src/librustc_ty/instance.rs

   1 use rustc_hir::def_id::DefId;
   2 use rustc_infer::infer::TyCtxtInferExt;
   3 use rustc_middle::ty::subst::SubstsRef;
   4 use rustc_middle::ty::{self, Instance, TyCtxt, TypeFoldable};
   5 use rustc_span::sym;
   6 use rustc_target::spec::abi::Abi;
   7 use rustc_trait_selection::traits;
   8 use traits::{translate_substs, Reveal};
   9
  10 use log::debug;
  11
  12 pub fn resolve_instance<'tcx>(
  13     tcx: TyCtxt<'tcx>,
  14     (param_env, def_id, substs): (ty::ParamEnv<'tcx>, DefId, 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             debug!(
  86                 "resolving VtableImpl: {:?}, {:?}, {:?}, {:?}",
  87                 param_env, trait_item, rcvr_substs, impl_data
  88             );
  89             assert!(!rcvr_substs.needs_infer());
  90             assert!(!trait_ref.needs_infer());
  91
  92             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
  93             let trait_def = tcx.trait_def(trait_def_id);
  94             let leaf_def = trait_def
  95                 .ancestors(tcx, impl_data.impl_def_id)
  96                 .ok()?
  97                 .leaf_def(tcx, trait_item.ident, trait_item.kind)
  98                 .unwrap_or_else(|| {
  99                     bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
 100                 });
 101             let def_id = leaf_def.item.def_id;
 102
 103             let substs = tcx.infer_ctxt().enter(|infcx| {
 104                 let param_env = param_env.with_reveal_all();
 105                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 106                 let substs = translate_substs(
 107                     &infcx,
 108                     param_env,
 109                     impl_data.impl_def_id,
 110                     substs,
 111                     leaf_def.defining_node,
 112                 );
 113                 infcx.tcx.erase_regions(&substs)
 114             });
 115
 116             // Since this is a trait item, we need to see if the item is either a trait default item
 117             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 118             // NOTE: This should be kept in sync with the similar code in
 119             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 120             let eligible = if leaf_def.is_final() {
 121                 // Non-specializable items are always projectable.
 122                 true
 123             } else {
 124                 // Only reveal a specializable default if we're past type-checking
 125                 // and the obligation is monomorphic, otherwise passes such as
 126                 // transmute checking and polymorphic MIR optimizations could
 127                 // get a result which isn't correct for all monomorphizations.
 128                 if param_env.reveal == Reveal::All {
 129                     !trait_ref.still_further_specializable()
 130                 } else {
 131                     false
 132                 }
 133             };
 134
 135             if !eligible {
 136                 return None;
 137             }
 138
 139             let substs = tcx.erase_regions(&substs);
 140             Some(ty::Instance::new(def_id, substs))
 141         }
 142         traits::VtableGenerator(generator_data) => Some(Instance {
 143             def: ty::InstanceDef::Item(generator_data.generator_def_id),
 144             substs: generator_data.substs,
 145         }),
 146         traits::VtableClosure(closure_data) => {
 147             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 148             Some(Instance::resolve_closure(
 149                 tcx,
 150                 closure_data.closure_def_id,
 151                 closure_data.substs,
 152                 trait_closure_kind,
 153             ))
 154         }
 155         traits::VtableFnPointer(ref data) => {
 156             // `FnPtrShim` requires a monomorphic aka concrete type.
 157             if data.fn_ty.needs_subst() {
 158                 return None;
 159             }
 160
 161             Some(Instance {
 162                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 163                 substs: rcvr_substs,
 164             })
 165         }
 166         traits::VtableObject(ref data) => {
 167             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 168             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 169         }
 170         traits::VtableBuiltin(..) => {
 171             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 172                 // FIXME(eddyb) use lang items for methods instead of names.
 173                 let name = tcx.item_name(def_id);
 174                 if name == sym::clone {
 175                     let self_ty = trait_ref.self_ty();
 176
 177                     // `CloneShim` requires a monomorphic aka concrete type.
 178                     if self_ty.needs_subst() {
 179                         return None;
 180                     }
 181
 182                     Some(Instance {
 183                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 184                         substs: rcvr_substs,
 185                     })
 186                 } else {
 187                     assert_eq!(name, sym::clone_from);
 188
 189                     // Use the default `fn clone_from` from `trait Clone`.
 190                     let substs = tcx.erase_regions(&rcvr_substs);
 191                     Some(ty::Instance::new(def_id, substs))
 192                 }
 193             } else {
 194                 None
 195             }
 196         }
 197         traits::VtableAutoImpl(..) | traits::VtableParam(..) | traits::VtableTraitAlias(..) => None,
 198     }
 199 }
 200
 201 pub fn provide(providers: &mut ty::query::Providers<'_>) {
 202     *providers = ty::query::Providers { resolve_instance, ..*providers };
 203 }