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//! # Feature gates
//!
//! This crate declares the set of past and present unstable features in the compiler.
//! Feature gate checking itself is done in `rustc_ast_passes/src/feature_gate.rs`
//! at the moment.
//!
//! 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 a feature gate is added,
//! even if it is stabilized or removed, *do not remove it*. Instead, move the
//! symbol to the `accepted` or `removed` modules respectively.
#![feature(once_cell)]
#![deny(rustc::untranslatable_diagnostic)]
#![deny(rustc::diagnostic_outside_of_impl)]
mod accepted;
mod active;
mod builtin_attrs;
mod removed;
#[cfg(test)]
mod tests;
use rustc_span::{edition::Edition, symbol::Symbol, Span};
use std::fmt;
use std::num::NonZeroU32;
#[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<NonZeroU32>,
pub edition: Option<Edition>,
}
#[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>),
}
#[derive(Clone, Copy, Debug, Hash)]
pub enum UnstableFeatures {
/// Hard errors for unstable features are active, as on beta/stable channels.
Disallow,
/// Allow features to be activated, as on nightly.
Allow,
/// Errors are bypassed for bootstrapping. This is required any time
/// during the build that feature-related lints are set to warn or above
/// because the build turns on warnings-as-errors and uses lots of unstable
/// features. As a result, this is always required for building Rust itself.
Cheat,
}
impl UnstableFeatures {
/// This takes into account `RUSTC_BOOTSTRAP`.
///
/// If `krate` is [`Some`], then setting `RUSTC_BOOTSTRAP=krate` will enable the nightly features.
/// Otherwise, only `RUSTC_BOOTSTRAP=1` will work.
pub fn from_environment(krate: Option<&str>) -> Self {
// `true` if this is a feature-staged build, i.e., on the beta or stable channel.
let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
// Returns whether `krate` should be counted as unstable
let is_unstable_crate = |var: &str| {
krate.map_or(false, |name| var.split(',').any(|new_krate| new_krate == name))
};
// `true` if we should enable unstable features for bootstrapping.
let bootstrap = std::env::var("RUSTC_BOOTSTRAP")
.map_or(false, |var| var == "1" || is_unstable_crate(&var));
match (disable_unstable_features, bootstrap) {
(_, true) => UnstableFeatures::Cheat,
(true, _) => UnstableFeatures::Disallow,
(false, _) => UnstableFeatures::Allow,
}
}
pub fn is_nightly_build(&self) -> bool {
match *self {
UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
UnstableFeatures::Disallow => false,
}
}
}
fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
// FIXME (#28244): enforce that active features have issue numbers
// assert!(info.issue.is_some())
info.issue
} else {
// search in Accepted, Removed, or Stable Removed features
let found = ACCEPTED_FEATURES
.iter()
.chain(REMOVED_FEATURES)
.chain(STABLE_REMOVED_FEATURES)
.find(|t| t.name == feature);
match found {
Some(found) => found.issue,
None => panic!("feature `{}` is not declared anywhere", feature),
}
}
}
const fn to_nonzero(n: Option<u32>) -> Option<NonZeroU32> {
// Can be replaced with `n.and_then(NonZeroU32::new)` if that is ever usable
// in const context. Requires https://github.com/rust-lang/rfcs/pull/2632.
match n {
None => None,
Some(n) => NonZeroU32::new(n),
}
}
pub enum GateIssue {
Language,
Library(Option<NonZeroU32>),
}
pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZeroU32> {
match issue {
GateIssue::Language => find_lang_feature_issue(feature),
GateIssue::Library(lib) => lib,
}
}
pub use accepted::ACCEPTED_FEATURES;
pub use active::{Features, ACTIVE_FEATURES, INCOMPATIBLE_FEATURES};
pub use builtin_attrs::AttributeDuplicates;
pub use builtin_attrs::{
deprecated_attributes, find_gated_cfg, is_builtin_attr_name, is_builtin_only_local,
is_valid_for_get_attr, AttributeGate, AttributeTemplate, AttributeType, BuiltinAttribute,
GatedCfg, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
};
pub use removed::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};
|
