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, MetaItemKind};
   8 use rustc_errors::struct_span_err;
   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 fn new_lib_features() -> LibFeatures {
  18     LibFeatures { stable: Default::default(), unstable: Default::default() }
  19 }
  20
  21 pub struct LibFeatureCollector<'tcx> {
  22     tcx: TyCtxt<'tcx>,
  23     lib_features: LibFeatures,
  24 }
  25
  26 impl<'tcx> LibFeatureCollector<'tcx> {
  27     fn new(tcx: TyCtxt<'tcx>) -> LibFeatureCollector<'tcx> {
  28         LibFeatureCollector { tcx, lib_features: new_lib_features() }
  29     }
  30
  31     fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
  32         let stab_attrs = [
  33             sym::stable,
  34             sym::unstable,
  35             sym::rustc_const_stable,
  36             sym::rustc_const_unstable,
  37             sym::rustc_default_body_unstable,
  38         ];
  39
  40         // Find a stability attribute: one of #[stable(…)], #[unstable(…)],
  41         // #[rustc_const_stable(…)], #[rustc_const_unstable(…)] or #[rustc_default_body_unstable].
  42         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
  43             let meta_kind = attr.meta_kind();
  44             if let Some(MetaItemKind::List(ref metas)) = meta_kind {
  45                 let mut feature = None;
  46                 let mut since = None;
  47                 for meta in metas {
  48                     if let Some(mi) = meta.meta_item() {
  49                         // Find the `feature = ".."` meta-item.
  50                         match (mi.name_or_empty(), mi.value_str()) {
  51                             (sym::feature, val) => feature = val,
  52                             (sym::since, val) => since = val,
  53                             _ => {}
  54                         }
  55                     }
  56                 }
  57                 if let Some(feature) = feature {
  58                     // This additional check for stability is to make sure we
  59                     // don't emit additional, irrelevant errors for malformed
  60                     // attributes.
  61                     let is_unstable = matches!(
  62                         *stab_attr,
  63                         sym::unstable
  64                             | sym::rustc_const_unstable
  65                             | sym::rustc_default_body_unstable
  66                     );
  67                     if since.is_some() || is_unstable {
  68                         return Some((feature, since, attr.span));
  69                     }
  70                 }
  71                 // We need to iterate over the other attributes, because
  72                 // `rustc_const_unstable` is not mutually exclusive with
  73                 // the other stability attributes, so we can't just `break`
  74                 // here.
  75             }
  76         }
  77
  78         None
  79     }
  80
  81     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  82         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  83         let already_in_unstable = self.lib_features.unstable.contains_key(&feature);
  84
  85         match (since, already_in_stable, already_in_unstable) {
  86             (Some(since), _, false) => {
  87                 if let Some((prev_since, _)) = self.lib_features.stable.get(&feature) {
  88                     if *prev_since != since {
  89                         self.span_feature_error(
  90                             span,
  91                             &format!(
  92                                 "feature `{}` is declared stable since {}, \
  93                                  but was previously declared stable since {}",
  94                                 feature, since, prev_since,
  95                             ),
  96                         );
  97                         return;
  98                     }
  99                 }
 100
 101                 self.lib_features.stable.insert(feature, (since, span));
 102             }
 103             (None, false, _) => {
 104                 self.lib_features.unstable.insert(feature, span);
 105             }
 106             (Some(_), _, true) | (None, true, _) => {
 107                 self.span_feature_error(
 108                     span,
 109                     &format!(
 110                         "feature `{}` is declared {}, but was previously declared {}",
 111                         feature,
 112                         if since.is_some() { "stable" } else { "unstable" },
 113                         if since.is_none() { "stable" } else { "unstable" },
 114                     ),
 115                 );
 116             }
 117         }
 118     }
 119
 120     fn span_feature_error(&self, span: Span, msg: &str) {
 121         struct_span_err!(self.tcx.sess, span, E0711, "{}", &msg).emit();
 122     }
 123 }
 124
 125 impl<'tcx> Visitor<'tcx> for LibFeatureCollector<'tcx> {
 126     type NestedFilter = nested_filter::All;
 127
 128     fn nested_visit_map(&mut self) -> Self::Map {
 129         self.tcx.hir()
 130     }
 131
 132     fn visit_attribute(&mut self, attr: &'tcx Attribute) {
 133         if let Some((feature, stable, span)) = self.extract(attr) {
 134             self.collect_feature(feature, stable, span);
 135         }
 136     }
 137 }
 138
 139 fn lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
 140     let mut collector = LibFeatureCollector::new(tcx);
 141     tcx.hir().walk_attributes(&mut collector);
 142     collector.lib_features
 143 }
 144
 145 pub fn provide(providers: &mut Providers) {
 146     providers.lib_features = lib_features;
 147 }