label_undefined

Can't reference an undefined label '{0}'.

The analyzer produces this diagnostic when it finds a reference to a label that isn't defined in the scope of the break or continue statement that is referencing it.

The following code produces this diagnostic because the label loop isn't defined anywhere:

void f() {
  for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
      if (j != 0) {
        break loop;
      }
    }
  }
}

If the label should be on the innermost enclosing do, for, switch, or while statement, then remove the label:

void f() {
  for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
      if (j != 0) {
        break;
      }
    }
  }
}

If the label should be on some other statement, then add the label:

void f() {
  loop: for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
      if (j != 0) {
        break loop;
      }
    }
  }
}