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::hir::map::Map;
   8 use rustc::middle::lib_features::LibFeatures;
   9 use rustc::ty::query::Providers;
  10 use rustc::ty::TyCtxt;
  11 use rustc_errors::struct_span_err;
  12 use rustc_hir::def_id::LOCAL_CRATE;
  13 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  14 use rustc_span::symbol::Symbol;
  15 use rustc_span::{sym, Span};
  16 use syntax::ast::{Attribute, MetaItem, MetaItemKind};
  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) = stab_attrs.iter().find(|stab_attr| attr.check_name(**stab_attr)) {
  38             let meta_item = attr.meta();
  39             if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta_item {
  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                     if *stab_attr != sym::stable || since.is_some() {
  57                         return Some((feature, since, attr.span));
  58                     }
  59                 }
  60                 // We need to iterate over the other attributes, because
  61                 // `rustc_const_unstable` is not mutually exclusive with
  62                 // the other stability attributes, so we can't just `break`
  63                 // here.
  64             }
  65         }
  66
  67         None
  68     }
  69
  70     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  71         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  72         let already_in_unstable = self.lib_features.unstable.contains(&feature);
  73
  74         match (since, already_in_stable, already_in_unstable) {
  75             (Some(since), _, false) => {
  76                 if let Some(prev_since) = self.lib_features.stable.get(&feature) {
  77                     if *prev_since != since {
  78                         self.span_feature_error(
  79                             span,
  80                             &format!(
  81                                 "feature `{}` is declared stable since {}, \
  82                                  but was previously declared stable since {}",
  83                                 feature, since, prev_since,
  84                             ),
  85                         );
  86                         return;
  87                     }
  88                 }
  89
  90                 self.lib_features.stable.insert(feature, since);
  91             }
  92             (None, false, _) => {
  93                 self.lib_features.unstable.insert(feature);
  94             }
  95             (Some(_), _, true) | (None, true, _) => {
  96                 self.span_feature_error(
  97                     span,
  98                     &format!(
  99                         "feature `{}` is declared {}, but was previously declared {}",
 100                         feature,
 101                         if since.is_some() { "stable" } else { "unstable" },
 102                         if since.is_none() { "stable" } else { "unstable" },
 103                     ),
 104                 );
 105             }
 106         }
 107     }
 108
 109     fn span_feature_error(&self, span: Span, msg: &str) {
 110         struct_span_err!(self.tcx.sess, span, E0711, "{}", &msg,).emit();
 111     }
 112 }
 113
 114 impl Visitor<'tcx> for LibFeatureCollector<'tcx> {
 115     type Map = Map<'tcx>;
 116
 117     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
 118         NestedVisitorMap::All(&self.tcx.hir())
 119     }
 120
 121     fn visit_attribute(&mut self, attr: &'tcx Attribute) {
 122         if let Some((feature, stable, span)) = self.extract(attr) {
 123             self.collect_feature(feature, stable, span);
 124         }
 125     }
 126 }
 127
 128 fn collect(tcx: TyCtxt<'_>) -> LibFeatures {
 129     let mut collector = LibFeatureCollector::new(tcx);
 130     let krate = tcx.hir().krate();
 131     for attr in krate.non_exported_macro_attrs {
 132         collector.visit_attribute(attr);
 133     }
 134     intravisit::walk_crate(&mut collector, krate);
 135     collector.lib_features
 136 }
 137
 138 pub fn provide(providers: &mut Providers<'_>) {
 139     providers.get_lib_features = |tcx, id| {
 140         assert_eq!(id, LOCAL_CRATE);
 141         tcx.arena.alloc(collect(tcx))
 142     };
 143 }