| // Copyright (c) 2018, the Dart project authors. Please see the AUTHORS file |
| // for details. All rights reserved. Use of this source code is governed by a |
| // BSD-style license that can be found in the LICENSE file. |
| |
| import 'package:analyzer/dart/ast/ast.dart'; |
| import 'package:analyzer/dart/ast/visitor.dart'; |
| import 'package:analyzer/dart/element/type.dart'; |
| |
| import '../analyzer.dart'; |
| |
| const _desc = r'Avoid returning null for void.'; |
| |
| const _details = r''' |
| |
| **AVOID** returning null for void. |
| |
| In a large variety of languages `void` as return type is used to indicate that |
| a function doesn't return anything. Dart allows returning `null` in functions |
| with `void` return type but it also allow using `return;` without specifying any |
| value. To have a consistent way you should not return `null` and only use an |
| empty return. |
| |
| **BAD:** |
| ```dart |
| void f1() { |
| return null; |
| } |
| Future<void> f2() async { |
| return null; |
| } |
| ``` |
| |
| **GOOD:** |
| ```dart |
| void f1() { |
| return; |
| } |
| Future<void> f2() async { |
| return; |
| } |
| ``` |
| |
| '''; |
| |
| class AvoidReturningNullForVoid extends LintRule implements NodeLintRule { |
| AvoidReturningNullForVoid() |
| : super( |
| name: 'avoid_returning_null_for_void', |
| description: _desc, |
| details: _details, |
| group: Group.style); |
| |
| @override |
| void registerNodeProcessors( |
| NodeLintRegistry registry, LinterContext context) { |
| var visitor = _Visitor(this); |
| registry.addExpressionFunctionBody(this, visitor); |
| registry.addReturnStatement(this, visitor); |
| } |
| } |
| |
| class _Visitor extends SimpleAstVisitor<void> { |
| final LintRule rule; |
| |
| _Visitor(this.rule); |
| |
| @override |
| void visitExpressionFunctionBody(ExpressionFunctionBody node) { |
| _visit(node, node.expression); |
| } |
| |
| @override |
| void visitReturnStatement(ReturnStatement node) { |
| if (node.expression != null) { |
| _visit(node, node.expression); |
| } |
| } |
| |
| void _visit(AstNode node, Expression? expression) { |
| if (expression is! NullLiteral) { |
| return; |
| } |
| |
| var parent = node.thisOrAncestorMatching( |
| (e) => e is FunctionExpression || e is MethodDeclaration); |
| if (parent == null) return; |
| |
| DartType? type; |
| bool? isAsync; |
| if (parent is FunctionExpression) { |
| type = parent.declaredElement?.returnType; |
| isAsync = parent.body.isAsynchronous; |
| } else if (parent is MethodDeclaration) { |
| type = parent.declaredElement?.returnType; |
| isAsync = parent.body.isAsynchronous; |
| } else { |
| throw StateError('unexpected type'); |
| } |
| if (type == null) return; |
| |
| if (!isAsync && type.isVoid) { |
| rule.reportLint(node); |
| } else if (isAsync && |
| type.isDartAsyncFuture && |
| (type as InterfaceType).typeArguments.first.isVoid) { |
| rule.reportLint(node); |
| } |
| } |
| } |