webpack/lib/FlagDependencyUsagePlugin.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support 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";

/** @typedef {import("./Module")} Module */
/** @typedef {import("./DependenciesBlock")} DependenciesBlock */

/** @typedef {false | true | string[]} UsedExports */

const addToSet = (a, b) => {
	for (const item of b) {
		if (!a.includes(item)) a.push(item);
	}
	return a;
};

const isSubset = (biggerSet, subset) => {
	if (biggerSet === true) return true;
	if (subset === true) return false;
	return subset.every(item => biggerSet.indexOf(item) >= 0);
};

class FlagDependencyUsagePlugin {
	apply(compiler) {
		compiler.hooks.compilation.tap("FlagDependencyUsagePlugin", compilation => {
			compilation.hooks.optimizeDependencies.tap(
				"FlagDependencyUsagePlugin",
				modules => {
					const processModule = (module, usedExports) => {
						module.used = true;
						if (module.usedExports === true) return;
						if (usedExports === true) {
							module.usedExports = true;
						} else if (Array.isArray(usedExports)) {
							const old = module.usedExports ? module.usedExports.length : -1;
							module.usedExports = addToSet(
								module.usedExports || [],
								usedExports
							);
							if (module.usedExports.length === old) {
								return;
							}
						} else if (Array.isArray(module.usedExports)) {
							return;
						} else {
							module.usedExports = false;
						}

						// for a module without side effects we stop tracking usage here when no export is used
						// This module won't be evaluated in this case
						if (module.factoryMeta.sideEffectFree) {
							if (module.usedExports === false) return;
							if (
								Array.isArray(module.usedExports) &&
								module.usedExports.length === 0
							)
								return;
						}

						queue.push([module, module, module.usedExports]);
					};

					const processDependenciesBlock = (module, depBlock, usedExports) => {
						for (const dep of depBlock.dependencies) {
							processDependency(module, dep);
						}
						for (const variable of depBlock.variables) {
							for (const dep of variable.dependencies) {
								processDependency(module, dep);
							}
						}
						for (const block of depBlock.blocks) {
							queue.push([module, block, usedExports]);
						}
					};

					const processDependency = (module, dep) => {
						const reference = compilation.getDependencyReference(module, dep);
						if (!reference) return;
						const referenceModule = reference.module;
						const importedNames = reference.importedNames;
						const oldUsed = referenceModule.used;
						const oldUsedExports = referenceModule.usedExports;
						if (
							!oldUsed ||
							(importedNames &&
								(!oldUsedExports || !isSubset(oldUsedExports, importedNames)))
						) {
							processModule(referenceModule, importedNames);
						}
					};

					for (const module of modules) {
						module.used = false;
					}

					/** @type {[Module, DependenciesBlock, UsedExports][]} */
					const queue = [];
					for (const preparedEntrypoint of compilation._preparedEntrypoints) {
						if (preparedEntrypoint.module) {
							processModule(preparedEntrypoint.module, true);
						}
					}

					while (queue.length) {
						const queueItem = queue.pop();
						processDependenciesBlock(queueItem[0], queueItem[1], queueItem[2]);
					}
				}
			);
		});
	}
}
module.exports = FlagDependencyUsagePlugin;