1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
use core::fmt::{self, Display, Debug};

use Fail;

without_std! {
    /// An error with context around it.
    ///
    /// The context is intended to be a human-readable, user-facing explanation for the
    /// error that has occurred. The underlying error is not assumed to be end-user-relevant
    /// information.
    ///
    /// The `Display` impl for `Context` only prints the human-readable context, while the
    /// `Debug` impl also prints the underlying error.
    pub struct Context<D: Display + Send + Sync + 'static> {
        context: D,
    }

    impl<D: Display + Send + Sync + 'static> Context<D> {
        /// Creates a new context without an underlying error message.
        pub fn new(context: D) -> Context<D> {
            Context { context }
        }

        /// Returns a reference to the context provided with this error.
        pub fn get_context(&self) -> &D {
            &self.context
        }

        pub(crate) fn with_err<E: Fail>(context: D, _: E) -> Context<D> {
            Context { context }
        }
    }

    impl<D: Display + Send + Sync + 'static> Fail for Context<D> { }

    impl<D: Display + Send + Sync + 'static> Debug for Context<D> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{}", self.context)
        }
    }

    impl<D: Display + Send + Sync + 'static> Display for Context<D> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{}", self.context)
        }
    }
}

with_std! {
    use {Error, Backtrace};

    /// An error with context around it.
    ///
    /// The context is intended to be a human-readable, user-facing explanation for the
    /// error that has occurred. The underlying error is not assumed to be end-user-relevant
    /// information.
    ///
    /// The `Display` impl for `Context` only prints the human-readable context, while the
    /// `Debug` impl also prints the underlying error.
    pub struct Context<D: Display + Send + Sync + 'static> {
        context: D,
        failure: Either<Backtrace, Error>,
    }

    impl<D: Display + Send + Sync + 'static> Context<D> {
        /// Creates a new context without an underlying error message.
        pub fn new(context: D) -> Context<D> {
            let failure = Either::This(Backtrace::new());
            Context { context, failure }
        }

        /// Returns a reference to the context provided with this error.
        pub fn get_context(&self) -> &D {
            &self.context
        }

        pub(crate) fn with_err<E: Into<Error>>(context: D, error: E) -> Context<D> {
            let failure = Either::That(error.into());
            Context { context, failure }
        }
    }

    impl<D: Display + Send + Sync + 'static> Fail for Context<D> {
        fn cause(&self) -> Option<&Fail> {
            self.failure.cause()
        }

        fn backtrace(&self) -> Option<&Backtrace> {
            Some(self.failure.backtrace())
        }
    }

    impl<D: Display + Send + Sync + 'static> Debug for Context<D> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{:?}\n\n{}", self.failure, self.context)
        }
    }

    impl<D: Display + Send + Sync + 'static> Display for Context<D> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{}", self.context)
        }
    }

    enum Either<A, B> {
        This(A),
        That(B),
    }

    impl Either<Backtrace, Error> {
        fn backtrace(&self) -> &Backtrace {
            match *self {
                Either::This(ref backtrace) => backtrace,
                Either::That(ref error)     => error.backtrace(),
            }
        }

        fn cause(&self) -> Option<&Fail> {
            match *self {
                Either::This(_)         => None,
                Either::That(ref error) => Some(error.cause())
            }
        }
    }

    impl Debug for Either<Backtrace, Error> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            match *self {
                Either::This(ref backtrace) => write!(f, "{:?}", backtrace),
                Either::That(ref error)     => write!(f, "{:?}", error),
            }
        }
    }
}