allow to disable some deprecations

add `experiments.backCompat: false` (default in `experiments.futureDefaults`)
remove unused `experiments.asset`
enable `experiments.topLevelAwait` and `experiments.asyncWebAssembly` by default in `experiments.futureDefaults`

declarations/WebpackOptions.d.ts

@@ -2738,14 +2738,14 @@ export interface EntryStaticNormalized {
  * Enables/Disables experiments (experimental features with relax SemVer compatibility).
  */
 export interface ExperimentsCommon {
-	/**
-	 * Allow module type 'asset' to generate assets.
-	 */
-	asset?: boolean;
 	/**
 	 * Support WebAssembly as asynchronous EcmaScript Module.
 	 */
 	asyncWebAssembly?: boolean;
+	/**
+	 * Enable backward-compat layer with deprecation warnings for many webpack 4 APIs.
+	 */
+	backCompat?: boolean;
 	/**
 	 * Enable additional in memory caching of modules that are unchanged and reference only unchanged modules.
 	 */
@@ -2755,7 +2755,7 @@ export interface ExperimentsCommon {
 	 */
 	futureDefaults?: boolean;
 	/**
-	 * Enable module and chunk layers.
+	 * Enable module layers.
 	 */
 	layers?: boolean;
 	/**

lib/Chunk.js

@@ -63,8 +63,9 @@ let debugId = 1000;
 class Chunk {
 	/**
 	 * @param {string=} name of chunk being created, is optional (for subclasses)
+	 * @param {boolean} backCompat enable backward-compatibility
 	 */
-	constructor(name) {
+	constructor(name, backCompat = true) {
 		/** @type {number | string | null} */
 		this.id = null;
 		/** @type {(number|string)[] | null} */
@@ -84,7 +85,7 @@ class Chunk {
 		/** @type {RuntimeSpec} */
 		this.runtime = undefined;
 		/** @type {Set<string>} */
-		this.files = new ChunkFilesSet();
+		this.files = backCompat ? new ChunkFilesSet() : new Set();
 		/** @type {Set<string>} */
 		this.auxiliaryFiles = new Set();
 		/** @type {boolean} */

lib/Compilation.js

@@ -429,6 +429,8 @@ class Compilation {
 	 * @param {CompilationParams} params the compilation parameters
 	 */
 	constructor(compiler, params) {
+		this._backCompat = compiler._backCompat;
+
 		const getNormalModuleLoader = () => deprecatedNormalModuleLoaderHook(this);
 		/** @typedef {{ additionalAssets?: true | Function }} ProcessAssetsAdditionalOptions */
 		/** @type {AsyncSeriesHook<[CompilationAssets], ProcessAssetsAdditionalOptions>} */
@@ -559,6 +561,7 @@ class Compilation {
 		 * @returns {FakeHook<Pick<AsyncSeriesHook<T>, "tap" | "tapAsync" | "tapPromise" | "name">>} fake hook which redirects
 		 */
 		const createProcessAssetsHook = (name, stage, getArgs, code) => {
+			if (!this._backCompat && code) return undefined;
 			const errorMessage =
 				reason => `Can't automatically convert plugin using Compilation.hooks.${name} to Compilation.hooks.processAssets because ${reason}.
 BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a single Compilation.hooks.processAssets hook.`;
@@ -983,7 +986,6 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 		this.asyncEntrypoints = [];
 		/** @type {Set<Chunk>} */
 		this.chunks = new Set();
-		arrayToSetDeprecation(this.chunks, "Compilation.chunks");
 		/** @type {ChunkGroup[]} */
 		this.chunkGroups = [];
 		/** @type {Map<string, ChunkGroup>} */
@@ -992,7 +994,10 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 		this.namedChunks = new Map();
 		/** @type {Set<Module>} */
 		this.modules = new Set();
+		if (this._backCompat) {
+			arrayToSetDeprecation(this.chunks, "Compilation.chunks");
 			arrayToSetDeprecation(this.modules, "Compilation.modules");
+		}
 		/** @private @type {Map<string, Module>} */
 		this._modules = new Map();
 		this.records = null;
@@ -1286,6 +1291,7 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 			}
 			this._modules.set(identifier, module);
 			this.modules.add(module);
+			if (this._backCompat)
 				ModuleGraph.setModuleGraphForModule(module, this.moduleGraph);
 			if (currentProfile !== undefined) {
 				currentProfile.markIntegrationEnd();
@@ -1701,6 +1707,7 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 
 		this._modules.set(module.identifier(), module);
 		this.modules.add(module);
+		if (this._backCompat)
 			ModuleGraph.setModuleGraphForModule(module, this.moduleGraph);
 
 		this._handleModuleBuildAndDependencies(
@@ -2777,9 +2784,11 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 		);
 		this.chunkGraph = chunkGraph;
 
+		if (this._backCompat) {
 			for (const module of this.modules) {
 				ChunkGraph.setChunkGraphForModule(module, chunkGraph);
 			}
+		}
 
 		this.hooks.seal.call();
 
@@ -3045,14 +3054,16 @@ Or do you want to use the entrypoints '${name}' and '${runtime}' independently o
 									}
 									this.hooks.afterProcessAssets.call(this.assets);
 									this.logger.timeEnd("process assets");
-									this.assets = soonFrozenObjectDeprecation(
+									this.assets = this._backCompat
+										? soonFrozenObjectDeprecation(
 												this.assets,
 												"Compilation.assets",
 												"DEP_WEBPACK_COMPILATION_ASSETS",
 												`BREAKING CHANGE: No more changes should happen to Compilation.assets after sealing the Compilation.
 	Do changes to assets earlier, e. g. in Compilation.hooks.processAssets.
 	Make sure to select an appropriate stage from Compilation.PROCESS_ASSETS_STAGE_*.`
-									);
+										  )
+										: Object.freeze(this.assets);
 
 									this.summarizeDependencies();
 									if (shouldRecord) {
@@ -3453,6 +3464,7 @@ Or do you want to use the entrypoints '${name}' and '${runtime}' independently o
 	 */
 	addRuntimeModule(chunk, module, chunkGraph = this.chunkGraph) {
 		// Deprecated ModuleGraph association
+		if (this._backCompat)
 			ModuleGraph.setModuleGraphForModule(module, this.moduleGraph);
 
 		// add it to the list
@@ -3589,8 +3601,9 @@ Or do you want to use the entrypoints '${name}' and '${runtime}' independently o
 				return chunk;
 			}
 		}
-		const chunk = new Chunk(name);
+		const chunk = new Chunk(name, this._backCompat);
 		this.chunks.add(chunk);
+		if (this._backCompat)
 			ChunkGraph.setChunkGraphForChunk(chunk, this.chunkGraph);
 		if (name) {
 			this.namedChunks.set(name, chunk);
@@ -4715,7 +4728,7 @@ This prevents using hashes of each other and should be avoided.`);
 					this.outputOptions;
 				const runtimeTemplate = this.runtimeTemplate;
 
-				const chunk = new Chunk("build time chunk");
+				const chunk = new Chunk("build time chunk", this._backCompat);
 				chunk.id = chunk.name;
 				chunk.ids = [chunk.id];
 				chunk.runtime = runtime;

lib/Compiler.js

@@ -119,8 +119,9 @@ const includesHash = (filename, hashes) => {
 class Compiler {
 	/**
 	 * @param {string} context the compilation path
+	 * @param {WebpackOptions} options options
 	 */
-	constructor(context) {
+	constructor(context, options = /** @type {WebpackOptions} */ ({})) {
 		this.hooks = Object.freeze({
 			/** @type {SyncHook<[]>} */
 			initialize: new SyncHook([]),
@@ -240,8 +241,7 @@ class Compiler {
 
 		this.infrastructureLogger = undefined;
 
-		/** @type {WebpackOptions} */
+		this.options = options;
-		this.options = /** @type {WebpackOptions} */ ({});
 
 		this.context = context;
 
@@ -263,6 +263,8 @@ class Compiler {
 		/** @type {boolean} */
 		this.watchMode = false;
 
+		this._backCompat = this.options.experiments.backCompat !== false;
+
 		/** @type {Compilation} */
 		this._lastCompilation = undefined;
 		/** @type {NormalModuleFactory} */
@@ -963,7 +965,13 @@ ${other}`);
 		outputOptions,
 		plugins
 	) {
-		const childCompiler = new Compiler(this.context);
+		const childCompiler = new Compiler(this.context, {
+			...this.options,
+			output: {
+				...this.options.output,
+				...outputOptions
+			}
+		});
 		childCompiler.name = compilerName;
 		childCompiler.outputPath = this.outputPath;
 		childCompiler.inputFileSystem = this.inputFileSystem;
@@ -976,6 +984,7 @@ ${other}`);
 		childCompiler.fsStartTime = this.fsStartTime;
 		childCompiler.cache = this.cache;
 		childCompiler.compilerPath = `${this.compilerPath}${compilerName}|${compilerIndex}|`;
+		childCompiler._backCompat = this._backCompat;
 
 		const relativeCompilerName = makePathsRelative(
 			this.context,
@@ -991,13 +1000,6 @@ ${other}`);
 			this.records[relativeCompilerName].push((childCompiler.records = {}));
 		}
 
-		childCompiler.options = {
-			...this.options,
-			output: {
-				...this.options.output,
-				...outputOptions
-			}
-		};
 		childCompiler.parentCompilation = compilation;
 		childCompiler.root = this.root;
 		if (Array.isArray(plugins)) {

lib/HotModuleReplacementPlugin.js

@@ -83,6 +83,7 @@ class HotModuleReplacementPlugin {
 	 * @returns {void}
 	 */
 	apply(compiler) {
+		const { _backCompat: backCompat } = compiler;
 		if (compiler.options.output.strictModuleErrorHandling === undefined)
 			compiler.options.output.strictModuleErrorHandling = true;
 		const runtimeRequirements = [RuntimeGlobals.module];
@@ -597,6 +598,7 @@ class HotModuleReplacementPlugin {
 								(newRuntimeModules && newRuntimeModules.length > 0)
 							) {
 								const hotUpdateChunk = new HotUpdateChunk();
+								if (backCompat)
 									ChunkGraph.setChunkGraphForChunk(hotUpdateChunk, chunkGraph);
 								hotUpdateChunk.id = chunkId;
 								hotUpdateChunk.runtime = newRuntime;

lib/config/defaults.js

@@ -265,15 +265,15 @@ const applyWebpackOptionsDefaults = options => {
  * @returns {void}
  */
 const applyExperimentsDefaults = (experiments, { production, development }) => {
-	D(experiments, "topLevelAwait", false);
+	D(experiments, "futureDefaults", false);
+	D(experiments, "backCompat", !experiments.futureDefaults);
+	D(experiments, "topLevelAwait", experiments.futureDefaults);
 	D(experiments, "syncWebAssembly", false);
-	D(experiments, "asyncWebAssembly", false);
+	D(experiments, "asyncWebAssembly", experiments.futureDefaults);
 	D(experiments, "outputModule", false);
-	D(experiments, "asset", false);
 	D(experiments, "layers", false);
 	D(experiments, "lazyCompilation", undefined);
 	D(experiments, "buildHttp", undefined);
-	D(experiments, "futureDefaults", false);
 	D(experiments, "cacheUnaffected", experiments.futureDefaults);
 
 	if (typeof experiments.buildHttp === "object") {

lib/optimize/ModuleConcatenationPlugin.js

@@ -56,6 +56,7 @@ class ModuleConcatenationPlugin {
 	 * @returns {void}
 	 */
 	apply(compiler) {
+		const { _backCompat: backCompat } = compiler;
 		compiler.hooks.compilation.tap("ModuleConcatenationPlugin", compilation => {
 			const moduleGraph = compilation.moduleGraph;
 			const bailoutReasonMap = new Map();
@@ -389,8 +390,10 @@ class ModuleConcatenationPlugin {
 							};
 
 							const integrate = () => {
+								if (backCompat) {
 									ChunkGraph.setChunkGraphForModule(newModule, chunkGraph);
 									ModuleGraph.setModuleGraphForModule(newModule, moduleGraph);
+								}
 
 								for (const warning of concatConfiguration.getWarningsSorted()) {
 									moduleGraph

lib/util/deprecation.js

@@ -165,8 +165,16 @@ exports.arrayToSetDeprecation = (set, name) => {
 };
 
 exports.createArrayToSetDeprecationSet = name => {
-	class SetDeprecatedArray extends Set {}
+	let initialized = false;
+	class SetDeprecatedArray extends Set {
+		constructor(items) {
+			super(items);
+			if (!initialized) {
+				initialized = true;
 				exports.arrayToSetDeprecation(SetDeprecatedArray.prototype, name);
+			}
+		}
+	}
 	return SetDeprecatedArray;
 };
 

lib/webpack.js

@@ -61,8 +61,7 @@ const createMultiCompiler = (childOptions, options) => {
 const createCompiler = rawOptions => {
 	const options = getNormalizedWebpackOptions(rawOptions);
 	applyWebpackOptionsBaseDefaults(options);
-	const compiler = new Compiler(options.context);
+	const compiler = new Compiler(options.context, options);
-	compiler.options = options;
 	new NodeEnvironmentPlugin({
 		infrastructureLogging: options.infrastructureLogging
 	}).apply(compiler);

schemas/WebpackOptions.json

@@ -681,14 +681,14 @@
       "implements": ["#/definitions/ExperimentsCommon"],
       "additionalProperties": false,
       "properties": {
-        "asset": {
-          "description": "Allow module type 'asset' to generate assets.",
-          "type": "boolean"
-        },
         "asyncWebAssembly": {
           "description": "Support WebAssembly as asynchronous EcmaScript Module.",
           "type": "boolean"
         },
+        "backCompat": {
+          "description": "Enable backward-compat layer with deprecation warnings for many webpack 4 APIs.",
+          "type": "boolean"
+        },
         "buildHttp": {
           "description": "Build http(s): urls using a lockfile and resource content cache.",
           "anyOf": [
@@ -709,7 +709,7 @@
           "type": "boolean"
         },
         "layers": {
-          "description": "Enable module and chunk layers.",
+          "description": "Enable module layers.",
           "type": "boolean"
         },
         "lazyCompilation": {
@@ -742,14 +742,14 @@
       "type": "object",
       "additionalProperties": false,
       "properties": {
-        "asset": {
-          "description": "Allow module type 'asset' to generate assets.",
-          "type": "boolean"
-        },
         "asyncWebAssembly": {
           "description": "Support WebAssembly as asynchronous EcmaScript Module.",
           "type": "boolean"
         },
+        "backCompat": {
+          "description": "Enable backward-compat layer with deprecation warnings for many webpack 4 APIs.",
+          "type": "boolean"
+        },
         "cacheUnaffected": {
           "description": "Enable additional in memory caching of modules that are unchanged and reference only unchanged modules.",
           "type": "boolean"
@@ -759,7 +759,7 @@
           "type": "boolean"
         },
         "layers": {
-          "description": "Enable module and chunk layers.",
+          "description": "Enable module layers.",
           "type": "boolean"
         },
         "outputModule": {
@@ -782,14 +782,14 @@
       "implements": ["#/definitions/ExperimentsCommon"],
       "additionalProperties": false,
       "properties": {
-        "asset": {
-          "description": "Allow module type 'asset' to generate assets.",
-          "type": "boolean"
-        },
         "asyncWebAssembly": {
           "description": "Support WebAssembly as asynchronous EcmaScript Module.",
           "type": "boolean"
         },
+        "backCompat": {
+          "description": "Enable backward-compat layer with deprecation warnings for many webpack 4 APIs.",
+          "type": "boolean"
+        },
         "buildHttp": {
           "description": "Build http(s): urls using a lockfile and resource content cache.",
           "oneOf": [
@@ -807,7 +807,7 @@
           "type": "boolean"
         },
         "layers": {
-          "description": "Enable module and chunk layers.",
+          "description": "Enable module layers.",
           "type": "boolean"
         },
         "lazyCompilation": {

test/TestCases.template.js

@@ -185,6 +185,7 @@ const describeCases = config => {
 								experiments: {
 									asyncWebAssembly: true,
 									topLevelAwait: true,
+									backCompat: false,
 									...(config.module ? { outputModule: true } : {})
 								}
 							};

types.d.ts

@@ -691,7 +691,7 @@ declare interface CallbackWebpack<T> {
 }
 type Cell<T> = undefined | T;
 declare class Chunk {
-	constructor(name?: string);
+	constructor(name?: string, backCompat?: boolean);
 	id: null | string | number;
 	ids: null | (string | number)[];
 	debugId: number;
@@ -1857,7 +1857,7 @@ declare interface CompilationParams {
 	contextModuleFactory: ContextModuleFactory;
 }
 declare class Compiler {
-	constructor(context: string);
+	constructor(context: string, options?: WebpackOptionsNormalized);
 	hooks: Readonly<{
 		initialize: SyncHook<[]>;
 		shouldEmit: SyncBailHook<[Compilation], boolean>;
@@ -3303,16 +3303,16 @@ type Experiments = ExperimentsCommon & ExperimentsExtra;
  * Enables/Disables experiments (experimental features with relax SemVer compatibility).
  */
 declare interface ExperimentsCommon {
-	/**
-	 * Allow module type 'asset' to generate assets.
-	 */
-	asset?: boolean;
-
 	/**
 	 * Support WebAssembly as asynchronous EcmaScript Module.
 	 */
 	asyncWebAssembly?: boolean;
 
+	/**
+	 * Enable backward-compat layer with deprecation warnings for many webpack 4 APIs.
+	 */
+	backCompat?: boolean;
+
 	/**
 	 * Enable additional in memory caching of modules that are unchanged and reference only unchanged modules.
 	 */
@@ -3324,7 +3324,7 @@ declare interface ExperimentsCommon {
 	futureDefaults?: boolean;
 
 	/**
-	 * Enable module and chunk layers.
+	 * Enable module layers.
 	 */
 	layers?: boolean;