| // 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 '../analyzer.dart'; |
| import '../util/dart_type_utilities.dart'; |
| |
| const _desc = |
| r"Don't reassign references to parameters of functions or methods."; |
| |
| const _details = r''' |
| |
| **DON'T** assign new values to parameters of methods or functions. |
| |
| Assigning new values to parameters is generally a bad practice unless an |
| operator such as `??=` is used. Otherwise, arbitrarily reassigning parameters |
| is usually a mistake. |
| |
| **BAD:** |
| ``` |
| void badFunction(int parameter) { // LINT |
| parameter = 4; |
| } |
| ``` |
| |
| **BAD:** |
| ``` |
| void badFunction(int required, {int optional: 42}) { // LINT |
| optional ??= 8; |
| } |
| ``` |
| |
| **BAD:** |
| ``` |
| void badFunctionPositional(int required, [int optional = 42]) { // LINT |
| optional ??= 8; |
| } |
| ``` |
| |
| **BAD:** |
| ``` |
| class A { |
| void badMethod(int parameter) { // LINT |
| parameter = 4; |
| } |
| } |
| ``` |
| |
| **GOOD:** |
| ``` |
| void ok(String parameter) { |
| print(parameter); |
| } |
| ``` |
| |
| **GOOD:** |
| ``` |
| void actuallyGood(int required, {int optional}) { // OK |
| optional ??= ...; |
| } |
| ``` |
| |
| **GOOD:** |
| ``` |
| void actuallyGoodPositional(int required, [int optional]) { // OK |
| optional ??= ...; |
| } |
| ``` |
| |
| **GOOD:** |
| ``` |
| class A { |
| void ok(String parameter) { |
| print(parameter); |
| } |
| } |
| ``` |
| |
| '''; |
| |
| bool _isDefaultFormalParameterWithDefaultValue(FormalParameter parameter) => |
| parameter is DefaultFormalParameter && parameter.defaultValue != null; |
| |
| bool _isDefaultFormalParameterWithoutDefaultValueReassigned( |
| FormalParameter parameter, AssignmentExpression assignment) => |
| parameter is DefaultFormalParameter && |
| parameter.defaultValue == null && |
| _isFormalParameterReassigned(parameter, assignment); |
| |
| bool _isFormalParameterReassigned( |
| FormalParameter parameter, AssignmentExpression assignment) => |
| assignment.leftHandSide is SimpleIdentifier && |
| (assignment.leftHandSide as SimpleIdentifier).staticElement == |
| parameter.declaredElement; |
| |
| bool _preOrPostFixExpressionMutation(FormalParameter parameter, AstNode n) => |
| n is PrefixExpression && |
| n.operand is SimpleIdentifier && |
| (n.operand as SimpleIdentifier).staticElement == |
| parameter.declaredElement || |
| n is PostfixExpression && |
| n.operand is SimpleIdentifier && |
| (n.operand as SimpleIdentifier).staticElement == |
| parameter.declaredElement; |
| |
| class ParameterAssignments extends LintRule implements NodeLintRule { |
| ParameterAssignments() |
| : super( |
| name: 'parameter_assignments', |
| description: _desc, |
| details: _details, |
| group: Group.style); |
| |
| @override |
| void registerNodeProcessors( |
| NodeLintRegistry registry, LinterContext context) { |
| final visitor = _Visitor(this); |
| registry.addFunctionDeclaration(this, visitor); |
| registry.addMethodDeclaration(this, visitor); |
| } |
| } |
| |
| class _Visitor extends SimpleAstVisitor<void> { |
| final LintRule rule; |
| |
| _Visitor(this.rule); |
| |
| @override |
| void visitFunctionDeclaration(FunctionDeclaration node) { |
| final parameters = node.functionExpression.parameters; |
| if (parameters != null) { |
| // Getter do not have formal parameters. |
| parameters.parameters.forEach((e) { |
| if (node.functionExpression.body |
| .isPotentiallyMutatedInScope(e.declaredElement)) { |
| _reportIfSimpleParameterOrWithDefaultValue(e, node); |
| } |
| }); |
| } |
| } |
| |
| @override |
| void visitMethodDeclaration(MethodDeclaration node) { |
| final parameterList = node?.parameters; |
| if (parameterList != null) { |
| // Getters don't have parameters. |
| parameterList.parameters.forEach((e) { |
| if (node.body.isPotentiallyMutatedInScope(e.declaredElement)) { |
| _reportIfSimpleParameterOrWithDefaultValue(e, node); |
| } |
| }); |
| } |
| } |
| |
| void _reportIfSimpleParameterOrWithDefaultValue( |
| FormalParameter parameter, AstNode functionOrMethodDeclaration) { |
| final nodes = |
| DartTypeUtilities.traverseNodesInDFS(functionOrMethodDeclaration); |
| |
| if (parameter is SimpleFormalParameter || |
| _isDefaultFormalParameterWithDefaultValue(parameter)) { |
| final mutatedNodes = nodes.where((n) => |
| (n is AssignmentExpression && |
| _isFormalParameterReassigned(parameter, n)) || |
| _preOrPostFixExpressionMutation(parameter, n)); |
| mutatedNodes.forEach(rule.reportLint); |
| return; |
| } |
| |
| final assignmentsNodes = nodes |
| .where((n) => |
| n is AssignmentExpression && |
| _isDefaultFormalParameterWithoutDefaultValueReassigned( |
| parameter, n)) |
| .toList(); |
| |
| final nonNullCoalescingAssignments = assignmentsNodes.where((n) => |
| (n as AssignmentExpression).operator.type != |
| TokenType.QUESTION_QUESTION_EQ); |
| |
| if (assignmentsNodes.length > 1 || |
| nonNullCoalescingAssignments.isNotEmpty) { |
| final node = assignmentsNodes.length > 1 |
| ? assignmentsNodes.last |
| : nonNullCoalescingAssignments.isNotEmpty |
| ? nonNullCoalescingAssignments.first |
| : parameter; |
| rule.reportLint(node); |
| } |
| } |
| } |