thiserror 1.0.7 on Rust Cargo

Support mixing shorthand and non-shorthand format args (#47)

#[derive(Error, Debug)]
pub enum Error {
    #[error("first letter must be lowercase but was {:?}", first_char(.0))]
    WrongCase(String),
    #[error("invalid index {idx}, expected at least {} and at most {}", .limits.lo, .limits.hi)]
    OutOfBounds { idx: usize, limits: Limits },
}

Add #[error(transparent)] attribute for delegating Error impl to one field (#50)

This is useful for hiding error variants from a library's public error type:

#[derive(Error, Debug)]
#[error(transparent)]  // source and Display delegate to ErrorKind
pub struct Error(ErrorKind);

#[derive(Error, Debug)]
/*private*/ enum ErrorKind {
    #[error("...")]
    E0,
    #[error("...")]
    E1(#[source] io::Error),
}

And also for enums that need an "anything else" variant; such variants tend not to have their own Display message but just forward through to the underlying error's Display and source:

#[derive(Error, Debug)]
pub enum MyError {
    ...

    #[error(transparent)]
    Other(#[from] anyhow::Error),  // source and Display delegate to anyhow::Error
}