webpack/lib/optimize/ModuleConcatenationPlugin.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

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

"use strict";

const asyncLib = require("neo-async");
const ChunkGraph = require("../ChunkGraph");
const Dependency = require("../Dependency");
const Module = require("../Module");
const ModuleGraph = require("../ModuleGraph");
const { JAVASCRIPT_TYPE } = require("../ModuleSourceTypeConstants");
const { STAGE_DEFAULT } = require("../OptimizationStages");
const CommonJsSelfReferenceDependency = require("../dependencies/CommonJsSelfReferenceDependency");
const HarmonyImportDependency = require("../dependencies/HarmonyImportDependency");
const { ImportPhaseUtils } = require("../dependencies/ImportPhase");
const { compareModulesByIdentifier } = require("../util/comparators");
const {
	filterRuntime,
	intersectRuntime,
	mergeRuntime,
	mergeRuntimeOwned,
	runtimeToString
} = require("../util/runtime");
const ConcatenatedModule = require("./ConcatenatedModule");

/** @typedef {import("../Chunk")} Chunk */
/** @typedef {import("../Compilation")} Compilation */
/** @typedef {import("../Compiler")} Compiler */
/** @typedef {import("../Module").BuildInfo} BuildInfo */
/** @typedef {import("../Module").BuildMeta} BuildMeta */
/** @typedef {import("../RequestShortener")} RequestShortener */
/** @typedef {import("../util/runtime").RuntimeSpec} RuntimeSpec */

/** @typedef {Module | ((requestShortener: RequestShortener) => string)} Problem */

/**
 * Merged runtime of all chunks a module is in, memoized for the whole pass.
 * Safe: the chunk graph is not mutated while configurations are built.
 * @param {ChunkGraph} chunkGraph the chunk graph
 * @param {Map<Module, RuntimeSpec>} cache memoization cache
 * @param {Module} module the module
 * @returns {RuntimeSpec} the merged runtime
 */
const getMergedModuleRuntime = (chunkGraph, cache, module) => {
	const cached = cache.get(module);
	if (cached !== undefined || cache.has(module)) return cached;
	/** @type {RuntimeSpec} */
	let runtime;
	for (const r of chunkGraph.getModuleRuntimes(module)) {
		runtime = mergeRuntimeOwned(runtime, r);
	}
	cache.set(module, runtime);
	return runtime;
};

/**
 * Defines the statistics type used by this module.
 * @typedef {object} Statistics
 * @property {number} cached
 * @property {number} alreadyInConfig
 * @property {number} invalidModule
 * @property {number} incorrectChunks
 * @property {number} incorrectDependency
 * @property {number} incorrectModuleDependency
 * @property {number} incorrectChunksOfImporter
 * @property {number} incorrectRuntimeCondition
 * @property {number} importerFailed
 * @property {number} added
 */

/**
 * Record why `module` can't be added (so retried lookups hit the cache), bump
 * the matching statistic, and return the problem to bubble up the recursion.
 * Only reached on failure, so it stays off the hot success path.
 * @param {Map<Module, Problem>} failureCache per-module failure cache
 * @param {Statistics} statistics running statistics
 * @param {keyof Statistics} statKey statistic to increment
 * @param {Module} module the module that couldn't be added
 * @param {Problem} problem the failure to cache and return
 * @returns {Problem} the same problem
 */
const cacheFailure = (failureCache, statistics, statKey, module, problem) => {
	statistics[statKey]++;
	failureCache.set(module, problem);
	return problem;
};

/**
 * Format bailout reason.
 * @param {string} msg message
 * @returns {string} formatted message
 */
const formatBailoutReason = (msg) => `ModuleConcatenation bailout: ${msg}`;

const PLUGIN_NAME = "ModuleConcatenationPlugin";

class ModuleConcatenationPlugin {
	/**
	 * Applies the plugin by registering its hooks on the compiler.
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		const { _backCompat: backCompat } = compiler;
		compiler.hooks.compilation.tap(PLUGIN_NAME, (compilation) => {
			if (compilation.moduleMemCaches) {
				throw new Error(
					"optimization.concatenateModules can't be used with cacheUnaffected as module concatenation is a global effect"
				);
			}
			const moduleGraph = compilation.moduleGraph;
			/** @type {Map<Module, string | ((requestShortener: RequestShortener) => string)>} */
			const bailoutReasonMap = new Map();

			/**
			 * Sets bailout reason.
			 * @param {Module} module the module
			 * @param {string | ((requestShortener: RequestShortener) => string)} reason the reason
			 */
			const setBailoutReason = (module, reason) => {
				setInnerBailoutReason(module, reason);
				moduleGraph
					.getOptimizationBailout(module)
					.push(
						typeof reason === "function"
							? (rs) => formatBailoutReason(reason(rs))
							: formatBailoutReason(reason)
					);
			};

			/**
			 * Sets inner bailout reason.
			 * @param {Module} module the module
			 * @param {string | ((requestShortener: RequestShortener) => string)} reason the reason
			 */
			const setInnerBailoutReason = (module, reason) => {
				bailoutReasonMap.set(module, reason);
			};

			/**
			 * Gets inner bailout reason.
			 * @param {Module} module the module
			 * @param {RequestShortener} requestShortener the request shortener
			 * @returns {string | ((requestShortener: RequestShortener) => string) | undefined} the reason
			 */
			const getInnerBailoutReason = (module, requestShortener) => {
				const reason = bailoutReasonMap.get(module);
				if (typeof reason === "function") return reason(requestShortener);
				return reason;
			};

			/**
			 * Format bailout warning.
			 * @param {Module} module the module
			 * @param {Problem} problem the problem
			 * @returns {(requestShortener: RequestShortener) => string} the reason
			 */
			const formatBailoutWarning = (module, problem) => (requestShortener) => {
				if (typeof problem === "function") {
					return formatBailoutReason(
						`Cannot concat with ${module.readableIdentifier(
							requestShortener
						)}: ${problem(requestShortener)}`
					);
				}
				const reason = getInnerBailoutReason(module, requestShortener);
				const reasonWithPrefix = reason ? `: ${reason}` : "";
				if (module === problem) {
					return formatBailoutReason(
						`Cannot concat with ${module.readableIdentifier(
							requestShortener
						)}${reasonWithPrefix}`
					);
				}
				return formatBailoutReason(
					`Cannot concat with ${module.readableIdentifier(
						requestShortener
					)} because of ${problem.readableIdentifier(
						requestShortener
					)}${reasonWithPrefix}`
				);
			};

			compilation.hooks.optimizeChunkModules.tapAsync(
				{
					name: PLUGIN_NAME,
					stage: STAGE_DEFAULT
				},
				(allChunks, modules, callback) => {
					const logger = compilation.getLogger(
						"webpack.ModuleConcatenationPlugin"
					);
					const { chunkGraph, moduleGraph } = compilation;
					/** @type {Module[]} */
					const relevantModules = [];
					/** @type {Set<Module>} */
					const possibleInners = new Set();
					const concatenateModules =
						compilation.options.optimization.concatenateModules;
					const context = {
						chunkGraph,
						moduleGraph,
						// commonjs concatenation defaults to on; { commonjs: false } opts out
						concatenateCommonJsModules:
							typeof concatenateModules === "object"
								? concatenateModules.commonjs !== false
								: concatenateModules === true
					};
					const deferEnabled = compilation.options.experiments.deferImport;
					logger.time("select relevant modules");
					for (const module of modules) {
						let canBeRoot = true;
						let canBeInner = true;

						const bailoutReason = module.getConcatenationBailoutReason(context);
						if (bailoutReason) {
							setBailoutReason(module, bailoutReason);
							continue;
						}

						// Must not be an async module
						if (moduleGraph.isAsync(module)) {
							setBailoutReason(module, "Module is async");
							continue;
						}
						// Must be in strict mode
						if (!(/** @type {BuildInfo} */ (module.buildInfo).strict)) {
							setBailoutReason(module, "Module is not in strict mode");
							continue;
						}

						// Module must be in any chunk (we don't want to do useless work)
						if (chunkGraph.getNumberOfModuleChunks(module) === 0) {
							setBailoutReason(module, "Module is not in any chunk");
							continue;
						}

						// Exports must be known (and not dynamic)
						const exportsInfo = moduleGraph.getExportsInfo(module);
						const relevantExports = exportsInfo.getRelevantExports(undefined);
						const unknownReexports = relevantExports.filter(
							(exportInfo) =>
								exportInfo.isReexport() && !exportInfo.getTarget(moduleGraph)
						);
						if (unknownReexports.length > 0) {
							setBailoutReason(
								module,
								`Reexports in this module do not have a static target (${Array.from(
									unknownReexports,
									(exportInfo) =>
										`${
											exportInfo.name || "other exports"
										}: ${exportInfo.getUsedInfo()}`
								).join(", ")})`
							);
							continue;
						}

						// Root modules must have a static list of exports
						const unknownProvidedExports = relevantExports.filter(
							(exportInfo) => exportInfo.provided !== true
						);
						if (unknownProvidedExports.length > 0) {
							setBailoutReason(
								module,
								`List of module exports is dynamic (${Array.from(
									unknownProvidedExports,
									(exportInfo) =>
										`${
											exportInfo.name || "other exports"
										}: ${exportInfo.getProvidedInfo()} and ${exportInfo.getUsedInfo()}`
								).join(", ")})`
							);
							canBeRoot = false;
						}

						// TODO: ConcatenatedModule.getSourceTypes only javascript now
						const basicTypes = Module.getSourceBasicTypes(module);
						if (basicTypes.size !== 1 || !basicTypes.has(JAVASCRIPT_TYPE)) {
							canBeRoot = false;
						}

						// A concatenated CommonJS module relies on the root's ESM export
						// rendering, so it can only be an inner module
						if (
							module.type.startsWith("javascript/") &&
							/** @type {BuildMeta} */
							(module.buildMeta).exportsType !== "namespace"
						) {
							canBeRoot = false;
						}

						// Module must not be an entry point
						if (chunkGraph.isEntryModule(module)) {
							setInnerBailoutReason(module, "Module is an entry point");
							canBeInner = false;
						}

						if (deferEnabled && moduleGraph.isDeferred(module)) {
							setInnerBailoutReason(module, "Module is deferred");
							canBeInner = false;
						}

						if (canBeRoot) relevantModules.push(module);
						if (canBeInner) possibleInners.add(module);
					}
					logger.timeEnd("select relevant modules");
					logger.debug(
						`${relevantModules.length} potential root modules, ${possibleInners.size} potential inner modules`
					);
					// sort by depth
					// modules with lower depth are more likely suited as roots
					// this improves performance, because modules already selected as inner are skipped
					logger.time("sort relevant modules");
					relevantModules.sort(
						(a, b) =>
							/** @type {number} */ (moduleGraph.getDepth(a)) -
							/** @type {number} */ (moduleGraph.getDepth(b))
					);
					logger.timeEnd("sort relevant modules");

					/** @type {Statistics} */
					const stats = {
						cached: 0,
						alreadyInConfig: 0,
						invalidModule: 0,
						incorrectChunks: 0,
						incorrectDependency: 0,
						incorrectModuleDependency: 0,
						incorrectChunksOfImporter: 0,
						incorrectRuntimeCondition: 0,
						importerFailed: 0,
						added: 0
					};
					let statsCandidates = 0;
					let statsSizeSum = 0;
					let statsEmptyConfigurations = 0;

					logger.time("find modules to concatenate");
					/** @type {ConcatConfiguration[]} */
					const concatConfigurations = [];
					/** @type {Set<Module>} */
					const usedAsInner = new Set();
					// module -> merged runtime of its chunks, shared across all roots
					/** @type {Map<Module, RuntimeSpec>} */
					const moduleRuntimeCache = new Map();
					for (const currentRoot of relevantModules) {
						// when used by another configuration as inner:
						// the other configuration is better and we can skip this one
						// TODO reconsider that when it's only used in a different runtime
						if (usedAsInner.has(currentRoot)) continue;

						const chunkRuntime = getMergedModuleRuntime(
							chunkGraph,
							moduleRuntimeCache,
							currentRoot
						);
						const exportsInfo = moduleGraph.getExportsInfo(currentRoot);
						const filteredRuntime = filterRuntime(chunkRuntime, (r) =>
							exportsInfo.isModuleUsed(r)
						);
						const activeRuntime =
							filteredRuntime === true
								? chunkRuntime
								: filteredRuntime === false
									? undefined
									: filteredRuntime;

						// create a configuration with the root; cache the root's chunks once
						// so every candidate check reuses them instead of re-materializing
						const currentConfiguration = new ConcatConfiguration(
							currentRoot,
							activeRuntime,
							[...chunkGraph.getModuleChunksIterable(currentRoot)]
						);

						// cache failures to add modules
						/** @type {Map<Module, Problem>} */
						const failureCache = new Map();

						// potential optional import candidates
						/** @type {Set<Module>} */
						const candidates = new Set();

						// try to add all imports
						for (const imp of this._getImports(
							compilation,
							currentRoot,
							activeRuntime
						)) {
							candidates.add(imp);
						}

						for (const imp of candidates) {
							/** @type {Set<Module>} */
							const impCandidates = new Set();
							const problem = this._tryToAdd(
								compilation,
								currentConfiguration,
								imp,
								chunkRuntime,
								activeRuntime,
								possibleInners,
								impCandidates,
								failureCache,
								moduleRuntimeCache,
								chunkGraph,
								true,
								stats
							);
							if (problem) {
								failureCache.set(imp, problem);
								currentConfiguration.addWarning(imp, problem);
							} else {
								for (const c of impCandidates) {
									candidates.add(c);
								}
							}
						}
						statsCandidates += candidates.size;
						if (!currentConfiguration.isEmpty()) {
							const modules = currentConfiguration.getModules();
							statsSizeSum += modules.size;
							concatConfigurations.push(currentConfiguration);
							for (const module of modules) {
								if (module !== currentConfiguration.rootModule) {
									usedAsInner.add(module);
								}
							}
						} else {
							statsEmptyConfigurations++;
							const optimizationBailouts =
								moduleGraph.getOptimizationBailout(currentRoot);
							for (const warning of currentConfiguration.getWarningsSorted()) {
								optimizationBailouts.push(
									formatBailoutWarning(warning[0], warning[1])
								);
							}
						}
					}
					logger.timeEnd("find modules to concatenate");
					logger.debug(
						`${
							concatConfigurations.length
						} successful concat configurations (avg size: ${
							statsSizeSum / concatConfigurations.length
						}), ${statsEmptyConfigurations} bailed out completely`
					);
					logger.debug(
						`${statsCandidates} candidates were considered for adding (${stats.cached} cached failure, ${stats.alreadyInConfig} already in config, ${stats.invalidModule} invalid module, ${stats.incorrectChunks} incorrect chunks, ${stats.incorrectDependency} incorrect dependency, ${stats.incorrectChunksOfImporter} incorrect chunks of importer, ${stats.incorrectModuleDependency} incorrect module dependency, ${stats.incorrectRuntimeCondition} incorrect runtime condition, ${stats.importerFailed} importer failed, ${stats.added} added)`
					);
					// Create the largest configurations first: if a root also ended up inside
					// a bigger configuration, the bigger one wins (smaller skipped below).
					// Configurations can't be reused across roots: a module shared by several
					// chunks is concatenated into each consumer (module duplication).
					logger.time("sort concat configurations");
					concatConfigurations.sort((a, b) => b.modules.size - a.modules.size);
					logger.timeEnd("sort concat configurations");
					/** @type {Set<Module>} */
					const usedModules = new Set();

					logger.time("create concatenated modules");
					asyncLib.each(
						concatConfigurations,
						(concatConfiguration, callback) => {
							const rootModule = concatConfiguration.rootModule;

							// Root already concatenated into a larger configuration: skip.
							// (Inner modules may still be shared, e.g. duplicated across entries.)
							if (usedModules.has(rootModule)) return callback();
							const modules = concatConfiguration.getModules();
							for (const m of modules) {
								usedModules.add(m);
							}

							// Create a new ConcatenatedModule
							const newModule = ConcatenatedModule.create(
								rootModule,
								modules,
								concatConfiguration.runtime,
								compilation,
								compiler.root,
								compilation.outputOptions.hashFunction
							);

							const build = () => {
								newModule.build(
									compilation.options,
									compilation,
									/** @type {EXPECTED_ANY} */
									(null),
									/** @type {EXPECTED_ANY} */
									(null),
									(err) => {
										if (err) {
											if (!err.module) {
												err.module = newModule;
											}
											return callback(err);
										}
										integrate();
									}
								);
							};

							const integrate = () => {
								if (backCompat) {
									ChunkGraph.setChunkGraphForModule(newModule, chunkGraph);
									ModuleGraph.setModuleGraphForModule(newModule, moduleGraph);
								}

								for (const warning of concatConfiguration.getWarningsSorted()) {
									moduleGraph
										.getOptimizationBailout(newModule)
										.push(formatBailoutWarning(warning[0], warning[1]));
								}
								moduleGraph.cloneModuleAttributes(rootModule, newModule);
								for (const m of modules) {
									// add to builtModules when one of the included modules was built
									if (compilation.builtModules.has(m)) {
										compilation.builtModules.add(newModule);
									}
									if (m !== rootModule) {
										// attach external references to the concatenated module too
										moduleGraph.copyOutgoingModuleConnections(
											m,
											newModule,
											(c) =>
												c.originModule === m &&
												!(
													c.dependency &&
													Dependency.canConcatenate(c.dependency) &&
													modules.has(c.module)
												)
										);
										// remove module from chunk
										for (const chunk of chunkGraph.getModuleChunksIterable(
											rootModule
										)) {
											const sourceTypes = chunkGraph.getChunkModuleSourceTypes(
												chunk,
												m
											);
											if (
												sourceTypes.size === 1 &&
												sourceTypes.has(JAVASCRIPT_TYPE)
											) {
												chunkGraph.disconnectChunkAndModule(chunk, m);
											} else {
												const newSourceTypes = new Set(sourceTypes);
												newSourceTypes.delete(JAVASCRIPT_TYPE);
												chunkGraph.setChunkModuleSourceTypes(
													chunk,
													m,
													newSourceTypes
												);
											}
										}
									}
								}
								compilation.modules.delete(rootModule);
								ChunkGraph.clearChunkGraphForModule(rootModule);
								ModuleGraph.clearModuleGraphForModule(rootModule);

								// remove module from chunk
								chunkGraph.replaceModule(rootModule, newModule);
								// replace module references with the concatenated module
								moduleGraph.moveModuleConnections(
									rootModule,
									newModule,
									(c) => {
										const otherModule =
											c.module === rootModule ? c.originModule : c.module;
										const innerConnection =
											c.dependency &&
											Dependency.canConcatenate(c.dependency) &&
											modules.has(/** @type {Module} */ (otherModule));
										return !innerConnection;
									}
								);
								// add concatenated module to the compilation
								compilation.modules.add(newModule);

								callback();
							};

							build();
						},
						(err) => {
							logger.timeEnd("create concatenated modules");
							process.nextTick(callback.bind(null, err));
						}
					);
				}
			);
		});
	}

	/**
	 * Checks whether the module `import defer`s a module already in the config.
	 * @param {ModuleGraph} moduleGraph the module graph
	 * @param {Module} module the candidate module
	 * @param {ConcatConfiguration} config the concat configuration
	 * @returns {boolean} true when a deferred import targets a module in the config
	 */
	_defersModuleIn(moduleGraph, module, config) {
		for (const dep of module.dependencies) {
			if (
				dep instanceof HarmonyImportDependency &&
				ImportPhaseUtils.isDefer(dep.phase)
			) {
				const target = moduleGraph.getModule(dep);
				if (target && config.has(target)) return true;
			}
		}
		return false;
	}

	/**
	 * Returns the imported modules.
	 * @param {Compilation} compilation the compilation
	 * @param {Module} module the module to be added
	 * @param {RuntimeSpec} runtime the runtime scope
	 * @returns {Set<Module>} the imported modules
	 */
	_getImports(compilation, module, runtime) {
		const moduleGraph = compilation.moduleGraph;
		/** @type {Set<Module>} */
		const set = new Set();
		for (const dep of module.dependencies) {
			// Get reference info only for dependencies that support concatenation
			if (!Dependency.canConcatenate(dep)) continue;

			const connection = moduleGraph.getConnection(dep);
			// Reference is valid and has a module
			if (
				!connection ||
				!connection.module ||
				!connection.isTargetActive(runtime)
			) {
				continue;
			}

			const importedNames = compilation.getDependencyReferencedExports(
				dep,
				undefined
			);

			if (
				importedNames.every((i) =>
					Array.isArray(i) ? i.length > 0 : i.name.length > 0
				) ||
				Array.isArray(moduleGraph.getProvidedExports(module))
			) {
				set.add(connection.module);
			}
		}
		return set;
	}

	/**
	 * Returns the problematic module.
	 * @param {Compilation} compilation webpack compilation
	 * @param {ConcatConfiguration} config concat configuration (will be modified when added)
	 * @param {Module} module the module to be added
	 * @param {RuntimeSpec} runtime the runtime scope of the generated code
	 * @param {RuntimeSpec} activeRuntime the runtime scope of the root module
	 * @param {Set<Module>} possibleModules modules that are candidates
	 * @param {Set<Module>} candidates list of potential candidates (will be added to)
	 * @param {Map<Module, Problem>} failureCache cache for problematic modules to be more performant
	 * @param {Map<Module, RuntimeSpec>} moduleRuntimeCache memoized merged runtime per module, shared across roots
	 * @param {ChunkGraph} chunkGraph the chunk graph
	 * @param {boolean} avoidMutateOnFailure avoid mutating the config when adding fails
	 * @param {Statistics} statistics gathering metrics
	 * @returns {null | Problem} the problematic module
	 */
	_tryToAdd(
		compilation,
		config,
		module,
		runtime,
		activeRuntime,
		possibleModules,
		candidates,
		failureCache,
		moduleRuntimeCache,
		chunkGraph,
		avoidMutateOnFailure,
		statistics
	) {
		const cacheEntry = failureCache.get(module);
		if (cacheEntry) {
			statistics.cached++;
			return cacheEntry;
		}

		// Already added?
		if (config.has(module)) {
			statistics.alreadyInConfig++;
			return null;
		}

		// Not possible to add?
		if (!possibleModules.has(module)) {
			return cacheFailure(
				failureCache,
				statistics,
				"invalidModule",
				module,
				module
			);
		}

		// A deferred import must stay a concatenation boundary: concatenating a
		// module with a module it `import defer`s (a cycle) would erase the
		// deferred namespace's lazy-evaluation and exotic-object semantics.
		if (
			compilation.options.experiments.deferImport &&
			this._defersModuleIn(compilation.moduleGraph, module, config)
		) {
			/**
			 * @param {RequestShortener} requestShortener request shortener
			 * @returns {string} problem description
			 */
			const problem = (requestShortener) =>
				`Module ${module.readableIdentifier(
					requestShortener
				)} imports a module in this configuration via import defer`;
			return cacheFailure(
				failureCache,
				statistics,
				"incorrectDependency",
				module,
				problem
			);
		}

		// Module must be in the correct chunks
		const missingChunks = config.rootChunks.filter(
			(chunk) => !chunkGraph.isModuleInChunk(module, chunk)
		);
		if (missingChunks.length > 0) {
			/**
			 * Returns problem description.
			 * @param {RequestShortener} requestShortener request shortener
			 * @returns {string} problem description
			 */
			const problem = (requestShortener) => {
				const missingChunksList = [
					...new Set(
						missingChunks.map((chunk) => chunk.name || "unnamed chunk(s)")
					)
				].sort();
				const chunks = [
					...new Set(
						[...chunkGraph.getModuleChunksIterable(module)].map(
							(chunk) => chunk.name || "unnamed chunk(s)"
						)
					)
				].sort();
				return `Module ${module.readableIdentifier(
					requestShortener
				)} is not in the same chunk(s) (expected in chunk(s) ${missingChunksList.join(
					", "
				)}, module is in chunk(s) ${chunks.join(", ")})`;
			};
			return cacheFailure(
				failureCache,
				statistics,
				"incorrectChunks",
				module,
				problem
			);
		}

		const moduleGraph = compilation.moduleGraph;

		const incomingConnections =
			moduleGraph.getIncomingConnectionsByOriginModule(module);

		const incomingConnectionsFromNonModules =
			incomingConnections.get(null) || incomingConnections.get(undefined);
		if (incomingConnectionsFromNonModules) {
			const activeNonModulesConnections =
				incomingConnectionsFromNonModules.filter((connection) =>
					// We are not interested in inactive connections
					// or connections without dependency
					connection.isActive(runtime)
				);
			if (activeNonModulesConnections.length > 0) {
				/**
				 * Returns problem description.
				 * @param {RequestShortener} requestShortener request shortener
				 * @returns {string} problem description
				 */
				const problem = (requestShortener) => {
					/** @type {Set<string>} */
					const importingExplanations = new Set(
						activeNonModulesConnections
							.map((c) => c.explanation)
							.filter(Boolean)
					);
					const explanations = [...importingExplanations].sort();
					return `Module ${module.readableIdentifier(
						requestShortener
					)} is referenced ${
						explanations.length > 0
							? `by: ${explanations.join(", ")}`
							: "in an unsupported way"
					}`;
				};
				return cacheFailure(
					failureCache,
					statistics,
					"incorrectDependency",
					module,
					problem
				);
			}
		}

		/** @type {Map<Module, ReadonlyArray<ModuleGraph.ModuleGraphConnection>>} */
		const incomingConnectionsFromModules = new Map();
		for (const [originModule, connections] of incomingConnections) {
			if (originModule) {
				// Ignore connection from orphan modules
				if (chunkGraph.getNumberOfModuleChunks(originModule) === 0) continue;

				// We don't care for connections from other runtimes
				const originRuntime = getMergedModuleRuntime(
					chunkGraph,
					moduleRuntimeCache,
					originModule
				);

				if (!intersectRuntime(runtime, originRuntime)) continue;

				// We are not interested in inactive connections
				const activeConnections = connections.filter((connection) =>
					connection.isActive(runtime)
				);
				if (activeConnections.length > 0) {
					incomingConnectionsFromModules.set(originModule, activeConnections);
				}
			}
		}

		const incomingModules = [...incomingConnectionsFromModules.keys()];

		// Module must be in the same chunks like the referencing module
		const otherChunkModules = incomingModules.filter((originModule) => {
			for (const chunk of config.rootChunks) {
				if (!chunkGraph.isModuleInChunk(originModule, chunk)) {
					return true;
				}
			}
			return false;
		});
		if (otherChunkModules.length > 0) {
			/**
			 * Returns problem description.
			 * @param {RequestShortener} requestShortener request shortener
			 * @returns {string} problem description
			 */
			const problem = (requestShortener) => {
				const names = otherChunkModules
					.map((m) => m.readableIdentifier(requestShortener))
					.sort();
				return `Module ${module.readableIdentifier(
					requestShortener
				)} is referenced from different chunks by these modules: ${names.join(
					", "
				)}`;
			};
			return cacheFailure(
				failureCache,
				statistics,
				"incorrectChunksOfImporter",
				module,
				problem
			);
		}

		/** @type {Map<Module, ReadonlyArray<ModuleGraph.ModuleGraphConnection>>} */
		const nonHarmonyConnections = new Map();
		for (const [originModule, connections] of incomingConnectionsFromModules) {
			const selected = connections.filter(
				(connection) =>
					!connection.dependency ||
					(!Dependency.canConcatenate(connection.dependency) &&
						// exports self-references of a concatenated CommonJS module
						// are rewritten in place, so they don't block concatenation
						!(
							originModule === module &&
							connection.dependency instanceof CommonJsSelfReferenceDependency
						))
			);
			if (selected.length > 0) {
				nonHarmonyConnections.set(originModule, connections);
			}
		}
		if (nonHarmonyConnections.size > 0) {
			/**
			 * Returns problem description.
			 * @param {RequestShortener} requestShortener request shortener
			 * @returns {string} problem description
			 */
			const problem = (requestShortener) => {
				const names = [...nonHarmonyConnections]
					.map(
						([originModule, connections]) =>
							`${originModule.readableIdentifier(
								requestShortener
							)} (referenced with ${[
								...new Set(
									connections
										.map((c) => c.dependency && c.dependency.type)
										.filter(Boolean)
								)
							]
								.sort()
								.join(", ")})`
					)
					.sort();
				return `Module ${module.readableIdentifier(
					requestShortener
				)} is referenced from these modules with unsupported syntax: ${names.join(
					", "
				)}`;
			};
			return cacheFailure(
				failureCache,
				statistics,
				"incorrectModuleDependency",
				module,
				problem
			);
		}

		if (runtime !== undefined && typeof runtime !== "string") {
			// Module must be consistently referenced in the same runtimes
			/** @type {{ originModule: Module, runtimeCondition: RuntimeSpec }[]} */
			const otherRuntimeConnections = [];
			outer: for (const [
				originModule,
				connections
			] of incomingConnectionsFromModules) {
				/** @type {false | RuntimeSpec} */
				let currentRuntimeCondition = false;
				for (const connection of connections) {
					const runtimeCondition = filterRuntime(runtime, (runtime) =>
						connection.isTargetActive(runtime)
					);
					if (runtimeCondition === false) continue;
					if (runtimeCondition === true) continue outer;
					currentRuntimeCondition =
						currentRuntimeCondition !== false
							? mergeRuntime(currentRuntimeCondition, runtimeCondition)
							: runtimeCondition;
				}
				if (currentRuntimeCondition !== false) {
					otherRuntimeConnections.push({
						originModule,
						runtimeCondition: currentRuntimeCondition
					});
				}
			}
			if (otherRuntimeConnections.length > 0) {
				/**
				 * Returns problem description.
				 * @param {RequestShortener} requestShortener request shortener
				 * @returns {string} problem description
				 */
				const problem = (requestShortener) =>
					`Module ${module.readableIdentifier(
						requestShortener
					)} is runtime-dependent referenced by these modules: ${Array.from(
						otherRuntimeConnections,
						({ originModule, runtimeCondition }) =>
							`${originModule.readableIdentifier(
								requestShortener
							)} (expected runtime ${runtimeToString(
								runtime
							)}, module is only referenced in ${runtimeToString(
								/** @type {RuntimeSpec} */ (runtimeCondition)
							)})`
					).join(", ")}`;
				return cacheFailure(
					failureCache,
					statistics,
					"incorrectRuntimeCondition",
					module,
					problem
				);
			}
		}

		/** @type {undefined | number} */
		let backup;
		if (avoidMutateOnFailure) {
			backup = config.snapshot();
		}

		// Add the module
		config.add(module);

		incomingModules.sort(compareModulesByIdentifier);

		// Every module which depends on the added module must be in the configuration too.
		for (const originModule of incomingModules) {
			const problem = this._tryToAdd(
				compilation,
				config,
				originModule,
				runtime,
				activeRuntime,
				possibleModules,
				candidates,
				failureCache,
				moduleRuntimeCache,
				chunkGraph,
				false,
				statistics
			);
			if (problem) {
				if (backup !== undefined) config.rollback(backup);
				return cacheFailure(
					failureCache,
					statistics,
					"importerFailed",
					module,
					problem
				);
			}
		}

		// Add imports to possible candidates list
		for (const imp of this._getImports(compilation, module, runtime)) {
			candidates.add(imp);
		}
		statistics.added++;
		return null;
	}
}

/** @typedef {Map<Module, Problem>} Warnings */

class ConcatConfiguration {
	/**
	 * Creates an instance of ConcatConfiguration.
	 * @param {Module} rootModule the root module
	 * @param {RuntimeSpec} runtime the runtime
	 * @param {Chunk[]} rootChunks the chunks the root module is in
	 */
	constructor(rootModule, runtime, rootChunks) {
		/** @type {Module} */
		this.rootModule = rootModule;
		/** @type {RuntimeSpec} */
		this.runtime = runtime;
		/** @type {Chunk[]} the root's chunks, reused for every candidate's chunk check */
		this.rootChunks = rootChunks;
		/** @type {Set<Module>} */
		this.modules = new Set();
		this.modules.add(rootModule);
		/** @type {Warnings} */
		this.warnings = new Map();
	}

	/**
	 * Processes the provided module.
	 * @param {Module} module the module
	 */
	add(module) {
		this.modules.add(module);
	}

	/**
	 * Returns true, when the module is in the module set.
	 * @param {Module} module the module
	 * @returns {boolean} true, when the module is in the module set
	 */
	has(module) {
		return this.modules.has(module);
	}

	isEmpty() {
		return this.modules.size === 1;
	}

	/**
	 * Adds the provided module to the concat configuration.
	 * @param {Module} module the module
	 * @param {Problem} problem the problem
	 */
	addWarning(module, problem) {
		this.warnings.set(module, problem);
	}

	/**
	 * Gets warnings sorted.
	 * @returns {Warnings} warnings
	 */
	getWarningsSorted() {
		return new Map(
			[...this.warnings].sort((a, b) => {
				const ai = a[0].identifier();
				const bi = b[0].identifier();
				if (ai < bi) return -1;
				if (ai > bi) return 1;
				return 0;
			})
		);
	}

	/**
	 * Returns modules as set.
	 * @returns {Set<Module>} modules as set
	 */
	getModules() {
		return this.modules;
	}

	snapshot() {
		return this.modules.size;
	}

	/**
	 * Processes the provided snapshot.
	 * @param {number} snapshot snapshot
	 */
	rollback(snapshot) {
		const modules = this.modules;
		for (const m of modules) {
			if (snapshot === 0) {
				modules.delete(m);
			} else {
				snapshot--;
			}
		}
	}
}

module.exports = ModuleConcatenationPlugin;