Flutter Custom Lints #

A collection of custom lint rules for Flutter and Dart projects that enforce best practices and prevent common coding mistakes.

Installation #

Add flutter_custom_lints to your dev_dependencies in pubspec.yaml:

dev_dependencies:
  custom_lint: ^0.7.5
  flutter_custom_lints: ^1.0.0

Then run:

dart pub get

Setup #

Add the following to your analysis_options.yaml:

analyzer:
  plugins:
    - custom_lint

custom_lint:
  rules:
    # Enable specific rules
    - no_as_type_assertion
    - no_direct_iterable_access
    - no_null_force
    - use_compare_without_case

Available Lints #

no_as_type_assertion #

Prevents using as for type assertions which can cause runtime errors.

❌ Bad:

var user = data as User; // Can throw at runtime

✅ Good:

if (data is User) {
  var user = data; // Safe type promotion
}

no_direct_iterable_access #

Prevents direct access to iterables without null checks.

❌ Bad:

var first = list.first; // Can throw if list is empty

✅ Good:

var first = list.isNotEmpty ? list.first : null;
// or create your own safe extension:
extension SafeIterable<T> on Iterable<T> {
  T? get safeFirst => isEmpty ? null : first;
  T? safeAt(int index) => index < 0 || index >= length ? null : elementAt(index);
}

no_null_force #

Prevents force unwrapping of nullable values.

❌ Bad:

String value = nullableString!; // Can throw at runtime

✅ Good:

String? value = nullableString;
if (value != null) {
  // Use value safely
}

use_compare_without_case #

Suggests using case-insensitive string comparison methods.

❌ Bad:

if (str1.toLowerCase() == str2.toLowerCase()) {
  // Less efficient
}

✅ Good:

// Create your own extension method:
extension StringComparisonExtension on String {
  bool compareWithoutCase(String other) =>
    toLowerCase() == other.toLowerCase();
}

// Then use it:
if (str1.compareWithoutCase(str2)) {
  // More efficient and readable
}

Running Lints #

After setup, you can run the lints using:

dart run custom_lint

For Flutter projects:

flutter packages pub run custom_lint

Contributing #

Contributions are welcome! Please feel free to submit a Pull Request.

License #

This project is licensed under the MIT License - see the LICENSE file for details.

Development Setup #

This project uses FVM (Flutter Version Management) to ensure consistent Flutter SDK versions across different development environments.

Prerequisites #

1. Install FVM globally:

   dart pub global activate fvm
   

2. Install the project's Flutter version:

   fvm install
   

Development Commands #

You can use FVM commands directly:

# Install dependencies
fvm dart pub get

# Run tests
fvm dart test

# Run static analysis
fvm dart analyze

# Format code
fvm dart format .

Debugging #

The project includes VS Code launch configurations for debugging:

• Debug Tests (FVM) - Debug all tests
• Debug Single Test File (FVM) - Debug the currently open test file

VS Code Configuration #

The project is configured to:

• Use FVM's Flutter SDK automatically
• Disable automatic pub get (use manual commands instead)
• Format code on save
• Apply code fixes on save