
					throw new Error(
						"optimization.mangleExports can't be used with cacheUnaffected as export mangling is a global effect"
					);
				}
				for (const module of modules) {
					const isNamespace =
						module.buildMeta && module.buildMeta.exportsType === "namespace";
					const exportsInfo = moduleGraph.getExportsInfo(module);
					mangleExportsInfo(deterministic, exportsInfo, isNamespace);
				}
			});
		});
	}
}

module.exports = MangleExportsPlugin;