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_hir::intravisit::Visitor;
  10 use rustc_middle::hir::nested_filter;
  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 use crate::errors::{FeaturePreviouslyDeclared, FeatureStableTwice};
  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<'tcx> 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 = [
  35             sym::stable,
  36             sym::unstable,
  37             sym::rustc_const_stable,
  38             sym::rustc_const_unstable,
  39             sym::rustc_default_body_unstable,
  40         ];
  41
  42         // Find a stability attribute: one of #[stable(…)], #[unstable(…)],
  43         // #[rustc_const_stable(…)], #[rustc_const_unstable(…)] or #[rustc_default_body_unstable].
  44         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
  45             let meta_kind = attr.meta_kind();
  46             if let Some(MetaItemKind::List(ref metas)) = meta_kind {
  47                 let mut feature = None;
  48                 let mut since = None;
  49                 for meta in metas {
  50                     if let Some(mi) = meta.meta_item() {
  51                         // Find the `feature = ".."` meta-item.
  52                         match (mi.name_or_empty(), mi.value_str()) {
  53                             (sym::feature, val) => feature = val,
  54                             (sym::since, val) => since = val,
  55                             _ => {}
  56                         }
  57                     }
  58                 }
  59
  60                 if let Some(s) = since && s.as_str() == VERSION_PLACEHOLDER {
  61                     since = Some(rust_version_symbol());
  62                 }
  63
  64                 if let Some(feature) = feature {
  65                     // This additional check for stability is to make sure we
  66                     // don't emit additional, irrelevant errors for malformed
  67                     // attributes.
  68                     let is_unstable = matches!(
  69                         *stab_attr,
  70                         sym::unstable
  71                             | sym::rustc_const_unstable
  72                             | sym::rustc_default_body_unstable
  73                     );
  74                     if since.is_some() || is_unstable {
  75                         return Some((feature, since, attr.span));
  76                     }
  77                 }
  78                 // We need to iterate over the other attributes, because
  79                 // `rustc_const_unstable` is not mutually exclusive with
  80                 // the other stability attributes, so we can't just `break`
  81                 // here.
  82             }
  83         }
  84
  85         None
  86     }
  87
  88     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  89         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  90         let already_in_unstable = self.lib_features.unstable.contains_key(&feature);
  91
  92         match (since, already_in_stable, already_in_unstable) {
  93             (Some(since), _, false) => {
  94                 if let Some((prev_since, _)) = self.lib_features.stable.get(&feature) {
  95                     if *prev_since != since {
  96                         self.tcx.sess.emit_err(FeatureStableTwice {
  97                             span,
  98                             feature,
  99                             since,
 100                             prev_since: *prev_since,
 101                         });
 102                         return;
 103                     }
 104                 }
 105
 106                 self.lib_features.stable.insert(feature, (since, span));
 107             }
 108             (None, false, _) => {
 109                 self.lib_features.unstable.insert(feature, span);
 110             }
 111             (Some(_), _, true) | (None, true, _) => {
 112                 let declared = if since.is_some() { "stable" } else { "unstable" };
 113                 let prev_declared = if since.is_none() { "stable" } else { "unstable" };
 114                 self.tcx.sess.emit_err(FeaturePreviouslyDeclared {
 115                     span,
 116                     feature,
 117                     declared,
 118                     prev_declared,
 119                 });
 120             }
 121         }
 122     }
 123 }
 124
 125 impl<'tcx> Visitor<'tcx> for LibFeatureCollector<'tcx> {
 126     type NestedFilter = nested_filter::All;
 127
 128     fn nested_visit_map(&mut self) -> Self::Map {
 129         self.tcx.hir()
 130     }
 131
 132     fn visit_attribute(&mut self, attr: &'tcx Attribute) {
 133         if let Some((feature, stable, span)) = self.extract(attr) {
 134             self.collect_feature(feature, stable, span);
 135         }
 136     }
 137 }
 138
 139 fn lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
 140     // If `staged_api` is not enabled then we aren't allowed to define lib
 141     // features; there is no point collecting them.
 142     if !tcx.features().staged_api {
 143         return new_lib_features();
 144     }
 145
 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 }