| // 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/visitor.dart'; |
| import 'package:analyzer/dart/element/type.dart'; |
| import 'package:linter/src/analyzer.dart'; |
| import 'package:linter/src/util/dart_type_utilities.dart'; |
| |
| const _desc = |
| r'Avoid returning null from members whose return type is bool, double, int,' |
| r' or num.'; |
| |
| const _details = r''' |
| |
| **AVOID** returning null from members whose return type is bool, double, int, |
| or num. |
| |
| Functions that return primitive types such as bool, double, int, and num are |
| generally expected to return non-nullable values. Thus, returning null where a |
| primitive type was expected can lead to runtime exceptions. |
| |
| **BAD:** |
| ``` |
| bool getBool() => null; |
| num getNum() => null; |
| int getInt() => null; |
| double getDouble() => null; |
| ``` |
| |
| **GOOD:** |
| ``` |
| bool getBool() => false; |
| num getNum() => -1; |
| int getInt() => -1; |
| double getDouble() => -1.0; |
| ``` |
| |
| '''; |
| |
| bool _isFunctionExpression(AstNode node) => node is FunctionExpression; |
| |
| bool _isPrimitiveType(DartType type) => |
| DartTypeUtilities.isClass(type, 'bool', 'dart.core') || |
| DartTypeUtilities.isClass(type, 'num', 'dart.core') || |
| DartTypeUtilities.isClass(type, 'int', 'dart.core') || |
| DartTypeUtilities.isClass(type, 'double', 'dart.core'); |
| |
| bool _isReturnNull(AstNode node) => |
| node is ReturnStatement && DartTypeUtilities.isNullLiteral(node.expression); |
| |
| class AvoidReturningNull extends LintRule { |
| _Visitor _visitor; |
| AvoidReturningNull() |
| : super( |
| name: 'avoid_returning_null', |
| description: _desc, |
| details: _details, |
| group: Group.style) { |
| _visitor = new _Visitor(this); |
| } |
| |
| @override |
| AstVisitor getVisitor() => _visitor; |
| } |
| |
| class _Visitor extends SimpleAstVisitor { |
| final LintRule rule; |
| _Visitor(this.rule); |
| |
| @override |
| visitFunctionExpression(FunctionExpression node) { |
| if (_isPrimitiveType(node.element.returnType)) { |
| _visitFunctionBody(node.body); |
| } |
| } |
| |
| @override |
| visitMethodDeclaration(MethodDeclaration node) { |
| if (_isPrimitiveType(node.element.returnType)) { |
| _visitFunctionBody(node.body); |
| } |
| } |
| |
| _visitFunctionBody(FunctionBody node) { |
| if (node is ExpressionFunctionBody && |
| DartTypeUtilities.isNullLiteral(node.expression)) { |
| rule.reportLint(node); |
| return; |
| } |
| DartTypeUtilities |
| .traverseNodesInDFS(node, excludeCriteria: _isFunctionExpression) |
| .where(_isReturnNull) |
| .forEach(rule.reportLint); |
| } |
| } |