fix warnings

lib/MultiCompiler.js

@@ -8,6 +8,7 @@
 const asyncLib = require("neo-async");
 const { SyncHook, MultiHook } = require("tapable");
 
+const { defaultCacheName } = require("./config/defaults");
 const ConcurrentCompilationError = require("./ConcurrentCompilationError");
 const MultiStats = require("./MultiStats");
 const MultiWatching = require("./MultiWatching");
@@ -127,19 +128,21 @@ module.exports = class MultiCompiler {
 		for (const compiler of this.compilers) {
 			if (compiler.options.cache && "name" in compiler.options.cache) {
 				const name = compiler.options.cache.name;
-				const warn = /__compiler(\d+)__$/.test(name);
-				if (warn) {
-					addWarning(
-						compiler,
-						new WebpackError(
-							`${
-								compiler.name
-									? `Compiler with name "${compiler.name}" doesn't use unique cache name. `
-									: ""
-							}Please set unique "cache.name" option.`
-						)
-					);
-				}
+				const match = /(.+)__compiler(\d+)__$/.exec(name);
+				// if there is no match it is unique name
+				if (!match || match[1] === defaultCacheName) continue;
+				addWarning(
+					compiler,
+					new WebpackError(
+						`${
+							compiler.name
+								? `Compiler with name "${compiler.name}" doesn't use unique cache name. `
+								: ""
+						}Please set unique "cache.name" option. Name "${
+							match[1]
+						}" already used.`
+					)
+				);
 			}
 		}
 	}

test/configCases/cache-filesystem/multicompiler-mode-cache/webpack.config.js → test/configCases/cache-filesystem/multicompiler-mode-cache-1/webpack.config.js

@@ -1,5 +1,7 @@
 "use strict";
 
+// default settings. should just work
+
 /** @type {import("../../../../").Configuration} */
 module.exports = [
 	{

test/configCases/cache-filesystem/multicompiler-mode-cache-warning/webpack.config.js → test/configCases/cache-filesystem/multicompiler-mode-cache-2/webpack.config.js

@@ -1,5 +1,7 @@
 "use strict";
 
+// no cache names
+
 /** @type {import("../../../../").Configuration} */
 module.exports = [
 	{

test/configCases/cache-filesystem/multicompiler-mode-cache-3/index.js

@@ -0,0 +1 @@
+it("should build", () => {});

test/configCases/cache-filesystem/multicompiler-mode-cache-3/webpack.config.js

@@ -0,0 +1,32 @@
+"use strict";
+
+// with explicit cache names
+
+/** @type {import("../../../../").Configuration} */
+module.exports = [
+	{
+		mode: "production",
+		entry: "./index",
+		cache: {
+			name: "filesystem",
+			type: "filesystem"
+		}
+	},
+	{
+		mode: "production",
+		entry: "./index",
+		cache: {
+			name: "filesystem",
+			type: "filesystem"
+		}
+	},
+	{
+		name: "3rd compiler",
+		mode: "production",
+		entry: "./index",
+		cache: {
+			name: "filesystem",
+			type: "filesystem"
+		}
+	}
+];