src/librustc/middle/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 crate::hir::intravisit::{self, NestedVisitorMap, Visitor};
   8 use crate::ty::TyCtxt;
   9 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  10 use rustc_macros::HashStable;
  11 use syntax::ast::{Attribute, MetaItem, MetaItemKind};
  12 use syntax::symbol::Symbol;
  13 use syntax_pos::{sym, Span};
  14
  15 use rustc_error_codes::*;
  16
  17 #[derive(HashStable)]
  18 pub struct LibFeatures {
  19     // A map from feature to stabilisation version.
  20     pub stable: FxHashMap<Symbol, Symbol>,
  21     pub unstable: FxHashSet<Symbol>,
  22 }
  23
  24 impl LibFeatures {
  25     fn new() -> LibFeatures {
  26         LibFeatures { stable: Default::default(), unstable: Default::default() }
  27     }
  28
  29     pub fn to_vec(&self) -> Vec<(Symbol, Option<Symbol>)> {
  30         let mut all_features: Vec<_> = self
  31             .stable
  32             .iter()
  33             .map(|(f, s)| (*f, Some(*s)))
  34             .chain(self.unstable.iter().map(|f| (*f, None)))
  35             .collect();
  36         all_features.sort_unstable_by_key(|f| f.0.as_str());
  37         all_features
  38     }
  39 }
  40
  41 pub struct LibFeatureCollector<'tcx> {
  42     tcx: TyCtxt<'tcx>,
  43     lib_features: LibFeatures,
  44 }
  45
  46 impl LibFeatureCollector<'tcx> {
  47     fn new(tcx: TyCtxt<'tcx>) -> LibFeatureCollector<'tcx> {
  48         LibFeatureCollector { tcx, lib_features: LibFeatures::new() }
  49     }
  50
  51     fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
  52         let stab_attrs = [sym::stable, sym::unstable, sym::rustc_const_unstable];
  53
  54         // Find a stability attribute (i.e., `#[stable (..)]`, `#[unstable (..)]`,
  55         // `#[rustc_const_unstable (..)]`).
  56         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.check_name(**stab_attr)) {
  57             let meta_item = attr.meta();
  58             if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta_item {
  59                 let mut feature = None;
  60                 let mut since = None;
  61                 for meta in metas {
  62                     if let Some(mi) = meta.meta_item() {
  63                         // Find the `feature = ".."` meta-item.
  64                         match (mi.name_or_empty(), mi.value_str()) {
  65                             (sym::feature, val) => feature = val,
  66                             (sym::since, val) => since = val,
  67                             _ => {}
  68                         }
  69                     }
  70                 }
  71                 if let Some(feature) = feature {
  72                     // This additional check for stability is to make sure we
  73                     // don't emit additional, irrelevant errors for malformed
  74                     // attributes.
  75                     if *stab_attr != sym::stable || since.is_some() {
  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(&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);
 110             }
 111             (None, false, _) => {
 112                 self.lib_features.unstable.insert(feature);
 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 Visitor<'tcx> for LibFeatureCollector<'tcx> {
 134     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 135         NestedVisitorMap::All(&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 pub fn collect(tcx: TyCtxt<'_>) -> LibFeatures {
 146     let mut collector = LibFeatureCollector::new(tcx);
 147     let krate = tcx.hir().krate();
 148     for attr in krate.non_exported_macro_attrs {
 149         collector.visit_attribute(attr);
 150     }
 151     intravisit::walk_crate(&mut collector, krate);
 152     collector.lib_features
 153 }