src/librustc_ty/instance.rs

   1 use rustc::ty::subst::SubstsRef;
   2 use rustc::ty::{self, Instance, TyCtxt, TypeFoldable};
   3 use rustc_hir::def_id::DefId;
   4 use rustc_span::sym;
   5 use rustc_target::spec::abi::Abi;
   6 use rustc_trait_selection::traits;
   7
   8 use log::debug;
   9
  10 pub fn resolve_instance<'tcx>(
  11     tcx: TyCtxt<'tcx>,
  12     param_env: ty::ParamEnv<'tcx>,
  13     def_id: DefId,
  14     substs: SubstsRef<'tcx>,
  15 ) -> Option<Instance<'tcx>> {
  16     debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
  17     let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
  18         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
  19         let item = tcx.associated_item(def_id);
  20         resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
  21     } else {
  22         let ty = tcx.type_of(def_id);
  23         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, &ty);
  24
  25         let def = match item_type.kind {
  26             ty::FnDef(..)
  27                 if {
  28                     let f = item_type.fn_sig(tcx);
  29                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
  30                 } =>
  31             {
  32                 debug!(" => intrinsic");
  33                 ty::InstanceDef::Intrinsic(def_id)
  34             }
  35             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
  36                 let ty = substs.type_at(0);
  37
  38                 if ty.needs_drop(tcx, param_env) {
  39                     // `DropGlue` requires a monomorphic aka concrete type.
  40                     if ty.needs_subst() {
  41                         return None;
  42                     }
  43
  44                     debug!(" => nontrivial drop glue");
  45                     ty::InstanceDef::DropGlue(def_id, Some(ty))
  46                 } else {
  47                     debug!(" => trivial drop glue");
  48                     ty::InstanceDef::DropGlue(def_id, None)
  49                 }
  50             }
  51             _ => {
  52                 debug!(" => free item");
  53                 ty::InstanceDef::Item(def_id)
  54             }
  55         };
  56         Some(Instance { def, substs })
  57     };
  58     debug!("resolve(def_id={:?}, substs={:?}) = {:?}", def_id, substs, result);
  59     result
  60 }
  61
  62 fn resolve_associated_item<'tcx>(
  63     tcx: TyCtxt<'tcx>,
  64     trait_item: &ty::AssocItem,
  65     param_env: ty::ParamEnv<'tcx>,
  66     trait_id: DefId,
  67     rcvr_substs: SubstsRef<'tcx>,
  68 ) -> Option<Instance<'tcx>> {
  69     let def_id = trait_item.def_id;
  70     debug!(
  71         "resolve_associated_item(trait_item={:?}, \
  72             param_env={:?}, \
  73             trait_id={:?}, \
  74             rcvr_substs={:?})",
  75         def_id, param_env, trait_id, rcvr_substs
  76     );
  77
  78     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
  79     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)))?;
  80
  81     // Now that we know which impl is being used, we can dispatch to
  82     // the actual function:
  83     match vtbl {
  84         traits::VtableImpl(impl_data) => {
  85             let (def_id, substs) =
  86                 traits::find_associated_item(tcx, param_env, trait_item, rcvr_substs, &impl_data);
  87
  88             let resolved_item = tcx.associated_item(def_id);
  89
  90             // Since this is a trait item, we need to see if the item is either a trait default item
  91             // or a specialization because we can't resolve those unless we can `Reveal::All`.
  92             // NOTE: This should be kept in sync with the similar code in
  93             // `rustc::traits::project::assemble_candidates_from_impls()`.
  94             let eligible = if !resolved_item.defaultness.is_default() {
  95                 true
  96             } else if param_env.reveal == traits::Reveal::All {
  97                 !trait_ref.needs_subst()
  98             } else {
  99                 false
 100             };
 101
 102             if !eligible {
 103                 return None;
 104             }
 105
 106             let substs = tcx.erase_regions(&substs);
 107             Some(ty::Instance::new(def_id, substs))
 108         }
 109         traits::VtableGenerator(generator_data) => Some(Instance {
 110             def: ty::InstanceDef::Item(generator_data.generator_def_id),
 111             substs: generator_data.substs,
 112         }),
 113         traits::VtableClosure(closure_data) => {
 114             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 115             Some(Instance::resolve_closure(
 116                 tcx,
 117                 closure_data.closure_def_id,
 118                 closure_data.substs,
 119                 trait_closure_kind,
 120             ))
 121         }
 122         traits::VtableFnPointer(ref data) => {
 123             // `FnPtrShim` requires a monomorphic aka concrete type.
 124             if data.fn_ty.needs_subst() {
 125                 return None;
 126             }
 127
 128             Some(Instance {
 129                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 130                 substs: rcvr_substs,
 131             })
 132         }
 133         traits::VtableObject(ref data) => {
 134             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 135             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 136         }
 137         traits::VtableBuiltin(..) => {
 138             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 139                 // FIXME(eddyb) use lang items for methods instead of names.
 140                 let name = tcx.item_name(def_id);
 141                 if name == sym::clone {
 142                     let self_ty = trait_ref.self_ty();
 143
 144                     // `CloneShim` requires a monomorphic aka concrete type.
 145                     if self_ty.needs_subst() {
 146                         return None;
 147                     }
 148
 149                     Some(Instance {
 150                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 151                         substs: rcvr_substs,
 152                     })
 153                 } else {
 154                     assert_eq!(name, sym::clone_from);
 155
 156                     // Use the default `fn clone_from` from `trait Clone`.
 157                     let substs = tcx.erase_regions(&rcvr_substs);
 158                     Some(ty::Instance::new(def_id, substs))
 159                 }
 160             } else {
 161                 None
 162             }
 163         }
 164         traits::VtableAutoImpl(..) | traits::VtableParam(..) | traits::VtableTraitAlias(..) => None,
 165     }
 166 }