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 errors::struct_span_err;
   8 use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
   9 use rustc::middle::lib_features::LibFeatures;
  10 use rustc::ty::query::Providers;
  11 use rustc::ty::TyCtxt;
  12 use rustc_hir::def_id::LOCAL_CRATE;
  13 use rustc_span::symbol::Symbol;
  14 use rustc_span::{sym, Span};
  15 use syntax::ast::{Attribute, MetaItem, MetaItemKind};
  16
  17 use rustc_error_codes::*;
  18
  19 fn new_lib_features() -> LibFeatures {
  20     LibFeatures { stable: Default::default(), unstable: Default::default() }
  21 }
  22
  23 pub struct LibFeatureCollector<'tcx> {
  24     tcx: TyCtxt<'tcx>,
  25     lib_features: LibFeatures,
  26 }
  27
  28 impl LibFeatureCollector<'tcx> {
  29     fn new(tcx: TyCtxt<'tcx>) -> LibFeatureCollector<'tcx> {
  30         LibFeatureCollector { tcx, lib_features: new_lib_features() }
  31     }
  32
  33     fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
  34         let stab_attrs = [sym::stable, sym::unstable, sym::rustc_const_unstable];
  35
  36         // Find a stability attribute (i.e., `#[stable (..)]`, `#[unstable (..)]`,
  37         // `#[rustc_const_unstable (..)]`).
  38         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.check_name(**stab_attr)) {
  39             let meta_item = attr.meta();
  40             if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta_item {
  41                 let mut feature = None;
  42                 let mut since = None;
  43                 for meta in metas {
  44                     if let Some(mi) = meta.meta_item() {
  45                         // Find the `feature = ".."` meta-item.
  46                         match (mi.name_or_empty(), mi.value_str()) {
  47                             (sym::feature, val) => feature = val,
  48                             (sym::since, val) => since = val,
  49                             _ => {}
  50                         }
  51                     }
  52                 }
  53                 if let Some(feature) = feature {
  54                     // This additional check for stability is to make sure we
  55                     // don't emit additional, irrelevant errors for malformed
  56                     // attributes.
  57                     if *stab_attr != sym::stable || since.is_some() {
  58                         return Some((feature, since, attr.span));
  59                     }
  60                 }
  61                 // We need to iterate over the other attributes, because
  62                 // `rustc_const_unstable` is not mutually exclusive with
  63                 // the other stability attributes, so we can't just `break`
  64                 // here.
  65             }
  66         }
  67
  68         None
  69     }
  70
  71     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  72         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  73         let already_in_unstable = self.lib_features.unstable.contains(&feature);
  74
  75         match (since, already_in_stable, already_in_unstable) {
  76             (Some(since), _, false) => {
  77                 if let Some(prev_since) = self.lib_features.stable.get(&feature) {
  78                     if *prev_since != since {
  79                         self.span_feature_error(
  80                             span,
  81                             &format!(
  82                                 "feature `{}` is declared stable since {}, \
  83                                  but was previously declared stable since {}",
  84                                 feature, since, prev_since,
  85                             ),
  86                         );
  87                         return;
  88                     }
  89                 }
  90
  91                 self.lib_features.stable.insert(feature, since);
  92             }
  93             (None, false, _) => {
  94                 self.lib_features.unstable.insert(feature);
  95             }
  96             (Some(_), _, true) | (None, true, _) => {
  97                 self.span_feature_error(
  98                     span,
  99                     &format!(
 100                         "feature `{}` is declared {}, but was previously declared {}",
 101                         feature,
 102                         if since.is_some() { "stable" } else { "unstable" },
 103                         if since.is_none() { "stable" } else { "unstable" },
 104                     ),
 105                 );
 106             }
 107         }
 108     }
 109
 110     fn span_feature_error(&self, span: Span, msg: &str) {
 111         struct_span_err!(self.tcx.sess, span, E0711, "{}", &msg,).emit();
 112     }
 113 }
 114
 115 impl Visitor<'tcx> for LibFeatureCollector<'tcx> {
 116     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 117         NestedVisitorMap::All(&self.tcx.hir())
 118     }
 119
 120     fn visit_attribute(&mut self, 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 collect(tcx: TyCtxt<'_>) -> LibFeatures {
 128     let mut collector = LibFeatureCollector::new(tcx);
 129     let krate = tcx.hir().krate();
 130     for attr in krate.non_exported_macro_attrs {
 131         collector.visit_attribute(attr);
 132     }
 133     intravisit::walk_crate(&mut collector, krate);
 134     collector.lib_features
 135 }
 136
 137 pub fn provide(providers: &mut Providers<'_>) {
 138     providers.get_lib_features = |tcx, id| {
 139         assert_eq!(id, LOCAL_CRATE);
 140         tcx.arena.alloc(collect(tcx))
 141     };
 142 }