rustc_feature/lib.rs
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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.
// tidy-alphabetical-start
#![allow(internal_features)]
#![doc(rust_logo)]
#![feature(rustdoc_internals)]
#![warn(unreachable_pub)]
// tidy-alphabetical-end
mod accepted;
mod builtin_attrs;
mod removed;
mod unstable;
#[cfg(test)]
mod tests;
use std::num::NonZero;
use rustc_span::symbol::Symbol;
#[derive(Debug, Clone)]
pub struct Feature {
pub name: Symbol,
/// For unstable features: the version the feature was added in.
/// For accepted features: the version the feature got stabilized in.
/// For removed features we are inconsistent; sometimes this is the
/// version it got added, sometimes the version it got removed.
pub since: &'static str,
issue: Option<NonZero<u32>>,
}
#[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 {
/// Disallow use of unstable features, as on beta/stable channels.
Disallow,
/// Allow use of unstable features, 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_and(|s| s != "0");
// Returns whether `krate` should be counted as unstable
let is_unstable_crate =
|var: &str| krate.is_some_and(|name| var.split(',').any(|new_krate| new_krate == name));
let bootstrap = std::env::var("RUSTC_BOOTSTRAP").ok();
if let Some(val) = bootstrap.as_deref() {
match val {
val if val == "1" || is_unstable_crate(val) => return UnstableFeatures::Cheat,
// Hypnotize ourselves so that we think we are a stable compiler and thus don't
// allow any unstable features.
"-1" => return UnstableFeatures::Disallow,
_ => {}
}
}
if disable_unstable_features { UnstableFeatures::Disallow } else { 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<NonZero<u32>> {
// Search in all the feature lists.
if let Some(f) = UNSTABLE_LANG_FEATURES.iter().find(|f| f.name == feature) {
return f.issue;
}
if let Some(f) = ACCEPTED_LANG_FEATURES.iter().find(|f| f.name == feature) {
return f.issue;
}
if let Some(f) = REMOVED_LANG_FEATURES.iter().find(|f| f.feature.name == feature) {
return f.feature.issue;
}
panic!("feature `{feature}` is not declared anywhere");
}
const fn to_nonzero(n: Option<u32>) -> Option<NonZero<u32>> {
// Can be replaced with `n.and_then(NonZero::new)` if that is ever usable
// in const context. Requires https://github.com/rust-lang/rfcs/pull/2632.
match n {
None => None,
Some(n) => NonZero::new(n),
}
}
pub enum GateIssue {
Language,
Library(Option<NonZero<u32>>),
}
pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZero<u32>> {
match issue {
GateIssue::Language => find_lang_feature_issue(feature),
GateIssue::Library(lib) => lib,
}
}
pub use accepted::ACCEPTED_LANG_FEATURES;
pub use builtin_attrs::{
AttributeDuplicates, AttributeGate, AttributeSafety, AttributeTemplate, AttributeType,
BUILTIN_ATTRIBUTE_MAP, BUILTIN_ATTRIBUTES, BuiltinAttribute, GatedCfg, deprecated_attributes,
encode_cross_crate, find_gated_cfg, is_builtin_attr_name, is_stable_diagnostic_attribute,
is_valid_for_get_attr,
};
pub use removed::REMOVED_LANG_FEATURES;
pub use unstable::{
EnabledLangFeature, EnabledLibFeature, Features, INCOMPATIBLE_FEATURES, UNSTABLE_LANG_FEATURES,
};