DCM Rules Quick Reference

Essential Dart Code Metrics rules for all Dart code in this project. Reference: https://dcm.dev/docs/rules/

Severity Levels#

Critical Rules (Must-Follow)#

Correctness#

avoid-collection-methods-with-unrelated-types

Collection methods should not receive unrelated types.

// Bad
final list = <String>['a', 'b'];
list.contains(1); // int vs String

// Good
list.contains('c');

avoid-recursive-calls

Functions should not call themselves recursively without termination.

no-empty-block

Empty blocks should not exist (except in catch).

// Bad
if (condition) {}

// Good
if (condition) {
  doSomething();
}

avoid-duplicate-exports

Files should not export the same URI multiple times.

Memory Leak Prevention#

dispose-class-fields

Disposable fields must be disposed in class dispose methods.

// Bad
class MyWidget extends StatefulWidget {
  final _controller = TextEditingController();
  // Missing dispose
}

// Good
@override
void dispose() {
  _controller.dispose();
  super.dispose();
}

avoid-unassigned-stream-subscriptions

Stream subscriptions must be assigned to variables for cancellation.

// Bad
stream.listen((data) => print(data));

// Good
final subscription = stream.listen((data) => print(data));
// Later: subscription.cancel();

Async Safety#

avoid-async-call-in-sync-function

Async functions should not be invoked in non-async blocks without handling.

avoid-uncaught-future-errors

Future errors in try/catch might not be caught properly.

// Bad
try {
  someFuture; // Not awaited
} catch (e) {}

// Good
try {
  await someFuture;
} catch (e) {}

Null Safety#

avoid-non-null-assertion

Avoid using ! operator on potentially null values.

// Bad
final name = user?.name!;

// Good
final name = user?.name ?? 'Unknown';

Code Quality#

avoid-dynamic

Avoid using dynamic type declarations.

// Bad
dynamic value = getData();

// Good
final Object value = getData();
// Or: final String value = getData() as String;

avoid-late-keyword

Minimize late keyword usage when possible.

prefer-correct-identifier-length

Identifiers should have appropriate length (min 3 characters).

// Bad
final e = items.first;

// Good
final item = items.first;

Performance Rules#

avoid-border-all (Flutter)

Use Border.fromBorderSide instead of Border.all.

prefer-const-border-radius (Flutter)

Use const BorderRadius.all instead of BorderRadius.circular.

avoid-incorrect-image-opacity (Flutter)

Image should not be wrapped in Opacity widget.

Project Exceptions#

Some rules have severity: style in this project. See project-config.md for details.

Common Exceptions#

Quick Commands#

# Run DCM analysis
dcm analyze .

# Run with fix suggestions
dcm analyze --fix .

# Check specific rules
dcm analyze --rule-ids=avoid-dynamic .

Related Files#

• BLoC Rules - BLoC/Cubit specific rules
• Flutter Rules - Widget specific rules
• Project Config - Project settings