src/librustc_feature/lib.rs

   1 //! # Feature gates
   2 //!
   3 //! This crate declares the set of past and present unstable features in the compiler.
   4 //! Feature gate checking itself is done in `libsyntax/feature_gate/check.rs` at the moment.
   5 //!
   6 //! Features are enabled in programs via the crate-level attributes of
   7 //! `#![feature(...)]` with a comma-separated list of features.
   8 //!
   9 //! For the purpose of future feature-tracking, once a feature gate is added,
  10 //! even if it is stabilized or removed, *do not remove it*. Instead, move the
  11 //! symbol to the `accepted` or `removed` modules respectively.
  12
  13 mod accepted;
  14 mod removed;
  15 mod active;
  16 mod builtin_attrs;
  17
  18 use std::fmt;
  19 use std::num::NonZeroU32;
  20 use syntax_pos::{Span, edition::Edition, symbol::Symbol};
  21
  22 #[derive(Clone, Copy)]
  23 pub enum State {
  24     Accepted,
  25     Active { set: fn(&mut Features, Span) },
  26     Removed { reason: Option<&'static str> },
  27     Stabilized { reason: Option<&'static str> },
  28 }
  29
  30 impl fmt::Debug for State {
  31     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  32         match self {
  33             State::Accepted { .. } => write!(f, "accepted"),
  34             State::Active { .. } => write!(f, "active"),
  35             State::Removed { .. } => write!(f, "removed"),
  36             State::Stabilized { .. } => write!(f, "stabilized"),
  37         }
  38     }
  39 }
  40
  41 #[derive(Debug, Clone)]
  42 pub struct Feature {
  43     pub state: State,
  44     pub name: Symbol,
  45     pub since: &'static str,
  46     issue: Option<u32>,  // FIXME: once #58732 is done make this an Option<NonZeroU32>
  47     pub edition: Option<Edition>,
  48     description: &'static str,
  49 }
  50
  51 impl Feature {
  52     fn issue(&self) -> Option<NonZeroU32> {
  53         self.issue.and_then(|i| NonZeroU32::new(i))
  54     }
  55 }
  56
  57 #[derive(Copy, Clone, Debug)]
  58 pub enum Stability {
  59     Unstable,
  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>),
  63 }
  64
  65 #[derive(Clone, Copy, Hash)]
  66 pub enum UnstableFeatures {
  67     /// Hard errors for unstable features are active, as on beta/stable channels.
  68     Disallow,
  69     /// Allow features to be activated, as on nightly.
  70     Allow,
  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.
  75     Cheat
  76 }
  77
  78 impl UnstableFeatures {
  79     pub fn from_environment() -> UnstableFeatures {
  80         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
  81         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
  82         // `true` if we should enable unstable features for bootstrapping.
  83         let bootstrap = std::env::var("RUSTC_BOOTSTRAP").is_ok();
  84         match (disable_unstable_features, bootstrap) {
  85             (_, true) => UnstableFeatures::Cheat,
  86             (true, _) => UnstableFeatures::Disallow,
  87             (false, _) => UnstableFeatures::Allow
  88         }
  89     }
  90
  91     pub fn is_nightly_build(&self) -> bool {
  92         match *self {
  93             UnstableFeatures::Allow | UnstableFeatures::Cheat => true,
  94             UnstableFeatures::Disallow => false,
  95         }
  96     }
  97 }
  98
  99 fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
 100     if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
 101         // FIXME (#28244): enforce that active features have issue numbers
 102         // assert!(info.issue().is_some())
 103         info.issue()
 104     } else {
 105         // search in Accepted, Removed, or Stable Removed features
 106         let found = ACCEPTED_FEATURES
 107             .iter()
 108             .chain(REMOVED_FEATURES)
 109             .chain(STABLE_REMOVED_FEATURES)
 110             .find(|t| t.name == feature);
 111         match found {
 112             Some(found) => found.issue(),
 113             None => panic!("feature `{}` is not declared anywhere", feature),
 114         }
 115     }
 116 }
 117
 118 pub enum GateIssue {
 119     Language,
 120     Library(Option<NonZeroU32>)
 121 }
 122
 123 pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZeroU32> {
 124     match issue {
 125         GateIssue::Language => find_lang_feature_issue(feature),
 126         GateIssue::Library(lib) => lib,
 127     }
 128 }
 129
 130 pub use accepted::ACCEPTED_FEATURES;
 131 pub use active::{ACTIVE_FEATURES, Features, INCOMPLETE_FEATURES};
 132 pub use removed::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES};
 133 pub use builtin_attrs::{
 134     AttributeGate, AttributeTemplate, AttributeType, find_gated_cfg, GatedCfg,
 135     BuiltinAttribute, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
 136     deprecated_attributes, is_builtin_attr_name,
 137 };