webpack/lib/performance/isOnlyReexported.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 HarmonyExportImportedSpecifierDependency = require("../dependencies/HarmonyExportImportedSpecifierDependency");
const HarmonyImportDependency = require("../dependencies/HarmonyImportDependency");

/** @import Module from "../Module" */
/** @import ModuleGraph from "../ModuleGraph" */

/**
 * Tells whether every module pulling this one in does so by re-exporting it.
 * One an importer wants for its side effects alone is deliberate, not a
 * barrel's leftover.
 * @param {Module} module the module to look up
 * @param {ModuleGraph} moduleGraph the module graph
 * @returns {boolean} true when only re-exports pull it in
 */
const isOnlyReexported = (module, moduleGraph) => {
	// A re-export emits a side-effect edge of its own, so edges are grouped by
	// the statement they come from — `sourceOrder` — rather than by their type.
	/** @type {Map<Module, Set<number | undefined>>} */
	const reexportedStatements = new Map();
	/** @type {[Module, number | undefined][]} */
	const edges = [];

	for (const connection of moduleGraph.getIncomingConnections(module)) {
		const origin = connection.originModule;

		// An entry has no origin: it is in the build because it was asked for.
		if (!origin) return false;

		const dependency = connection.dependency;

		// Only an ESM import statement can carry a re-export.
		if (!(dependency instanceof HarmonyImportDependency)) return false;

		if (dependency instanceof HarmonyExportImportedSpecifierDependency) {
			const statements = reexportedStatements.get(origin);

			if (statements === undefined) {
				reexportedStatements.set(origin, new Set([dependency.sourceOrder]));
			} else {
				statements.add(dependency.sourceOrder);
			}
		}

		edges.push([origin, dependency.sourceOrder]);
	}

	if (edges.length === 0) return false;

	for (const [origin, sourceOrder] of edges) {
		const statements = reexportedStatements.get(origin);

		if (statements === undefined || !statements.has(sourceOrder)) return false;
	}

	return true;
};

module.exports = isOnlyReexported;