webpack/lib/optimize/MergeDuplicateChunksPlugin.js

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

class MergeDuplicateChunksPlugin {

	apply(compiler) {
		compiler.hooks.compilation.tap("MergeDuplicateChunksPlugin", (compilation) => {
			compilation.hooks.optimizeChunksBasic.tap("MergeDuplicateChunksPlugin", (chunks) => {
				// 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 chunk.modulesIterable) {
						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 module.chunksIterable) {
								if(dup !== chunk && chunk.getNumberOfModules() === dup.getNumberOfModules() && !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(!dup.containsModule(module))
									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(chunk.integrate(otherChunk, "duplicate"))
								chunks.splice(chunks.indexOf(otherChunk), 1);
						}
					}

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