compiler/rustc_typeck/src/collect/item_bounds.rs

   1 use super::ItemCtxt;
   2 use crate::astconv::AstConv;
   3 use rustc_hir as hir;
   4 use rustc_infer::traits::util;
   5 use rustc_middle::ty::subst::InternalSubsts;
   6 use rustc_middle::ty::{self, TyCtxt};
   7 use rustc_span::def_id::DefId;
   8 use rustc_span::Span;
   9
  10 /// For associated types we include both bounds written on the type
  11 /// (`type X: Trait`) and predicates from the trait: `where Self::X: Trait`.
  12 ///
  13 /// Note that this filtering is done with the items identity substs to
  14 /// simplify checking that these bounds are met in impls. This means that
  15 /// a bound such as `for<'b> <Self as X<'b>>::U: Clone` can't be used, as in
  16 /// `hr-associated-type-bound-1.rs`.
  17 fn associated_type_bounds<'tcx>(
  18     tcx: TyCtxt<'tcx>,
  19     assoc_item_def_id: DefId,
  20     ast_bounds: &'tcx [hir::GenericBound<'tcx>],
  21     span: Span,
  22 ) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
  23     let item_ty = tcx.mk_projection(
  24         assoc_item_def_id,
  25         InternalSubsts::identity_for_item(tcx, assoc_item_def_id),
  26     );
  27
  28     let icx = ItemCtxt::new(tcx, assoc_item_def_id);
  29     let mut bounds = <dyn AstConv<'_>>::compute_bounds(&icx, item_ty, ast_bounds);
  30     // Associated types are implicitly sized unless a `?Sized` bound is found
  31     <dyn AstConv<'_>>::add_implicitly_sized(&icx, &mut bounds, ast_bounds, None, span);
  32
  33     let trait_def_id = tcx.associated_item(assoc_item_def_id).container.id();
  34     let trait_predicates = tcx.trait_explicit_predicates_and_bounds(trait_def_id.expect_local());
  35
  36     let bounds_from_parent = trait_predicates.predicates.iter().copied().filter(|(pred, _)| {
  37         match pred.kind().skip_binder() {
  38             ty::PredicateKind::Trait(tr) => tr.self_ty() == item_ty,
  39             ty::PredicateKind::Projection(proj) => proj.projection_ty.self_ty() == item_ty,
  40             ty::PredicateKind::TypeOutlives(outlives) => outlives.0 == item_ty,
  41             _ => false,
  42         }
  43     });
  44
  45     let all_bounds = tcx
  46         .arena
  47         .alloc_from_iter(bounds.predicates(tcx, item_ty).into_iter().chain(bounds_from_parent));
  48     debug!("associated_type_bounds({}) = {:?}", tcx.def_path_str(assoc_item_def_id), all_bounds);
  49     all_bounds
  50 }
  51
  52 /// Opaque types don't inherit bounds from their parent: for return position
  53 /// impl trait it isn't possible to write a suitable predicate on the
  54 /// containing function and for type-alias impl trait we don't have a backwards
  55 /// compatibility issue.
  56 fn opaque_type_bounds<'tcx>(
  57     tcx: TyCtxt<'tcx>,
  58     opaque_def_id: DefId,
  59     ast_bounds: &'tcx [hir::GenericBound<'tcx>],
  60     span: Span,
  61 ) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
  62     ty::print::with_no_queries!({
  63         let item_ty =
  64             tcx.mk_opaque(opaque_def_id, InternalSubsts::identity_for_item(tcx, opaque_def_id));
  65
  66         let icx = ItemCtxt::new(tcx, opaque_def_id);
  67         let mut bounds = <dyn AstConv<'_>>::compute_bounds(&icx, item_ty, ast_bounds);
  68         // Opaque types are implicitly sized unless a `?Sized` bound is found
  69         <dyn AstConv<'_>>::add_implicitly_sized(&icx, &mut bounds, ast_bounds, None, span);
  70         tcx.arena.alloc_from_iter(bounds.predicates(tcx, item_ty))
  71     })
  72 }
  73
  74 pub(super) fn explicit_item_bounds(
  75     tcx: TyCtxt<'_>,
  76     def_id: DefId,
  77 ) -> &'_ [(ty::Predicate<'_>, Span)] {
  78     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
  79     match tcx.hir().get(hir_id) {
  80         hir::Node::TraitItem(hir::TraitItem {
  81             kind: hir::TraitItemKind::Type(bounds, _),
  82             span,
  83             ..
  84         }) => associated_type_bounds(tcx, def_id, bounds, *span),
  85         hir::Node::Item(hir::Item {
  86             kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, .. }),
  87             span,
  88             ..
  89         }) => opaque_type_bounds(tcx, def_id, bounds, *span),
  90         _ => bug!("item_bounds called on {:?}", def_id),
  91     }
  92 }
  93
  94 pub(super) fn item_bounds(tcx: TyCtxt<'_>, def_id: DefId) -> &'_ ty::List<ty::Predicate<'_>> {
  95     tcx.mk_predicates(
  96         util::elaborate_predicates(
  97             tcx,
  98             tcx.explicit_item_bounds(def_id).iter().map(|&(bound, _span)| bound),
  99         )
 100         .map(|obligation| obligation.predicate),
 101     )
 102 }