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[rust.git] / compiler / rustc_passes / src / lib_features.rs
1 //! Detecting lib features (i.e., features that are not lang features).
2 //!
3 //! These are declared using stability attributes (e.g., `#[stable (..)]` and `#[unstable (..)]`),
4 //! but are not declared in one single location (unlike lang features), which means we need to
5 //! collect them instead.
6
7 use rustc_ast::Attribute;
8 use rustc_attr::{rust_version_symbol, VERSION_PLACEHOLDER};
9 use rustc_hir::intravisit::Visitor;
10 use rustc_middle::hir::nested_filter;
11 use rustc_middle::middle::lib_features::LibFeatures;
12 use rustc_middle::ty::query::Providers;
13 use rustc_middle::ty::TyCtxt;
14 use rustc_span::symbol::Symbol;
15 use rustc_span::{sym, Span};
16
17 use crate::errors::{FeaturePreviouslyDeclared, FeatureStableTwice};
18
19 fn new_lib_features() -> LibFeatures {
20     LibFeatures { stable: Default::default(), unstable: Default::default() }
21 }
22
23 pub struct LibFeatureCollector<'tcx> {
24     tcx: TyCtxt<'tcx>,
25     lib_features: LibFeatures,
26 }
27
28 impl<'tcx> LibFeatureCollector<'tcx> {
29     fn new(tcx: TyCtxt<'tcx>) -> LibFeatureCollector<'tcx> {
30         LibFeatureCollector { tcx, lib_features: new_lib_features() }
31     }
32
33     fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
34         let stab_attrs = [
35             sym::stable,
36             sym::unstable,
37             sym::rustc_const_stable,
38             sym::rustc_const_unstable,
39             sym::rustc_default_body_unstable,
40         ];
41
42         // Find a stability attribute: one of #[stable(…)], #[unstable(…)],
43         // #[rustc_const_stable(…)], #[rustc_const_unstable(…)] or #[rustc_default_body_unstable].
44         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
45             if let Some(metas) = attr.meta_item_list() {
46                 let mut feature = None;
47                 let mut since = None;
48                 for meta in metas {
49                     if let Some(mi) = meta.meta_item() {
50                         // Find the `feature = ".."` meta-item.
51                         match (mi.name_or_empty(), mi.value_str()) {
52                             (sym::feature, val) => feature = val,
53                             (sym::since, val) => since = val,
54                             _ => {}
55                         }
56                     }
57                 }
58
59                 if let Some(s) = since && s.as_str() == VERSION_PLACEHOLDER {
60                     since = Some(rust_version_symbol());
61                 }
62
63                 if let Some(feature) = feature {
64                     // This additional check for stability is to make sure we
65                     // don't emit additional, irrelevant errors for malformed
66                     // attributes.
67                     let is_unstable = matches!(
68                         *stab_attr,
69                         sym::unstable
70                             | sym::rustc_const_unstable
71                             | sym::rustc_default_body_unstable
72                     );
73                     if since.is_some() || is_unstable {
74                         return Some((feature, since, attr.span));
75                     }
76                 }
77                 // We need to iterate over the other attributes, because
78                 // `rustc_const_unstable` is not mutually exclusive with
79                 // the other stability attributes, so we can't just `break`
80                 // here.
81             }
82         }
83
84         None
85     }
86
87     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
88         let already_in_stable = self.lib_features.stable.contains_key(&feature);
89         let already_in_unstable = self.lib_features.unstable.contains_key(&feature);
90
91         match (since, already_in_stable, already_in_unstable) {
92             (Some(since), _, false) => {
93                 if let Some((prev_since, _)) = self.lib_features.stable.get(&feature) {
94                     if *prev_since != since {
95                         self.tcx.sess.emit_err(FeatureStableTwice {
96                             span,
97                             feature,
98                             since,
99                             prev_since: *prev_since,
100                         });
101                         return;
102                     }
103                 }
104
105                 self.lib_features.stable.insert(feature, (since, span));
106             }
107             (None, false, _) => {
108                 self.lib_features.unstable.insert(feature, span);
109             }
110             (Some(_), _, true) | (None, true, _) => {
111                 let declared = if since.is_some() { "stable" } else { "unstable" };
112                 let prev_declared = if since.is_none() { "stable" } else { "unstable" };
113                 self.tcx.sess.emit_err(FeaturePreviouslyDeclared {
114                     span,
115                     feature,
116                     declared,
117                     prev_declared,
118                 });
119             }
120         }
121     }
122 }
123
124 impl<'tcx> Visitor<'tcx> for LibFeatureCollector<'tcx> {
125     type NestedFilter = nested_filter::All;
126
127     fn nested_visit_map(&mut self) -> Self::Map {
128         self.tcx.hir()
129     }
130
131     fn visit_attribute(&mut self, attr: &'tcx Attribute) {
132         if let Some((feature, stable, span)) = self.extract(attr) {
133             self.collect_feature(feature, stable, span);
134         }
135     }
136 }
137
138 fn lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
139     // If `staged_api` is not enabled then we aren't allowed to define lib
140     // features; there is no point collecting them.
141     if !tcx.features().staged_api {
142         return new_lib_features();
143     }
144
145     let mut collector = LibFeatureCollector::new(tcx);
146     tcx.hir().walk_attributes(&mut collector);
147     collector.lib_features
148 }
149
150 pub fn provide(providers: &mut Providers) {
151     providers.lib_features = lib_features;
152 }