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;
  12 use rustc_data_structures::fx::{FxHashSet, FxHashMap};
  13 use rustc_macros::HashStable;
  14 use errors::DiagnosticId;
  15
  16 #[derive(HashStable)]
  17 pub struct LibFeatures {
  18     // A map from feature to stabilisation version.
  19     pub stable: FxHashMap<Symbol, Symbol>,
  20     pub unstable: FxHashSet<Symbol>,
  21 }
  22
  23 impl LibFeatures {
  24     fn new() -> LibFeatures {
  25         LibFeatures {
  26             stable: Default::default(),
  27             unstable: Default::default(),
  28         }
  29     }
  30
  31     pub fn to_vec(&self) -> Vec<(Symbol, Option<Symbol>)> {
  32         let mut all_features: Vec<_> = self.stable.iter().map(|(f, s)| (*f, Some(*s)))
  33             .chain(self.unstable.iter().map(|f| (*f, None)))
  34             .collect();
  35         all_features.sort_unstable_by_key(|f| f.0.as_str());
  36         all_features
  37     }
  38 }
  39
  40 pub struct LibFeatureCollector<'a, 'tcx: 'a> {
  41     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  42     lib_features: LibFeatures,
  43 }
  44
  45 impl<'a, 'tcx> LibFeatureCollector<'a, 'tcx> {
  46     fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> LibFeatureCollector<'a, 'tcx> {
  47         LibFeatureCollector {
  48             tcx,
  49             lib_features: LibFeatures::new(),
  50         }
  51     }
  52
  53     fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
  54         let stab_attrs = vec!["stable", "unstable", "rustc_const_unstable"];
  55
  56         // Find a stability attribute (i.e., `#[stable (..)]`, `#[unstable (..)]`,
  57         // `#[rustc_const_unstable (..)]`).
  58         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| {
  59             attr.check_name(stab_attr)
  60         }) {
  61             let meta_item = attr.meta();
  62             if let Some(MetaItem { node: MetaItemKind::List(ref metas), .. }) = meta_item {
  63                 let mut feature = None;
  64                 let mut since = None;
  65                 for meta in metas {
  66                     if let Some(mi) = meta.meta_item() {
  67                         // Find the `feature = ".."` meta-item.
  68                         match (mi.name_or_empty().get(), mi.value_str()) {
  69                             ("feature", val) => feature = val,
  70                             ("since", val) => since = val,
  71                             _ => {}
  72                         }
  73                     }
  74                 }
  75                 if let Some(feature) = feature {
  76                     // This additional check for stability is to make sure we
  77                     // don't emit additional, irrelevant errors for malformed
  78                     // attributes.
  79                     if *stab_attr != "stable" || since.is_some() {
  80                         return Some((feature, since, attr.span));
  81                     }
  82                 }
  83                 // We need to iterate over the other attributes, because
  84                 // `rustc_const_unstable` is not mutually exclusive with
  85                 // the other stability attributes, so we can't just `break`
  86                 // here.
  87             }
  88         }
  89
  90         None
  91     }
  92
  93     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
  94         let already_in_stable = self.lib_features.stable.contains_key(&feature);
  95         let already_in_unstable = self.lib_features.unstable.contains(&feature);
  96
  97         match (since, already_in_stable, already_in_unstable) {
  98             (Some(since), _, false) => {
  99                 if let Some(prev_since) = self.lib_features.stable.get(&feature) {
 100                     if *prev_since != since {
 101                         let msg = format!(
 102                             "feature `{}` is declared stable since {}, \
 103                              but was previously declared stable since {}",
 104                             feature,
 105                             since,
 106                             prev_since,
 107                         );
 108                         self.tcx.sess.struct_span_err_with_code(span, &msg,
 109                             DiagnosticId::Error("E0711".into())).emit();
 110                         return;
 111                     }
 112                 }
 113
 114                 self.lib_features.stable.insert(feature, since);
 115             }
 116             (None, false, _) => {
 117                 self.lib_features.unstable.insert(feature);
 118             }
 119             (Some(_), _, true) | (None, true, _) => {
 120                 let msg = format!(
 121                     "feature `{}` is declared {}, but was previously declared {}",
 122                     feature,
 123                     if since.is_some() { "stable" } else { "unstable" },
 124                     if since.is_none() { "stable" } else { "unstable" },
 125                 );
 126                 self.tcx.sess.struct_span_err_with_code(span, &msg,
 127                     DiagnosticId::Error("E0711".into())).emit();
 128             }
 129         }
 130     }
 131 }
 132
 133 impl<'a, 'tcx> Visitor<'tcx> for LibFeatureCollector<'a, '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<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> LibFeatures {
 146     let mut collector = LibFeatureCollector::new(tcx);
 147     intravisit::walk_crate(&mut collector, tcx.hir().krate());
 148     collector.lib_features
 149 }