| // Copyright (c) 2017, 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 'package:linter/src/analyzer.dart'; |
| import 'package:linter/src/util/dart_type_utilities.dart'; |
| |
| const _desc = r'Prefer using `??=` over testing for null.'; |
| |
| const _details = r''' |
| |
| **PREFER** using `??=` over testing for null. |
| |
| As Dart has the `??=` operator, it is advisable to use it where applicable to |
| improve the brevity of your code. |
| |
| **BAD:** |
| ``` |
| String get fullName { |
| if (_fullName == null) { |
| _fullName = getFullUserName(this); |
| } |
| return _fullName; |
| } |
| ``` |
| |
| **GOOD:** |
| ``` |
| String get fullName { |
| return _fullName ??= getFullUserName(this);; |
| } |
| ``` |
| |
| '''; |
| |
| bool _checkExpression(Expression expression, Expression condition) => |
| expression is AssignmentExpression && |
| DartTypeUtilities.canonicalElementsFromIdentifiersAreEqual( |
| expression.leftHandSide, condition); |
| |
| bool _checkStatement(Statement statement, Expression condition) { |
| if (statement is ExpressionStatement) { |
| return _checkExpression(statement.expression, condition); |
| } |
| if (statement is Block && statement.statements.length == 1) { |
| return _checkStatement(statement.statements.first, condition); |
| } |
| return false; |
| } |
| |
| Expression _getExpressionCondition(Expression rawExpression) { |
| final expression = rawExpression.unParenthesized; |
| if (expression is BinaryExpression && |
| expression.operator.type == TokenType.EQ_EQ) { |
| if (DartTypeUtilities.isNullLiteral(expression.rightOperand)) { |
| return expression.leftOperand; |
| } |
| if (DartTypeUtilities.isNullLiteral(expression.leftOperand)) { |
| return expression.rightOperand; |
| } |
| } |
| return null; |
| } |
| |
| class PreferConditionalAssignment extends LintRule implements NodeLintRule { |
| PreferConditionalAssignment() |
| : super( |
| name: 'prefer_conditional_assignment', |
| description: _desc, |
| details: _details, |
| group: Group.style); |
| |
| @override |
| void registerNodeProcessors(NodeLintRegistry registry, |
| [LinterContext context]) { |
| final visitor = new _Visitor(this); |
| registry.addIfStatement(this, visitor); |
| } |
| } |
| |
| class _Visitor extends SimpleAstVisitor<void> { |
| final LintRule rule; |
| |
| _Visitor(this.rule); |
| |
| @override |
| void visitIfStatement(IfStatement node) { |
| if (node.elseStatement != null) { |
| return; |
| } |
| final expressionInCondition = _getExpressionCondition(node.condition); |
| if (expressionInCondition != null && |
| _checkStatement(node.thenStatement, expressionInCondition)) { |
| rule.reportLint(node); |
| } |
| } |
| } |