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1 | //! # Feature gates |
2 | //! | |
3 | //! This crate declares the set of past and present unstable features in the compiler. | |
dfeec247 XL |
4 | //! Feature gate checking itself is done in `librustc_ast_passes/feature_gate.rs` |
5 | //! at the moment. | |
60c5eb7d XL |
6 | //! |
7 | //! Features are enabled in programs via the crate-level attributes of | |
8 | //! `#![feature(...)]` with a comma-separated list of features. | |
9 | //! | |
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. | |
13 | ||
14 | mod accepted; | |
60c5eb7d XL |
15 | mod active; |
16 | mod builtin_attrs; | |
dfeec247 | 17 | mod removed; |
60c5eb7d | 18 | |
dfeec247 | 19 | use rustc_span::{edition::Edition, symbol::Symbol, Span}; |
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20 | use std::fmt; |
21 | use std::num::NonZeroU32; | |
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22 | |
23 | #[derive(Clone, Copy)] | |
24 | pub enum State { | |
25 | Accepted, | |
26 | Active { set: fn(&mut Features, Span) }, | |
27 | Removed { reason: Option<&'static str> }, | |
28 | Stabilized { reason: Option<&'static str> }, | |
29 | } | |
30 | ||
31 | impl fmt::Debug for State { | |
32 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
33 | match self { | |
34 | State::Accepted { .. } => write!(f, "accepted"), | |
35 | State::Active { .. } => write!(f, "active"), | |
36 | State::Removed { .. } => write!(f, "removed"), | |
37 | State::Stabilized { .. } => write!(f, "stabilized"), | |
38 | } | |
39 | } | |
40 | } | |
41 | ||
42 | #[derive(Debug, Clone)] | |
43 | pub struct Feature { | |
44 | pub state: State, | |
45 | pub name: Symbol, | |
46 | pub since: &'static str, | |
dfeec247 | 47 | issue: Option<u32>, // FIXME: once #58732 is done make this an Option<NonZeroU32> |
60c5eb7d XL |
48 | pub edition: Option<Edition>, |
49 | description: &'static str, | |
50 | } | |
51 | ||
52 | impl Feature { | |
53 | fn issue(&self) -> Option<NonZeroU32> { | |
ba9703b0 | 54 | self.issue.and_then(NonZeroU32::new) |
60c5eb7d XL |
55 | } |
56 | } | |
57 | ||
58 | #[derive(Copy, Clone, Debug)] | |
59 | pub enum Stability { | |
60 | Unstable, | |
61 | // First argument is tracking issue link; second argument is an optional | |
62 | // help message, which defaults to "remove this attribute". | |
63 | Deprecated(&'static str, Option<&'static str>), | |
64 | } | |
65 | ||
66 | #[derive(Clone, Copy, Hash)] | |
67 | pub enum UnstableFeatures { | |
68 | /// Hard errors for unstable features are active, as on beta/stable channels. | |
69 | Disallow, | |
70 | /// Allow features to be activated, as on nightly. | |
71 | Allow, | |
72 | /// Errors are bypassed for bootstrapping. This is required any time | |
73 | /// during the build that feature-related lints are set to warn or above | |
74 | /// because the build turns on warnings-as-errors and uses lots of unstable | |
75 | /// features. As a result, this is always required for building Rust itself. | |
dfeec247 | 76 | Cheat, |
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77 | } |
78 | ||
79 | impl UnstableFeatures { | |
80 | pub fn from_environment() -> UnstableFeatures { | |
81 | // `true` if this is a feature-staged build, i.e., on the beta or stable channel. | |
82 | let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some(); | |
83 | // `true` if we should enable unstable features for bootstrapping. | |
84 | let bootstrap = std::env::var("RUSTC_BOOTSTRAP").is_ok(); | |
85 | match (disable_unstable_features, bootstrap) { | |
86 | (_, true) => UnstableFeatures::Cheat, | |
87 | (true, _) => UnstableFeatures::Disallow, | |
dfeec247 | 88 | (false, _) => UnstableFeatures::Allow, |
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89 | } |
90 | } | |
91 | ||
92 | pub fn is_nightly_build(&self) -> bool { | |
93 | match *self { | |
94 | UnstableFeatures::Allow | UnstableFeatures::Cheat => true, | |
95 | UnstableFeatures::Disallow => false, | |
96 | } | |
97 | } | |
98 | } | |
99 | ||
100 | fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> { | |
101 | if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) { | |
102 | // FIXME (#28244): enforce that active features have issue numbers | |
103 | // assert!(info.issue().is_some()) | |
104 | info.issue() | |
105 | } else { | |
106 | // search in Accepted, Removed, or Stable Removed features | |
107 | let found = ACCEPTED_FEATURES | |
108 | .iter() | |
109 | .chain(REMOVED_FEATURES) | |
110 | .chain(STABLE_REMOVED_FEATURES) | |
111 | .find(|t| t.name == feature); | |
112 | match found { | |
113 | Some(found) => found.issue(), | |
114 | None => panic!("feature `{}` is not declared anywhere", feature), | |
115 | } | |
116 | } | |
117 | } | |
118 | ||
119 | pub enum GateIssue { | |
120 | Language, | |
dfeec247 | 121 | Library(Option<NonZeroU32>), |
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122 | } |
123 | ||
124 | pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZeroU32> { | |
125 | match issue { | |
126 | GateIssue::Language => find_lang_feature_issue(feature), | |
127 | GateIssue::Library(lib) => lib, | |
128 | } | |
129 | } | |
130 | ||
131 | pub use accepted::ACCEPTED_FEATURES; | |
dfeec247 | 132 | pub use active::{Features, ACTIVE_FEATURES, INCOMPLETE_FEATURES}; |
60c5eb7d | 133 | pub use builtin_attrs::{ |
dfeec247 XL |
134 | deprecated_attributes, find_gated_cfg, is_builtin_attr_name, AttributeGate, AttributeTemplate, |
135 | AttributeType, BuiltinAttribute, GatedCfg, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP, | |
60c5eb7d | 136 | }; |
dfeec247 | 137 | pub use removed::{REMOVED_FEATURES, STABLE_REMOVED_FEATURES}; |