| // Copyright (c) 2016, 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:analyzer/dart/element/type.dart'; |
| |
| import '../analyzer.dart'; |
| import '../util/dart_type_utilities.dart'; |
| |
| const alwaysFalse = 'Always false because length is always greater or equal 0.'; |
| |
| const alwaysTrue = 'Always true because length is always greater or equal 0.'; |
| |
| const useIsEmpty = 'Use isEmpty instead of length'; |
| const useIsNotEmpty = 'Use isNotEmpty instead of length'; |
| const _desc = r'Use `isEmpty` for Iterables and Maps.'; |
| const _details = r''' |
| |
| **DON'T** use `length` to see if a collection is empty. |
| |
| The `Iterable` contract does not require that a collection know its length or be |
| able to provide it in constant time. Calling `length` just to see if the |
| collection contains anything can be painfully slow. |
| |
| Instead, there are faster and more readable getters: `isEmpty` and |
| `isNotEmpty`. Use the one that doesn't require you to negate the result. |
| |
| **GOOD:** |
| ``` |
| if (lunchBox.isEmpty) return 'so hungry...'; |
| if (words.isNotEmpty) return words.join(' '); |
| ``` |
| |
| **BAD:** |
| ``` |
| if (lunchBox.length == 0) return 'so hungry...'; |
| if (words.length != 0) return words.join(' '); |
| ``` |
| |
| '''; |
| |
| class PreferIsEmpty extends LintRule implements NodeLintRule { |
| PreferIsEmpty() |
| : super( |
| name: 'prefer_is_empty', |
| description: _desc, |
| details: _details, |
| group: Group.style); |
| |
| @override |
| void registerNodeProcessors( |
| NodeLintRegistry registry, LinterContext context) { |
| final visitor = _Visitor(this, context); |
| registry.addSimpleIdentifier(this, visitor); |
| } |
| |
| void reportLintWithDescription(AstNode node, String description) { |
| if (node != null) { |
| reporter.reportErrorForNode(_LintCode(name, description), node, []); |
| } |
| } |
| } |
| |
| class _LintCode extends LintCode { |
| static final registry = <String, _LintCode>{}; |
| |
| factory _LintCode(String name, String message) => |
| registry.putIfAbsent(name + message, () => _LintCode._(name, message)); |
| |
| _LintCode._(String name, String message) : super(name, message); |
| } |
| |
| class _Visitor extends SimpleAstVisitor<void> { |
| final PreferIsEmpty rule; |
| |
| final LinterContext context; |
| |
| _Visitor(this.rule, this.context); |
| |
| @override |
| void visitSimpleIdentifier(SimpleIdentifier identifier) { |
| // Should be "length". |
| final propertyElement = identifier.staticElement; |
| if (propertyElement?.name != 'length') { |
| return; |
| } |
| |
| AstNode lengthAccess; |
| InterfaceType type; |
| |
| final parent = identifier.parent; |
| if (parent is PropertyAccess && identifier == parent.propertyName) { |
| lengthAccess = parent; |
| var parentType = parent.target?.staticType; |
| if (parentType is InterfaceType) { |
| type = parentType; |
| } |
| } else if (parent is PrefixedIdentifier && |
| identifier == parent.identifier) { |
| lengthAccess = parent; |
| var parentType = parent.prefix.staticType; |
| if (parentType is InterfaceType) { |
| type = parentType; |
| } |
| } |
| |
| if (type == null) { |
| return; |
| } |
| |
| // Should be subtype of Iterable, Map or String. |
| if (!DartTypeUtilities.implementsInterface(type, 'Iterable', 'dart.core') && |
| !DartTypeUtilities.implementsInterface(type, 'Map', 'dart.core') && |
| !type.isDartCoreString) { |
| return; |
| } |
| |
| var search = lengthAccess; |
| while ( |
| search != null && search is Expression && search is! BinaryExpression) { |
| search = search.parent; |
| } |
| |
| if (search is! BinaryExpression) { |
| return; |
| } |
| final binaryExpression = search as BinaryExpression; |
| |
| final operator = binaryExpression.operator; |
| |
| // Comparing constants with length. |
| var value = _getIntValue(binaryExpression.rightOperand); |
| |
| if (value != null) { |
| // Constant is on right side of comparison operator. |
| if (value == 0) { |
| if (operator.type == TokenType.EQ_EQ || |
| operator.type == TokenType.LT_EQ) { |
| rule.reportLintWithDescription(binaryExpression, useIsEmpty); |
| } else if (operator.type == TokenType.GT || |
| operator.type == TokenType.BANG_EQ) { |
| rule.reportLintWithDescription(binaryExpression, useIsNotEmpty); |
| } else if (operator.type == TokenType.LT) { |
| rule.reportLintWithDescription(binaryExpression, alwaysFalse); |
| } else if (operator.type == TokenType.GT_EQ) { |
| rule.reportLintWithDescription(binaryExpression, alwaysTrue); |
| } |
| } else if (value == 1) { |
| // 'length >= 1' is same as 'isNotEmpty', |
| // and 'length < 1' is same as 'isEmpty' |
| if (operator.type == TokenType.GT_EQ) { |
| rule.reportLintWithDescription(binaryExpression, useIsNotEmpty); |
| } else if (operator.type == TokenType.LT) { |
| rule.reportLintWithDescription(binaryExpression, useIsEmpty); |
| } |
| } else if (value < 0) { |
| // 'length' is always >= 0, so comparing with negative makes no sense. |
| if (operator.type == TokenType.EQ_EQ || |
| operator.type == TokenType.LT_EQ || |
| operator.type == TokenType.LT) { |
| rule.reportLintWithDescription(binaryExpression, alwaysFalse); |
| } else if (operator.type == TokenType.BANG_EQ || |
| operator.type == TokenType.GT_EQ || |
| operator.type == TokenType.GT) { |
| rule.reportLintWithDescription(binaryExpression, alwaysTrue); |
| } |
| } |
| return; |
| } |
| |
| value = _getIntValue(binaryExpression.leftOperand); |
| |
| // ignore: invariant_booleans |
| if (value != null) { |
| // Constant is on left side of comparison operator. |
| if (value == 0) { |
| if (operator.type == TokenType.EQ_EQ || |
| operator.type == TokenType.GT_EQ) { |
| rule.reportLintWithDescription(binaryExpression, useIsEmpty); |
| } else if (operator.type == TokenType.LT || |
| operator.type == TokenType.BANG_EQ) { |
| rule.reportLintWithDescription(binaryExpression, useIsNotEmpty); |
| } else if (operator.type == TokenType.GT) { |
| rule.reportLintWithDescription(binaryExpression, alwaysFalse); |
| } else if (operator.type == TokenType.LT_EQ) { |
| rule.reportLintWithDescription(binaryExpression, alwaysTrue); |
| } |
| } else if (value == 1) { |
| // '1 <= length' is same as 'isNotEmpty', |
| // and '1 > length' is same as 'isEmpty' |
| if (operator.type == TokenType.LT_EQ) { |
| rule.reportLintWithDescription(binaryExpression, useIsNotEmpty); |
| } else if (operator.type == TokenType.GT) { |
| rule.reportLintWithDescription(binaryExpression, useIsEmpty); |
| } |
| } else if (value < 0) { |
| // 'length' is always >= 0, so comparing with negative makes no sense. |
| if (operator.type == TokenType.EQ_EQ || |
| operator.type == TokenType.GT_EQ || |
| operator.type == TokenType.GT) { |
| rule.reportLintWithDescription(binaryExpression, alwaysFalse); |
| } else if (operator.type == TokenType.BANG_EQ || |
| operator.type == TokenType.LT_EQ || |
| operator.type == TokenType.LT) { |
| rule.reportLintWithDescription(binaryExpression, alwaysTrue); |
| } |
| } |
| } |
| } |
| |
| /// Returns the value of an [IntegerLiteral] or [PrefixExpression] with a |
| /// minus and then an [IntegerLiteral]. For anything else, returns `null`. |
| int _getIntValue(Expression expressions) { |
| if (expressions is IntegerLiteral) { |
| return expressions.value; |
| } else if (expressions is PrefixExpression) { |
| var operand = expressions.operand; |
| if (expressions.operator.type == TokenType.MINUS && |
| operand is IntegerLiteral) { |
| return -operand.value; |
| } |
| } |
| // ignore: avoid_returning_null |
| return null; |
| } |
| } |