pkg/linter/lib/src/rules/unnecessary_null_aware_assignments.dart

// 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/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/dart/element/element.dart';
import 'package:analyzer/error/error.dart';

import '../analyzer.dart';
import '../extensions.dart';

const _desc = r'Avoid `null` in `null`-aware assignment.';

class UnnecessaryNullAwareAssignments extends LintRule {
  UnnecessaryNullAwareAssignments()
    : super(
        name: LintNames.unnecessary_null_aware_assignments,
        description: _desc,
      );

  @override
  DiagnosticCode get diagnosticCode =>
      LinterLintCode.unnecessaryNullAwareAssignments;

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

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

  _Visitor(this.rule);

  @override
  void visitAssignmentExpression(AssignmentExpression node) {
    if (node.writeElement is SetterElement) return;

    if (node.operator.type == TokenType.QUESTION_QUESTION_EQ &&
        node.rightHandSide.isNullLiteral) {
      rule.reportAtNode(node);
    }
  }
}