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
// Copyright 2021 Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.

//! Expansion for `fatal`-annotations
//!
//! Expand `#[fatal]` annotations on `enum` variants into
//! two additional `enum`s that can be converted back, or
//! the original split into two.
//!
//! Stands on the shoulders of `thiserror`.

pub use fatality_proc_macro::fatality;
pub use thiserror;

/// Determine the fatality of an error.
pub trait Fatality: std::error::Error + std::fmt::Debug {
    /// Returns `true` if the error variant is _fatal_
    /// or `false` if it is more of a informational error.
    fn is_fatal(&self) -> bool;
}

/// Allows to split an error into two types - a fatal
/// and a informational enum error type, that can be further consumed.
pub trait Split: std::error::Error + std::fmt::Debug {
    type Jfyi: std::error::Error + Send + Sync + 'static;
    type Fatal: std::error::Error + Send + Sync + 'static;

    /// Split the error into it's fatal and non-fatal variants.
    ///
    /// `Ok(jfyi)` contains a enum representing all non-fatal variants, `Err(fatal)`
    /// contains all fatal variants.
    ///
    /// Attention: If the type is splitable, it must _not_ use any `forward`ed finality
    /// evaluations, or it must be splitable up the point where no more `forward` annotations
    /// were used.
    fn split(self) -> std::result::Result<Self::Jfyi, Self::Fatal>;
}

/// Converts a flat, yet `splitable` error into a nested `Result<Result<_,Jfyi>, Fatal>`
/// error type.
pub trait Nested<T, E: Split>
where
    Self: Sized,
{
    /// Convert into a nested error rather than a flat one, commonly for direct handling.
    fn into_nested(
        self,
    ) -> std::result::Result<std::result::Result<T, <E as Split>::Jfyi>, <E as Split>::Fatal>;
}

impl<T, E: Split> Nested<T, E> for std::result::Result<T, E> {
    fn into_nested(
        self,
    ) -> std::result::Result<std::result::Result<T, <E as Split>::Jfyi>, <E as Split>::Fatal> {
        match self {
            Ok(t) => Ok(Ok(t)),
            Err(e) => match e.split() {
                Ok(jfyi) => Ok(Err(jfyi)),
                Err(fatal) => Err(fatal),
            },
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[derive(Debug, thiserror::Error)]
    #[error("X")]
    struct X;

    impl Fatality for X {
        fn is_fatal(&self) -> bool {
            false
        }
    }

    #[derive(Debug, thiserror::Error)]
    #[error("Y")]
    struct Y;

    impl Fatality for Y {
        fn is_fatal(&self) -> bool {
            true
        }
    }

    #[fatality]
    enum Acc {
        #[error("0")]
        Zero,

        #[error("X={0}")]
        A(#[source] X),

        #[fatal]
        #[error(transparent)]
        B(Y),

        #[fatal(forward)]
        #[error("X={0}")]
        Aaaaa(#[source] X),

        #[fatal(forward)]
        #[error(transparent)]
        Bbbbbb(Y),
    }

    #[test]
    fn all_in_one() {
        assert_eq!(false, Fatality::is_fatal(&Acc::A(X)));
        assert_eq!(true, Fatality::is_fatal(&Acc::B(Y)));
        assert_eq!(false, Fatality::is_fatal(&Acc::Aaaaa(X)));
        assert_eq!(true, Fatality::is_fatal(&Acc::Bbbbbb(Y)));
        assert_eq!(false, Fatality::is_fatal(&Acc::Zero));
    }
}