validate compiler options in multicompiler mode

lib/MultiCompiler.js

@@ -11,6 +11,7 @@ const { SyncHook, MultiHook } = require("tapable");
 const ConcurrentCompilationError = require("./ConcurrentCompilationError");
 const MultiStats = require("./MultiStats");
 const MultiWatching = require("./MultiWatching");
+const WebpackError = require("./WebpackError");
 const ArrayQueue = require("./util/ArrayQueue");
 
 /** @template T @typedef {import("tapable").AsyncSeriesHook<T>} AsyncSeriesHook<T> */
@@ -104,6 +105,34 @@ module.exports = class MultiCompiler {
 				}
 			});
 		}
+		this._validateCompilersOptions();
+	}
+
+	_validateCompilersOptions() {
+		if (this.compilers.length < 2) return;
+		const cacheNames = new Set();
+		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)) {
+					addWarning(
+						compiler,
+						new WebpackError(
+							`Compiler cache with name ${JSON.stringify(
+								cacheName
+							)} is already defined. Please set unique "cache.name" option.`
+						)
+					);
+				} else {
+					cacheNames.add(cacheName);
+				}
+			}
+		}
 	}
 
 	get options() {

test/StatsTestCases.basictest.js

@@ -78,6 +78,17 @@ describe("StatsTestCases", () => {
 				if (!options.optimization) options.optimization = {};
 				if (options.optimization.minimize === undefined)
 					options.optimization.minimize = false;
+				if (
+					options.cache &&
+					options.cache !== true &&
+					options.cache.type === "filesystem"
+				) {
+					options.cache.cacheLocation = path.resolve(
+						outputBase,
+						".cache",
+						testName
+					);
+				}
 			});
 			const c = webpack(options);
 			const compilers = c.compilers ? c.compilers : [c];

test/__snapshots__/StatsTestCases.basictest.js.snap

@@ -1620,6 +1620,19 @@ You may need an appropriate loader to handle this file type, currently no loader
 webpack x.x.x compiled with 2 errors in X ms"
 `;
 
+exports[`StatsTestCases should print correct stats for multicompiler-mode-cache 1`] = `
+"1 asset
+1 module
+webpack x.x.x compiled successfully in X ms
+
+1 asset
+1 module
+
+WARNING in Compiler cache with name \\"name1\\" is already defined. Please set unique \\"cache.name\\" option.
+
+webpack x.x.x compiled with 1 warning in X ms"
+`;
+
 exports[`StatsTestCases should print correct stats for named-chunk-groups 1`] = `
 "Chunk Group main 11.7 KiB = a-main.js
 Chunk Group async-a 1.07 KiB = a-52.js 257 bytes a-async-a.js 836 bytes

test/statsCases/multicompiler-mode-cache/webpack.config.js

@@ -0,0 +1,23 @@
+"use strict";
+
+/** @type {import("../../../").Configuration} */
+module.exports = [
+	{
+		mode: "production",
+		entry: "./index",
+		cache: {
+			type: "filesystem",
+			name: "name1"
+		},
+		stats: { preset: "minimal" }
+	},
+	{
+		mode: "production",
+		entry: "./index",
+		cache: {
+			type: "filesystem",
+			name: "name1"
+		},
+		stats: { preset: "minimal" }
+	}
+];