E0036

Warning name: block_label_shadowing

The label on a block or loop shadows a label that is already in scope.

Block and loop labels share the same namespace. When a label name is reused on a nested block or loop, it shadows the outer label, which can make the target of a labelled break or continue unclear.

Because break can target either a block or a loop while continue can target a loop, shadowing can redirect control flow to a different construct than intended. Use distinct, descriptive names for nested block and loop labels.

Erroneous example

///|
fn has_positive(xs : Array[Int]) -> Bool {
  found~: {
    // Warning: The label name `found` shadows a label name that is already in scope.
    found~: for x in xs {
      if x > 0 {
        break found~
      }
    }
    false
  }
}

Suggestion

Use distinct, descriptive label names for nested blocks and loops so each control-flow target is unambiguous.

///|
fn has_positive(xs : Array[Int]) -> Bool {
  found~: {
    search~: for x in xs {
      if x > 0 {
        break found~ true
      }
      continue search~
    }
    false
  }
}