3 //! This crate declares the set of past and present unstable features in the compiler.
4 //! Feature gate checking itself is done in `librustc_ast_passes/feature_gate.rs`
7 //! Features are enabled in programs via the crate-level attributes of
8 //! `#![feature(...)]` with a comma-separated list of features.
10 //! For the purpose of future feature-tracking, once a feature gate is added,
11 //! even if it is stabilized or removed, *do not remove it*. Instead, move the
12 //! symbol to the `accepted` or `removed` modules respectively.
14 #![feature(once_cell)]
24 use rustc_span::{edition::Edition, symbol::Symbol, Span};
26 use std::num::NonZeroU32;
28 #[derive(Clone, Copy)]
31 Active { set: fn(&mut Features, Span) },
32 Removed { reason: Option<&'static str> },
33 Stabilized { reason: Option<&'static str> },
36 impl fmt::Debug for State {
37 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
39 State::Accepted { .. } => write!(f, "accepted"),
40 State::Active { .. } => write!(f, "active"),
41 State::Removed { .. } => write!(f, "removed"),
42 State::Stabilized { .. } => write!(f, "stabilized"),
47 #[derive(Debug, Clone)]
51 pub since: &'static str,
52 issue: Option<NonZeroU32>,
53 pub edition: Option<Edition>,
54 description: &'static str,
57 #[derive(Copy, Clone, Debug)]
60 // First argument is tracking issue link; second argument is an optional
61 // help message, which defaults to "remove this attribute".
62 Deprecated(&'static str, Option<&'static str>),
65 #[derive(Clone, Copy, Debug, Hash)]
66 pub enum UnstableFeatures {
67 /// Hard errors for unstable features are active, as on beta/stable channels.
69 /// Allow features to be activated, as on nightly.
71 /// Errors are bypassed for bootstrapping. This is required any time
72 /// during the build that feature-related lints are set to warn or above
73 /// because the build turns on warnings-as-errors and uses lots of unstable
74 /// features. As a result, this is always required for building Rust itself.
78 impl UnstableFeatures {
79 /// This takes into account `RUSTC_BOOTSTRAP`.
81 /// If `krate` is [`Some`], then setting `RUSTC_BOOTSTRAP=krate` will enable the nightly features.
82 /// Otherwise, only `RUSTC_BOOTSTRAP=1` will work.
83 pub fn from_environment(krate: Option<&str>) -> Self {
84 // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
85 let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
86 // Returns whether `krate` should be counted as unstable
87 let is_unstable_crate = |var: &str| {
88 krate.map_or(false, |name| var.split(',').any(|new_krate| new_krate == name))
90 // `true` if we should enable unstable features for bootstrapping.
91 let bootstrap = std::env::var("RUSTC_BOOTSTRAP")
92 .map_or(false, |var| var == "1" || is_unstable_crate(&var));
93 match (disable_unstable_features, bootstrap) {
94 (_, true) => UnstableFeatures::Cheat,
95 (true, _) => UnstableFeatures::Disallow,
96 (false, _) => UnstableFeatures::Allow,
100 pub fn is_nightly_build(&self) -> bool {
102 UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
103 UnstableFeatures::Disallow => false,
108 fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
109 if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
110 // FIXME (#28244): enforce that active features have issue numbers
111 // assert!(info.issue.is_some())
114 // search in Accepted, Removed, or Stable Removed features
115 let found = ACCEPTED_FEATURES
117 .chain(REMOVED_FEATURES)
118 .chain(STABLE_REMOVED_FEATURES)
119 .find(|t| t.name == feature);
121 Some(found) => found.issue,
122 None => panic!("feature `{}` is not declared anywhere", feature),
127 const fn to_nonzero(n: Option<u32>) -> Option<NonZeroU32> {
128 // Can be replaced with `n.and_then(NonZeroU32::new)` if that is ever usable
129 // in const context. Requires https://github.com/rust-lang/rfcs/pull/2632.
132 Some(n) => NonZeroU32::new(n),
138 Library(Option<NonZeroU32>),
141 pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZeroU32> {
143 GateIssue::Language => find_lang_feature_issue(feature),
144 GateIssue::Library(lib) => lib,
148 pub use accepted::ACCEPTED_FEATURES;
149 pub use active::{Features, ACTIVE_FEATURES, INCOMPATIBLE_FEATURES, INCOMPLETE_FEATURES};
150 pub use builtin_attrs::{
151 deprecated_attributes, find_gated_cfg, is_builtin_attr_name, AttributeGate, AttributeTemplate,
152 AttributeType, BuiltinAttribute, GatedCfg, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
154 pub use removed::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};