| // Copyright (c) 2021, 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 '../analyzer.dart'; |
| |
| const _desc = |
| r'Prefer final for parameter declarations if they are not reassigned.'; |
| |
| const _details = r''' |
| |
| **DO** prefer declaring parameters as final if they are not reassigned in |
| the function body. |
| |
| Declaring parameters as final when possible is a good practice because it helps |
| avoid accidental reassignments. |
| |
| **BAD:** |
| ```dart |
| void badParameter(String label) { // LINT |
| print(label); |
| } |
| ``` |
| |
| **GOOD:** |
| ```dart |
| void goodParameter(final String label) { // OK |
| print(label); |
| } |
| ``` |
| |
| **BAD:** |
| ```dart |
| void badExpression(int value) => print(value); // LINT |
| ``` |
| |
| **GOOD:** |
| ```dart |
| void goodExpression(final int value) => print(value); // OK |
| ``` |
| |
| **BAD:** |
| ```dart |
| [1, 4, 6, 8].forEach((value) => print(value + 2)); // LINT |
| ``` |
| |
| **GOOD:** |
| ```dart |
| [1, 4, 6, 8].forEach((final value) => print(value + 2)); // OK |
| ``` |
| |
| **GOOD:** |
| ```dart |
| void mutableParameter(String label) { // OK |
| print(label); |
| label = 'Hello Linter!'; |
| print(label); |
| } |
| ``` |
| |
| '''; |
| |
| class PreferFinalParameters extends LintRule implements NodeLintRule { |
| PreferFinalParameters() |
| : super( |
| name: 'prefer_final_parameters', |
| description: _desc, |
| details: _details, |
| group: Group.style); |
| |
| @override |
| List<String> get incompatibleRules => const ['unnecessary_final']; |
| |
| @override |
| void registerNodeProcessors( |
| NodeLintRegistry registry, LinterContext context) { |
| var visitor = _Visitor(this); |
| registry.addConstructorDeclaration(this, visitor); |
| registry.addFunctionExpression(this, visitor); |
| registry.addMethodDeclaration(this, visitor); |
| } |
| } |
| |
| class _Visitor extends SimpleAstVisitor<void> { |
| final LintRule rule; |
| |
| _Visitor(this.rule); |
| |
| /// Report the lint for parameters in the [parameters] list that are not |
| /// const or final already and not potentially mutated in the function [body]. |
| void _reportApplicableParameters( |
| FormalParameterList? parameters, FunctionBody body) { |
| if (parameters != null) { |
| for (var param in parameters.parameters) { |
| if (param.isFinal || param.isConst || param is FieldFormalParameter) { |
| continue; |
| } |
| var declaredElement = param.declaredElement; |
| if (declaredElement != null && |
| !body.isPotentiallyMutatedInScope(declaredElement)) { |
| rule.reportLint(param); |
| } |
| } |
| } |
| } |
| |
| @override |
| void visitConstructorDeclaration(ConstructorDeclaration node) => |
| _reportApplicableParameters(node.parameters, node.body); |
| |
| @override |
| void visitFunctionExpression(FunctionExpression node) => |
| _reportApplicableParameters(node.parameters, node.body); |
| |
| @override |
| void visitMethodDeclaration(MethodDeclaration node) => |
| _reportApplicableParameters(node.parameters, node.body); |
| } |