rust/src/librustc_feature/lib.rs

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//! # Feature gating
//!
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//! This module implements the gating necessary for preventing certain compiler
//! features from being used by default. This module will crawl a pre-expanded
//! AST to ensure that there are no features which are used that are not
//! enabled.
//!
//! Features are enabled in programs via the crate-level attributes of
//! `#![feature(...)]` with a comma-separated list of features.
//!
//! For the purpose of future feature-tracking, once code for detection of feature
//! gate usage is added, *do not remove it again* even once the feature
//! becomes stable.
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mod accepted;
mod removed;
mod active;
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use std::fmt;
use std::num::NonZeroU32;
use syntax_pos::{Span, edition::Edition, symbol::Symbol};
#[derive(Clone, Copy)]
pub enum State {
Accepted,
Active { set: fn(&mut Features, Span) },
Removed { reason: Option<&'static str> },
Stabilized { reason: Option<&'static str> },
}
impl fmt::Debug for State {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
State::Accepted { .. } => write!(f, "accepted"),
State::Active { .. } => write!(f, "active"),
State::Removed { .. } => write!(f, "removed"),
State::Stabilized { .. } => write!(f, "stabilized"),
}
}
}
#[derive(Debug, Clone)]
pub struct Feature {
pub state: State,
pub name: Symbol,
pub since: &'static str,
issue: Option<u32>, // FIXME: once #58732 is done make this an Option<NonZeroU32>
pub edition: Option<Edition>,
description: &'static str,
}
impl Feature {
// FIXME(Centril): privatize again.
pub fn issue(&self) -> Option<NonZeroU32> {
self.issue.and_then(|i| NonZeroU32::new(i))
}
}
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#[derive(Copy, Clone, Debug)]
pub enum Stability {
Unstable,
// First argument is tracking issue link; second argument is an optional
// help message, which defaults to "remove this attribute".
Deprecated(&'static str, Option<&'static str>),
}
pub use accepted::ACCEPTED_FEATURES;
pub use active::{ACTIVE_FEATURES, Features, INCOMPLETE_FEATURES};
pub use removed::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};