Allow functions to redeclare vars and functions in function scopes

src/ast/scopes/CatchBodyScope.ts

@@ -70,13 +70,6 @@ export default class CatchBodyScope extends ChildScope {
 			this.addHoistedVariable(name, declaredVariable);
 			return declaredVariable;
 		}
-		// Functions can never re-declare catch parameters
-		if (kind === VariableKind.function) {
-			const name = identifier.name;
-			if (this.hoistedVariables?.get(name)) {
-				context.error(logRedeclarationError(name), identifier.start);
-			}
-		}
 		return super.addDeclaration(identifier, context, init, kind);
 	}
 }

src/ast/scopes/FunctionBodyScope.ts

@@ -0,0 +1,46 @@
+import type { AstContext } from '../../Module';
+import { logRedeclarationError } from '../../utils/logs';
+import type Identifier from '../nodes/Identifier';
+import type { ExpressionEntity } from '../nodes/shared/Expression';
+import { VariableKind } from '../nodes/shared/VariableKinds';
+import LocalVariable from '../variables/LocalVariable';
+import ChildScope from './ChildScope';
+import type ParameterScope from './ParameterScope';
+
+export default class FunctionBodyScope extends ChildScope {
+	constructor(
+		readonly parent: ParameterScope,
+		readonly context: AstContext
+	) {
+		super(parent, context);
+	}
+
+	// There is stuff that is only allowed in function scopes, i.e. functions can
+	// be redeclared, functions and var can redeclare each other
+	addDeclaration(
+		identifier: Identifier,
+		context: AstContext,
+		init: ExpressionEntity,
+		kind: VariableKind
+	): LocalVariable {
+		const name = identifier.name;
+		const existingVariable =
+			this.hoistedVariables?.get(name) || (this.variables.get(name) as LocalVariable);
+		if (existingVariable) {
+			const existingKind = existingVariable.kind;
+			if (
+				(kind === VariableKind.var || kind === VariableKind.function) &&
+				(existingKind === VariableKind.var ||
+					existingKind === VariableKind.function ||
+					existingKind === VariableKind.parameter)
+			) {
+				existingVariable.addDeclaration(identifier, init);
+				return existingVariable;
+			}
+			context.error(logRedeclarationError(name), identifier.start);
+		}
+		const newVariable = new LocalVariable(identifier.name, identifier, init, context, kind);
+		this.variables.set(name, newVariable);
+		return newVariable;
+	}
+}

src/ast/scopes/ParameterScope.ts

@@ -7,6 +7,7 @@ import type { ExpressionEntity } from '../nodes/shared/Expression';
 import ParameterVariable from '../variables/ParameterVariable';
 import CatchBodyScope from './CatchBodyScope';
 import ChildScope from './ChildScope';
+import FunctionBodyScope from './FunctionBodyScope';
 import type Scope from './Scope';
 
 export default class ParameterScope extends ChildScope {
@@ -19,7 +20,7 @@ export default class ParameterScope extends ChildScope {
 		super(parent, context);
 		this.bodyScope = isCatchScope
 			? new CatchBodyScope(this, context)
-			: new ChildScope(this, context);
+			: new FunctionBodyScope(this, context);
 	}
 
 	/**

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
@@ -34,11 +35,7 @@ export default class Scope {
 			this.hoistedVariables?.get(name) || (this.variables.get(name) as LocalVariable);
 		if (existingVariable) {
 			const existingKind = existingVariable.kind;
-			if (
-				(kind === VariableKind.var &&
-					(existingKind === VariableKind.var || existingKind === VariableKind.parameter)) ||
-				(kind === VariableKind.function && existingKind === VariableKind.parameter)
-			) {
+			if (kind === VariableKind.var && existingKind === VariableKind.var) {
 				existingVariable.addDeclaration(identifier, init);
 				return existingVariable;
 			}

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

@@ -0,0 +1,24 @@
+const path = require('node:path');
+const ID_MAIN = path.join(__dirname, 'main.js');
+
+module.exports = defineTest({
+	description: 'throws when redeclaring a function binding as a function in a block scope',
+	error: {
+		code: 'REDECLARATION_ERROR',
+		frame: `
+			1: {
+			2:   function foo() {}
+			3:   function foo() {}
+			              ^
+			4: }`,
+		id: ID_MAIN,
+		loc: {
+			column: 10,
+			file: ID_MAIN,
+			line: 3
+		},
+		message: 'Identifier "foo" has already been declared',
+		pos: 31,
+		watchFiles: [ID_MAIN]
+	}
+});

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

@@ -0,0 +1,4 @@
+{
+	function foo() {}
+	function foo() {}
+}

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();