Custom error in history api

[Kl4rry]

Currently the history trait requires the error return to be a readline error. That means that one cannot return other error types that are not included in:

pub enum ReadlineError {
    Io(Error),
    Eof,
    Interrupted,
    Errno(Error),
    WindowResized,
}

This can be fixed by either adding a Box<dyn std::error::Error> variant that can be used to return any std::error::Error or by adding a optional generic error type like this:

pub enum ReadlineError<E = std::convert::Infallible> {
    Io(Error),
    Eof,
    Interrupted,
    Errno(Error),
    WindowResized,
    UserError(E),
}

[gwenn]

Indeed, I had to introduce this variant for the SQLite based history:

rustyline/src/error.rs

Lines 33 to 34 in 4a7dfe9

	#[cfg(feature = "with-sqlite-history")]
	SQLiteError(rusqlite::Error),

[Kl4rry]

Another possible solution is to make History generic over the error type and having a trait bound that it must implement into for ReadlineError.

[gwenn]

Just for reference:

• https://docs.rs/termwiz/latest/termwiz/lineedit/trait.History.html (no error)
• https://docs.rs/reedline/latest/reedline/trait.History.html (only https://docs.rs/reedline/latest/reedline/enum.ReedlineErrorVariants.html)

As far as I know, other rust libraries doesn't support custom History impl.

[Kl4rry]

Termwiz kinda supports every error type as you can just to .ok() on every error type.
There is a work around that can be used in both reedline and rustyline and that is to put the error in a IO error like this
std::io::Error::new(std::io::ErrorKind::InvalidData, Box::new(custom_error))