source: frontend/node_modules/webpack/lib/optimize/EnsureChunkConditionsPlugin.js

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

"use strict";

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

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

const PLUGIN_NAME = "EnsureChunkConditionsPlugin";

class EnsureChunkConditionsPlugin {
        /**
         * Applies the plugin by registering its hooks on the compiler.
         * @param {Compiler} compiler the compiler instance
         * @returns {void}
         */
        apply(compiler) {
                compiler.hooks.compilation.tap(PLUGIN_NAME, (compilation) => {
                        /**
                         * Handles the hook callback for this code path.
                         * @param {Iterable<Chunk>} chunks the chunks
                         */
                        const handler = (chunks) => {
                                const chunkGraph = compilation.chunkGraph;
                                // These sets are hoisted here to save memory
                                // They are cleared at the end of every loop
                                /** @type {Set<Chunk>} */
                                const sourceChunks = new Set();
                                /** @type {Set<ChunkGroup>} */
                                const chunkGroups = new Set();
                                for (const module of compilation.modules) {
                                        if (!module.hasChunkCondition()) continue;
                                        for (const chunk of chunkGraph.getModuleChunksIterable(module)) {
                                                if (!module.chunkCondition(chunk, compilation)) {
                                                        sourceChunks.add(chunk);
                                                        for (const group of chunk.groupsIterable) {
                                                                chunkGroups.add(group);
                                                        }
                                                }
                                        }
                                        if (sourceChunks.size === 0) continue;
                                        /** @type {Set<Chunk>} */
                                        const targetChunks = new Set();
                                        chunkGroupLoop: for (const chunkGroup of chunkGroups) {
                                                // Can module be placed in a chunk of this group?
                                                for (const chunk of chunkGroup.chunks) {
                                                        if (module.chunkCondition(chunk, compilation)) {
                                                                targetChunks.add(chunk);
                                                                continue chunkGroupLoop;
                                                        }
                                                }
                                                // We reached the entrypoint: fail
                                                if (chunkGroup.isInitial()) {
                                                        throw new Error(
                                                                `Cannot fulfil chunk condition of ${module.identifier()}`
                                                        );
                                                }
                                                // Try placing in all parents
                                                for (const group of chunkGroup.parentsIterable) {
                                                        chunkGroups.add(group);
                                                }
                                        }
                                        for (const sourceChunk of sourceChunks) {
                                                chunkGraph.disconnectChunkAndModule(sourceChunk, module);
                                        }
                                        for (const targetChunk of targetChunks) {
                                                chunkGraph.connectChunkAndModule(targetChunk, module);
                                        }
                                        sourceChunks.clear();
                                        chunkGroups.clear();
                                }
                        };
                        compilation.hooks.optimizeChunks.tap(
                                {
                                        name: PLUGIN_NAME,
                                        stage: STAGE_BASIC
                                },
                                handler
                        );
                });
        }
}

module.exports = EnsureChunkConditionsPlugin;