add default cache names in multicompiler mode

lib/MultiCompiler.js

@@ -115,26 +115,30 @@ module.exports = class MultiCompiler {
 
 	_validateCompilersOptions() {
 		if (this.compilers.length < 2) return;
-		const cacheNames = new Set();
+		/**
+		 * @param {Compiler} compiler compiler
+		 * @param {WebpackError} warning warning
+		 */
 		const addWarning = (compiler, warning) => {
 			compiler.hooks.thisCompilation.tap("MultiCompiler", compilation => {
 				compilation.warnings.push(warning);
 			});
 		};
 		for (const compiler of this.compilers) {
 			if (compiler.options.cache && "name" in compiler.options.cache) {
-				const cacheName = compiler.options.cache && compiler.options.cache.name;
-				if (cacheNames.has(cacheName)) {
+				const name = compiler.options.cache.name;
+				const warn = /__compiler(\d+)__$/.test(name);
+				if (warn) {
 					addWarning(
 						compiler,
 						new WebpackError(
-							`Compiler cache with name ${JSON.stringify(
-								cacheName
-							)} is already defined. Please set unique "cache.name" option.`
+							`${
+								compiler.name
+									? `Compiler with name "${compiler.name}" doesn't use cache name. `
+									: ""
+							}Please set "cache.name" option.`
 						)
 					);
-				} else {
-					cacheNames.add(cacheName);
 				}
 			}
 		}

lib/WebpackOptionsDefaulter.js

@@ -6,7 +6,9 @@
 "use strict";
 
 const { applyWebpackOptionsDefaults } = require("./config/defaults");
-const { getNormalizedWebpackOptions } = require("./config/normalization");
+const {
+	getNormalizedWebpackCompilerOptions
+} = require("./config/normalization");
 
 /** @typedef {import("./config/normalization").WebpackOptions} WebpackOptions */
 /** @typedef {import("./config/normalization").WebpackOptionsNormalized} WebpackOptionsNormalized */
@@ -17,7 +19,7 @@ class WebpackOptionsDefaulter {
 	 * @returns {WebpackOptionsNormalized} normalized webpack options
 	 */
 	process(options) {
-		const normalizedOptions = getNormalizedWebpackOptions(options);
+		const normalizedOptions = getNormalizedWebpackCompilerOptions(options);
 		applyWebpackOptionsDefaults(normalizedOptions);
 		return normalizedOptions;
 	}

lib/config/defaults.js

@@ -66,6 +66,7 @@ const {
 /** @typedef {import("./target").TargetProperties} TargetProperties */
 
 const NODE_MODULES_REGEXP = /[\\/]node_modules[\\/]/i;
+const DEFAULT_CACHE_NAME = "default";
 
 /**
  * Sets a constant default value when undefined
@@ -201,7 +202,7 @@ const applyWebpackOptionsDefaults = options => {
 		development ? { type: /** @type {"memory"} */ ("memory") } : false
 	);
 	applyCacheDefaults(options.cache, {
-		name: name || "default",
+		name: name || DEFAULT_CACHE_NAME,
 		mode: mode || "production",
 		development,
 		cacheUnaffected: options.experiments.cacheUnaffected
@@ -1583,5 +1584,6 @@ const applyInfrastructureLoggingDefaults = infrastructureLogging => {
 	D(infrastructureLogging, "appendOnly", !tty);
 };
 
+exports.defaultCacheName = DEFAULT_CACHE_NAME;
 exports.applyWebpackOptionsBaseDefaults = applyWebpackOptionsBaseDefaults;
 exports.applyWebpackOptionsDefaults = applyWebpackOptionsDefaults;

lib/config/normalization.js

@@ -6,12 +6,15 @@
 "use strict";
 
 const util = require("util");
+const { defaultCacheName } = require("./defaults");
 
 /** @typedef {import("../../declarations/WebpackOptions").CacheOptionsNormalized} CacheOptions */
 /** @typedef {import("../../declarations/WebpackOptions").EntryDescriptionNormalized} EntryDescriptionNormalized */
 /** @typedef {import("../../declarations/WebpackOptions").EntryStatic} EntryStatic */
 /** @typedef {import("../../declarations/WebpackOptions").EntryStaticNormalized} EntryStaticNormalized */
 /** @typedef {import("../../declarations/WebpackOptions").Externals} Externals */
+/** @typedef {import("../../declarations/WebpackOptions").MemoryCacheOptions} MemoryCacheOptions */
+/** @typedef {import("../../declarations/WebpackOptions").FileCacheOptions} FileCacheOptions */
 /** @typedef {import("../../declarations/WebpackOptions").LibraryName} LibraryName */
 /** @typedef {import("../../declarations/WebpackOptions").LibraryOptions} LibraryOptions */
 /** @typedef {import("../../declarations/WebpackOptions").ModuleOptionsNormalized} ModuleOptionsNormalized */
@@ -22,6 +25,7 @@ const util = require("util");
 /** @typedef {import("../../declarations/WebpackOptions").WebpackOptions} WebpackOptions */
 /** @typedef {import("../../declarations/WebpackOptions").WebpackOptionsNormalized} WebpackOptionsNormalized */
 /** @typedef {import("../Entrypoint")} Entrypoint */
+/** @typedef {import("../MultiCompiler").MultiCompilerOptions} MultiCompilerOptions */
 
 const handledDeprecatedNoEmitOnErrors = util.deprecate(
 	/**
@@ -120,11 +124,35 @@ const keyedNestedConfig = (value, fn, customKeys) => {
 	return result;
 };
 
+/**
+ * @param {ReadonlyArray<WebpackOptions>} options input config
+ * @returns {ReadonlyArray<WebpackOptions>} normalized options
+ */
+const getNormalizedWebpackMultiCompilerOptions = options => {
+	/** @type {Array<WebpackOptions>} */
+	const resultedOptions = [];
+
+	for (let i = 0; i < options.length; i++) {
+		const config = options[i];
+		resultedOptions.push({
+			...config,
+			cache: optionalNestedConfig(config.cache, cache => {
+				if (typeof cache === "boolean") return cache;
+				if (i === 0 || cache.type !== "filesystem" || "name" in cache)
+					return { ...cache };
+				return { ...cache, name: `${defaultCacheName}__compiler${i + 1}__` };
+			})
+		});
+	}
+
+	return /** @type {ReadonlyArray<WebpackOptions>} */ (resultedOptions);
+};
+
 /**
  * @param {WebpackOptions} config input config
  * @returns {WebpackOptionsNormalized} normalized options
  */
-const getNormalizedWebpackOptions = config => {
+const getNormalizedWebpackCompilerOptions = config => {
 	return {
 		amd: config.amd,
 		bail: config.bail,
@@ -565,4 +593,9 @@ const getNormalizedOptimizationRuntimeChunk = runtimeChunk => {
 	};
 };
 
-exports.getNormalizedWebpackOptions = getNormalizedWebpackOptions;
+exports.getNormalizedWebpackMultiCompilerOptions =
+	getNormalizedWebpackMultiCompilerOptions;
+exports.getNormalizedWebpackCompilerOptions =
+	getNormalizedWebpackCompilerOptions;
+// for backward compatability
+exports.getNormalizedWebpackOptions = getNormalizedWebpackCompilerOptions;

lib/webpack.js

@@ -15,7 +15,10 @@ const {
 	applyWebpackOptionsDefaults,
 	applyWebpackOptionsBaseDefaults
 } = require("./config/defaults");
-const { getNormalizedWebpackOptions } = require("./config/normalization");
+const {
+	getNormalizedWebpackCompilerOptions,
+	getNormalizedWebpackMultiCompilerOptions
+} = require("./config/normalization");
 const NodeEnvironmentPlugin = require("./node/NodeEnvironmentPlugin");
 const memoize = require("./util/memoize");
 
@@ -42,7 +45,9 @@ const getValidateSchema = memoize(() => require("./validateSchema"));
  * @returns {MultiCompiler} a multi-compiler
  */
 const createMultiCompiler = (childOptions, options) => {
-	const compilers = childOptions.map(options => createCompiler(options));
+	const normalizedOptions =
+		getNormalizedWebpackMultiCompilerOptions(childOptions);
+	const compilers = normalizedOptions.map(options => createCompiler(options));
 	const compiler = new MultiCompiler(compilers, options);
 	for (const childCompiler of compilers) {
 		if (childCompiler.options.dependencies) {
@@ -60,7 +65,7 @@ const createMultiCompiler = (childOptions, options) => {
  * @returns {Compiler} a compiler
  */
 const createCompiler = rawOptions => {
-	const options = getNormalizedWebpackOptions(rawOptions);
+	const options = getNormalizedWebpackCompilerOptions(rawOptions);
 	applyWebpackOptionsBaseDefaults(options);
 	const compiler = new Compiler(
 		/** @type {string} */ (options.context),