src/librustc_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 (..)]`
   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::def_id::LOCAL_CRATE;
  10 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  11 use rustc_middle::hir::map::Map;
  12 use rustc_middle::middle::lib_features::LibFeatures;
  13 use rustc_middle::ty::query::Providers;
  14 use rustc_middle::ty::TyCtxt;
  15 use rustc_span::symbol::Symbol;
  16 use rustc_span::{sym, Span};
  17
  18 fn new_lib_features() -> LibFeatures {
  19     LibFeatures { stable: Default::default(), unstable: Default::default() }
  20 }
  21
  22 pub struct LibFeatureCollector<'tcx> {
  23     tcx: TyCtxt<'tcx>,
  24     lib_features: LibFeatures,
  25 }
  26
  27 impl LibFeatureCollector<'tcx> {
  28     fn new(tcx: TyCtxt<'tcx>) -> LibFeatureCollector<'tcx> {
  29         LibFeatureCollector { tcx, lib_features: new_lib_features() }
  30     }
  31
  32     fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
  33         let stab_attrs = [sym::stable, sym::unstable, sym::rustc_const_unstable];
  34
  35         // Find a stability attribute (i.e., `#[stable (..)]`, `#[unstable (..)]`,
  36         // `#[rustc_const_unstable (..)]`).
  37         if let Some(stab_attr) =
  38             stab_attrs.iter().find(|stab_attr| self.tcx.sess.check_name(attr, **stab_attr))
  39         {
  40             let meta_item = attr.meta();
  41             if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta_item {
  42                 let mut feature = None;
  43                 let mut since = None;
  44                 for meta in metas {
  45                     if let Some(mi) = meta.meta_item() {
  46                         // Find the `feature = ".."` meta-item.
  47                         match (mi.name_or_empty(), mi.value_str()) {
  48                             (sym::feature, val) => feature = val,
  49                             (sym::since, val) => since = val,
  50                             _ => {}
  51                         }
  52                     }
  53                 }
  54                 if let Some(feature) = feature {
  55                     // This additional check for stability is to make sure we
  56                     // don't emit additional, irrelevant errors for malformed
  57                     // attributes.
  58                     if *stab_attr != sym::stable || since.is_some() {
  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(&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);
  93             }
  94             (None, false, _) => {
  95                 self.lib_features.unstable.insert(feature);
  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 Visitor<'tcx> for LibFeatureCollector<'tcx> {
 117     type Map = Map<'tcx>;
 118
 119     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 120         NestedVisitorMap::All(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 collect(tcx: TyCtxt<'_>) -> LibFeatures {
 131     let mut collector = LibFeatureCollector::new(tcx);
 132     let krate = tcx.hir().krate();
 133     for attr in krate.non_exported_macro_attrs {
 134         collector.visit_attribute(attr);
 135     }
 136     intravisit::walk_crate(&mut collector, krate);
 137     collector.lib_features
 138 }
 139
 140 pub fn provide(providers: &mut Providers) {
 141     providers.get_lib_features = |tcx, id| {
 142         assert_eq!(id, LOCAL_CRATE);
 143         collect(tcx)
 144     };
 145 }