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All Lint Rules

Table of Contents

Configuring Lints

All lints have configuration options available, these can be specified in the analysis_options.yaml or the pubspec.yaml file, an example is shown below. Each lint may also have additional options available that are covered in their respective sections below.

All lints have the following options:

  • severity: This can be set to none, info, warning or error.
  • include: Only lint files matching these regular expressions.
  • exclude: Skip linting files matching these regular expressions.
navi_light:
  rules_exclude:
    - "test/.*\\.dart"
  rules:
    lines_longer_than_maximum_chars:
      maximum_chars: 100
      severity: info
      include:
        - "lib/.*\\.dart"
      exclude:
        - "lib/.*_temp\\.dart"
    prefer_named_parameters:
      threshold: 2
      severity: warning
    incorrect_todo_comment:
      severity: error

Dart

lines_longer_than_maximum_chars

The number of characters per line of code must not exceed the maximum character limit.

lines_longer_than_maximum_chars:
  maximum_chars: 100
  severity: info

Bad:

const a = 'very long long long long long long long long long long long long long long long long long long long long long comment'; // LINT

prefer_named_parameters

If a function or constructor takes more parameters than the threshold, use named parameters.

prefer_named_parameters:
  threshold: 2
  severity: warning

Good:

class A {
  final String a;
  final String b;

  A({
    required this.a,
    required this.b,
  });

  A.a({
    required this.a,
    this.b = '',
  });

  A.b({
    required this.a,
    String? b,
  }) : b = b ?? '';

  void test2({
    required String a,
    String b = '',
  }) {}
}

void test2({
  String a = '',
  String? b,
}) {}

Bad:

class B {
  final String a;
  final String b;

  B(this.a, this.b); // LINT
  B.a(this.a, [this.b = '']); // LINT
  B.b(this.a, {this.b = ''}); // LINT
  B.c(this.a, {required this.b}); // LINT
  B.d(this.a, String? b) : b = b ?? ''; // LINT
}

void test4(String a, String b) {} // LINT
void test5(String a, [String b = '']) {} // LINT
void test6(String a, {required String b}) {} // LINT
void test7(String a, {String b = ''}) {} // LINT
void test8(String a, {String? b}) {} // LINT
void test9([String? a, String? b = '']) {} // LINT

incorrect_todo_comment

TODO comments must have username, description and issue number (or #0 if no issue).

Example: // TODO(username): some description text #123.

incorrect_todo_comment:
  severity: warning

Good:

// TODO(minhnt3): Remove this file when the issue is fixed #123 issue number.

// TODO(minhnt3): Remove this file when the issue is fixed #0

Bad:

// TODO(minhnt3): Remove this file when the issue is fixed.

// TODO: Remove this file when the issue is fixed #123.

// TODO(minhnt3): Remove this file when the issue is fixed #-123 .

// TODO(minhnt3)     : Remove this file when the issue is fixed #-123 .

// TODO   (minhnt3): Remove this file when the issue is fixed #123 .

// TODO(minhnt3):               #123  .

// TODO() Remove this file when the issue is fixed #123.

prefer_is_empty_string

Use isEmpty instead of == to test whether the string is empty.

prefer_is_empty_string:
  severity: warning

Good:

void test(String a) {
  if (a.isEmpty) {}
}

Bad:

void test(String a) {
  if (a == '') {}

  if ('' == a) {}
}

prefer_is_not_empty_string

Use isNotEmpty instead of == to test whether the string is empty..

prefer_is_not_empty_string:
  severity: warning

Good:

void test(String a) {
  if (a.isNotEmpty) {}
}

Bad:

void test(String a) {
  if (a != '') {}

  if ('' != a) {}
}

avoid_unnecessary_async_function

If a function does not have any asynchronous computation, there is no need to create an async function.

avoid_unnecessary_async_function:
  severity: warning

Good:

Future<void> login() async {
  await Future<dynamic>.delayed(const Duration(milliseconds: 2000));
  print('login');
}

FutureOr<String> getName() async {
  return Future(() => 'name');
}

FutureOr<int?> getAge() async {
  try {
    print('do something');

    return Future.value(3);
  } catch (e) {
    return null;
  }
}

class AsyncNotifier {
  Future<void> login() async {
    await Future<dynamic>.delayed(const Duration(milliseconds: 2000));
    print('login');
  }

  FutureOr<String> getName() async {
    return Future(() => 'name');
  }

  FutureOr<int?> getAge() async {
    try {
      print('do something');

      return Future.value(3);
    } catch (e) {
      return null;
    }
  }
}

Bad:

Future<void> logout() async {
  print('logout');
}

FutureOr<String> getFullName() async {
  return 'name';
}

FutureOr<int?> getUserAge() async {
  try {
    print('do something');

    return 3;
  } catch (e) {
    return null;
  }
}

class Notifier {
  Future<void> login() async {
    Future(() => print('hello'));

    print('login');
  }

  FutureOr<String> getName() async {
    unawaited(Future<dynamic>.delayed(const Duration(milliseconds: 2000)));

    return 'name';
  }
}