bash-interop 0.2.0

Run bash under instrumentation and hear what it says: a session per run, a pipe and a task per shell, words a script speaks and answers it runs.
Documentation 
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//! One error for anything that stops a piece of work: what was being done,
//! and what went wrong underneath.

use std::error::Error;
use std::fmt;

type Cause = Box<dyn Error + Send + Sync>;

/// A context and a cause rather than an enum, since every use is `Display`
/// or `source()`.
#[derive(Debug)]
pub struct Failure {
    doing: String,
    cause: Cause,
}

impl Failure {
    pub fn new(doing: impl Into<String>, cause: impl Into<Cause>) -> Self {
        Self {
            doing: doing.into(),
            cause: cause.into(),
        }
    }
}

impl fmt::Display for Failure {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}: {}", self.doing, self.cause)
    }
}

impl Error for Failure {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        Some(&*self.cause)
    }
}

/// Says what was being attempted when a `Result` went wrong.
pub trait Doing<T> {
    fn doing(self, what: impl FnOnce() -> String) -> Result<T, Failure>;
}

impl<T, E: Into<Cause>> Doing<T> for Result<T, E> {
    fn doing(self, what: impl FnOnce() -> String) -> Result<T, Failure> {
        self.map_err(|cause| Failure::new(what(), cause))
    }
}