Missing variable pattern in one branch of logical-or patternDRT-W1483

The analyzer produces this diagnostic when one branch of a logical-or pattern doesn't declare a variable that is declared on the other branch of the same pattern.

Example

The following code produces this diagnostic because the right-hand side of the logical-or pattern doesn't declare the variable a:

void f((int, int) r) {
  if (r case (var a, 0) || (0, _)) {
    print(a);
  }
}

Common fixes

If the variable needs to be referenced in the controlled statements, then add a declaration of the variable to every branch of the logical-or pattern:

void f((int, int) r) {
  if (r case (var a, 0) || (0, var a)) {
    print(a);
  }
}

If the variable doesn't need to be referenced in the controlled statements, then remove the declaration of the variable from every branch of the logical-or pattern:

void f((int, int) r) {
  if (r case (_, 0) || (0, _)) {
    print('found a zero');
  }
}

If the variable needs to be referenced if one branch of the pattern matches but not when the other matches, then break the pattern into two pieces:

void f((int, int) r) {
  switch (r) {
    case (var a, 0):
      print(a);
    case (0, _):
      print('found a zero');
  }
}