lib/src/rules/prefer_generic_function_type_aliases.dart

// Copyright (c) 2018, 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 generic function type aliases.';

const _details = r'''
**PREFER** generic function type aliases.

With the introduction of generic functions, function type aliases
(`typedef void F()`) couldn't express all of the possible kinds of
parameterization that users might want to express. Generic function type aliases
(`typedef F = void Function()`) fixed that issue.

For consistency and readability reasons, it's better to only use one syntax and
thus prefer generic function type aliases.

**BAD:**
```dart
typedef void F();
```

**GOOD:**
```dart
typedef F = void Function();
```

''';

class PreferGenericFunctionTypeAliases extends LintRule {
  static const LintCode code = LintCode('prefer_generic_function_type_aliases',
      "Use the generic function type syntax in 'typedef's.",
      correctionMessage: "Try using the generic function type syntax ('{0}').");

  PreferGenericFunctionTypeAliases()
      : super(
            name: 'prefer_generic_function_type_aliases',
            description: _desc,
            details: _details,
            group: Group.style);

  @override
  LintCode get lintCode => code;

  @override
  void registerNodeProcessors(
      NodeLintRegistry registry, LinterContext context) {
    var visitor = _Visitor(this);
    registry.addFunctionTypeAlias(this, visitor);
  }
}

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

  _Visitor(this.rule);

  @override
  void visitFunctionTypeAlias(FunctionTypeAlias node) {
    //https://github.com/dart-lang/linter/issues/2777
    if (node.semicolon.isSynthetic) return;

    var returnType = node.returnType;
    var typeParameters = node.typeParameters;
    var parameters = node.parameters;
    var returnTypeSource =
        returnType == null ? '' : '${returnType.toSource()} ';
    var typeParameterSource =
        typeParameters == null ? '' : typeParameters.toSource();
    var parameterSource = parameters.toSource();
    var replacement =
        '${returnTypeSource}Function$typeParameterSource$parameterSource';
    rule.reportLintForToken(node.name, arguments: [replacement]);
  }
}