| // Copyright (c) 2019, 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/token.dart'; |
| import 'package:analyzer/dart/ast/visitor.dart'; |
| |
| import '../analyzer.dart'; |
| |
| const _desc = r'Prefer using null aware operators.'; |
| |
| const _details = r''' |
| |
| Prefer using null aware operators instead of null checks in conditional |
| expressions. |
| |
| **BAD:** |
| ```dart |
| v = a == null ? null : a.b; |
| ``` |
| |
| **GOOD:** |
| ```dart |
| v = a?.b; |
| ``` |
| |
| '''; |
| |
| class PreferNullAwareOperators extends LintRule implements NodeLintRule { |
| PreferNullAwareOperators() |
| : super( |
| name: 'prefer_null_aware_operators', |
| description: _desc, |
| details: _details, |
| group: Group.style); |
| |
| @override |
| void registerNodeProcessors( |
| NodeLintRegistry registry, LinterContext context) { |
| var visitor = _Visitor(this); |
| registry.addConditionalExpression(this, visitor); |
| } |
| } |
| |
| class _Visitor extends SimpleAstVisitor { |
| final LintRule rule; |
| |
| _Visitor(this.rule); |
| |
| @override |
| void visitConditionalExpression(ConditionalExpression node) { |
| var condition = node.condition; |
| if (condition is BinaryExpression && |
| (condition.operator.type == TokenType.EQ_EQ || |
| condition.operator.type == TokenType.BANG_EQ)) { |
| // ensure pattern `xx == null ? null : yy` or `xx != null ? yy : null` |
| if (condition.operator.type == TokenType.EQ_EQ) { |
| if (node.thenExpression is! NullLiteral) { |
| return; |
| } |
| } else { |
| if (node.elseExpression is! NullLiteral) { |
| return; |
| } |
| } |
| |
| // ensure condition is a null check |
| Expression expression; |
| if (condition.leftOperand is NullLiteral) { |
| expression = condition.rightOperand; |
| } else if (condition.rightOperand is NullLiteral) { |
| expression = condition.leftOperand; |
| } else { |
| return; |
| } |
| |
| Expression? exp = condition.operator.type == TokenType.EQ_EQ |
| ? node.elseExpression |
| : node.thenExpression; |
| while (exp is PrefixedIdentifier || |
| exp is MethodInvocation || |
| exp is PropertyAccess) { |
| if (exp is PrefixedIdentifier) { |
| exp = exp.prefix; |
| } else if (exp is MethodInvocation) { |
| exp = exp.target; |
| } else if (exp is PropertyAccess) { |
| exp = exp.target; |
| } |
| if (exp.toString() == expression.toString()) { |
| rule.reportLint(node); |
| return; |
| } |
| } |
| } |
| } |
| } |