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::ty::TyCtxt;
   8 use crate::hir::intravisit::{self, NestedVisitorMap, Visitor};
   9 use syntax::symbol::Symbol;
  10 use syntax::ast::{Attribute, MetaItem, MetaItemKind};
  11 use syntax_pos::{Span, sym};
  12 use rustc_data_structures::fx::{FxHashSet, FxHashMap};
  13 use rustc_macros::HashStable;
  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 {
  27             stable: Default::default(),
  28             unstable: Default::default(),
  29         }
  30     }
  31
  32     pub fn to_vec(&self) -> Vec<(Symbol, Option<Symbol>)> {
  33         let mut all_features: Vec<_> = self.stable.iter().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 {
  49             tcx,
  50             lib_features: LibFeatures::new(),
  51         }
  52     }
  53
  54     fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
  55         let stab_attrs = [sym::stable, sym::unstable, sym::rustc_const_unstable];
  56
  57         // Find a stability attribute (i.e., `#[stable (..)]`, `#[unstable (..)]`,
  58         // `#[rustc_const_unstable (..)]`).
  59         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| {
  60             attr.check_name(**stab_attr)
  61         }) {
  62             let meta_item = attr.meta();
  63             if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta_item {
  64                 let mut feature = None;
  65                 let mut since = None;
  66                 for meta in metas {
  67                     if let Some(mi) = meta.meta_item() {
  68                         // Find the `feature = ".."` meta-item.
  69                         match (mi.name_or_empty(), mi.value_str()) {
  70                             (sym::feature, val) => feature = val,
  71                             (sym::since, val) => since = val,
  72                             _ => {}
  73                         }
  74                     }
  75                 }
  76                 if let Some(feature) = feature {
  77                     // This additional check for stability is to make sure we
  78                     // don't emit additional, irrelevant errors for malformed
  79                     // attributes.
  80                     if *stab_attr != sym::stable || since.is_some() {
  81                         return Some((feature, since, attr.span));
  82                     }
  83                 }
  84                 // We need to iterate over the other attributes, because
  85                 // `rustc_const_unstable` is not mutually exclusive with
  86                 // the other stability attributes, so we can't just `break`
  87                 // here.
  88             }
  89         }
  90
  91         None
  92     }
  93
  94     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  95         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  96         let already_in_unstable = self.lib_features.unstable.contains(&feature);
  97
  98         match (since, already_in_stable, already_in_unstable) {
  99             (Some(since), _, false) => {
 100                 if let Some(prev_since) = self.lib_features.stable.get(&feature) {
 101                     if *prev_since != since {
 102                         self.span_feature_error(
 103                             span,
 104                             &format!(
 105                                 "feature `{}` is declared stable since {}, \
 106                                  but was previously declared stable since {}",
 107                                 feature,
 108                                 since,
 109                                 prev_since,
 110                             ),
 111                         );
 112                         return;
 113                     }
 114                 }
 115
 116                 self.lib_features.stable.insert(feature, since);
 117             }
 118             (None, false, _) => {
 119                 self.lib_features.unstable.insert(feature);
 120             }
 121             (Some(_), _, true) | (None, true, _) => {
 122                 self.span_feature_error(
 123                     span,
 124                     &format!(
 125                         "feature `{}` is declared {}, but was previously declared {}",
 126                         feature,
 127                         if since.is_some() { "stable" } else { "unstable" },
 128                         if since.is_none() { "stable" } else { "unstable" },
 129                     ),
 130                 );
 131             }
 132         }
 133     }
 134
 135     fn span_feature_error(&self, span: Span, msg: &str) {
 136         struct_span_err!(
 137             self.tcx.sess,
 138             span,
 139             E0711,
 140             "{}", &msg,
 141         ).emit();
 142     }
 143 }
 144
 145 impl Visitor<'tcx> for LibFeatureCollector<'tcx> {
 146     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 147         NestedVisitorMap::All(&self.tcx.hir())
 148     }
 149
 150     fn visit_attribute(&mut self, attr: &'tcx Attribute) {
 151         if let Some((feature, stable, span)) = self.extract(attr) {
 152             self.collect_feature(feature, stable, span);
 153         }
 154     }
 155 }
 156
 157 pub fn collect(tcx: TyCtxt<'_>) -> LibFeatures {
 158     let mut collector = LibFeatureCollector::new(tcx);
 159     let krate = tcx.hir().krate();
 160     for attr in &krate.non_exported_macro_attrs {
 161         collector.visit_attribute(attr);
 162     }
 163     intravisit::walk_crate(&mut collector, krate);
 164     collector.lib_features
 165 }