136 lines
3.8 KiB
Markdown
136 lines
3.8 KiB
Markdown
Remain sorted
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=============
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[](https://travis-ci.com/dtolnay/remain)
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[](https://crates.io/crates/remain)
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[](https://docs.rs/remain)
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This crate provides an attribute macro to check at compile time that the
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variants of an enum or the arms of a match expression are written in sorted
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order.
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```toml
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[dependencies]
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remain = "0.1"
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```
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## Syntax
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Place a `#[remain::sorted]` attribute on enums, structs, match-expressions, or
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let-statements whose value is a match-expression.
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Alternatively, import as `use remain::sorted;` and use `#[sorted]` as the
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attribute.
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```rust
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#[remain::sorted]
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#[derive(Debug)]
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pub enum Error {
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BlockSignal(signal::Error),
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CreateCrasClient(libcras::Error),
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CreateEventFd(sys_util::Error),
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CreateSignalFd(sys_util::SignalFdError),
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CreateSocket(io::Error),
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DetectImageType(qcow::Error),
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DeviceJail(io_jail::Error),
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NetDeviceNew(virtio::NetError),
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SpawnVcpu(io::Error),
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}
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#[remain::sorted]
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#[derive(Debug)]
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pub enum Registers {
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ax: u16,
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cx: u16,
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di: u16,
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si: u16,
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sp: u16,
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}
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impl Display for Error {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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use self::Error::*;
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#[remain::sorted]
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match self {
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BlockSignal(e) => write!(f, "failed to block signal: {}", e),
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CreateCrasClient(e) => write!(f, "failed to create cras client: {}", e),
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CreateEventFd(e) => write!(f, "failed to create eventfd: {}", e),
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CreateSignalFd(e) => write!(f, "failed to create signalfd: {}", e),
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CreateSocket(e) => write!(f, "failed to create socket: {}", e),
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DetectImageType(e) => write!(f, "failed to detect disk image type: {}", e),
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DeviceJail(e) => write!(f, "failed to jail device: {}", e),
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NetDeviceNew(e) => write!(f, "failed to set up virtio networking: {}", e),
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SpawnVcpu(e) => write!(f, "failed to spawn VCPU thread: {}", e),
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}
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}
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}
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```
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If an enum variant, struct field, or match arm is inserted out of order,
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```diff
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NetDeviceNew(virtio::NetError),
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SpawnVcpu(io::Error),
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+ AaaUhOh(Box<dyn StdError>),
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}
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```
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then the macro produces a compile error.
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```console
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error: AaaUhOh should sort before BlockSignal
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--> tests/stable.rs:49:5
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49 | AaaUhOh(Box<dyn StdError>),
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| ^^^^^^^
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```
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## Compiler support
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The attribute on enums and structs is supported on any rustc version 1.31+.
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Rust does not yet have stable support for user-defined attributes within a
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function body, so the attribute on match-expressions and let-statements requires
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a nightly compiler and the following two features enabled:
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```rust
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#![feature(proc_macro_hygiene, stmt_expr_attributes)]
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```
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As a stable alternative, this crate provides a function-level attribute called
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`#[remain::check]` which makes match-expression and let-statement attributes
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work on any rustc version 1.31+. Place this attribute on any function containing
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`#[sorted]` to make them work on a stable compiler.
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```rust
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impl Display for Error {
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#[remain::check]
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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use self::Error::*;
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#[sorted]
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match self {
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/* ... */
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}
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}
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}
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```
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<br>
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#### License
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<sup>
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Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
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2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
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</sup>
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<br>
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<sub>
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
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be dual licensed as above, without any additional terms or conditions.
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</sub>
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