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

// 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/analysis_rule/analysis_rule.dart';
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/visitor.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/type.dart';
import 'package:analyzer/error/error.dart';

import '../analyzer.dart';
import '../diagnostic.dart' as diag;
import '../extensions.dart';

const _desc = r"Don't explicitly initialize variables to `null`.";

class AvoidInitToNull extends AnalysisRule {
  new() : super(name: LintNames.avoid_init_to_null, description: _desc);

  @override
  DiagnosticCode get diagnosticCode => diag.avoidInitToNull;

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

class _Visitor(final AnalysisRule rule, final RuleContext context)
    extends SimpleAstVisitor<void> {
  bool isNullable(DartType type) => context.typeSystem.isNullable(type);

  @override
  void visitFieldFormalParameter(FieldFormalParameter node) {
    _checkFormalParameter(node);
  }

  @override
  void visitRegularFormalParameter(RegularFormalParameter node) {
    _checkFormalParameter(node);
  }

  @override
  void visitSuperFormalParameter(SuperFormalParameter node) {
    _checkFormalParameter(node);
  }

  @override
  void visitVariableDeclaration(VariableDeclaration node) {
    var declaredElement = node.declaredFragment?.element;
    if (declaredElement != null &&
        !node.isConst &&
        !node.isFinal &&
        node.initializer.isNullLiteral &&
        isNullable(declaredElement.type)) {
      rule.reportAtNode(node);
    }
  }

  void _checkFormalParameter(FormalParameter node) {
    var defaultValue = node.defaultClause?.value;
    if (defaultValue == null) return;

    var declaredElement = node.declaredFragment?.element;
    if (declaredElement == null) return;

    if (declaredElement is SuperFormalParameterElement) {
      var superConstructorParameter = declaredElement.superConstructorParameter;
      if (superConstructorParameter is! FormalParameterElement) return;
      var defaultValue = superConstructorParameter.defaultValueCode ?? 'null';
      if (defaultValue != 'null') return;
    }

    if (defaultValue.isNullLiteral && isNullable(declaredElement.type)) {
      rule.reportAtNode(node);
    }
  }
}