rustc_passes/
lib_features.rs

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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
7use rustc_attr_parsing::{AttributeKind, StabilityLevel, StableSince};
8use rustc_hir::Attribute;
9use rustc_hir::intravisit::Visitor;
10use rustc_middle::hir::nested_filter;
11use rustc_middle::middle::lib_features::{FeatureStability, LibFeatures};
12use rustc_middle::query::{LocalCrate, Providers};
13use rustc_middle::ty::TyCtxt;
14use rustc_span::{Span, Symbol, sym};
15
16use crate::errors::{FeaturePreviouslyDeclared, FeatureStableTwice};
17
18struct LibFeatureCollector<'tcx> {
19    tcx: TyCtxt<'tcx>,
20    lib_features: LibFeatures,
21}
22
23impl<'tcx> LibFeatureCollector<'tcx> {
24    fn new(tcx: TyCtxt<'tcx>) -> LibFeatureCollector<'tcx> {
25        LibFeatureCollector { tcx, lib_features: LibFeatures::default() }
26    }
27
28    fn extract(&self, attr: &Attribute) -> Option<(Symbol, FeatureStability, Span)> {
29        let (feature, level, span) = match attr {
30            Attribute::Parsed(AttributeKind::Stability { stability, span }) => {
31                (stability.feature, stability.level, *span)
32            }
33            Attribute::Parsed(AttributeKind::ConstStability { stability, span }) => {
34                (stability.feature, stability.level, *span)
35            }
36            Attribute::Parsed(AttributeKind::BodyStability { stability, span }) => {
37                (stability.feature, stability.level, *span)
38            }
39            _ => return None,
40        };
41
42        let feature_stability = match level {
43            StabilityLevel::Unstable { .. } => FeatureStability::Unstable,
44            StabilityLevel::Stable { since, .. } => FeatureStability::AcceptedSince(match since {
45                StableSince::Version(v) => Symbol::intern(&v.to_string()),
46                StableSince::Current => sym::env_CFG_RELEASE,
47                StableSince::Err => return None,
48            }),
49        };
50
51        Some((feature, feature_stability, span))
52    }
53
54    fn collect_feature(&mut self, feature: Symbol, stability: FeatureStability, span: Span) {
55        let existing_stability = self.lib_features.stability.get(&feature).cloned();
56
57        match (stability, existing_stability) {
58            (_, None) => {
59                self.lib_features.stability.insert(feature, (stability, span));
60            }
61            (
62                FeatureStability::AcceptedSince(since),
63                Some((FeatureStability::AcceptedSince(prev_since), _)),
64            ) => {
65                if prev_since != since {
66                    self.tcx.dcx().emit_err(FeatureStableTwice {
67                        span,
68                        feature,
69                        since,
70                        prev_since,
71                    });
72                }
73            }
74            (FeatureStability::AcceptedSince(_), Some((FeatureStability::Unstable, _))) => {
75                self.tcx.dcx().emit_err(FeaturePreviouslyDeclared {
76                    span,
77                    feature,
78                    declared: "stable",
79                    prev_declared: "unstable",
80                });
81            }
82            (FeatureStability::Unstable, Some((FeatureStability::AcceptedSince(_), _))) => {
83                self.tcx.dcx().emit_err(FeaturePreviouslyDeclared {
84                    span,
85                    feature,
86                    declared: "unstable",
87                    prev_declared: "stable",
88                });
89            }
90            // duplicate `unstable` feature is ok.
91            (FeatureStability::Unstable, Some((FeatureStability::Unstable, _))) => {}
92        }
93    }
94}
95
96impl<'tcx> Visitor<'tcx> for LibFeatureCollector<'tcx> {
97    type NestedFilter = nested_filter::All;
98
99    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
100        self.tcx
101    }
102
103    fn visit_attribute(&mut self, attr: &'tcx Attribute) {
104        if let Some((feature, stable, span)) = self.extract(attr) {
105            self.collect_feature(feature, stable, span);
106        }
107    }
108}
109
110fn lib_features(tcx: TyCtxt<'_>, LocalCrate: LocalCrate) -> LibFeatures {
111    // If `staged_api` is not enabled then we aren't allowed to define lib
112    // features; there is no point collecting them.
113    if !tcx.features().staged_api() {
114        return LibFeatures::default();
115    }
116
117    let mut collector = LibFeatureCollector::new(tcx);
118    tcx.hir_walk_attributes(&mut collector);
119    collector.lib_features
120}
121
122pub(crate) fn provide(providers: &mut Providers) {
123    providers.lib_features = lib_features;
124}
rustc_passes/lib_features.rs

rustc_passes/
lib_features.rs
