src/librustc_ty/instance.rs

   1 use rustc_hir::def_id::DefId;
   2 use rustc_middle::ty::subst::SubstsRef;
   3 use rustc_middle::ty::{self, Instance, TyCtxt, TypeFoldable};
   4 use rustc_infer::infer::TyCtxtInferExt;
   5 use rustc_span::sym;
   6 use rustc_target::spec::abi::Abi;
   7 use rustc_trait_selection::traits;
   8 use traits::{Reveal, translate_substs};
   9
  10 use log::debug;
  11
  12 pub fn resolve_instance<'tcx>(
  13     tcx: TyCtxt<'tcx>,
  14     param_env: ty::ParamEnv<'tcx>,
  15     def_id: DefId,
  16     substs: SubstsRef<'tcx>,
  17 ) -> Option<Instance<'tcx>> {
  18     debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
  19     let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
  20         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
  21         let item = tcx.associated_item(def_id);
  22         resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
  23     } else {
  24         let ty = tcx.type_of(def_id);
  25         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, &ty);
  26
  27         let def = match item_type.kind {
  28             ty::FnDef(..)
  29                 if {
  30                     let f = item_type.fn_sig(tcx);
  31                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
  32                 } =>
  33             {
  34                 debug!(" => intrinsic");
  35                 ty::InstanceDef::Intrinsic(def_id)
  36             }
  37             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
  38                 let ty = substs.type_at(0);
  39
  40                 if ty.needs_drop(tcx, param_env) {
  41                     // `DropGlue` requires a monomorphic aka concrete type.
  42                     if ty.needs_subst() {
  43                         return None;
  44                     }
  45
  46                     debug!(" => nontrivial drop glue");
  47                     ty::InstanceDef::DropGlue(def_id, Some(ty))
  48                 } else {
  49                     debug!(" => trivial drop glue");
  50                     ty::InstanceDef::DropGlue(def_id, None)
  51                 }
  52             }
  53             _ => {
  54                 debug!(" => free item");
  55                 ty::InstanceDef::Item(def_id)
  56             }
  57         };
  58         Some(Instance { def, substs })
  59     };
  60     debug!("resolve(def_id={:?}, substs={:?}) = {:?}", def_id, substs, result);
  61     result
  62 }
  63
  64 fn resolve_associated_item<'tcx>(
  65     tcx: TyCtxt<'tcx>,
  66     trait_item: &ty::AssocItem,
  67     param_env: ty::ParamEnv<'tcx>,
  68     trait_id: DefId,
  69     rcvr_substs: SubstsRef<'tcx>,
  70 ) -> Option<Instance<'tcx>> {
  71     let def_id = trait_item.def_id;
  72     debug!(
  73         "resolve_associated_item(trait_item={:?}, \
  74             param_env={:?}, \
  75             trait_id={:?}, \
  76             rcvr_substs={:?})",
  77         def_id, param_env, trait_id, rcvr_substs
  78     );
  79
  80     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
  81     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)))?;
  82
  83     // Now that we know which impl is being used, we can dispatch to
  84     // the actual function:
  85     match vtbl {
  86         traits::VtableImpl(impl_data) => {
  87             debug!(
  88                 "resolving VtableImpl: {:?}, {:?}, {:?}, {:?}",
  89                 param_env, trait_item, rcvr_substs, impl_data
  90             );
  91             assert!(!rcvr_substs.needs_infer());
  92             assert!(!trait_ref.needs_infer());
  93
  94             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
  95             let trait_def = tcx.trait_def(trait_def_id);
  96             let leaf_def = trait_def
  97                 .ancestors(tcx, impl_data.impl_def_id)
  98                 .ok()?
  99                 .leaf_def(tcx, trait_item.ident, trait_item.kind)
 100                 .unwrap_or_else(|| {
 101                     bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
 102                 });
 103             let def_id = leaf_def.item.def_id;
 104
 105             let substs = tcx.infer_ctxt().enter(|infcx| {
 106                 let param_env = param_env.with_reveal_all();
 107                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 108                 let substs = translate_substs(
 109                     &infcx,
 110                     param_env,
 111                     impl_data.impl_def_id,
 112                     substs,
 113                     leaf_def.defining_node,
 114                 );
 115                 infcx.tcx.erase_regions(&substs)
 116             });
 117
 118             // Since this is a trait item, we need to see if the item is either a trait default item
 119             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 120             // NOTE: This should be kept in sync with the similar code in
 121             // `rustc_middle::traits::project::assemble_candidates_from_impls()`.
 122             let eligible = if leaf_def.is_final() {
 123                 // Non-specializable items are always projectable.
 124                 true
 125             } else {
 126                 // Only reveal a specializable default if we're past type-checking
 127                 // and the obligation is monomorphic, otherwise passes such as
 128                 // transmute checking and polymorphic MIR optimizations could
 129                 // get a result which isn't correct for all monomorphizations.
 130                 if param_env.reveal == Reveal::All { !trait_ref.needs_subst() } else { false }
 131             };
 132
 133             if !eligible {
 134                 return None;
 135             }
 136
 137             let substs = tcx.erase_regions(&substs);
 138             Some(ty::Instance::new(def_id, substs))
 139         }
 140         traits::VtableGenerator(generator_data) => Some(Instance {
 141             def: ty::InstanceDef::Item(generator_data.generator_def_id),
 142             substs: generator_data.substs,
 143         }),
 144         traits::VtableClosure(closure_data) => {
 145             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 146             Some(Instance::resolve_closure(
 147                 tcx,
 148                 closure_data.closure_def_id,
 149                 closure_data.substs,
 150                 trait_closure_kind,
 151             ))
 152         }
 153         traits::VtableFnPointer(ref data) => {
 154             // `FnPtrShim` requires a monomorphic aka concrete type.
 155             if data.fn_ty.needs_subst() {
 156                 return None;
 157             }
 158
 159             Some(Instance {
 160                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 161                 substs: rcvr_substs,
 162             })
 163         }
 164         traits::VtableObject(ref data) => {
 165             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 166             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 167         }
 168         traits::VtableBuiltin(..) => {
 169             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 170                 // FIXME(eddyb) use lang items for methods instead of names.
 171                 let name = tcx.item_name(def_id);
 172                 if name == sym::clone {
 173                     let self_ty = trait_ref.self_ty();
 174
 175                     // `CloneShim` requires a monomorphic aka concrete type.
 176                     if self_ty.needs_subst() {
 177                         return None;
 178                     }
 179
 180                     Some(Instance {
 181                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 182                         substs: rcvr_substs,
 183                     })
 184                 } else {
 185                     assert_eq!(name, sym::clone_from);
 186
 187                     // Use the default `fn clone_from` from `trait Clone`.
 188                     let substs = tcx.erase_regions(&rcvr_substs);
 189                     Some(ty::Instance::new(def_id, substs))
 190                 }
 191             } else {
 192                 None
 193             }
 194         }
 195         traits::VtableAutoImpl(..) | traits::VtableParam(..) | traits::VtableTraitAlias(..) => None,
 196     }
 197 }