Don't use pub keyword in examples, and don't derive everything but the kitchen sink in examples

[Kixunil]

pub is useless in binaries and unused derives are not helpful.
Example offender: pub enum SighashError in examples/ecdsa-psbt.rs (disclaimer: didn't actually check if the derives are unused but seems almost certain some are)

[tcharding]

As author of ecdsa-psbt.rs I confirm the derives are useless and got there through my mindless cargo cult programming - can definitely be removed.

[sanket1729]

FTR, I was assuming that the example would be cleaned up #957 which was the main reason that I ACKed it #940 (review).

[lorenzolfm]

Removing pub from psbt_sign::SighashError and from psbt_sign::sign yields visibility erros when running ./contrib/test.sh (see log bellow).

I'm not that experienced in Rust, but from what I've read in the visibility and privacy chapter from the rust book the sign function and SighashError enum should remain pub so both are visible outside the psbt_sign module.

Am I missing something here?

error[E0412]: cannot find type `SighashError` in this scope
   --> examples/ecdsa-psbt.rs:323:17
    |
323 |     PsbtSighash(SighashError),
    |                 ^^^^^^^^^^^^ not found in this scope
    |
help: possible candidate is found in another module, you can import it into scope
    |
31  | use crate::psbt_sign::SighashError;
    |

error[E0412]: cannot find type `SighashError` in this scope
   --> examples/ecdsa-psbt.rs:358:11
    |
358 | impl From<SighashError> for Error {
    |           ^^^^^^^^^^^^ not found in this scope
    |
help: possible candidate is found in another module, you can import it into scope
    |
31  | use crate::psbt_sign::SighashError;
    |

error[E0412]: cannot find type `SighashError` in this scope
   --> examples/ecdsa-psbt.rs:359:16
    |
359 |     fn from(e: SighashError) -> Error { Error::PsbtSighash(e) }
    |                ^^^^^^^^^^^^ not found in this scope
    |
help: possible candidate is found in another module, you can import it into scope
    |
31  | use crate::psbt_sign::SighashError;
    |

error[E0603]: function `sign` is private
   --> examples/ecdsa-psbt.rs:145:20
    |
145 |         psbt_sign::sign(&mut psbt, &sk, 0, secp)?;
    |                    ^^^^

warning: unused import: `self::psbt_sign::*`
  --> examples/ecdsa-psbt.rs:50:5
   |
50 | use self::psbt_sign::*;
   |     ^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default

error: aborting due to 4 previous errors

[apoelstra]

@lorenzolfm thanks for checking on this. For the stuff inside the inline psbt_sign module, we should change the pubs to pub(crate) or even pub(super) to explicitly indicate that we only intend to give visibility to the surrounding module.

I'm not sure in detail what @sanket1729 means by "cleaning up" this example but it may be that we can entirely delete the module after #957 merges and then we can avoid this altogether :).

[tcharding]

Yes correct, the module is temporary while we work on the signing API (#957). I like pub(super) if that makes the compiler happy.

[tcharding]

With the removal of the signing code from ecdsa-psbt this issue no longer exists.