Macro impl_error 

macro_rules! impl_error {
    ($ErrorName:ident, $ErrorType:ident) => { ... };
}

Available on crate feature alloc only.

Macro to build a fairly standard error struct.

extern crate alloc;
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct ErrorName {
    error_type: ErrorType,
    msg: alloc::string::String,
}
impl core::fmt::Display for ErrorName {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.write_fmt(format_args!("{:?}: {}", self.error_type, self.msg))
    }
}
#[cfg(feature = "std")]
impl std::error::Error for ErrorName {}