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

rustc_passes/
lib_features.rs
