source: trip-planner-front/node_modules/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");
const { runtimeEqual } = require("../util/runtime");

/** @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(
                                        {
                                                name: "MergeDuplicateChunksPlugin",
                                                stage: STAGE_BASIC
                                        },
                                        chunks => {
                                                const { chunkGraph, moduleGraph } = compilation;

                                                // 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
                                                        ) {
                                                                outer: for (const otherChunk of possibleDuplicates) {
                                                                        if (otherChunk.hasRuntime() !== chunk.hasRuntime()) continue;
                                                                        if (chunkGraph.getNumberOfEntryModules(chunk) > 0) continue;
                                                                        if (chunkGraph.getNumberOfEntryModules(otherChunk) > 0)
                                                                                continue;
                                                                        if (!runtimeEqual(chunk.runtime, otherChunk.runtime)) {
                                                                                for (const module of chunkGraph.getChunkModulesIterable(
                                                                                        chunk
                                                                                )) {
                                                                                        const exportsInfo = moduleGraph.getExportsInfo(module);
                                                                                        if (
                                                                                                !exportsInfo.isEquallyUsed(
                                                                                                        chunk.runtime,
                                                                                                        otherChunk.runtime
                                                                                                )
                                                                                        ) {
                                                                                                continue outer;
                                                                                        }
                                                                                }
                                                                        }
                                                                        // merge them
                                                                        if (chunkGraph.canChunksBeIntegrated(chunk, otherChunk)) {
                                                                                chunkGraph.integrateChunks(chunk, otherChunk);
                                                                                compilation.chunks.delete(otherChunk);
                                                                        }
                                                                }
                                                        }

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