error: 'T' does not implement protocol 'P': method 'val' has a mismatched signature — return type: protocol declares 'i64', impl declares 'bool' (a protocol-method impl must match the protocol's declared types exactly, with `Self` written as `T`)
  --> examples/diagnostics/1201-diagnostics-protocol-impl-signature-mismatch.sx:20:3
   |
20 |   p : P = t;                  // <- 'T' does not implement 'P' (return type)
   |   ^^^^^^^^^^