common_failures 0.2.0

//! Utilities for formatting and displaying errors.

use std::fmt;

use failure;

use crate::Error;

/// A wrapper which prints a human-readable list of the causes of an error, plus
/// a backtrace if present.
pub struct DisplayCausesAndBacktrace<'a> {
    err: &'a Error,
    include_backtrace: bool,
}

impl<'a> fmt::Display for DisplayCausesAndBacktrace<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut first = true;
        for cause in self.err.iter_chain() {
            if first {
                first = false;
                writeln!(f, "Error: {}", cause)?;
            } else {
                writeln!(f, "  caused by: {}", cause)?;
            }
        }
        if self.include_backtrace {
            write!(f, "{}", self.err.backtrace())?;
        }
        Ok(())
    }
}

/// Extensions to standard `failure::Error` trait.
pub trait DisplayCausesAndBacktraceExt {
    /// Wrap the error in `DisplayCausesAndBacktrace`, causing it to be
    /// formatted with a human-readable list of all causes, plus an optional
    /// backtrace.
    fn display_causes_and_backtrace(&self) -> DisplayCausesAndBacktrace;

    /// Wrap the error in `DisplayCausesAndBacktrace`, causing it to be
    /// formatted with a human-readable list of all causes. However, the
    /// backtrace will be omitted even if `RUST_BACKTRACE` is set. This is
    /// intended to be used in situations where the backtrace needed to be
    /// handled separately, as with APIs like Rollbar's.
    fn display_causes_without_backtrace(&self) -> DisplayCausesAndBacktrace;
}

impl DisplayCausesAndBacktraceExt for failure::Error {
    fn display_causes_and_backtrace(&self) -> DisplayCausesAndBacktrace {
        DisplayCausesAndBacktrace {
            err: self,
            include_backtrace: true,
        }
    }

    fn display_causes_without_backtrace(&self) -> DisplayCausesAndBacktrace {
        DisplayCausesAndBacktrace {
            err: self,
            include_backtrace: false,
        }
    }
}