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 (..)]`
   4 // and `#[unstable (..)]`), but are not declared in one single location
   5 // (unlike lang features), which means we need to collect them instead.
   6
   7 use rustc_ast::{Attribute, MetaItem, MetaItemKind};
   8 use rustc_errors::struct_span_err;
   9 use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
  10 use rustc_middle::hir::map::Map;
  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 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 = [sym::stable, sym::unstable, sym::rustc_const_unstable];
  33
  34         // Find a stability attribute (i.e., `#[stable (..)]`, `#[unstable (..)]`,
  35         // `#[rustc_const_unstable (..)]`).
  36         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
  37             let meta_item = attr.meta();
  38             if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta_item {
  39                 let mut feature = None;
  40                 let mut since = None;
  41                 for meta in metas {
  42                     if let Some(mi) = meta.meta_item() {
  43                         // Find the `feature = ".."` meta-item.
  44                         match (mi.name_or_empty(), mi.value_str()) {
  45                             (sym::feature, val) => feature = val,
  46                             (sym::since, val) => since = val,
  47                             _ => {}
  48                         }
  49                     }
  50                 }
  51                 if let Some(feature) = feature {
  52                     // This additional check for stability is to make sure we
  53                     // don't emit additional, irrelevant errors for malformed
  54                     // attributes.
  55                     if *stab_attr != sym::stable || since.is_some() {
  56                         return Some((feature, since, attr.span));
  57                     }
  58                 }
  59                 // We need to iterate over the other attributes, because
  60                 // `rustc_const_unstable` is not mutually exclusive with
  61                 // the other stability attributes, so we can't just `break`
  62                 // here.
  63             }
  64         }
  65
  66         None
  67     }
  68
  69     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  70         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  71         let already_in_unstable = self.lib_features.unstable.contains(&feature);
  72
  73         match (since, already_in_stable, already_in_unstable) {
  74             (Some(since), _, false) => {
  75                 if let Some(prev_since) = self.lib_features.stable.get(&feature) {
  76                     if *prev_since != since {
  77                         self.span_feature_error(
  78                             span,
  79                             &format!(
  80                                 "feature `{}` is declared stable since {}, \
  81                                  but was previously declared stable since {}",
  82                                 feature, since, prev_since,
  83                             ),
  84                         );
  85                         return;
  86                     }
  87                 }
  88
  89                 self.lib_features.stable.insert(feature, since);
  90             }
  91             (None, false, _) => {
  92                 self.lib_features.unstable.insert(feature);
  93             }
  94             (Some(_), _, true) | (None, true, _) => {
  95                 self.span_feature_error(
  96                     span,
  97                     &format!(
  98                         "feature `{}` is declared {}, but was previously declared {}",
  99                         feature,
 100                         if since.is_some() { "stable" } else { "unstable" },
 101                         if since.is_none() { "stable" } else { "unstable" },
 102                     ),
 103                 );
 104             }
 105         }
 106     }
 107
 108     fn span_feature_error(&self, span: Span, msg: &str) {
 109         struct_span_err!(self.tcx.sess, span, E0711, "{}", &msg).emit();
 110     }
 111 }
 112
 113 impl Visitor<'tcx> for LibFeatureCollector<'tcx> {
 114     type Map = Map<'tcx>;
 115
 116     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 117         NestedVisitorMap::All(self.tcx.hir())
 118     }
 119
 120     fn visit_attribute(&mut self, _: rustc_hir::HirId, attr: &'tcx Attribute) {
 121         if let Some((feature, stable, span)) = self.extract(attr) {
 122             self.collect_feature(feature, stable, span);
 123         }
 124     }
 125 }
 126
 127 fn get_lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
 128     let mut collector = LibFeatureCollector::new(tcx);
 129     tcx.hir().walk_attributes(&mut collector);
 130     collector.lib_features
 131 }
 132
 133 pub fn provide(providers: &mut Providers) {
 134     providers.get_lib_features = get_lib_features;
 135 }