webpack/lib/optimize/MergeDuplicateChunksPlugin.js

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

"use strict";

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

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

class MergeDuplicateChunksPlugin {
	/**
	 * @param {Compiler} compiler the compiler
	 * @returns {void}
	 */
	apply(compiler) {
		compiler.hooks.compilation.tap(
			"MergeDuplicateChunksPlugin",
			compilation => {
				compilation.hooks.optimizeChunks.tap(
					/** @type {TODO} */ ({
						name: "MergeDuplicateChunksPlugin",
						stage: STAGE_BASIC
					}),
					chunks => {
						const chunkGraph = compilation.chunkGraph;

						// remember already tested chunks for performance
						const notDuplicates = new Set();

						// for each chunk
						for (const chunk of chunks) {
							// track a Set of all chunk that could be duplicates
							let possibleDuplicates;
							for (const module of chunkGraph.getChunkModulesIterable(chunk)) {
								if (possibleDuplicates === undefined) {
									// when possibleDuplicates is not yet set,
									// create a new Set from chunks of the current module
									// including only chunks with the same number of modules
									for (const dup of chunkGraph.getModuleChunksIterable(
										module
									)) {
										if (
											dup !== chunk &&
											chunkGraph.getNumberOfChunkModules(chunk) ===
												chunkGraph.getNumberOfChunkModules(dup) &&
											!notDuplicates.has(dup)
										) {
											// delay allocating the new Set until here, reduce memory pressure
											if (possibleDuplicates === undefined) {
												possibleDuplicates = new Set();
											}
											possibleDuplicates.add(dup);
										}
									}
									// when no chunk is possible we can break here
									if (possibleDuplicates === undefined) break;
								} else {
									// validate existing possible duplicates
									for (const dup of possibleDuplicates) {
										// remove possible duplicate when module is not contained
										if (!chunkGraph.isModuleInChunk(module, dup)) {
											possibleDuplicates.delete(dup);
										}
									}
									// when all chunks has been removed we can break here
									if (possibleDuplicates.size === 0) break;
								}
							}

							// when we found duplicates
							if (
								possibleDuplicates !== undefined &&
								possibleDuplicates.size > 0
							) {
								for (const otherChunk of possibleDuplicates) {
									if (otherChunk.hasRuntime() !== chunk.hasRuntime()) continue;
									// merge them
									if (chunkGraph.canChunksBeIntegrated(chunk, otherChunk)) {
										chunkGraph.integrateChunks(chunk, otherChunk);
										chunks.splice(chunks.indexOf(otherChunk), 1);
									}
								}
							}

							// don't check already processed chunks twice
							notDuplicates.add(chunk);
						}
					}
				);
			}
		);
	}
}
module.exports = MergeDuplicateChunksPlugin;