webpack/lib/optimize/FlagIncludedChunksPlugin.js

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

const { compareIds } = require("../util/comparators");

/** @typedef {import("../Chunk")} Chunk */
/** @typedef {import("../Chunk").ChunkId} ChunkId */
/** @typedef {import("../Compiler")} Compiler */
/** @typedef {import("../Module")} Module */

const PLUGIN_NAME = "FlagIncludedChunksPlugin";

class FlagIncludedChunksPlugin {
	/**
	 * Apply the plugin
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		compiler.hooks.compilation.tap(PLUGIN_NAME, (compilation) => {
			compilation.hooks.optimizeChunkIds.tap(PLUGIN_NAME, (chunks) => {
				const chunkGraph = compilation.chunkGraph;

				// prepare two bit integers for each module
				// 2^31 is the max number represented as SMI in v8
				// we want the bits distributed this way:
				// the bit 2^31 is pretty rar and only one module should get it
				// so it has a probability of 1 / modulesCount
				// the first bit (2^0) is the easiest and every module could get it
				// if it doesn't get a better bit
				// from bit 2^n to 2^(n+1) there is a probability of p
				// so 1 / modulesCount == p^31
				// <=> p = sqrt31(1 / modulesCount)
				// so we use a modulo of 1 / sqrt31(1 / modulesCount)
				/** @type {WeakMap<Module, number>} */
				const moduleBits = new WeakMap();
				const modulesCount = compilation.modules.size;

				// precalculate the modulo values for each bit
				const modulo = 1 / (1 / modulesCount) ** (1 / 31);
				const modulos = Array.from({ length: 31 }, (x, i) => (modulo ** i) | 0);

				// iterate all modules to generate bit values
				let i = 0;
				for (const module of compilation.modules) {
					let bit = 30;
					while (i % modulos[bit] !== 0) {
						bit--;
					}
					moduleBits.set(module, 1 << bit);
					i++;
				}

				// iterate all chunks to generate bitmaps
				/** @type {WeakMap<Chunk, number>} */
				const chunkModulesHash = new WeakMap();
				for (const chunk of chunks) {
					let hash = 0;
					for (const module of chunkGraph.getChunkModulesIterable(chunk)) {
						hash |= /** @type {number} */ (moduleBits.get(module));
					}
					chunkModulesHash.set(chunk, hash);
				}

				for (const chunkA of chunks) {
					const chunkAHash =
						/** @type {number} */
						(chunkModulesHash.get(chunkA));
					const chunkAModulesCount = chunkGraph.getNumberOfChunkModules(chunkA);
					if (chunkAModulesCount === 0) continue;
					let bestModule;
					for (const module of chunkGraph.getChunkModulesIterable(chunkA)) {
						if (
							bestModule === undefined ||
							chunkGraph.getNumberOfModuleChunks(bestModule) >
								chunkGraph.getNumberOfModuleChunks(module)
						) {
							bestModule = module;
						}
					}
					loopB: for (const chunkB of chunkGraph.getModuleChunksIterable(
						/** @type {Module} */ (bestModule)
					)) {
						// as we iterate the same iterables twice
						// skip if we find ourselves
						if (chunkA === chunkB) continue;

						const chunkBModulesCount =
							chunkGraph.getNumberOfChunkModules(chunkB);

						// ids for empty chunks are not included
						if (chunkBModulesCount === 0) continue;

						// instead of swapping A and B just bail
						// as we loop twice the current A will be B and B then A
						if (chunkAModulesCount > chunkBModulesCount) continue;

						// is chunkA in chunkB?

						// we do a cheap check for the hash value
						const chunkBHash =
							/** @type {number} */
							(chunkModulesHash.get(chunkB));
						if ((chunkBHash & chunkAHash) !== chunkAHash) continue;

						// compare all modules
						for (const m of chunkGraph.getChunkModulesIterable(chunkA)) {
							if (!chunkGraph.isModuleInChunk(m, chunkB)) continue loopB;
						}

						/** @type {ChunkId[]} */
						(chunkB.ids).push(/** @type {ChunkId} */ (chunkA.id));
						// https://github.com/webpack/webpack/issues/18837
						/** @type {ChunkId[]} */
						(chunkB.ids).sort(compareIds);
					}
				}
			});
		});
	}
}

module.exports = FlagIncludedChunksPlugin;