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Many Lints

no_equal_switch_case

v1.0.0 Warning Control Flow

This rule flags two branches of a switch that produce identical bodies, where sharing the patterns would say the same thing once.

Two copies of a body drift: one gets fixed and the other keeps the old behaviour, with nothing to show they were ever meant to agree. case a || b says the outcome is deliberately the same and can only ever change in one place.

Don’t

Section titled “Don’t”

A switch expression with a body written twice:

enum DeliveryStage { packed, shipped, delivered, returned }


String tracking(DeliveryStage stage) => switch (stage) {
  DeliveryStage.packed => 'In the warehouse',
  DeliveryStage.shipped => 'On its way',
  DeliveryStage.delivered => 'Complete',
  DeliveryStage.returned => 'Complete',
};

Switch statements are checked the same way:

enum DeliveryStage { packed, shipped, delivered, returned }


void notify(DeliveryStage stage) {
  switch (stage) {
    case DeliveryStage.packed:
      print('In the warehouse');
    case DeliveryStage.shipped:
      print('On its way');
    case DeliveryStage.delivered:
      print('Complete');
    case DeliveryStage.returned:
      print('Complete');
  }
}

Do

Section titled “Do”

Share the patterns with ||:

enum DeliveryStage { packed, shipped, delivered, returned }


String tracking(DeliveryStage stage) => switch (stage) {
  DeliveryStage.packed => 'In the warehouse',
  DeliveryStage.shipped => 'On its way',
  DeliveryStage.delivered || DeliveryStage.returned => 'Complete',
};

Known limitations

Section titled “Known limitations”

Bodies are compared by source text, so two branches that reach the same result by different code are not reported.

Three shapes are never reported, because none of them can be merged into an || pattern:

enum DeliveryStage { packed, shipped, delivered, returned }


String tracking(DeliveryStage stage, int retries) => switch (stage) {
  // A guarded case — each `when` belongs to its own pattern.
  DeliveryStage.packed when retries > 3 => 'Stuck',
  DeliveryStage.shipped when retries > 3 => 'Stuck',
  DeliveryStage.packed => 'In the warehouse',
  DeliveryStage.shipped => 'On its way',
  DeliveryStage.delivered => 'Complete',
  // The catch-all has to stay last, so folding a case into it would change
  // which values it covers.
  _ => 'Complete',
};

An empty body is skipped too: several empty cases in a row are how a fallthrough is written in a switch statement.

Configuration

Section titled “Configuration”

This rule is in the pedantic preset — whether two independent branches that happen to agree today should be merged is a genuine judgement call, and the strictest tier resolves it in favour of one canonical branch.

Enable it by name:

many_lints.yaml
rules:
  no_equal_switch_case: true

To turn it off again:

many_lints.yaml
rules:
  no_equal_switch_case: false

To keep the rule on but skip certain paths, use per-rule exclude.

Section titled “Related rules”