| // Copyright (c) 2015, 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' |
| show AsExpression, AstNode, AstVisitor, NamedType; |
| import 'package:analyzer/dart/ast/visitor.dart'; |
| import 'package:linter/src/analyzer.dart'; |
| |
| const _desc = r'Avoid using `as`.'; |
| |
| const _details = r''' |
| |
| From the [flutter style guide](https://github.com/flutter/engine/blob/master/sky/specs/style-guide.md): |
| |
| **AVOID** using `as`. |
| |
| If you know the type is correct, use an assertion or assign to a more |
| narrowly-typed variable (this avoids the type check in release mode; `as` is not |
| compiled out in release mode). If you don't know whether the type is |
| correct, check using `is` (this avoids the exception that `as` raises). |
| |
| **BAD:** |
| ``` |
| (pm as Person).firstName = 'Seth'; |
| ``` |
| |
| **GOOD:** |
| ``` |
| Person person = pm; |
| person.firstName = 'Seth'; |
| ``` |
| |
| or |
| |
| **GOOD:** |
| ``` |
| if (pm is Person) |
| pm.firstName = 'Seth'; |
| ``` |
| |
| but certainly not |
| |
| **BAD:** |
| ``` |
| try { |
| (pm as Person).firstName = 'Seth'; |
| } on CastError { } |
| |
| ``` |
| |
| Note that an exception is made in the case of `dynamic` since the cast has no |
| performance impact. |
| |
| **OK:** |
| ``` |
| HasScrollDirection scrollable = renderObject as dynamic; |
| ``` |
| |
| '''; |
| |
| class AvoidAs extends LintRule { |
| AvoidAs() |
| : super( |
| name: 'avoid_as', |
| description: _desc, |
| details: _details, |
| group: Group.style); |
| |
| @override |
| AstVisitor getVisitor() => new Visitor(this); |
| } |
| |
| class Visitor extends SimpleAstVisitor { |
| final LintRule rule; |
| Visitor(this.rule); |
| |
| @override |
| visitAsExpression(AsExpression node) { |
| // TODO(brianwilkerson) Use TypeAnnotation rather than AstNode below. |
| AstNode typeAnnotation = node.type; |
| if (typeAnnotation is NamedType && typeAnnotation.name.name != 'dynamic') { |
| rule.reportLint(node); |
| } |
| } |
| } |