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