| // Copyright (c) 2020, 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'; |
| |
| const _desc = r'Unnecessary null checks.'; |
| |
| const _details = r''' |
| **DON'T** apply a null check when a nullable value is accepted. |
| |
| **BAD:** |
| ```dart |
| f(int? i); |
| m() { |
| int? j; |
| f(j!); |
| } |
| |
| ``` |
| |
| **GOOD:** |
| ```dart |
| f(int? i); |
| m() { |
| int? j; |
| f(j); |
| } |
| ``` |
| |
| '''; |
| |
| DartType? getExpectedType(PostfixExpression node) { |
| var realNode = |
| node.thisOrAncestorMatching((e) => e.parent is! ParenthesizedExpression); |
| var parent = realNode?.parent; |
| var withAwait = parent is AwaitExpression; |
| if (withAwait) { |
| parent = parent.parent; |
| } |
| |
| // in return value |
| if (parent is ReturnStatement || parent is ExpressionFunctionBody) { |
| var parentExpression = parent?.thisOrAncestorOfType<FunctionExpression>(); |
| if (parentExpression == null) { |
| return null; |
| } |
| var staticType = parentExpression.staticType; |
| if (staticType is! FunctionType) { |
| return null; |
| } |
| staticType = staticType.returnType; |
| if (withAwait || parentExpression.body.keyword?.lexeme == 'async') { |
| return staticType.isDartAsyncFuture || staticType.isDartAsyncFutureOr |
| ? (staticType as ParameterizedType?)?.typeArguments.first |
| : null; |
| } else { |
| return staticType; |
| } |
| } |
| // in yield value |
| if (parent is YieldStatement) { |
| var parentExpression = parent.thisOrAncestorOfType<FunctionExpression>(); |
| if (parentExpression == null) { |
| return null; |
| } |
| var staticType = parentExpression.staticType; |
| if (staticType is! FunctionType) { |
| return null; |
| } |
| staticType = staticType.returnType; |
| return staticType.isDartCoreIterable || staticType.isDartAsyncStream |
| ? (staticType as ParameterizedType).typeArguments.first |
| : null; |
| } |
| // assignment |
| if (parent is AssignmentExpression && |
| parent.operator.type == TokenType.EQ && |
| (parent.leftHandSide is! Identifier || |
| node.operand is! Identifier || |
| (parent.leftHandSide as Identifier).name != |
| (node.operand as Identifier).name)) { |
| return parent.writeType; |
| } |
| // in variable declaration |
| if (parent is VariableDeclaration) { |
| return parent.declaredElement?.type; |
| } |
| // as right member of binary operator |
| if (parent is BinaryExpression && parent.rightOperand == realNode) { |
| var parentElement = parent.staticElement; |
| if (parentElement == null) { |
| return null; |
| } |
| return parentElement.parameters.first.type; |
| } |
| // as member of list |
| if (parent is ListLiteral) { |
| return (parent.staticType as ParameterizedType?)?.typeArguments.first; |
| } |
| // as member of set |
| if (parent is SetOrMapLiteral && parent.isSet) { |
| return (parent.staticType as ParameterizedType?)?.typeArguments.first; |
| } |
| // as member of map |
| if (parent is MapLiteralEntry) { |
| var grandParent = parent.parent; |
| while (true) { |
| if (grandParent is ForElement) { |
| grandParent = grandParent.parent; |
| } else if (grandParent is IfElement) { |
| grandParent = grandParent.parent; |
| } else if (grandParent is SetOrMapLiteral) { |
| var type = grandParent.staticType as InterfaceType?; |
| return type?.typeArguments[parent.key == node ? 0 : 1]; |
| } else { |
| return null; |
| } |
| } |
| } |
| // as parameter of function |
| if (parent is NamedExpression) { |
| realNode = parent; |
| parent = parent.parent; |
| } |
| if (parent is ArgumentList && realNode is Expression) { |
| return realNode.staticParameterElement?.type; |
| } |
| return null; |
| } |
| |
| class UnnecessaryNullChecks extends LintRule { |
| UnnecessaryNullChecks() |
| : super( |
| name: 'unnecessary_null_checks', |
| description: _desc, |
| details: _details, |
| maturity: Maturity.experimental, |
| group: Group.style); |
| |
| @override |
| void registerNodeProcessors( |
| NodeLintRegistry registry, LinterContext context) { |
| var visitor = _Visitor(this, context); |
| registry.addPostfixExpression(this, visitor); |
| } |
| } |
| |
| class _Visitor extends SimpleAstVisitor<void> { |
| final LintRule rule; |
| |
| final LinterContext context; |
| _Visitor(this.rule, this.context); |
| |
| @override |
| void visitPostfixExpression(PostfixExpression node) { |
| if (node.operator.type != TokenType.BANG) return; |
| |
| var expectedType = getExpectedType(node); |
| if (expectedType != null && context.typeSystem.isNullable(expectedType)) { |
| rule.reportLintForToken(node.operator); |
| } |
| } |
| } |