pkg/linter/lib/src/rules/prefer_is_not_operator.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/analysis_rule/rule_context.dart';
import 'package:analyzer/analysis_rule/rule_visitor_registry.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/token.dart';
import 'package:analyzer/dart/ast/visitor.dart';
import 'package:analyzer/error/error.dart';

import '../analyzer.dart';

const _desc = r'Prefer is! operator.';

class PreferIsNotOperator extends LintRule {
  PreferIsNotOperator()
    : super(name: LintNames.prefer_is_not_operator, description: _desc);

  @override
  DiagnosticCode get diagnosticCode => LinterLintCode.preferIsNotOperator;

  @override
  void registerNodeProcessors(
    RuleVisitorRegistry registry,
    RuleContext context,
  ) {
    var visitor = _Visitor(this);
    registry.addIsExpression(this, visitor);
  }
}

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

  _Visitor(this.rule);

  @override
  void visitIsExpression(IsExpression node) {
    // Return if it is `is!` expression
    if (node.notOperator != null) {
      return;
    }

    var parent = node.parent;
    // Check whether is expression is inside parenthesis
    if (parent is ParenthesizedExpression) {
      var prefixExpression = parent.parent;
      // Check for NOT (!) operator
      if (prefixExpression is PrefixExpression &&
          prefixExpression.operator.type == TokenType.BANG) {
        rule.reportAtNode(prefixExpression);
      }
    }
  }
}