An awesome linter rule that saves me a ton of time and keeps code consistent throughout my codebases is require_trailing_commas.

“DO use trailing commas for all function calls and declarations unless the function call or definition, from the start of the function name up to the closing parenthesis, fits in a single line.” - Dart Docs

When you combine this linter rule with formatting your code on save, it’ll speed up your productivity!

To add this linter rule, go into the analysis_options.yaml and add it to the rules section.

// analysis_options.yaml

linter:
  rules:
    - require_trailing_commas

We can test this out by pasting the following code into a dart file.

// Before
class User {
  User({required this.name,
  required this.email, required this.age}); // <- Missing comma

  final String name;
  final String email;
  final int age;
}

class Fun extends StatelessWidget {
  const Fun({super.key});

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(
          color: Colors.red, borderRadius: BorderRadius.circular(10)), // <- Missing comma
      child: Text('Hello World'),
    );
  }
}

Once we format with Ctrl/Alt + Shift + F or save our file with format on save, our code is updated with commas added to the proper locations.

// After
class User {
  User({
    required this.name,
    required this.email,
    required this.age, // <- New comma
  });

  final String name;
  final String email;
  final int age;
}

class Fun extends StatelessWidget {
  const Fun({super.key});

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(
        color: Colors.red,
        borderRadius: BorderRadius.circular(10), // <- New comma
      ),
      child: const Text('Hello, world!'),
    );
  }
}