improve merging of resolve and parsing options

by rules and via loader API

Arrays overwrite by default, but can reference old value with "..."

lib/NormalModuleFactory.js

@@ -17,7 +17,7 @@ const {
 const NormalModule = require("./NormalModule");
 const RawModule = require("./RawModule");
 const RuleSet = require("./RuleSet");
-const cachedMerge = require("./util/cachedMerge");
+const { cachedCleverMerge } = require("./util/cleverMerge");
 
 const EMPTY_RESOLVE_OPTIONS = {};
 
@@ -304,7 +304,7 @@ class NormalModuleFactory extends Tapable {
 							typeof settings[r.type] === "object" &&
 							settings[r.type] !== null
 						) {
-							settings[r.type] = cachedMerge(settings[r.type], r.value);
+							settings[r.type] = cachedCleverMerge(settings[r.type], r.value);
 						} else {
 							settings[r.type] = r.value;
 						}

lib/ResolverFactory.js

@@ -6,6 +6,7 @@
 
 const { Tapable, HookMap, SyncHook, SyncWaterfallHook } = require("tapable");
 const Factory = require("enhanced-resolve").ResolverFactory;
+const { cachedCleverMerge } = require("./util/cleverMerge");
 
 /** @typedef {import("enhanced-resolve").Resolver} Resolver */
 
@@ -66,7 +67,7 @@ module.exports = class ResolverFactory extends Tapable {
 		resolver.withOptions = options => {
 			const cacheEntry = childCache.get(options);
 			if (cacheEntry !== undefined) return cacheEntry;
-			const mergedOptions = Object.assign({}, originalResolveOptions, options);
+			const mergedOptions = cachedCleverMerge(originalResolveOptions, options);
 			const resolver = this.get(type, mergedOptions);
 			childCache.set(options, resolver);
 			return resolver;

lib/WebpackOptionsApply.js

@@ -37,6 +37,8 @@ const RequireContextPlugin = require("./dependencies/RequireContextPlugin");
 const RequireEnsurePlugin = require("./dependencies/RequireEnsurePlugin");
 const RequireIncludePlugin = require("./dependencies/RequireIncludePlugin");
 
+const { cachedCleverMerge } = require("./util/cleverMerge");
+
 /** @typedef {import("../declarations/WebpackOptions").WebpackOptions} WebpackOptions */
 /** @typedef {import("./Compiler")} Compiler */
 
@@ -512,8 +514,7 @@ class WebpackOptionsApply extends OptionsApply {
 					{
 						fileSystem: compiler.inputFileSystem
 					},
-					options.resolve,
-					resolveOptions
+					cachedCleverMerge(options.resolve, resolveOptions)
 				);
 			});
 		compiler.resolverFactory.hooks.resolveOptions
@@ -524,8 +525,7 @@ class WebpackOptionsApply extends OptionsApply {
 						fileSystem: compiler.inputFileSystem,
 						resolveToContext: true
 					},
-					options.resolve,
-					resolveOptions
+					cachedCleverMerge(options.resolve, resolveOptions)
 				);
 			});
 		compiler.resolverFactory.hooks.resolveOptions
@@ -535,8 +535,7 @@ class WebpackOptionsApply extends OptionsApply {
 					{
 						fileSystem: compiler.inputFileSystem
 					},
-					options.resolveLoader,
-					resolveOptions
+					cachedCleverMerge(options.resolveLoader, resolveOptions)
 				);
 			});
 		compiler.hooks.afterResolvers.call(compiler);

lib/util/cleverMerge.js

@@ -0,0 +1,77 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+const mergeCache = new WeakMap();
+
+/**
+ * Merges two given objects and caches the result to avoid computation if same objects passed as arguments again.
+ * @example
+ * // performs cleverMerge(first, second), stores the result in WeakMap and returns result
+ * cachedCleverMerge({a: 1}, {a: 2})
+ * {a: 2}
+ *  // when same arguments passed, gets the result from WeakMap and returns it.
+ * cachedCleverMerge({a: 1}, {a: 2})
+ * {a: 2}
+ * @param {object} first first object
+ * @param {object} second second object
+ * @returns {object} merged object of first and second object
+ */
+const cachedCleverMerge = (first, second) => {
+	let innerCache = mergeCache.get(first);
+	if (innerCache === undefined) {
+		innerCache = new WeakMap();
+		mergeCache.set(first, innerCache);
+	}
+	const prevMerge = innerCache.get(second);
+	if (prevMerge !== undefined) return prevMerge;
+	const newMerge = cleverMerge(first, second);
+	innerCache.set(second, newMerge);
+	return newMerge;
+};
+
+/**
+ * Merges two objects. Objects are not deeply merged.
+ * TODO webpack 5: merge objects deeply clever.
+ * Arrays might reference the old value with "..."
+ * @param {object} first first object
+ * @param {object} second second object
+ * @returns {object} merged object of first and second object
+ */
+const cleverMerge = (first, second) => {
+	const newObject = Object.assign({}, first);
+	for (const key of Object.keys(second)) {
+		if (!(key in newObject)) {
+			newObject[key] = second[key];
+			continue;
+		}
+		const secondValue = second[key];
+		if (!Array.isArray(secondValue)) {
+			newObject[key] = secondValue;
+			continue;
+		}
+		const firstValue = newObject[key];
+		if (Array.isArray(firstValue)) {
+			const newArray = [];
+			for (const item of secondValue) {
+				if (item === "...") {
+					for (const item of firstValue) {
+						newArray.push(item);
+					}
+				} else {
+					newArray.push(item);
+				}
+			}
+			newObject[key] = newArray;
+		} else {
+			newObject[key] = secondValue;
+		}
+	}
+	return newObject;
+};
+
+exports.cachedCleverMerge = cachedCleverMerge;
+exports.cleverMerge = cleverMerge;

test/cases/loaders/resolve/index.js

@@ -2,6 +2,9 @@ it("should be possible to create resolver with different options", () => {
 	const result = require("./loader!");
 	expect(result).toEqual({
 		one: "index.js",
-		two: "index.xyz"
+		two: "index.xyz",
+		three: "index.js",
+		four: "index.xyz",
+		five: "index.js"
 	});
-})
+});

test/cases/loaders/resolve/loader.js

@@ -4,13 +4,28 @@ module.exports = function() {
 	const resolve2 = this.getResolve({
 		extensions: [".xyz", ".js"]
 	});
+	const resolve3 = this.getResolve({
+		extensions: [".hee", "..."]
+	});
+	const resolve4 = this.getResolve({
+		extensions: [".xyz", "..."]
+	});
+	const resolve5 = this.getResolve({
+		extensions: ["...", ".xyz"]
+	});
 	return Promise.all([
 		resolve1(__dirname, "./index"),
-		resolve2(__dirname, "./index")
-	]).then(([one, two]) => {
+		resolve2(__dirname, "./index"),
+		resolve3(__dirname, "./index"),
+		resolve4(__dirname, "./index"),
+		resolve5(__dirname, "./index")
+	]).then(([one, two, three, four, five]) => {
 		return `module.exports = ${JSON.stringify({
 			one: path.basename(one),
 			two: path.basename(two),
+			three: path.basename(three),
+			four: path.basename(four),
+			five: path.basename(five)
 		})}`;
 	});
 };

test/configCases/rule-set/resolve-options/a.js

@@ -1 +1 @@
-module.exports = require("./wrong");
+module.exports = require("./wrong") + require("./normal") + require("./wrong2");

test/configCases/rule-set/resolve-options/b.js

@@ -1 +1 @@
-module.exports = require("./wrong");
+module.exports = require("./wrong") + require("./normal") + require("./wrong2");

test/configCases/rule-set/resolve-options/c.js

@@ -0,0 +1 @@
+module.exports = require("./wrong") + require("./normal") + require("./wrong2");

test/configCases/rule-set/resolve-options/index.js

@@ -1,6 +1,8 @@
 it("should allow to set custom resolving rules", function() {
 	var a = require("./a");
-	expect(a).toBe("ok");
+	expect(a).toBe("ok-normal-wrong2");
 	var b = require("./b");
-	expect(b).toBe("wrong");
+	expect(b).toBe("ok-normal-wrong2-yes");
+	var c = require("./c");
+	expect(c).toBe("wrong-normal-ok2");
 });

test/configCases/rule-set/resolve-options/normal.js

@@ -0,0 +1 @@
+module.exports = "-normal-";

test/configCases/rule-set/resolve-options/ok.ok.js

@@ -0,0 +1 @@
+module.exports = "ok-ok";

test/configCases/rule-set/resolve-options/ok2.js

@@ -0,0 +1 @@
+module.exports = "ok2";

test/configCases/rule-set/resolve-options/ok2.yes.js

@@ -0,0 +1 @@
+module.exports = "ok2-yes";

test/configCases/rule-set/resolve-options/webpack.config.js

@@ -1,12 +1,33 @@
 module.exports = {
+	resolve: {
+		alias: {
+			"./wrong2": "./ok2"
+		}
+	},
 	module: {
 		rules: [
 			{
 				test: require.resolve("./a"),
 				resolve: {
 					alias: {
 						"./wrong": "./ok"
-					}
+					},
+					extensions: [".js", ".ok.js"]
+				}
+			},
+			{
+				test: require.resolve("./b"),
+				resolve: {
+					alias: {
+						"./wrong": "./ok"
+					},
+					extensions: ["...", ".ok.js"]
+				}
+			},
+			{
+				test: require.resolve("./b"),
+				resolve: {
+					extensions: [".yes.js", "..."]
 				}
 			}
 		]

test/configCases/rule-set/resolve-options/wrong2.js

@@ -0,0 +1 @@
+module.exports = "wrong2";

test/configCases/rule-set/resolve-options/wrong2.yes.js

@@ -0,0 +1 @@
+module.exports = "wrong2-yes";