Remain sorted

This crate provides an attribute macro to check at compile time that the variants of an enum or the arms of a match expression are written in sorted order.

[dependencies]
remain = "0.2"

Syntax

Place a #[remain::sorted] attribute on enums, structs, match-expressions, or let-statements whose value is a match-expression.

Alternatively, import as use remain::sorted; and use #[sorted] as the attribute.

#[remain::sorted]#[derive(Debug)]pubenumError{BlockSignal(signal::Error),CreateCrasClient(libcras::Error),CreateEventFd(sys_util::Error),CreateSignalFd(sys_util::SignalFdError),CreateSocket(io::Error),DetectImageType(qcow::Error),DeviceJail(io_jail::Error),NetDeviceNew(virtio::NetError),SpawnVcpu(io::Error),}#[remain::sorted]#[derive(Debug)]pubstructRegisters{ax:u16,cx:u16,di:u16,si:u16,sp:u16,}implDisplayforError{fnfmt(&self,f:&mut fmt::Formatter) -> fmt::Result{useself::Error::*;#[remain::sorted]matchself{BlockSignal(e) => write!(f,"failed to block signal: {}", e),CreateCrasClient(e) => write!(f,"failed to create cras client: {}", e),CreateEventFd(e) => write!(f,"failed to create eventfd: {}", e),CreateSignalFd(e) => write!(f,"failed to create signalfd: {}", e),CreateSocket(e) => write!(f,"failed to create socket: {}", e),DetectImageType(e) => write!(f,"failed to detect disk image type: {}", e),DeviceJail(e) => write!(f,"failed to jail device: {}", e),NetDeviceNew(e) => write!(f,"failed to set up virtio networking: {}", e),SpawnVcpu(e) => write!(f,"failed to spawn VCPU thread: {}", e),}}}

If an enum variant, struct field, or match arm is inserted out of order,

 NetDeviceNew(virtio::NetError),
SpawnVcpu(io::Error),
+ AaaUhOh(Box<dyn StdError>),
}

then the macro produces a compile error.

error: AaaUhOh should sort before BlockSignal --> tests/stable.rs:49:5 |49 | AaaUhOh(Box<dyn StdError>), | ^^^^^^^

Compiler support

The attribute on enums and structs is supported on any rustc version 1.31+.

Rust does not yet have stable support for user-defined attributes within a function body, so the attribute on match-expressions and let-statements requires a nightly compiler and the following two features enabled:

#![feature(proc_macro_hygiene, stmt_expr_attributes)]

As a stable alternative, this crate provides a function-level attribute called #[remain::check] which makes match-expression and let-statement attributes work on any rustc version 1.31+. Place this attribute on any function containing #[sorted] to make them work on a stable compiler.

implDisplayforError{#[remain::check]fnfmt(&self,f:&mut fmt::Formatter) -> fmt::Result{useself::Error::*;#[sorted]matchself{/* ... */}}}

License

^{Licensed under either of Apache License, Version 2.0 or MIT license at your option.}
_{Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.}