add experimental support for build time execution

allow to execute a part of the module graph at build time
e. g. to generate code or other assets

loaders have access to that via `this.importModule(request, options)`

lib/Compilation.js

@@ -32,7 +32,10 @@ const {
 	connectChunkGroupAndChunk,
 	connectChunkGroupParentAndChild
 } = require("./GraphHelpers");
-const { makeWebpackError } = require("./HookWebpackError");
+const {
+	makeWebpackError,
+	tryRunOrWebpackError
+} = require("./HookWebpackError");
 const MainTemplate = require("./MainTemplate");
 const Module = require("./Module");
 const ModuleDependencyError = require("./ModuleDependencyError");
@@ -71,6 +74,7 @@ const {
 	soonFrozenObjectDeprecation,
 	createFakeHook
 } = require("./util/deprecation");
+const processAsyncTree = require("./util/processAsyncTree");
 const { getRuntimeKey } = require("./util/runtime");
 const { isSourceEqual } = require("./util/source");
 
@@ -119,6 +123,13 @@ const { isSourceEqual } = require("./util/source");
  * @returns {void}
  */
 
+/**
+ * @callback ExportsCallback
+ * @param {WebpackError=} err
+ * @param {any=} exports
+ * @returns {void}
+ */
+
 /**
  * @callback DepBlockVarDependenciesCallback
  * @param {Dependency} dependency
@@ -158,6 +169,31 @@ const { isSourceEqual } = require("./util/source");
  * @property {ChunkGraph} chunkGraph the chunk graph
  */
 
+/**
+ * @typedef {Object} RuntimeRequirementsContext
+ * @property {ChunkGraph} chunkGraph the chunk graph
+ * @property {CodeGenerationResults} codeGenerationResults the code generation results
+ */
+
+/**
+ * @typedef {Object} RunModuleOptions
+ * @property {EntryOptions=} entryOptions
+ */
+
+/**
+ * @typedef {Object} RunModuleArgument
+ * @property {Module} module
+ * @property {object} moduleObject
+ * @property {CodeGenerationResult} codeGenerationResult
+ */
+
+/**
+ * @typedef {Object} RunModuleContext
+ * @property {Chunk} chunk
+ * @property {ChunkGraph} chunkGraph
+ * @property {Function} __webpack_require__
+ */
+
 /**
  * @typedef {Object} EntryData
  * @property {Dependency[]} dependencies dependencies of the entrypoint that should be evaluated at startup
@@ -525,6 +561,9 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 				"runtime"
 			]),
 
+			/** @type {SyncHook<[RunModuleArgument, RunModuleContext]>} */
+			runModule: new SyncHook(["options", "context"]),
+
 			/** @type {AsyncSeriesHook<[Iterable<Module>]>} */
 			finishModules: new AsyncSeriesHook(["modules"]),
 			/** @type {AsyncSeriesHook<[Module]>} */
@@ -568,32 +607,35 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 			/** @type {SyncBailHook<[], boolean>} */
 			shouldRecord: new SyncBailHook([]),
 
-			/** @type {SyncHook<[Chunk, Set<string>]>} */
+			/** @type {SyncHook<[Chunk, Set<string>, RuntimeRequirementsContext]>} */
 			additionalChunkRuntimeRequirements: new SyncHook([
 				"chunk",
-				"runtimeRequirements"
+				"runtimeRequirements",
+				"context"
 			]),
-			/** @type {HookMap<SyncBailHook<[Chunk, Set<string>]>>} */
+			/** @type {HookMap<SyncBailHook<[Chunk, Set<string>, RuntimeRequirementsContext]>>} */
 			runtimeRequirementInChunk: new HookMap(
-				() => new SyncBailHook(["chunk", "runtimeRequirements"])
+				() => new SyncBailHook(["chunk", "runtimeRequirements", "context"])
 			),
-			/** @type {SyncHook<[Module, Set<string>]>} */
+			/** @type {SyncHook<[Module, Set<string>, RuntimeRequirementsContext]>} */
 			additionalModuleRuntimeRequirements: new SyncHook([
 				"module",
-				"runtimeRequirements"
+				"runtimeRequirements",
+				"context"
 			]),
-			/** @type {HookMap<SyncBailHook<[Module, Set<string>]>>} */
+			/** @type {HookMap<SyncBailHook<[Module, Set<string>, RuntimeRequirementsContext]>>} */
 			runtimeRequirementInModule: new HookMap(
-				() => new SyncBailHook(["module", "runtimeRequirements"])
+				() => new SyncBailHook(["module", "runtimeRequirements", "context"])
 			),
-			/** @type {SyncHook<[Chunk, Set<string>]>} */
+			/** @type {SyncHook<[Chunk, Set<string>, RuntimeRequirementsContext]>} */
 			additionalTreeRuntimeRequirements: new SyncHook([
 				"chunk",
-				"runtimeRequirements"
+				"runtimeRequirements",
+				"context"
 			]),
-			/** @type {HookMap<SyncBailHook<[Chunk, Set<string>]>>} */
+			/** @type {HookMap<SyncBailHook<[Chunk, Set<string>, RuntimeRequirementsContext]>>} */
 			runtimeRequirementInTree: new HookMap(
-				() => new SyncBailHook(["chunk", "runtimeRequirements"])
+				() => new SyncBailHook(["chunk", "runtimeRequirements", "context"])
 			),
 
 			/** @type {SyncHook<[RuntimeModule, Chunk]>} */
@@ -928,6 +970,8 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 		this.builtModules = new WeakSet();
 		/** @type {WeakSet<Module>} */
 		this.codeGeneratedModules = new WeakSet();
+		/** @type {WeakSet<Module>} */
+		this.buildTimeExecutedModules = new WeakSet();
 		/** @private @type {Map<Module, Callback[]>} */
 		this._rebuildingModules = new Map();
 		/** @type {Set<string>} */
@@ -2644,59 +2688,7 @@ Or do you want to use the entrypoints '${name}' and '${runtime}' independently o
 		});
 	}
 
-	/**
-	 * @returns {void}
-	 */
-	processRuntimeRequirements() {
-		const { chunkGraph } = this;
-
-		const additionalModuleRuntimeRequirements = this.hooks
-			.additionalModuleRuntimeRequirements;
-		const runtimeRequirementInModule = this.hooks.runtimeRequirementInModule;
-		for (const module of this.modules) {
-			if (chunkGraph.getNumberOfModuleChunks(module) > 0) {
-				for (const runtime of chunkGraph.getModuleRuntimes(module)) {
-					let set;
-					const runtimeRequirements = this.codeGenerationResults.getRuntimeRequirements(
-						module,
-						runtime
-					);
-					if (runtimeRequirements && runtimeRequirements.size > 0) {
-						set = new Set(runtimeRequirements);
-					} else if (additionalModuleRuntimeRequirements.isUsed()) {
-						set = new Set();
-					} else {
-						continue;
-					}
-					additionalModuleRuntimeRequirements.call(module, set);
-
-					for (const r of set) {
-						const hook = runtimeRequirementInModule.get(r);
-						if (hook !== undefined) hook.call(module, set);
-					}
-					chunkGraph.addModuleRuntimeRequirements(module, runtime, set);
-				}
-			}
-		}
-
-		for (const chunk of this.chunks) {
-			const set = new Set();
-			for (const module of chunkGraph.getChunkModulesIterable(chunk)) {
-				const runtimeRequirements = chunkGraph.getModuleRuntimeRequirements(
-					module,
-					chunk.runtime
-				);
-				for (const r of runtimeRequirements) set.add(r);
-			}
-			this.hooks.additionalChunkRuntimeRequirements.call(chunk, set);
-
-			for (const r of set) {
-				this.hooks.runtimeRequirementInChunk.for(r).call(chunk, set);
-			}
-
-			chunkGraph.addChunkRuntimeRequirements(chunk, set);
-		}
-
+	_getChunkGraphEntries() {
 		/** @type {Set<Chunk>} */
 		const treeEntries = new Set();
 		for (const ep of this.entrypoints.values()) {
@@ -2707,8 +2699,74 @@ Or do you want to use the entrypoints '${name}' and '${runtime}' independently o
 			const chunk = ep.getRuntimeChunk();
 			if (chunk) treeEntries.add(chunk);
 		}
+		return treeEntries;
+	}
 
-		for (const treeEntry of treeEntries) {
+	/**
+	 * @param {Object} options options
+	 * @param {ChunkGraph=} options.chunkGraph the chunk graph
+	 * @param {Iterable<Module>=} options.modules modules
+	 * @param {Iterable<Chunk>=} options.chunks chunks
+	 * @param {CodeGenerationResults=} options.codeGenerationResults codeGenerationResults
+	 * @param {Iterable<Chunk>=} options.chunkGraphEntries chunkGraphEntries
+	 * @returns {void}
+	 */
+	processRuntimeRequirements({
+		chunkGraph = this.chunkGraph,
+		modules = this.modules,
+		chunks = this.chunks,
+		codeGenerationResults = this.codeGenerationResults,
+		chunkGraphEntries = this._getChunkGraphEntries()
+	} = {}) {
+		const context = { chunkGraph, codeGenerationResults };
+		const additionalModuleRuntimeRequirements = this.hooks
+			.additionalModuleRuntimeRequirements;
+		const runtimeRequirementInModule = this.hooks.runtimeRequirementInModule;
+		for (const module of modules) {
+			if (chunkGraph.getNumberOfModuleChunks(module) > 0) {
+				for (const runtime of chunkGraph.getModuleRuntimes(module)) {
+					let set;
+					const runtimeRequirements = codeGenerationResults.getRuntimeRequirements(
+						module,
+						runtime
+					);
+					if (runtimeRequirements && runtimeRequirements.size > 0) {
+						set = new Set(runtimeRequirements);
+					} else if (additionalModuleRuntimeRequirements.isUsed()) {
+						set = new Set();
+					} else {
+						continue;
+					}
+					additionalModuleRuntimeRequirements.call(module, set, context);
+
+					for (const r of set) {
+						const hook = runtimeRequirementInModule.get(r);
+						if (hook !== undefined) hook.call(module, set, context);
+					}
+					chunkGraph.addModuleRuntimeRequirements(module, runtime, set);
+				}
+			}
+		}
+
+		for (const chunk of chunks) {
+			const set = new Set();
+			for (const module of chunkGraph.getChunkModulesIterable(chunk)) {
+				const runtimeRequirements = chunkGraph.getModuleRuntimeRequirements(
+					module,
+					chunk.runtime
+				);
+				for (const r of runtimeRequirements) set.add(r);
+			}
+			this.hooks.additionalChunkRuntimeRequirements.call(chunk, set, context);
+
+			for (const r of set) {
+				this.hooks.runtimeRequirementInChunk.for(r).call(chunk, set, context);
+			}
+
+			chunkGraph.addChunkRuntimeRequirements(chunk, set);
+		}
+
+		for (const treeEntry of chunkGraphEntries) {
 			const set = new Set();
 			for (const chunk of treeEntry.getAllReferencedChunks()) {
 				const runtimeRequirements = chunkGraph.getChunkRuntimeRequirements(
@@ -2717,22 +2775,30 @@ Or do you want to use the entrypoints '${name}' and '${runtime}' independently o
 				for (const r of runtimeRequirements) set.add(r);
 			}
 
-			this.hooks.additionalTreeRuntimeRequirements.call(treeEntry, set);
+			this.hooks.additionalTreeRuntimeRequirements.call(
+				treeEntry,
+				set,
+				context
+			);
 
 			for (const r of set) {
-				this.hooks.runtimeRequirementInTree.for(r).call(treeEntry, set);
+				this.hooks.runtimeRequirementInTree
+					.for(r)
+					.call(treeEntry, set, context);
 			}
 
 			chunkGraph.addTreeRuntimeRequirements(treeEntry, set);
 		}
 	}
 
+	// TODO webpack 6 make chunkGraph argument non-optional
 	/**
 	 * @param {Chunk} chunk target chunk
 	 * @param {RuntimeModule} module runtime module
+	 * @param {ChunkGraph} chunkGraph the chunk graph
 	 * @returns {void}
 	 */
-	addRuntimeModule(chunk, module) {
+	addRuntimeModule(chunk, module, chunkGraph = this.chunkGraph) {
 		// Deprecated ModuleGraph association
 		ModuleGraph.setModuleGraphForModule(module, this.moduleGraph);
 
@@ -2741,10 +2807,10 @@ Or do you want to use the entrypoints '${name}' and '${runtime}' independently o
 		this._modules.set(module.identifier(), module);
 
 		// connect to the chunk graph
-		this.chunkGraph.connectChunkAndModule(chunk, module);
-		this.chunkGraph.connectChunkAndRuntimeModule(chunk, module);
+		chunkGraph.connectChunkAndModule(chunk, module);
+		chunkGraph.connectChunkAndRuntimeModule(chunk, module);
 		if (module.fullHash) {
-			this.chunkGraph.addFullHashModuleToChunk(chunk, module);
+			chunkGraph.addFullHashModuleToChunk(chunk, module);
 		}
 
 		// attach runtime module
@@ -2762,14 +2828,14 @@ Or do you want to use the entrypoints '${name}' and '${runtime}' independently o
 				exportsInfo.setUsedForSideEffectsOnly(runtime);
 			}
 		}
-		this.chunkGraph.addModuleRuntimeRequirements(
+		chunkGraph.addModuleRuntimeRequirements(
 			module,
 			chunk.runtime,
 			new Set([RuntimeGlobals.requireScope])
 		);
 
 		// runtime modules don't need ids
-		this.chunkGraph.setModuleId(module, "");
+		chunkGraph.setModuleId(module, "");
 
 		// Call hook
 		this.hooks.runtimeModule.call(module, chunk);
@@ -3889,6 +3955,236 @@ This prevents using hashes of each other and should be avoided.`);
 		);
 	}
 
+	/**
+	 * @param {Module} module the module
+	 * @param {RunModuleOptions} options options
+	 * @param {ExportsCallback} callback callback
+	 */
+	runModule(module, options, callback) {
+		// Aggregate all referenced modules and ensure they are ready
+		const modules = new Set([module]);
+		processAsyncTree(
+			modules,
+			10,
+			(module, push, callback) => {
+				this.addModuleQueue.waitFor(module, err => {
+					if (err) return callback(err);
+					this.buildQueue.waitFor(module, err => {
+						if (err) return callback(err);
+						this.processDependenciesQueue.waitFor(module, err => {
+							if (err) return callback(err);
+							for (const {
+								module: m
+							} of this.moduleGraph.getOutgoingConnections(module)) {
+								const size = modules.size;
+								modules.add(m);
+								if (modules.size !== size) push(m);
+							}
+							callback();
+						});
+					});
+				});
+			},
+			err => {
+				if (err) return callback(makeWebpackError(err, "runModule"));
+
+				// Create new chunk graph, chunk and entrypoint for the build time execution
+				const chunkGraph = new ChunkGraph(this.moduleGraph);
+				const runtime = "build time";
+				const {
+					hashFunction,
+					hashDigest,
+					hashDigestLength
+				} = this.outputOptions;
+				const runtimeTemplate = this.runtimeTemplate;
+
+				const chunk = new Chunk("build time chunk");
+				chunk.id = chunk.name;
+				chunk.ids = [chunk.id];
+				chunk.runtime = runtime;
+
+				const entrypoint = new Entrypoint({
+					runtime,
+					...options.entryOptions
+				});
+				chunkGraph.connectChunkAndEntryModule(chunk, module, entrypoint);
+				connectChunkGroupAndChunk(entrypoint, chunk);
+				entrypoint.setRuntimeChunk(chunk);
+				entrypoint.setEntrypointChunk(chunk);
+
+				const chunks = new Set([chunk]);
+
+				const modulesById = new Map();
+
+				// Assign ids to modules and modules to the chunk
+				for (const module of modules) {
+					const id = module.identifier();
+					modulesById.set(id, module);
+					chunkGraph.setModuleId(module, id);
+					chunkGraph.connectChunkAndModule(chunk, module);
+				}
+
+				// Hash modules
+				for (const module of modules) {
+					this._createModuleHash(
+						module,
+						chunkGraph,
+						runtime,
+						hashFunction,
+						runtimeTemplate,
+						hashDigest,
+						hashDigestLength
+					);
+				}
+
+				const codeGenerationResults = new CodeGenerationResults();
+				/** @type {WebpackError[]} */
+				const errors = [];
+				const codeGen = (module, callback) => {
+					this._codeGenerationModule(
+						module,
+						runtime,
+						[runtime],
+						chunkGraph.getModuleHash(module, runtime),
+						this.dependencyTemplates,
+						chunkGraph,
+						this.moduleGraph,
+						runtimeTemplate,
+						errors,
+						codeGenerationResults,
+						(err, codeGenerated) => {
+							callback(err);
+						}
+					);
+				};
+
+				// Generate code for all aggregated modules
+				asyncLib.eachLimit(modules, 10, codeGen, err => {
+					if (err) return callback(makeWebpackError(err, "runModule"));
+
+					// for backward-compat temporary set the chunk graph
+					// TODO webpack 6
+					const old = this.chunkGraph;
+					this.chunkGraph = chunkGraph;
+					this.processRuntimeRequirements({
+						chunkGraph,
+						modules,
+						chunks,
+						codeGenerationResults,
+						chunkGraphEntries: chunks
+					});
+					this.chunkGraph = old;
+
+					const runtimeModules = chunkGraph.getChunkRuntimeModulesIterable(
+						chunk
+					);
+
+					// Hash runtime modules
+					for (const module of runtimeModules) {
+						this._createModuleHash(
+							module,
+							chunkGraph,
+							runtime,
+							hashFunction,
+							runtimeTemplate,
+							hashDigest,
+							hashDigestLength
+						);
+					}
+
+					// Generate code for all runtime modules
+					asyncLib.eachLimit(runtimeModules, 10, codeGen, err => {
+						if (err) return callback(makeWebpackError(err, "runModule"));
+
+						let result;
+						try {
+							const {
+								strictModuleErrorHandling,
+								strictModuleExceptionHandling
+							} = this.outputOptions;
+							const moduleCache = new Map();
+							const __webpack_require__ = id => {
+								const module = modulesById.get(id);
+								return __webpack_require_module__(module, id);
+							};
+							const __webpack_require_module__ = (module, id) => {
+								const cached = moduleCache.get(module);
+								if (cached !== undefined) {
+									if (cached.error) throw cached.error;
+									return cached.exports;
+								}
+								const moduleObject = {
+									id,
+									exports: {},
+									loaded: false,
+									error: undefined
+								};
+								this.buildTimeExecutedModules.add(module);
+								try {
+									moduleCache.set(module, moduleObject);
+									const codeGenerationResult = codeGenerationResults.get(
+										module,
+										runtime
+									);
+									tryRunOrWebpackError(
+										() =>
+											this.hooks.runModule.call(
+												{
+													codeGenerationResult,
+													module,
+													moduleObject
+												},
+												context
+											),
+										"Compilation.hooks.runModule"
+									);
+									moduleObject.loaded = true;
+									return moduleObject.exports;
+								} catch (e) {
+									if (strictModuleExceptionHandling) {
+										moduleCache.delete(module);
+									} else if (strictModuleErrorHandling) {
+										moduleObject.error = e;
+									}
+									if (!e.module) e.module = module;
+									throw e;
+								}
+							};
+
+							/** @type {RunModuleContext} */
+							const context = {
+								__webpack_require__,
+								chunk,
+								chunkGraph
+							};
+
+							for (const runtimeModule of chunkGraph.getChunkRuntimeModulesInOrder(
+								chunk
+							)) {
+								__webpack_require_module__(
+									runtimeModule,
+									runtimeModule.identifier()
+								);
+							}
+							result = __webpack_require__(module.identifier());
+						} catch (e) {
+							const err = new WebpackError(
+								`Execution of module code from module graph (${module.readableIdentifier(
+									this.requestShortener
+								)}) failed: ${e.message}`
+							);
+							err.stack = e.stack;
+							err.module = e.module;
+							return callback(err);
+						}
+
+						callback(null, result);
+					});
+				});
+			}
+		);
+	}
+
 	checkConstraints() {
 		const chunkGraph = this.chunkGraph;
 

lib/asset/AssetModulesPlugin.js

@@ -176,6 +176,20 @@ class AssetModulesPlugin {
 
 					return result;
 				});
+
+				compilation.hooks.runModule.tap(
+					"AssetModulesPlugin",
+					(options, context) => {
+						const { codeGenerationResult } = options;
+						const source = codeGenerationResult.sources.get("asset");
+						if (source === undefined) return;
+						compilation.emitAsset(
+							codeGenerationResult.data.get("filename"),
+							source,
+							codeGenerationResult.data.get("assetInfo")
+						);
+					}
+				);
 			}
 		);
 	}

lib/dependencies/LoaderImportDependency.js

@@ -0,0 +1,28 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+const ModuleDependency = require("./ModuleDependency");
+
+class LoaderImportDependency extends ModuleDependency {
+	/**
+	 * @param {string} request request string
+	 */
+	constructor(request) {
+		super(request);
+		this.weak = true;
+	}
+
+	get type() {
+		return "loader import";
+	}
+
+	get category() {
+		return "loaderImport";
+	}
+}
+
+module.exports = LoaderImportDependency;

lib/dependencies/LoaderPlugin.js

@@ -8,18 +8,37 @@
 const NormalModule = require("../NormalModule");
 const LazySet = require("../util/LazySet");
 const LoaderDependency = require("./LoaderDependency");
+const LoaderImportDependency = require("./LoaderImportDependency");
 
+/** @typedef {import("../Compilation").DepConstructor} DepConstructor */
+/** @typedef {import("../Compiler")} Compiler */
 /** @typedef {import("../Module")} Module */
 
 /**
  * @callback LoadModuleCallback
  * @param {Error=} err error object
- * @param {string=} source source code
+ * @param {string | Buffer=} source source code
  * @param {object=} map source map
  * @param {Module=} module loaded module if successful
  */
 
+/**
+ * @callback ImportModuleCallback
+ * @param {Error=} err error object
+ * @param {any=} exports exports of the evaluated module
+ */
+
+/**
+ * @typedef {Object} ImportModuleOptions
+ * @property {string=} layer the target layer
+ */
+
 class LoaderPlugin {
+	/**
+	 * Apply the plugin
+	 * @param {Compiler} compiler the compiler instance
+	 * @returns {void}
+	 */
 	apply(compiler) {
 		compiler.hooks.compilation.tap(
 			"LoaderPlugin",
@@ -28,6 +47,10 @@ class LoaderPlugin {
 					LoaderDependency,
 					normalModuleFactory
 				);
+				compilation.dependencyFactories.set(
+					LoaderImportDependency,
+					normalModuleFactory
+				);
 			}
 		);
 
@@ -47,7 +70,7 @@ class LoaderPlugin {
 							name: request
 						};
 						const factory = compilation.dependencyFactories.get(
-							dep.constructor
+							/** @type {DepConstructor} */ (dep.constructor)
 						);
 						if (factory === undefined) {
 							return callback(
@@ -123,6 +146,71 @@ class LoaderPlugin {
 							}
 						);
 					};
+
+					/**
+					 * @param {string} request the request string to load the module from
+					 * @param {ImportModuleOptions=} options options
+					 * @param {ImportModuleCallback=} callback callback returning the exports
+					 * @returns {void}
+					 */
+					const importModule = (request, options, callback) => {
+						const dep = new LoaderImportDependency(request);
+						dep.loc = {
+							name: request
+						};
+						const factory = compilation.dependencyFactories.get(
+							/** @type {DepConstructor} */ (dep.constructor)
+						);
+						if (factory === undefined) {
+							return callback(
+								new Error(
+									`No module factory available for dependency type: ${dep.constructor.name}`
+								)
+							);
+						}
+						compilation.buildQueue.increaseParallelism();
+						compilation.handleModuleCreation(
+							{
+								factory,
+								dependencies: [dep],
+								originModule: loaderContext._module,
+								contextInfo: {
+									issuerLayer: options.layer
+								},
+								context: loaderContext.context,
+								recursive: true
+							},
+							err => {
+								compilation.buildQueue.decreaseParallelism();
+								if (err) {
+									return callback(err);
+								}
+								const referencedModule = moduleGraph.getModule(dep);
+								if (!referencedModule) {
+									return callback(new Error("Cannot load the module"));
+								}
+								compilation.runModule(referencedModule, {}, callback);
+							}
+						);
+					};
+
+					/**
+					 * @param {string} request the request string to load the module from
+					 * @param {ImportModuleOptions} options options
+					 * @param {ImportModuleCallback=} callback callback returning the exports
+					 * @returns {Promise<any> | void} exports
+					 */
+					loaderContext.importModule = (request, options, callback) => {
+						if (!callback) {
+							return new Promise((resolve, reject) => {
+								importModule(request, options || {}, (err, result) => {
+									if (err) reject(err);
+									else resolve(result);
+								});
+							});
+						}
+						return importModule(request, options || {}, callback);
+					};
 				}
 			);
 		});

lib/javascript/ArrayPushCallbackChunkFormatPlugin.js

@@ -29,9 +29,9 @@ class ArrayPushCallbackChunkFormatPlugin {
 			compilation => {
 				compilation.hooks.additionalChunkRuntimeRequirements.tap(
 					"ArrayPushCallbackChunkFormatPlugin",
-					(chunk, set) => {
+					(chunk, set, { chunkGraph }) => {
 						if (chunk.hasRuntime()) return;
-						if (compilation.chunkGraph.getNumberOfEntryModules(chunk) > 0) {
+						if (chunkGraph.getNumberOfEntryModules(chunk) > 0) {
 							set.add(RuntimeGlobals.onChunksLoaded);
 							set.add(RuntimeGlobals.require);
 						}

lib/javascript/CommonJsChunkFormatPlugin.js

@@ -31,9 +31,9 @@ class CommonJsChunkFormatPlugin {
 			compilation => {
 				compilation.hooks.additionalChunkRuntimeRequirements.tap(
 					"CommonJsChunkLoadingPlugin",
-					(chunk, set) => {
+					(chunk, set, { chunkGraph }) => {
 						if (chunk.hasRuntime()) return;
-						if (compilation.chunkGraph.getNumberOfEntryModules(chunk) > 0) {
+						if (chunkGraph.getNumberOfEntryModules(chunk) > 0) {
 							set.add(RuntimeGlobals.require);
 							set.add(RuntimeGlobals.startupEntrypoint);
 							set.add(RuntimeGlobals.externalInstallChunk);

lib/javascript/JavascriptModulesPlugin.js

@@ -6,6 +6,7 @@
 "use strict";
 
 const { SyncWaterfallHook, SyncHook, SyncBailHook } = require("tapable");
+const vm = require("vm");
 const {
 	ConcatSource,
 	OriginalSource,
@@ -369,16 +370,58 @@ class JavascriptModulesPlugin {
 				});
 				compilation.hooks.additionalTreeRuntimeRequirements.tap(
 					"JavascriptModulesPlugin",
-					(chunk, set) => {
+					(chunk, set, { chunkGraph }) => {
 						if (
 							!set.has(RuntimeGlobals.startupNoDefault) &&
-							compilation.chunkGraph.hasChunkEntryDependentChunks(chunk)
+							chunkGraph.hasChunkEntryDependentChunks(chunk)
 						) {
 							set.add(RuntimeGlobals.onChunksLoaded);
 							set.add(RuntimeGlobals.require);
 						}
 					}
 				);
+				compilation.hooks.runModule.tap(
+					"JavascriptModulesPlugin",
+					(options, context) => {
+						const source = options.codeGenerationResult.sources.get(
+							"javascript"
+						);
+						if (source === undefined) return;
+						const { module, moduleObject } = options;
+						const code = source.source();
+
+						const fn = vm.runInThisContext(
+							`(function(${module.moduleArgument}, ${module.exportsArgument}, __webpack_require__) {\n${code}\n/**/})`,
+							{
+								filename: module.identifier(),
+								lineOffset: -1
+							}
+						);
+						fn.call(
+							moduleObject.exports,
+							moduleObject,
+							moduleObject.exports,
+							context.__webpack_require__
+						);
+					}
+				);
+				compilation.hooks.runModule.tap(
+					"JavascriptModulesPlugin",
+					(options, context) => {
+						const source = options.codeGenerationResult.sources.get("runtime");
+						if (source === undefined) return;
+						const code = source.source();
+
+						const fn = vm.runInThisContext(
+							`(function(__webpack_require__) {\n${code}\n/**/})`,
+							{
+								filename: options.module.identifier(),
+								lineOffset: -1
+							}
+						);
+						fn.call(null, context.__webpack_require__);
+					}
+				);
 			}
 		);
 	}

lib/library/AbstractLibraryPlugin.js

@@ -12,6 +12,7 @@ const JavascriptModulesPlugin = require("../javascript/JavascriptModulesPlugin")
 /** @typedef {import("../../declarations/WebpackOptions").LibraryOptions} LibraryOptions */
 /** @typedef {import("../../declarations/WebpackOptions").LibraryType} LibraryType */
 /** @typedef {import("../Chunk")} Chunk */
+/** @typedef {import("../ChunkGraph")} ChunkGraph */
 /** @typedef {import("../Compilation")} Compilation */
 /** @typedef {import("../Compilation").ChunkHashContext} ChunkHashContext */
 /** @typedef {import("../Compiler")} Compiler */
@@ -27,6 +28,7 @@ const COMMON_LIBRARY_NAME_MESSAGE =
  * @template T
  * @typedef {Object} LibraryContext
  * @property {Compilation} compilation
+ * @property {ChunkGraph} chunkGraph
  * @property {T} options
  */
 
@@ -75,7 +77,8 @@ class AbstractLibraryPlugin {
 								if (module) {
 									this.finishEntryModule(module, name, {
 										options,
-										compilation
+										compilation,
+										chunkGraph: compilation.chunkGraph
 									});
 								}
 							}
@@ -101,10 +104,14 @@ class AbstractLibraryPlugin {
 			) {
 				compilation.hooks.additionalChunkRuntimeRequirements.tap(
 					_pluginName,
-					(chunk, set) => {
+					(chunk, set, { chunkGraph }) => {
 						const options = getOptionsForChunk(chunk);
 						if (options !== false) {
-							this.runtimeRequirements(chunk, set, { options, compilation });
+							this.runtimeRequirements(chunk, set, {
+								options,
+								compilation,
+								chunkGraph
+							});
 						}
 					}
 				);
@@ -116,7 +123,11 @@ class AbstractLibraryPlugin {
 				hooks.render.tap(_pluginName, (source, renderContext) => {
 					const options = getOptionsForChunk(renderContext.chunk);
 					if (options === false) return source;
-					return this.render(source, renderContext, { options, compilation });
+					return this.render(source, renderContext, {
+						options,
+						compilation,
+						chunkGraph: compilation.chunkGraph
+					});
 				});
 			}
 
@@ -131,7 +142,8 @@ class AbstractLibraryPlugin {
 						if (options === false) return;
 						return this.embedInRuntimeBailout(module, renderContext, {
 							options,
-							compilation
+							compilation,
+							chunkGraph: compilation.chunkGraph
 						});
 					}
 				);
@@ -146,7 +158,8 @@ class AbstractLibraryPlugin {
 					if (options === false) return;
 					return this.strictRuntimeBailout(renderContext, {
 						options,
-						compilation
+						compilation,
+						chunkGraph: compilation.chunkGraph
 					});
 				});
 			}
@@ -161,7 +174,8 @@ class AbstractLibraryPlugin {
 						if (options === false) return source;
 						return this.renderStartup(source, module, renderContext, {
 							options,
-							compilation
+							compilation,
+							chunkGraph: compilation.chunkGraph
 						});
 					}
 				);
@@ -170,7 +184,11 @@ class AbstractLibraryPlugin {
 			hooks.chunkHash.tap(_pluginName, (chunk, hash, context) => {
 				const options = getOptionsForChunk(chunk);
 				if (options === false) return;
-				this.chunkHash(chunk, hash, context, { options, compilation });
+				this.chunkHash(chunk, hash, context, {
+					options,
+					compilation,
+					chunkGraph: compilation.chunkGraph
+				});
 			});
 		});
 	}

lib/prefetch/ChunkPrefetchPreloadPlugin.js

@@ -24,8 +24,7 @@ class ChunkPrefetchPreloadPlugin {
 			compilation => {
 				compilation.hooks.additionalChunkRuntimeRequirements.tap(
 					"ChunkPrefetchPreloadPlugin",
-					(chunk, set) => {
-						const { chunkGraph } = compilation;
+					(chunk, set, { chunkGraph }) => {
 						if (chunkGraph.getNumberOfEntryModules(chunk) === 0) return;
 						const startupChildChunks = chunk.getChildrenOfTypeInOrder(
 							chunkGraph,
@@ -43,8 +42,7 @@ class ChunkPrefetchPreloadPlugin {
 				);
 				compilation.hooks.additionalTreeRuntimeRequirements.tap(
 					"ChunkPrefetchPreloadPlugin",
-					(chunk, set) => {
-						const { chunkGraph } = compilation;
+					(chunk, set, { chunkGraph }) => {
 						const chunkMap = chunk.getChildIdsByOrdersMap(chunkGraph, false);
 
 						if (chunkMap.prefetch) {

lib/runtime/StartupChunkDependenciesPlugin.js

@@ -37,9 +37,9 @@ class StartupChunkDependenciesPlugin {
 				};
 				compilation.hooks.additionalTreeRuntimeRequirements.tap(
 					"StartupChunkDependenciesPlugin",
-					(chunk, set) => {
+					(chunk, set, { chunkGraph }) => {
 						if (!isEnabledForChunk(chunk)) return;
-						if (compilation.chunkGraph.hasChunkEntryDependentChunks(chunk)) {
+						if (chunkGraph.hasChunkEntryDependentChunks(chunk)) {
 							set.add(RuntimeGlobals.startup);
 							set.add(RuntimeGlobals.ensureChunk);
 							set.add(RuntimeGlobals.ensureChunkIncludeEntries);

lib/stats/DefaultStatsFactoryPlugin.js

@@ -148,6 +148,7 @@ const { makePathsRelative, parseResource } = require("../util/identifier");
  * @property {boolean=} cacheable
  * @property {boolean=} built
  * @property {boolean=} codeGenerated
+ * @property {boolean=} buildTimeExecuted
  * @property {boolean=} cached
  * @property {boolean=} optional
  * @property {boolean=} orphan
@@ -1077,6 +1078,9 @@ const SIMPLE_EXTRACTORS = {
 			const { compilation, type } = context;
 			const built = compilation.builtModules.has(module);
 			const codeGenerated = compilation.codeGeneratedModules.has(module);
+			const buildTimeExecuted = compilation.buildTimeExecutedModules.has(
+				module
+			);
 			/** @type {{[x: string]: number}} */
 			const sizes = {};
 			for (const sourceType of module.getSourceTypes()) {
@@ -1091,6 +1095,7 @@ const SIMPLE_EXTRACTORS = {
 				sizes,
 				built,
 				codeGenerated,
+				buildTimeExecuted,
 				cached: !built && !codeGenerated
 			};
 			Object.assign(object, statsModule);

lib/stats/DefaultStatsPrinterPlugin.js

@@ -306,6 +306,8 @@ const SIMPLE_PRINTERS = {
 		built ? yellow(formatFlag("built")) : undefined,
 	"module.codeGenerated": (codeGenerated, { formatFlag, yellow }) =>
 		codeGenerated ? yellow(formatFlag("code generated")) : undefined,
+	"module.buildTimeExecuted": (buildTimeExecuted, { formatFlag, green }) =>
+		buildTimeExecuted ? green(formatFlag("build time executed")) : undefined,
 	"module.cached": (cached, { formatFlag, green }) =>
 		cached ? green(formatFlag("cached")) : undefined,
 	"module.assets": (assets, { formatFlag, magenta }) =>

lib/util/AsyncQueue.js

@@ -99,7 +99,7 @@ class AsyncQueue {
 	}
 
 	/**
-	 * @param {T} item a item
+	 * @param {T} item an item
 	 * @param {Callback<R>} callback callback function
 	 * @returns {void}
 	 */
@@ -144,7 +144,7 @@ class AsyncQueue {
 	}
 
 	/**
-	 * @param {T} item a item
+	 * @param {T} item an item
 	 * @returns {void}
 	 */
 	invalidate(item) {
@@ -156,6 +156,29 @@ class AsyncQueue {
 		}
 	}
 
+	/**
+	 * Waits for an already started item
+	 * @param {T} item an item
+	 * @param {Callback<R>} callback callback function
+	 * @returns {void}
+	 */
+	waitFor(item, callback) {
+		const key = this._getKey(item);
+		const entry = this._entries.get(key);
+		if (entry === undefined) {
+			return callback(
+				new Error("waitFor can only be called for an already started item")
+			);
+		}
+		if (entry.state === DONE_STATE) {
+			process.nextTick(() => callback(entry.error, entry.result));
+		} else if (entry.callbacks === undefined) {
+			entry.callbacks = [callback];
+		} else {
+			entry.callbacks.push(callback);
+		}
+	}
+
 	/**
 	 * @returns {void}
 	 */

test/Defaults.unittest.js

@@ -421,6 +421,26 @@ describe("Defaults", () => {
 		          "...",
 		        ],
 		      },
+		      "loaderImport": Object {
+		        "aliasFields": Array [
+		          "browser",
+		        ],
+		        "conditionNames": Array [
+		          "import",
+		          "module",
+		          "...",
+		        ],
+		        "extensions": Array [
+		          ".js",
+		          ".json",
+		          ".wasm",
+		        ],
+		        "mainFields": Array [
+		          "browser",
+		          "module",
+		          "...",
+		        ],
+		      },
 		      "undefined": Object {
 		        "aliasFields": Array [
 		          "browser",
@@ -1089,6 +1109,13 @@ describe("Defaults", () => {
 		@@ ... @@
 		-           "browser",
 		@@ ... @@
+		-         "aliasFields": Array [
+		-           "browser",
+		-         ],
+		+         "aliasFields": Array [],
+		@@ ... @@
+		-           "browser",
+		@@ ... @@
 		-       "browser",
 		+       "node",
 		@@ ... @@
@@ -1223,6 +1250,13 @@ describe("Defaults", () => {
 		@@ ... @@
 		-           "browser",
 		@@ ... @@
+		-         "aliasFields": Array [
+		-           "browser",
+		-         ],
+		+         "aliasFields": Array [],
+		@@ ... @@
+		-           "browser",
+		@@ ... @@
 		-       "browser",
 		+       "node",
 		+       "electron",
@@ -1339,6 +1373,13 @@ describe("Defaults", () => {
 		@@ ... @@
 		-           "browser",
 		@@ ... @@
+		-         "aliasFields": Array [
+		-           "browser",
+		-         ],
+		+         "aliasFields": Array [],
+		@@ ... @@
+		-           "browser",
+		@@ ... @@
 		+       "node",
 		@@ ... @@
 		+       "electron",

test/configCases/loader-import-module/css/colors.js

@@ -0,0 +1,2 @@
+export const red = "#f00";
+export const green = "#0f0";

test/configCases/loader-import-module/css/index.js

@@ -0,0 +1,13 @@
+import stylesheet from "./stylesheet";
+import stylesheet1 from "./stylesheet?1";
+import otherStylesheet from "./other-stylesheet";
+
+it("should be able to use build-time code", () => {
+	expect(stylesheet).toBe(
+		'body { background: url("/public/assets/file.png"); color: #f00; }'
+	);
+	expect(stylesheet1).toBe(
+		'body { background: url("/public/assets/file.png?1"); color: #f00; }'
+	);
+	expect(otherStylesheet).toBe("body { background-color: #0f0; }");
+});

test/configCases/loader-import-module/css/loader.js

@@ -0,0 +1,6 @@
+exports.pitch = async function (remaining) {
+	const result = await this.importModule(
+		this.resourcePath + ".webpack[javascript/auto]" + "!=!" + remaining
+	);
+	return result.default || result;
+};

test/configCases/loader-import-module/css/other-stylesheet.js

@@ -0,0 +1,2 @@
+import { green } from "./colors.js";
+export default `body { background-color: ${green}; }`;

test/configCases/loader-import-module/css/stylesheet.js

@@ -0,0 +1,4 @@
+import { red } from "./colors.js";
+export default `body { background: url("${
+	new URL("./file.png", import.meta.url).href + __resourceQuery
+}"); color: ${red}; }`;

test/configCases/loader-import-module/css/webpack.config.js

@@ -0,0 +1,34 @@
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	output: {
+		publicPath: "/public/"
+	},
+	module: {
+		parser: {
+			javascript: {
+				url: "relative"
+			}
+		},
+		generator: {
+			asset: {
+				filename: "assets/[name][ext][query]"
+			}
+		},
+		rules: [
+			{
+				test: /stylesheet\.js$/,
+				use: "./loader",
+				type: "asset/source"
+			}
+		]
+	},
+	plugins: [
+		compiler =>
+			compiler.hooks.done.tap("test case", stats =>
+				expect(stats.compilation.getAsset("assets/file.png")).toHaveProperty(
+					"info",
+					expect.objectContaining({ sourceFilename: "file.png" })
+				)
+			)
+	]
+};

types.d.ts

@@ -345,6 +345,11 @@ declare abstract class AsyncQueue<T, K, R> {
 	};
 	add(item: T, callback: CallbackFunction<R>): void;
 	invalidate(item: T): void;
+
+	/**
+	 * Waits for an already started item
+	 */
+	waitFor(item: T, callback: CallbackFunction<R>): void;
 	stop(): void;
 	increaseParallelism(): void;
 	decreaseParallelism(): void;
@@ -1242,6 +1247,7 @@ declare class Compilation {
 		dependencyReferencedExports: SyncWaterfallHook<
 			[(string[] | ReferencedExport)[], Dependency, RuntimeSpec]
 		>;
+		runModule: SyncHook<[RunModuleArgument, RunModuleContext]>;
 		finishModules: AsyncSeriesHook<[Iterable<Module>]>;
 		finishRebuildingModule: AsyncSeriesHook<[Module]>;
 		unseal: SyncHook<[]>;
@@ -1263,14 +1269,24 @@ declare class Compilation {
 		>;
 		afterOptimizeChunkModules: SyncHook<[Iterable<Chunk>, Iterable<Module>]>;
 		shouldRecord: SyncBailHook<[], boolean>;
-		additionalChunkRuntimeRequirements: SyncHook<[Chunk, Set<string>]>;
-		runtimeRequirementInChunk: HookMap<SyncBailHook<[Chunk, Set<string>], any>>;
-		additionalModuleRuntimeRequirements: SyncHook<[Module, Set<string>]>;
-		runtimeRequirementInModule: HookMap<
-			SyncBailHook<[Module, Set<string>], any>
+		additionalChunkRuntimeRequirements: SyncHook<
+			[Chunk, Set<string>, RuntimeRequirementsContext]
+		>;
+		runtimeRequirementInChunk: HookMap<
+			SyncBailHook<[Chunk, Set<string>, RuntimeRequirementsContext], any>
+		>;
+		additionalModuleRuntimeRequirements: SyncHook<
+			[Module, Set<string>, RuntimeRequirementsContext]
+		>;
+		runtimeRequirementInModule: HookMap<
+			SyncBailHook<[Module, Set<string>, RuntimeRequirementsContext], any>
+		>;
+		additionalTreeRuntimeRequirements: SyncHook<
+			[Chunk, Set<string>, RuntimeRequirementsContext]
+		>;
+		runtimeRequirementInTree: HookMap<
+			SyncBailHook<[Chunk, Set<string>, RuntimeRequirementsContext], any>
 		>;
-		additionalTreeRuntimeRequirements: SyncHook<[Chunk, Set<string>]>;
-		runtimeRequirementInTree: HookMap<SyncBailHook<[Chunk, Set<string>], any>>;
 		runtimeModule: SyncHook<[RuntimeModule, Chunk]>;
 		reviveModules: SyncHook<[Iterable<Module>, any]>;
 		beforeModuleIds: SyncHook<[Iterable<Module>]>;
@@ -1376,7 +1392,7 @@ declare class Compilation {
 	runtimeTemplate: RuntimeTemplate;
 	moduleTemplates: { javascript: ModuleTemplate };
 	moduleGraph: ModuleGraph;
-	chunkGraph?: ChunkGraph;
+	chunkGraph: any;
 	codeGenerationResults: CodeGenerationResults;
 	processDependenciesQueue: AsyncQueue<Module, Module, Module>;
 	addModuleQueue: AsyncQueue<Module, string, Module>;
@@ -1415,6 +1431,7 @@ declare class Compilation {
 	needAdditionalPass: boolean;
 	builtModules: WeakSet<Module>;
 	codeGeneratedModules: WeakSet<Module>;
+	buildTimeExecutedModules: WeakSet<Module>;
 	emittedAssets: Set<string>;
 	comparedForEmitAssets: Set<string>;
 	fileDependencies: LazySet<string>;
@@ -1512,8 +1529,33 @@ declare class Compilation {
 		blocks: DependenciesBlock[]
 	): void;
 	codeGeneration(callback?: any): void;
-	processRuntimeRequirements(): void;
-	addRuntimeModule(chunk: Chunk, module: RuntimeModule): void;
+	processRuntimeRequirements(__0?: {
+		/**
+		 * the chunk graph
+		 */
+		chunkGraph?: ChunkGraph;
+		/**
+		 * modules
+		 */
+		modules?: Iterable<Module>;
+		/**
+		 * chunks
+		 */
+		chunks?: Iterable<Chunk>;
+		/**
+		 * codeGenerationResults
+		 */
+		codeGenerationResults?: CodeGenerationResults;
+		/**
+		 * chunkGraphEntries
+		 */
+		chunkGraphEntries?: Iterable<Chunk>;
+	}): void;
+	addRuntimeModule(
+		chunk: Chunk,
+		module: RuntimeModule,
+		chunkGraph?: ChunkGraph
+	): void;
 	addChunkInGroup(
 		groupOptions: string | ChunkGroupOptions,
 		module: Module,
@@ -1601,6 +1643,11 @@ declare class Compilation {
 			| WebpackPluginInstance
 		)[]
 	): Compiler;
+	runModule(
+		module: Module,
+		options: RunModuleOptions,
+		callback: (err?: WebpackError, exports?: any) => void
+	): void;
 	checkConstraints(): void;
 
 	/**
@@ -5348,6 +5395,7 @@ declare interface KnownStatsModule {
 	cacheable?: boolean;
 	built?: boolean;
 	codeGenerated?: boolean;
+	buildTimeExecuted?: boolean;
 	cached?: boolean;
 	optional?: boolean;
 	orphan?: boolean;
@@ -5484,6 +5532,7 @@ declare class LibManifestPlugin {
 }
 declare interface LibraryContext<T> {
 	compilation: Compilation;
+	chunkGraph: ChunkGraph;
 	options: T;
 }
 
@@ -9253,6 +9302,19 @@ type RuleSetUseItem =
 			options?: string | { [index: string]: any };
 	  }
 	| __TypeWebpackOptions;
+declare interface RunModuleArgument {
+	module: Module;
+	moduleObject: object;
+	codeGenerationResult: CodeGenerationResult;
+}
+declare interface RunModuleContext {
+	chunk: Chunk;
+	chunkGraph: ChunkGraph;
+	__webpack_require__: Function;
+}
+declare interface RunModuleOptions {
+	entryOptions?: EntryOptions;
+}
 declare class RuntimeChunkPlugin {
 	constructor(options?: any);
 	options: any;
@@ -9294,6 +9356,17 @@ declare class RuntimeModule extends Module {
 	 */
 	static STAGE_TRIGGER: number;
 }
+declare interface RuntimeRequirementsContext {
+	/**
+	 * the chunk graph
+	 */
+	chunkGraph: ChunkGraph;
+
+	/**
+	 * the code generation results
+	 */
+	codeGenerationResults: CodeGenerationResults;
+}
 type RuntimeSpec = undefined | string | SortableSet<string>;
 declare abstract class RuntimeSpecMap<T> {
 	get(runtime: RuntimeSpec): T;