Allow functions to redeclare vars and functions in function scopes

src/ast/scopes/ModuleScope.ts

@@ -30,8 +30,12 @@ export default class ModuleScope extends ChildScope {
 		init: ExpressionEntity,
 		kind: VariableKind
 	): LocalVariable {
-		if (this.context.module.importDescriptions.has(identifier.name)) {
-			context.error(logRedeclarationError(identifier.name), identifier.start);
+		const name = identifier.name;
+		if (
+			this.context.module.importDescriptions.has(name) ||
+			(this.variables.has(name) && kind === VariableKind.function)
+		) {
+			context.error(logRedeclarationError(name), identifier.start);
 		}
 		return super.addDeclaration(identifier, context, init, kind);
 	}

src/ast/scopes/Scope.ts

@@ -15,6 +15,7 @@ export default class Scope {
 	/*
 	Redeclaration rules:
 	- var can redeclare var
+	- in function scopes, function and var can redeclare function and var
 	- var is hoisted across scopes, function remains in the scope it is declared
 	- var and function can redeclare function parameters, but parameters cannot redeclare parameters
 	- function cannot redeclare catch scope parameters
@@ -35,9 +36,10 @@ export default class Scope {
 		if (existingVariable) {
 			const existingKind = existingVariable.kind;
 			if (
-				(kind === VariableKind.var &&
-					(existingKind === VariableKind.var || existingKind === VariableKind.parameter)) ||
-				(kind === VariableKind.function && existingKind === VariableKind.parameter)
+				(kind === VariableKind.var || kind === VariableKind.function) &&
+				(existingKind === VariableKind.var ||
+					existingKind === VariableKind.function ||
+					existingKind === VariableKind.parameter)
 			) {
 				existingVariable.addDeclaration(identifier, init);
 				return existingVariable;

test/function/samples/ast-validations/redeclare-top-level-function-function/_config.js

@@ -0,0 +1,22 @@
+const path = require('node:path');
+const ID_MAIN = path.join(__dirname, 'main.js');
+
+module.exports = defineTest({
+	description: 'throws when redeclaring a top-level function binding as a function',
+	error: {
+		code: 'REDECLARATION_ERROR',
+		frame: `
+			1: function foo() {}
+			2: function foo() {}
+			            ^`,
+		id: ID_MAIN,
+		loc: {
+			column: 9,
+			file: ID_MAIN,
+			line: 2
+		},
+		message: 'Identifier "foo" has already been declared',
+		pos: 27,
+		watchFiles: [ID_MAIN]
+	}
+});

test/function/samples/ast-validations/redeclare-top-level-function-function/main.js

@@ -0,0 +1,2 @@
+function foo() {}
+function foo() {}

test/function/samples/ast-validations/redeclare-top-level-var-function/_config.js

@@ -0,0 +1,22 @@
+const path = require('node:path');
+const ID_MAIN = path.join(__dirname, 'main.js');
+
+module.exports = defineTest({
+	description: 'throws when redeclaring a top-level var binding as a function',
+	error: {
+		code: 'REDECLARATION_ERROR',
+		frame: `
+			1: var foo;
+			2: function foo() {}
+			            ^`,
+		id: ID_MAIN,
+		loc: {
+			column: 9,
+			file: ID_MAIN,
+			line: 2
+		},
+		message: 'Identifier "foo" has already been declared',
+		pos: 18,
+		watchFiles: [ID_MAIN]
+	}
+});

test/function/samples/ast-validations/redeclare-top-level-var-function/main.js

@@ -0,0 +1,2 @@
+var foo;
+function foo() {}

test/function/samples/ast-validations/redeclare-var-function/_config.js

@@ -0,0 +1,3 @@
+module.exports = defineTest({
+	description: 'allows to redeclare vars and functions as vars and functions in function scopes'
+});

test/function/samples/ast-validations/redeclare-var-function/main.js

@@ -0,0 +1,10 @@
+function foo() {
+	var fn = 1;
+	function fn() {}
+	function fn() {}
+	var fn = 2;
+
+	assert.equal(fn, 2);
+}
+
+foo();