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::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                     let version = option_env!("CFG_VERSION").unwrap_or("<current>");
  61                     let version = version.split(' ').next().unwrap();
  62                     since = Some(Symbol::intern(&version));
  63                 }
  64
  65                 if let Some(feature) = feature {
  66                     // This additional check for stability is to make sure we
  67                     // don't emit additional, irrelevant errors for malformed
  68                     // attributes.
  69                     let is_unstable = matches!(
  70                         *stab_attr,
  71                         sym::unstable
  72                             | sym::rustc_const_unstable
  73                             | sym::rustc_default_body_unstable
  74                     );
  75                     if since.is_some() || is_unstable {
  76                         return Some((feature, since, attr.span));
  77                     }
  78                 }
  79                 // We need to iterate over the other attributes, because
  80                 // `rustc_const_unstable` is not mutually exclusive with
  81                 // the other stability attributes, so we can't just `break`
  82                 // here.
  83             }
  84         }
  85
  86         None
  87     }
  88
  89     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  90         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  91         let already_in_unstable = self.lib_features.unstable.contains_key(&feature);
  92
  93         match (since, already_in_stable, already_in_unstable) {
  94             (Some(since), _, false) => {
  95                 if let Some((prev_since, _)) = self.lib_features.stable.get(&feature) {
  96                     if *prev_since != since {
  97                         self.span_feature_error(
  98                             span,
  99                             &format!(
 100                                 "feature `{}` is declared stable since {}, \
 101                                  but was previously declared stable since {}",
 102                                 feature, since, prev_since,
 103                             ),
 104                         );
 105                         return;
 106                     }
 107                 }
 108
 109                 self.lib_features.stable.insert(feature, (since, span));
 110             }
 111             (None, false, _) => {
 112                 self.lib_features.unstable.insert(feature, span);
 113             }
 114             (Some(_), _, true) | (None, true, _) => {
 115                 self.span_feature_error(
 116                     span,
 117                     &format!(
 118                         "feature `{}` is declared {}, but was previously declared {}",
 119                         feature,
 120                         if since.is_some() { "stable" } else { "unstable" },
 121                         if since.is_none() { "stable" } else { "unstable" },
 122                     ),
 123                 );
 124             }
 125         }
 126     }
 127
 128     fn span_feature_error(&self, span: Span, msg: &str) {
 129         struct_span_err!(self.tcx.sess, span, E0711, "{}", &msg).emit();
 130     }
 131 }
 132
 133 impl<'tcx> Visitor<'tcx> for LibFeatureCollector<'tcx> {
 134     type NestedFilter = nested_filter::All;
 135
 136     fn nested_visit_map(&mut self) -> Self::Map {
 137         self.tcx.hir()
 138     }
 139
 140     fn visit_attribute(&mut self, attr: &'tcx Attribute) {
 141         if let Some((feature, stable, span)) = self.extract(attr) {
 142             self.collect_feature(feature, stable, span);
 143         }
 144     }
 145 }
 146
 147 fn lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
 148     let mut collector = LibFeatureCollector::new(tcx);
 149     tcx.hir().walk_attributes(&mut collector);
 150     collector.lib_features
 151 }
 152
 153 pub fn provide(providers: &mut Providers) {
 154     providers.lib_features = lib_features;
 155 }