src/librustc_ty/instance.rs

   1 use rustc::traits;
   2 use rustc::ty::subst::SubstsRef;
   3 use rustc::ty::{self, Instance, TyCtxt, TypeFoldable};
   4 use rustc_hir::def_id::DefId;
   5 use rustc_target::spec::abi::Abi;
   6
   7 use log::debug;
   8
   9 pub fn resolve_instance<'tcx>(
  10     tcx: TyCtxt<'tcx>,
  11     param_env: ty::ParamEnv<'tcx>,
  12     def_id: DefId,
  13     substs: SubstsRef<'tcx>,
  14 ) -> Option<Instance<'tcx>> {
  15     debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
  16     let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
  17         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
  18         let item = tcx.associated_item(def_id);
  19         resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
  20     } else {
  21         let ty = tcx.type_of(def_id);
  22         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, &ty);
  23
  24         let def = match item_type.kind {
  25             ty::FnDef(..)
  26                 if {
  27                     let f = item_type.fn_sig(tcx);
  28                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
  29                 } =>
  30             {
  31                 debug!(" => intrinsic");
  32                 ty::InstanceDef::Intrinsic(def_id)
  33             }
  34             _ => {
  35                 if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
  36                     let ty = substs.type_at(0);
  37                     if ty.needs_drop(tcx, param_env.with_reveal_all()) {
  38                         debug!(" => nontrivial drop glue");
  39                         ty::InstanceDef::DropGlue(def_id, Some(ty))
  40                     } else {
  41                         debug!(" => trivial drop glue");
  42                         ty::InstanceDef::DropGlue(def_id, None)
  43                     }
  44                 } else {
  45                     debug!(" => free item");
  46                     ty::InstanceDef::Item(def_id)
  47                 }
  48             }
  49         };
  50         Some(Instance { def: def, substs: substs })
  51     };
  52     debug!("resolve(def_id={:?}, substs={:?}) = {:?}", def_id, substs, result);
  53     result
  54 }
  55
  56 fn resolve_associated_item<'tcx>(
  57     tcx: TyCtxt<'tcx>,
  58     trait_item: &ty::AssocItem,
  59     param_env: ty::ParamEnv<'tcx>,
  60     trait_id: DefId,
  61     rcvr_substs: SubstsRef<'tcx>,
  62 ) -> Option<Instance<'tcx>> {
  63     let def_id = trait_item.def_id;
  64     debug!(
  65         "resolve_associated_item(trait_item={:?}, \
  66             param_env={:?}, \
  67             trait_id={:?}, \
  68             rcvr_substs={:?})",
  69         def_id, param_env, trait_id, rcvr_substs
  70     );
  71
  72     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
  73     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)));
  74
  75     // Now that we know which impl is being used, we can dispatch to
  76     // the actual function:
  77     match vtbl {
  78         traits::VtableImpl(impl_data) => {
  79             let (def_id, substs) =
  80                 traits::find_associated_item(tcx, param_env, trait_item, rcvr_substs, &impl_data);
  81
  82             let resolved_item = tcx.associated_item(def_id);
  83
  84             // Since this is a trait item, we need to see if the item is either a trait default item
  85             // or a specialization because we can't resolve those unless we can `Reveal::All`.
  86             // NOTE: This should be kept in sync with the similar code in
  87             // `rustc::traits::project::assemble_candidates_from_impls()`.
  88             let eligible = if !resolved_item.defaultness.is_default() {
  89                 true
  90             } else if param_env.reveal == traits::Reveal::All {
  91                 !trait_ref.needs_subst()
  92             } else {
  93                 false
  94             };
  95
  96             if !eligible {
  97                 return None;
  98             }
  99
 100             let substs = tcx.erase_regions(&substs);
 101             Some(ty::Instance::new(def_id, substs))
 102         }
 103         traits::VtableGenerator(generator_data) => Some(Instance {
 104             def: ty::InstanceDef::Item(generator_data.generator_def_id),
 105             substs: generator_data.substs,
 106         }),
 107         traits::VtableClosure(closure_data) => {
 108             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 109             Some(Instance::resolve_closure(
 110                 tcx,
 111                 closure_data.closure_def_id,
 112                 closure_data.substs,
 113                 trait_closure_kind,
 114             ))
 115         }
 116         traits::VtableFnPointer(ref data) => Some(Instance {
 117             def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 118             substs: rcvr_substs,
 119         }),
 120         traits::VtableObject(ref data) => {
 121             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 122             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 123         }
 124         traits::VtableBuiltin(..) => {
 125             if tcx.lang_items().clone_trait().is_some() {
 126                 Some(Instance {
 127                     def: ty::InstanceDef::CloneShim(def_id, trait_ref.self_ty()),
 128                     substs: rcvr_substs,
 129                 })
 130             } else {
 131                 None
 132             }
 133         }
 134         traits::VtableAutoImpl(..) | traits::VtableParam(..) | traits::VtableTraitAlias(..) => None,
 135     }
 136 }