1Remain sorted
2=============
3
4[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/remain-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/remain)
5[<img alt="crates.io" src="https://img.shields.io/crates/v/remain.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/remain)
6[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-remain-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/remain)
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8
9This crate provides an attribute macro to check at compile time that the
10variants of an enum or the arms of a match expression are written in sorted
11order.
12
13```toml
14[dependencies]
15remain = "0.2"
16```
17
18## Syntax
19
20Place a `#[remain::sorted]` attribute on enums, structs, match-expressions, or
21let-statements whose value is a match-expression.
22
23Alternatively, import as `use remain::sorted;` and use `#[sorted]` as the
24attribute.
25
26```rust
27#[remain::sorted]
28#[derive(Debug)]
29pub enum Error {
30    BlockSignal(signal::Error),
31    CreateCrasClient(libcras::Error),
32    CreateEventFd(sys_util::Error),
33    CreateSignalFd(sys_util::SignalFdError),
34    CreateSocket(io::Error),
35    DetectImageType(qcow::Error),
36    DeviceJail(io_jail::Error),
37    NetDeviceNew(virtio::NetError),
38    SpawnVcpu(io::Error),
39}
40
41#[remain::sorted]
42#[derive(Debug)]
43pub struct Registers {
44    ax: u16,
45    cx: u16,
46    di: u16,
47    si: u16,
48    sp: u16,
49}
50
51impl Display for Error {
52    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
53        use self::Error::*;
54
55        #[remain::sorted]
56        match self {
57            BlockSignal(e) => write!(f, "failed to block signal: {}", e),
58            CreateCrasClient(e) => write!(f, "failed to create cras client: {}", e),
59            CreateEventFd(e) => write!(f, "failed to create eventfd: {}", e),
60            CreateSignalFd(e) => write!(f, "failed to create signalfd: {}", e),
61            CreateSocket(e) => write!(f, "failed to create socket: {}", e),
62            DetectImageType(e) => write!(f, "failed to detect disk image type: {}", e),
63            DeviceJail(e) => write!(f, "failed to jail device: {}", e),
64            NetDeviceNew(e) => write!(f, "failed to set up virtio networking: {}", e),
65            SpawnVcpu(e) => write!(f, "failed to spawn VCPU thread: {}", e),
66        }
67    }
68}
69```
70
71If an enum variant, struct field, or match arm is inserted out of order,
72
73```diff
74      NetDeviceNew(virtio::NetError),
75      SpawnVcpu(io::Error),
76+     AaaUhOh(Box<dyn StdError>),
77  }
78```
79
80then the macro produces a compile error.
81
82```console
83error: AaaUhOh should sort before BlockSignal
84  --> tests/stable.rs:49:5
85   |
8649 |     AaaUhOh(Box<dyn StdError>),
87   |     ^^^^^^^
88```
89
90## Compiler support
91
92The attribute on enums and structs is supported on any rustc version 1.31+.
93
94Rust does not yet have stable support for user-defined attributes within a
95function body, so the attribute on match-expressions and let-statements requires
96a nightly compiler and the following two features enabled:
97
98```rust
99#![feature(proc_macro_hygiene, stmt_expr_attributes)]
100```
101
102As a stable alternative, this crate provides a function-level attribute called
103`#[remain::check]` which makes match-expression and let-statement attributes
104work on any rustc version 1.31+. Place this attribute on any function containing
105`#[sorted]` to make them work on a stable compiler.
106
107```rust
108impl Display for Error {
109    #[remain::check]
110    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
111        use self::Error::*;
112
113        #[sorted]
114        match self {
115            /* ... */
116        }
117    }
118}
119```
120
121<br>
122
123#### License
124
125<sup>
126Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
1272.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
128</sup>
129
130<br>
131
132<sub>
133Unless you explicitly state otherwise, any contribution intentionally submitted
134for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
135be dual licensed as above, without any additional terms or conditions.
136</sub>
137