src/libsyntax/feature_gate/mod.rs

   1 //! # Feature gating
   2 //!
   3 //! This module implements the gating necessary for preventing certain compiler
   4 //! features from being used by default. This module will crawl a pre-expanded
   5 //! AST to ensure that there are no features which are used that are not
   6 //! enabled.
   7 //!
   8 //! Features are enabled in programs via the crate-level attributes of
   9 //! `#![feature(...)]` with a comma-separated list of features.
  10 //!
  11 //! For the purpose of future feature-tracking, once code for detection of feature
  12 //! gate usage is added, *do not remove it again* even once the feature
  13 //! becomes stable.
  14
  15 mod accepted;
  16 mod removed;
  17 mod active;
  18 mod builtin_attrs;
  19 mod check;
  20
  21 use crate::{edition::Edition, symbol::Symbol};
  22 use std::fmt;
  23 use std::num::NonZeroU32;
  24 use syntax_pos::Span;
  25
  26 #[derive(Clone, Copy)]
  27 pub enum State {
  28     Accepted,
  29     Active { set: fn(&mut Features, Span) },
  30     Removed { reason: Option<&'static str> },
  31     Stabilized { reason: Option<&'static str> },
  32 }
  33
  34 impl fmt::Debug for State {
  35     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  36         match self {
  37             State::Accepted { .. } => write!(f, "accepted"),
  38             State::Active { .. } => write!(f, "active"),
  39             State::Removed { .. } => write!(f, "removed"),
  40             State::Stabilized { .. } => write!(f, "stabilized"),
  41         }
  42     }
  43 }
  44
  45 #[derive(Debug, Clone)]
  46 pub struct Feature {
  47     state: State,
  48     name: Symbol,
  49     since: &'static str,
  50     issue: Option<u32>,  // FIXME: once #58732 is done make this an Option<NonZeroU32>
  51     edition: Option<Edition>,
  52     description: &'static str,
  53 }
  54
  55 impl Feature {
  56     fn issue(&self) -> Option<NonZeroU32> {
  57         self.issue.and_then(|i| NonZeroU32::new(i))
  58     }
  59 }
  60
  61 pub use active::{Features, INCOMPLETE_FEATURES};
  62 pub use builtin_attrs::{
  63     AttributeGate, AttributeType, GatedCfg,
  64     BuiltinAttribute, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
  65     deprecated_attributes, is_builtin_attr,  is_builtin_attr_name,
  66 };
  67 pub use check::{
  68     check_crate, check_attribute, get_features, feature_err, emit_feature_err,
  69     Stability, GateIssue, UnstableFeatures,
  70     EXPLAIN_STMT_ATTR_SYNTAX, EXPLAIN_UNSIZED_TUPLE_COERCION,
  71 };