[
  // Still okay:
  0b__111111111111111111111111111111111111111111111111111111111111111,
  // Overflow:
  0b1_000000000000000000000000000000000000000000000000000000000000000,
]

# output:
stdin:5:3
  ╷
5 │   0b1_000000000000000000000000000000000000000000000000000000000000000,
  ╵   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Error: Overflow in integer literal.