Merge pull request #6904 from webpack/performance/concat

avoid walking scopes multiple times for performance reasons

lib/optimize/ConcatenatedModule.js

@@ -168,17 +168,29 @@ const getFinalName = (
 	}
 };
 
-const getSymbolsFromScope = (s, untilScope) => {
+const addScopeSymbols1 = (s, nameSet, scopeSet) => {
-	const allUsedNames = new Set();
 	let scope = s;
 	while (scope) {
+		if (scopeSet.has(scope)) break;
+		scopeSet.add(scope);
 		for (const variable of scope.variables) {
-			allUsedNames.add(variable.name);
+			nameSet.add(variable.name);
+		}
+		scope = scope.upper;
+	}
+};
+
+const addScopeSymbols2 = (s, nameSet, scopeSet1, scopeSet2) => {
+	let scope = s;
+	while (scope) {
+		if (scopeSet1.has(scope)) break;
+		if (scopeSet2.has(scope)) break;
+		scopeSet1.add(scope);
+		for (const variable of scope.variables) {
+			nameSet.add(variable.name);
 		}
-		if (untilScope === scope) break;
 		scope = scope.upper;
 	}
-	return allUsedNames;
 };
 
 const getAllReferences = variable => {
@@ -196,11 +208,6 @@ const getAllReferences = variable => {
 	return set;
 };
 
-const reduceSet = (a, b) => {
-	for (const item of b) a.add(item);
-	return a;
-};
-
 const getPathInAst = (ast, node) => {
 	if (ast === node) {
 		return [];
@@ -816,8 +823,31 @@ class ConcatenatedModule extends Module {
 			"onsubmit"
 		]);
 
+		// Set of already checked scopes
+		const alreadyCheckedScopes = new Set();
+
 		// get all global names
 		for (const info of modulesWithInfo) {
+			const superClassExpressions = [];
+
+			// ignore symbols from moduleScope
+			if (info.moduleScope) {
+				alreadyCheckedScopes.add(info.moduleScope);
+
+				// The super class expression in class scopes behaves weird
+				// We store ranges of all super class expressions to make
+				// renaming to work correctly
+				for (const childScope of info.moduleScope.childScopes) {
+					if (childScope.type !== "class") continue;
+					if (!childScope.block.superClass) continue;
+					superClassExpressions.push({
+						range: childScope.block.superClass.range,
+						variables: childScope.variables
+					});
+				}
+			}
+
+			// add global symbols
 			if (info.globalScope) {
 				for (const reference of info.globalScope.through) {
 					const name = reference.identifier.name;
@@ -826,12 +856,21 @@ class ConcatenatedModule extends Module {
 							name
 						)
 					) {
-						for (const s of getSymbolsFromScope(
+						for (const expr of superClassExpressions) {
-							reference.from,
+							if (
-							info.moduleScope
+								expr.range[0] <= reference.identifier.range[0] &&
-						)) {
+								expr.range[1] >= reference.identifier.range[1]
-							allUsedNames.add(s);
+							) {
+								for (const variable of expr.variables) {
+									allUsedNames.add(variable.name);
 								}
+							}
+						}
+						addScopeSymbols1(
+							reference.from,
+							allUsedNames,
+							alreadyCheckedScopes
+						);
 					} else {
 						allUsedNames.add(name);
 					}
@@ -856,9 +895,16 @@ class ConcatenatedModule extends Module {
 						const name = variable.name;
 						if (allUsedNames.has(name)) {
 							const references = getAllReferences(variable);
-							const symbolsInReferences = references
+							const symbolsInReferences = new Set();
-								.map(ref => getSymbolsFromScope(ref.from, info.moduleScope))
+							const alreadyCheckedInnerScopes = new Set();
-								.reduce(reduceSet, new Set());
+							for (const ref of references) {
+								addScopeSymbols2(
+									ref.from,
+									symbolsInReferences,
+									alreadyCheckedInnerScopes,
+									alreadyCheckedScopes
+								);
+							}
 							const newName = this.findNewName(
 								name,
 								allUsedNames,

test/cases/scope-hoisting/renaming-4967/file1.js

@@ -6,5 +6,15 @@ export function test() {
 	function file1_js_a() {
 		return "fail";
 	}
+	function file1_a() {
+		return "fail";
+	}
 	return a();
 }
+
+function renaming_4967_file1_js_a() {
+	return "fail";
+}
+function renaming_4967_file1_a() {
+	return "fail";
+}