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 (..)]` and `#[unstable (..)]`),
   4 //! but are not declared in one single location (unlike lang features), which means we need to
   5 //! collect them instead.
   6
   7 use rustc_ast::{Attribute, MetaItemKind};
   8 use rustc_attr::{rust_version_symbol, VERSION_PLACEHOLDER};
   9 use rustc_errors::struct_span_err;
  10 use rustc_hir::intravisit::Visitor;
  11 use rustc_middle::hir::nested_filter;
  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<'tcx> 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 = [
  34             sym::stable,
  35             sym::unstable,
  36             sym::rustc_const_stable,
  37             sym::rustc_const_unstable,
  38             sym::rustc_default_body_unstable,
  39         ];
  40
  41         // Find a stability attribute: one of #[stable(…)], #[unstable(…)],
  42         // #[rustc_const_stable(…)], #[rustc_const_unstable(…)] or #[rustc_default_body_unstable].
  43         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
  44             let meta_kind = attr.meta_kind();
  45             if let Some(MetaItemKind::List(ref metas)) = meta_kind {
  46                 let mut feature = None;
  47                 let mut since = None;
  48                 for meta in metas {
  49                     if let Some(mi) = meta.meta_item() {
  50                         // Find the `feature = ".."` meta-item.
  51                         match (mi.name_or_empty(), mi.value_str()) {
  52                             (sym::feature, val) => feature = val,
  53                             (sym::since, val) => since = val,
  54                             _ => {}
  55                         }
  56                     }
  57                 }
  58
  59                 if let Some(s) = since && s.as_str() == VERSION_PLACEHOLDER {
  60                     since = Some(rust_version_symbol());
  61                 }
  62
  63                 if let Some(feature) = feature {
  64                     // This additional check for stability is to make sure we
  65                     // don't emit additional, irrelevant errors for malformed
  66                     // attributes.
  67                     let is_unstable = matches!(
  68                         *stab_attr,
  69                         sym::unstable
  70                             | sym::rustc_const_unstable
  71                             | sym::rustc_default_body_unstable
  72                     );
  73                     if since.is_some() || is_unstable {
  74                         return Some((feature, since, attr.span));
  75                     }
  76                 }
  77                 // We need to iterate over the other attributes, because
  78                 // `rustc_const_unstable` is not mutually exclusive with
  79                 // the other stability attributes, so we can't just `break`
  80                 // here.
  81             }
  82         }
  83
  84         None
  85     }
  86
  87     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  88         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  89         let already_in_unstable = self.lib_features.unstable.contains_key(&feature);
  90
  91         match (since, already_in_stable, already_in_unstable) {
  92             (Some(since), _, false) => {
  93                 if let Some((prev_since, _)) = self.lib_features.stable.get(&feature) {
  94                     if *prev_since != since {
  95                         self.span_feature_error(
  96                             span,
  97                             &format!(
  98                                 "feature `{}` is declared stable since {}, \
  99                                  but was previously declared stable since {}",
 100                                 feature, since, prev_since,
 101                             ),
 102                         );
 103                         return;
 104                     }
 105                 }
 106
 107                 self.lib_features.stable.insert(feature, (since, span));
 108             }
 109             (None, false, _) => {
 110                 self.lib_features.unstable.insert(feature, span);
 111             }
 112             (Some(_), _, true) | (None, true, _) => {
 113                 self.span_feature_error(
 114                     span,
 115                     &format!(
 116                         "feature `{}` is declared {}, but was previously declared {}",
 117                         feature,
 118                         if since.is_some() { "stable" } else { "unstable" },
 119                         if since.is_none() { "stable" } else { "unstable" },
 120                     ),
 121                 );
 122             }
 123         }
 124     }
 125
 126     fn span_feature_error(&self, span: Span, msg: &str) {
 127         struct_span_err!(self.tcx.sess, span, E0711, "{}", &msg).emit();
 128     }
 129 }
 130
 131 impl<'tcx> Visitor<'tcx> for LibFeatureCollector<'tcx> {
 132     type NestedFilter = nested_filter::All;
 133
 134     fn nested_visit_map(&mut self) -> Self::Map {
 135         self.tcx.hir()
 136     }
 137
 138     fn visit_attribute(&mut self, attr: &'tcx Attribute) {
 139         if let Some((feature, stable, span)) = self.extract(attr) {
 140             self.collect_feature(feature, stable, span);
 141         }
 142     }
 143 }
 144
 145 fn lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
 146     let mut collector = LibFeatureCollector::new(tcx);
 147     tcx.hir().walk_attributes(&mut collector);
 148     collector.lib_features
 149 }
 150
 151 pub fn provide(providers: &mut Providers) {
 152     providers.lib_features = lib_features;
 153 }