src/librustc_typeck/outlives/mod.rs

   1 use hir::Node;
   2 use rustc::hir;
   3 use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
   4 use rustc::ty::query::Providers;
   5 use rustc::ty::subst::UnpackedKind;
   6 use rustc::ty::{self, CratePredicatesMap, TyCtxt};
   7 use syntax::symbol::sym;
   8
   9 mod explicit;
  10 mod implicit_infer;
  11 /// Code to write unit test for outlives.
  12 pub mod test;
  13 mod utils;
  14
  15 pub fn provide(providers: &mut Providers<'_>) {
  16     *providers = Providers {
  17         inferred_outlives_of,
  18         inferred_outlives_crate,
  19         ..*providers
  20     };
  21 }
  22
  23 fn inferred_outlives_of<'tcx>(
  24     tcx: TyCtxt<'tcx>,
  25     item_def_id: DefId,
  26 ) -> &'tcx [ty::Predicate<'tcx>] {
  27     let id = tcx
  28         .hir()
  29         .as_local_hir_id(item_def_id)
  30         .expect("expected local def-id");
  31
  32     match tcx.hir().get(id) {
  33         Node::Item(item) => match item.node {
  34             hir::ItemKind::Struct(..) | hir::ItemKind::Enum(..) | hir::ItemKind::Union(..) => {
  35                 let crate_map = tcx.inferred_outlives_crate(LOCAL_CRATE);
  36
  37                 let predicates = crate_map
  38                     .predicates
  39                     .get(&item_def_id)
  40                     .map(|p| *p)
  41                     .unwrap_or(&[]);
  42
  43                 if tcx.has_attr(item_def_id, sym::rustc_outlives) {
  44                     let mut pred: Vec<String> = predicates
  45                         .iter()
  46                         .map(|out_pred| match out_pred {
  47                             ty::Predicate::RegionOutlives(p) => p.to_string(),
  48                             ty::Predicate::TypeOutlives(p) => p.to_string(),
  49                             err => bug!("unexpected predicate {:?}", err),
  50                         }).collect();
  51                     pred.sort();
  52
  53                     let span = tcx.def_span(item_def_id);
  54                     let mut err = tcx.sess.struct_span_err(span, "rustc_outlives");
  55                     for p in &pred {
  56                         err.note(p);
  57                     }
  58                     err.emit();
  59                 }
  60
  61                 debug!("inferred_outlives_of({:?}) = {:?}", item_def_id, predicates);
  62
  63                 predicates
  64             }
  65
  66             _ => &[],
  67         },
  68
  69         _ => &[],
  70     }
  71 }
  72
  73 fn inferred_outlives_crate<'tcx>(
  74     tcx: TyCtxt<'tcx>,
  75     crate_num: CrateNum,
  76 ) -> &'tcx CratePredicatesMap<'tcx> {
  77     assert_eq!(crate_num, LOCAL_CRATE);
  78
  79     // Compute a map from each struct/enum/union S to the **explicit**
  80     // outlives predicates (`T: 'a`, `'a: 'b`) that the user wrote.
  81     // Typically there won't be many of these, except in older code where
  82     // they were mandatory. Nonetheless, we have to ensure that every such
  83     // predicate is satisfied, so they form a kind of base set of requirements
  84     // for the type.
  85
  86     // Compute the inferred predicates
  87     let mut exp_map = explicit::ExplicitPredicatesMap::new();
  88
  89     let global_inferred_outlives = implicit_infer::infer_predicates(tcx, &mut exp_map);
  90
  91     // Convert the inferred predicates into the "collected" form the
  92     // global data structure expects.
  93     //
  94     // FIXME -- consider correcting impedance mismatch in some way,
  95     // probably by updating the global data structure.
  96     let predicates = global_inferred_outlives
  97         .iter()
  98         .map(|(&def_id, set)| {
  99             let predicates = tcx.arena.alloc_from_iter(set
 100                 .iter()
 101                 .filter_map(
 102                     |ty::OutlivesPredicate(kind1, region2)| match kind1.unpack() {
 103                         UnpackedKind::Type(ty1) => {
 104                             Some(ty::Predicate::TypeOutlives(ty::Binder::bind(
 105                                 ty::OutlivesPredicate(ty1, region2)
 106                             )))
 107                         }
 108                         UnpackedKind::Lifetime(region1) => {
 109                             Some(ty::Predicate::RegionOutlives(
 110                                 ty::Binder::bind(ty::OutlivesPredicate(region1, region2))
 111                             ))
 112                         }
 113                         UnpackedKind::Const(_) => {
 114                             // Generic consts don't impose any constraints.
 115                             None
 116                         }
 117                     },
 118                 ));
 119             (def_id, &*predicates)
 120         }).collect();
 121
 122     tcx.arena.alloc(ty::CratePredicatesMap {
 123         predicates,
 124     })
 125 }