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::{self, 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) =
  37             stab_attrs.iter().find(|stab_attr| self.tcx.sess.check_name(attr, **stab_attr))
  38         {
  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     type Map = Map<'tcx>;
 117
 118     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 119         NestedVisitorMap::All(self.tcx.hir())
 120     }
 121
 122     fn visit_attribute(&mut self, _: rustc_hir::HirId, attr: &'tcx Attribute) {
 123         if let Some((feature, stable, span)) = self.extract(attr) {
 124             self.collect_feature(feature, stable, span);
 125         }
 126     }
 127 }
 128
 129 fn get_lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
 130     let mut collector = LibFeatureCollector::new(tcx);
 131     let krate = tcx.hir().krate();
 132     for attr in krate.non_exported_macro_attrs {
 133         collector.visit_attribute(rustc_hir::CRATE_HIR_ID, attr);
 134     }
 135     intravisit::walk_crate(&mut collector, krate);
 136     collector.lib_features
 137 }
 138
 139 pub fn provide(providers: &mut Providers) {
 140     providers.get_lib_features = get_lib_features;
 141 }