only warn when there is really a casing difference

lib/CaseSensitiveModulesWarning.js

@@ -15,7 +15,7 @@ const WebpackError = require("./WebpackError");
  * @returns {Module[]} sorted version of original modules
  */
 const sortModules = modules => {
-	return modules.slice().sort((a, b) => {
+	return modules.sort((a, b) => {
 		const aIdent = a.identifier();
 		const bIdent = b.identifier();
 		/* istanbul ignore next */
@@ -52,11 +52,11 @@ const createModulesListMessage = (modules, moduleGraph) => {
 class CaseSensitiveModulesWarning extends WebpackError {
 	/**
 	 * Creates an instance of CaseSensitiveModulesWarning.
-	 * @param {Module[]} modules modules that were detected
+	 * @param {Iterable<Module>} modules modules that were detected
 	 * @param {ModuleGraph} moduleGraph the module graph
 	 */
 	constructor(modules, moduleGraph) {
-		const sortedModules = sortModules(modules);
+		const sortedModules = sortModules(Array.from(modules));
 		const modulesList = createModulesListMessage(sortedModules, moduleGraph);
 		super(`There are multiple modules with names that only differ in casing.
 This can lead to unexpected behavior when compiling on a filesystem with other case-semantic.

lib/WarnCaseSensitiveModulesPlugin.js

@@ -8,6 +8,7 @@
 const CaseSensitiveModulesWarning = require("./CaseSensitiveModulesWarning");
 
 /** @typedef {import("./Compiler")} Compiler */
+/** @typedef {import("./Module")} Module */
 
 class WarnCaseSensitiveModulesPlugin {
 	/**
@@ -20,21 +21,26 @@ class WarnCaseSensitiveModulesPlugin {
 			"WarnCaseSensitiveModulesPlugin",
 			compilation => {
 				compilation.hooks.seal.tap("WarnCaseSensitiveModulesPlugin", () => {
+					/** @type {Map<string, Map<string, Module>>} */
 					const moduleWithoutCase = new Map();
 					for (const module of compilation.modules) {
-						const identifier = module.identifier().toLowerCase();
-						const array = moduleWithoutCase.get(identifier);
-						if (array) {
-							array.push(module);
-						} else {
-							moduleWithoutCase.set(identifier, [module]);
+						const identifier = module.identifier();
+						const lowerIdentifier = identifier.toLowerCase();
+						let map = moduleWithoutCase.get(lowerIdentifier);
+						if (map === undefined) {
+							map = new Map();
+							moduleWithoutCase.set(lowerIdentifier, map);
 						}
+						map.set(identifier, module);
 					}
 					for (const pair of moduleWithoutCase) {
-						const array = pair[1];
-						if (array.length > 1) {
+						const map = pair[1];
+						if (map.size > 1) {
 							compilation.warnings.push(
-								new CaseSensitiveModulesWarning(array, compilation.moduleGraph)
+								new CaseSensitiveModulesWarning(
+									map.values(),
+									compilation.moduleGraph
+								)
 							);
 						}
 					}