webpack/lib/optimize/AggressiveMergingPlugin.js

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

"use strict";

const { STAGE_ADVANCED } = require("../OptimizationStages");

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

/**
 * @typedef {object} AggressiveMergingPluginOptions
 * @property {number=} minSizeReduce minimal size reduction to trigger merging
 */

class AggressiveMergingPlugin {
	/**
	 * @param {AggressiveMergingPluginOptions=} options options object
	 */
	constructor(options) {
		if (
			(options !== undefined && typeof options !== "object") ||
			Array.isArray(options)
		) {
			throw new Error(
				"Argument should be an options object. To use defaults, pass in nothing.\nFor more info on options, see https://webpack.js.org/plugins/"
			);
		}
		this.options = options || {};
	}

	/**
	 * Apply the plugin
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		const options = this.options;
		const minSizeReduce = options.minSizeReduce || 1.5;

		compiler.hooks.thisCompilation.tap(
			"AggressiveMergingPlugin",
			compilation => {
				compilation.hooks.optimizeChunks.tap(
					{
						name: "AggressiveMergingPlugin",
						stage: STAGE_ADVANCED
					},
					chunks => {
						const chunkGraph = compilation.chunkGraph;
						/** @type {{a: Chunk, b: Chunk, improvement: number}[]} */
						const combinations = [];
						for (const a of chunks) {
							if (a.canBeInitial()) continue;
							for (const b of chunks) {
								if (b.canBeInitial()) continue;
								if (b === a) break;
								if (!chunkGraph.canChunksBeIntegrated(a, b)) {
									continue;
								}
								const aSize = chunkGraph.getChunkSize(b, {
									chunkOverhead: 0
								});
								const bSize = chunkGraph.getChunkSize(a, {
									chunkOverhead: 0
								});
								const abSize = chunkGraph.getIntegratedChunksSize(b, a, {
									chunkOverhead: 0
								});
								const improvement = (aSize + bSize) / abSize;
								combinations.push({
									a,
									b,
									improvement
								});
							}
						}

						combinations.sort((a, b) => b.improvement - a.improvement);

						const pair = combinations[0];

						if (!pair) return;
						if (pair.improvement < minSizeReduce) return;

						chunkGraph.integrateChunks(pair.b, pair.a);
						compilation.chunks.delete(pair.a);
						return true;
					}
				);
			}
		);
	}
}

module.exports = AggressiveMergingPlugin;