lib/src/rules/unnecessary_final.dart

// Copyright (c) 2019, 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 = "Don't use `final` for local variables.";

const _details = r'''
**DON'T** use `final` for local variables.

`var` is shorter, and `final` does not change the meaning of the code.

**BAD:**
```
void badMethod() {
  final label = 'Final or var?';
  for (final char in ['v', 'a', 'r']) {
    print(char);
  }
}
```

**GOOD:**
```
void goodMethod() {
  var label = 'Final or var?';
  for (var char in ['v', 'a', 'r']) {
    print(char);
  }
}
```
''';

class UnnecessaryFinal extends LintRule implements NodeLintRule {
  UnnecessaryFinal()
      : super(
            name: 'unnecessary_final',
            description: _desc,
            details: _details,
            group: Group.style);

  @override
  List<String> get incompatibleRules => const ['prefer_final_locals'];

  @override
  void registerNodeProcessors(
      NodeLintRegistry registry, LinterContext context) {
    final visitor = _Visitor(this);
    registry
      ..addFormalParameterList(this, visitor)
      ..addForStatement(this, visitor)
      ..addVariableDeclarationStatement(this, visitor);
  }
}

class _Visitor extends SimpleAstVisitor<void> {
  final LintRule rule;

  _Visitor(this.rule);

  @override
  void visitFormalParameterList(FormalParameterList parameterList) {
    for (var node in parameterList.parameters) {
      if (node.isFinal) {
        // TODO(davidmorgan): for consistency this should report on the
        // `final` keyword, not the node, but it's hard to get to from
        // FormalParameter.
        rule.reportLint(node);
      }
    }
  }

  @override
  void visitForStatement(ForStatement node) {
    var forLoopParts = node.forLoopParts;
    // If the following `if` test fails, then either the statement is not a
    // for-each loop, or it is something like `for(a in b) { ... }`.  In the
    // second case, notice `a` is not actually declared from within the
    // loop. `a` is a variable declared outside the loop.
    if (forLoopParts is ForEachPartsWithDeclaration) {
      final loopVariable = forLoopParts.loopVariable;

      if (loopVariable.isFinal) {
        rule.reportLintForToken(loopVariable.keyword);
      }
    }
  }

  @override
  void visitVariableDeclarationStatement(VariableDeclarationStatement node) {
    if (node.variables.isFinal) {
      rule.reportLintForToken(node.variables.keyword);
    }
  }
}