| // 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/analysis/features.dart'; |
| import 'package:analyzer/dart/ast/ast.dart'; |
| import 'package:analyzer/dart/ast/visitor.dart'; |
| import 'package:analyzer/dart/element/element.dart'; |
| |
| import '../analyzer.dart'; |
| import '../extensions.dart'; |
| import '../util/dart_type_utilities.dart'; |
| |
| const _desc = r"Don't create a lambda when a tear-off will do."; |
| |
| const _details = r''' |
| **DON'T** create a lambda when a tear-off will do. |
| |
| **BAD:** |
| ```dart |
| names.forEach((name) { |
| print(name); |
| }); |
| ``` |
| |
| **GOOD:** |
| ```dart |
| names.forEach(print); |
| ``` |
| |
| '''; |
| |
| Set<Element?> _extractElementsOfSimpleIdentifiers(AstNode node) => |
| _IdentifierVisitor().extractElements(node); |
| |
| class UnnecessaryLambdas extends LintRule { |
| static const LintCode code = LintCode( |
| 'unnecessary_lambdas', 'Closure should be a tearoff.', |
| correctionMessage: 'Try using a tearoff rather than a closure.'); |
| |
| UnnecessaryLambdas() |
| : super( |
| name: 'unnecessary_lambdas', |
| description: _desc, |
| details: _details, |
| group: Group.style); |
| |
| @override |
| LintCode get lintCode => code; |
| |
| @override |
| void registerNodeProcessors( |
| NodeLintRegistry registry, LinterContext context) { |
| var visitor = _Visitor(this, context); |
| registry.addFunctionExpression(this, visitor); |
| } |
| } |
| |
| class _FinalExpressionChecker { |
| final Set<ParameterElement?> parameters; |
| |
| _FinalExpressionChecker(this.parameters); |
| |
| bool isFinalNode(Expression? node_) { |
| if (node_ == null) { |
| return true; |
| } |
| |
| var node = node_.unParenthesized; |
| |
| if (node is FunctionExpression) { |
| var referencedElements = _extractElementsOfSimpleIdentifiers(node); |
| return !referencedElements.any(parameters.contains); |
| } |
| |
| if (node is PrefixedIdentifier) { |
| return isFinalNode(node.prefix) && isFinalNode(node.identifier); |
| } |
| |
| if (node is PropertyAccess) { |
| return isFinalNode(node.target) && isFinalNode(node.propertyName); |
| } |
| |
| if (node is SimpleIdentifier) { |
| var element = node.staticElement; |
| if (parameters.contains(element)) { |
| return false; |
| } |
| return element.isFinal; |
| } |
| |
| return false; |
| } |
| } |
| |
| class _IdentifierVisitor extends RecursiveAstVisitor { |
| final _elements = <Element?>{}; |
| |
| _IdentifierVisitor(); |
| |
| Set<Element?> extractElements(AstNode node) { |
| node.accept(this); |
| return _elements; |
| } |
| |
| @override |
| visitSimpleIdentifier(SimpleIdentifier node) { |
| _elements.add(node.staticElement); |
| super.visitSimpleIdentifier(node); |
| } |
| } |
| |
| class _Visitor extends SimpleAstVisitor<void> { |
| final bool constructorTearOffsEnabled; |
| final LintRule rule; |
| final TypeSystem typeSystem; |
| |
| _Visitor(this.rule, LinterContext context) |
| : constructorTearOffsEnabled = context.libraryElement!.featureSet |
| .isEnabled(Feature.constructor_tearoffs), |
| typeSystem = context.typeSystem; |
| |
| @override |
| void visitFunctionExpression(FunctionExpression node) { |
| if (node.declaredElement?.name != '' || node.body.keyword != null) { |
| return; |
| } |
| var body = node.body; |
| if (body is BlockFunctionBody && body.block.statements.length == 1) { |
| var statement = body.block.statements.single; |
| if (statement is ExpressionStatement && |
| statement.expression is InvocationExpression) { |
| _visitInvocationExpression( |
| statement.expression as InvocationExpression, node); |
| } else if (statement is ReturnStatement && |
| statement.expression is InvocationExpression) { |
| var expression = statement.expression; |
| if (expression is InvocationExpression) { |
| // In the code, `(e) { f(e); }`, check `f(e)`. |
| _visitInvocationExpression(expression, node); |
| } |
| } |
| } else if (body is ExpressionFunctionBody) { |
| var expression = body.expression; |
| if (expression is InvocationExpression) { |
| // In the code, `(e) { return f(e); }`, check `f(e)`. |
| _visitInvocationExpression(expression, node); |
| } else if (constructorTearOffsEnabled && |
| expression is InstanceCreationExpression) { |
| // In the code, `(e) => C(e)`, check `C(e)`. |
| _visitInstanceCreation(expression, node); |
| } |
| } |
| } |
| |
| /// Checks [expression], the singular child the body of [node], to see whether |
| /// [node] unnecessarily wraps [node]. |
| void _visitInstanceCreation( |
| InstanceCreationExpression expression, FunctionExpression node) { |
| if (expression.isConst || expression.constructorName.type.isDeferred) { |
| return; |
| } |
| |
| var nodeType = node.declaredElement?.type; |
| var invocationType = expression.constructorName.staticElement?.type; |
| if (nodeType == null) return; |
| if (invocationType == null) return; |
| // It is possible that the invocation function type is a valid replacement |
| // for the node's function type, even if each of the parameters of `node` |
| // is a valid argument for the corresponding parameter of `expression`. |
| if (!typeSystem.isAssignableTo(invocationType, nodeType)) { |
| return; |
| } |
| |
| var arguments = expression.argumentList.arguments; |
| if (arguments.any((a) => a is! SimpleIdentifier)) return; |
| |
| var identifierArguments = arguments.cast<SimpleIdentifier>(); |
| var parameters = node.parameters?.parameters ?? <FormalParameter>[]; |
| if (parameters.length != arguments.length) return; |
| |
| for (var i = 0; i < arguments.length; ++i) { |
| if (identifierArguments[i].name != parameters[i].name?.lexeme) { |
| return; |
| } |
| } |
| |
| rule.reportLint(node); |
| } |
| |
| void _visitInvocationExpression( |
| InvocationExpression node, FunctionExpression nodeToLint) { |
| var nodeToLintParams = nodeToLint.parameters?.parameters; |
| if (nodeToLintParams == null || |
| !argumentsMatchParameters( |
| node.argumentList.arguments, nodeToLintParams)) { |
| return; |
| } |
| |
| var parameters = nodeToLintParams.map((e) => e.declaredElement).toSet(); |
| if (node is FunctionExpressionInvocation) { |
| if (node.function.mightBeDeferred) return; |
| |
| // TODO(pq): consider checking for assignability |
| // see: https://github.com/dart-lang/linter/issues/1561 |
| var checker = _FinalExpressionChecker(parameters); |
| if (checker.isFinalNode(node.function)) { |
| rule.reportLint(nodeToLint); |
| } |
| } else if (node is MethodInvocation) { |
| if (node.target.mightBeDeferred) return; |
| |
| var tearoffType = node.staticInvokeType; |
| if (tearoffType == null) return; |
| |
| var parent = nodeToLint.parent; |
| if (parent is NamedExpression) { |
| var argType = parent.staticType; |
| if (argType == null) return; |
| if (!typeSystem.isSubtypeOf(tearoffType, argType)) return; |
| } else if (parent is VariableDeclaration) { |
| var variableType = parent.declaredElement?.type; |
| if (variableType == null) return; |
| if (!typeSystem.isSubtypeOf(tearoffType, variableType)) return; |
| } |
| |
| var checker = _FinalExpressionChecker(parameters); |
| if (!node.containsNullAwareInvocationInChain() && |
| checker.isFinalNode(node.target) && |
| node.methodName.staticElement.isFinal && |
| node.typeArguments == null) { |
| rule.reportLint(nodeToLint); |
| } |
| } |
| } |
| } |
| |
| extension on Expression? { |
| bool get mightBeDeferred { |
| var self = this; |
| var element = switch (self) { |
| PrefixedIdentifier() => self.prefix.staticElement, |
| SimpleIdentifier() => self.staticElement, |
| _ => null, |
| }; |
| return element is PrefixElement && |
| element.imports.any((e) => e.prefix is DeferredImportElementPrefix); |
| } |
| } |
| |
| extension on Element? { |
| /// Returns whether this is a `final` variable or property and not `late`. |
| bool get isFinal { |
| var self = this; |
| if (self is PropertyAccessorElement) { |
| var variable = self.variable2; |
| return self.isSynthetic && |
| variable != null && |
| variable.isFinal && |
| !variable.isLate; |
| } else if (self is VariableElement) { |
| return self.isFinal && !self.isLate; |
| } |
| return true; |
| } |
| } |