src/librustc_ty/instance.rs

   1 use rustc_errors::ErrorReported;
   2 use rustc_hir::def_id::{DefId, LocalDefId};
   3 use rustc_infer::infer::TyCtxtInferExt;
   4 use rustc_middle::ty::subst::SubstsRef;
   5 use rustc_middle::ty::{self, Instance, TyCtxt, TypeFoldable};
   6 use rustc_span::{sym, DUMMY_SP};
   7 use rustc_target::spec::abi::Abi;
   8 use rustc_trait_selection::traits;
   9 use traits::{translate_substs, Reveal};
  10
  11 use log::debug;
  12
  13 fn resolve_instance<'tcx>(
  14     tcx: TyCtxt<'tcx>,
  15     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
  16 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  17     let (param_env, (did, substs)) = key.into_parts();
  18     if let Some(did) = did.as_local() {
  19         if let Some(param_did) = tcx.opt_const_param_of(did) {
  20             return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
  21         }
  22     }
  23
  24     inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::unknown(did), substs)))
  25 }
  26
  27 fn resolve_instance_of_const_arg<'tcx>(
  28     tcx: TyCtxt<'tcx>,
  29     key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
  30 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  31     let (param_env, (did, const_param_did, substs)) = key.into_parts();
  32     inner_resolve_instance(
  33         tcx,
  34         param_env.and((
  35             ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
  36             substs,
  37         )),
  38     )
  39 }
  40
  41 fn inner_resolve_instance<'tcx>(
  42     tcx: TyCtxt<'tcx>,
  43     key: ty::ParamEnvAnd<'tcx, (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>)>,
  44 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  45     let (param_env, (def, substs)) = key.into_parts();
  46
  47     debug!("resolve(def={:?}, substs={:?})", def.did, substs);
  48     let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
  49         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
  50         let item = tcx.associated_item(def.did);
  51         resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
  52     } else {
  53         let ty = tcx.type_of(def.def_id_for_type_of());
  54         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, &ty);
  55
  56         let def = match item_type.kind {
  57             ty::FnDef(..)
  58                 if {
  59                     let f = item_type.fn_sig(tcx);
  60                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
  61                 } =>
  62             {
  63                 debug!(" => intrinsic");
  64                 ty::InstanceDef::Intrinsic(def.did)
  65             }
  66             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
  67                 let ty = substs.type_at(0);
  68
  69                 if ty.needs_drop(tcx, param_env) {
  70                     debug!(" => nontrivial drop glue");
  71                     match ty.kind {
  72                         ty::Closure(..)
  73                         | ty::Generator(..)
  74                         | ty::Tuple(..)
  75                         | ty::Adt(..)
  76                         | ty::Dynamic(..)
  77                         | ty::Array(..)
  78                         | ty::Slice(..) => {}
  79                         // Drop shims can only be built from ADTs.
  80                         _ => return Ok(None),
  81                     }
  82
  83                     ty::InstanceDef::DropGlue(def_id, Some(ty))
  84                 } else {
  85                     debug!(" => trivial drop glue");
  86                     ty::InstanceDef::DropGlue(def_id, None)
  87                 }
  88             }
  89             _ => {
  90                 debug!(" => free item");
  91                 ty::InstanceDef::Item(def)
  92             }
  93         };
  94         Ok(Some(Instance { def, substs }))
  95     };
  96     debug!("resolve(def.did={:?}, substs={:?}) = {:?}", def.did, substs, result);
  97     result
  98 }
  99
 100 fn resolve_associated_item<'tcx>(
 101     tcx: TyCtxt<'tcx>,
 102     trait_item: &ty::AssocItem,
 103     param_env: ty::ParamEnv<'tcx>,
 104     trait_id: DefId,
 105     rcvr_substs: SubstsRef<'tcx>,
 106 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 107     let def_id = trait_item.def_id;
 108     debug!(
 109         "resolve_associated_item(trait_item={:?}, \
 110             param_env={:?}, \
 111             trait_id={:?}, \
 112             rcvr_substs={:?})",
 113         def_id, param_env, trait_id, rcvr_substs
 114     );
 115
 116     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 117     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)))?;
 118
 119     // Now that we know which impl is being used, we can dispatch to
 120     // the actual function:
 121     Ok(match vtbl {
 122         traits::ImplSourceUserDefined(impl_data) => {
 123             debug!(
 124                 "resolving ImplSourceUserDefined: {:?}, {:?}, {:?}, {:?}",
 125                 param_env, trait_item, rcvr_substs, impl_data
 126             );
 127             assert!(!rcvr_substs.needs_infer());
 128             assert!(!trait_ref.needs_infer());
 129
 130             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 131             let trait_def = tcx.trait_def(trait_def_id);
 132             let leaf_def = trait_def
 133                 .ancestors(tcx, impl_data.impl_def_id)?
 134                 .leaf_def(tcx, trait_item.ident, trait_item.kind)
 135                 .unwrap_or_else(|| {
 136                     bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
 137                 });
 138
 139             let substs = tcx.infer_ctxt().enter(|infcx| {
 140                 let param_env = param_env.with_reveal_all_normalized(tcx);
 141                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 142                 let substs = translate_substs(
 143                     &infcx,
 144                     param_env,
 145                     impl_data.impl_def_id,
 146                     substs,
 147                     leaf_def.defining_node,
 148                 );
 149                 infcx.tcx.erase_regions(&substs)
 150             });
 151
 152             // Since this is a trait item, we need to see if the item is either a trait default item
 153             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 154             // NOTE: This should be kept in sync with the similar code in
 155             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 156             let eligible = if leaf_def.is_final() {
 157                 // Non-specializable items are always projectable.
 158                 true
 159             } else {
 160                 // Only reveal a specializable default if we're past type-checking
 161                 // and the obligation is monomorphic, otherwise passes such as
 162                 // transmute checking and polymorphic MIR optimizations could
 163                 // get a result which isn't correct for all monomorphizations.
 164                 if param_env.reveal() == Reveal::All {
 165                     !trait_ref.still_further_specializable()
 166                 } else {
 167                     false
 168                 }
 169             };
 170
 171             if !eligible {
 172                 return Ok(None);
 173             }
 174
 175             let substs = tcx.erase_regions(&substs);
 176
 177             // Check if we just resolved an associated `const` declaration from
 178             // a `trait` to an associated `const` definition in an `impl`, where
 179             // the definition in the `impl` has the wrong type (for which an
 180             // error has already been/will be emitted elsewhere).
 181             //
 182             // NB: this may be expensive, we try to skip it in all the cases where
 183             // we know the error would've been caught (e.g. in an upstream crate).
 184             //
 185             // A better approach might be to just introduce a query (returning
 186             // `Result<(), ErrorReported>`) for the check that `rustc_typeck`
 187             // performs (i.e. that the definition's type in the `impl` matches
 188             // the declaration in the `trait`), so that we can cheaply check
 189             // here if it failed, instead of approximating it.
 190             if trait_item.kind == ty::AssocKind::Const
 191                 && trait_item.def_id != leaf_def.item.def_id
 192                 && leaf_def.item.def_id.is_local()
 193             {
 194                 let normalized_type_of = |def_id, substs| {
 195                     tcx.subst_and_normalize_erasing_regions(substs, param_env, &tcx.type_of(def_id))
 196                 };
 197
 198                 let original_ty = normalized_type_of(trait_item.def_id, rcvr_substs);
 199                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 200
 201                 if original_ty != resolved_ty {
 202                     let msg = format!(
 203                         "Instance::resolve: inconsistent associated `const` type: \
 204                          was `{}: {}` but resolved to `{}: {}`",
 205                         tcx.def_path_str_with_substs(trait_item.def_id, rcvr_substs),
 206                         original_ty,
 207                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 208                         resolved_ty,
 209                     );
 210                     let span = tcx.def_span(leaf_def.item.def_id);
 211                     tcx.sess.delay_span_bug(span, &msg);
 212
 213                     return Err(ErrorReported);
 214                 }
 215             }
 216
 217             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 218         }
 219         traits::ImplSourceGenerator(generator_data) => Some(Instance {
 220             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 221                 generator_data.generator_def_id,
 222             )),
 223             substs: generator_data.substs,
 224         }),
 225         traits::ImplSourceClosure(closure_data) => {
 226             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 227             Some(Instance::resolve_closure(
 228                 tcx,
 229                 closure_data.closure_def_id,
 230                 closure_data.substs,
 231                 trait_closure_kind,
 232             ))
 233         }
 234         traits::ImplSourceFnPointer(ref data) => match data.fn_ty.kind {
 235             ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
 236                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 237                 substs: rcvr_substs,
 238             }),
 239             _ => None,
 240         },
 241         traits::ImplSourceObject(ref data) => {
 242             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 243             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 244         }
 245         traits::ImplSourceBuiltin(..) => {
 246             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 247                 // FIXME(eddyb) use lang items for methods instead of names.
 248                 let name = tcx.item_name(def_id);
 249                 if name == sym::clone {
 250                     let self_ty = trait_ref.self_ty();
 251
 252                     let is_copy = self_ty.is_copy_modulo_regions(tcx.at(DUMMY_SP), param_env);
 253                     match self_ty.kind {
 254                         _ if is_copy => (),
 255                         ty::Array(..) | ty::Closure(..) | ty::Tuple(..) => {}
 256                         _ => return Ok(None),
 257                     };
 258
 259                     Some(Instance {
 260                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 261                         substs: rcvr_substs,
 262                     })
 263                 } else {
 264                     assert_eq!(name, sym::clone_from);
 265
 266                     // Use the default `fn clone_from` from `trait Clone`.
 267                     let substs = tcx.erase_regions(&rcvr_substs);
 268                     Some(ty::Instance::new(def_id, substs))
 269                 }
 270             } else {
 271                 None
 272             }
 273         }
 274         traits::ImplSourceAutoImpl(..)
 275         | traits::ImplSourceParam(..)
 276         | traits::ImplSourceTraitAlias(..)
 277         | traits::ImplSourceDiscriminantKind(..) => None,
 278     })
 279 }
 280
 281 pub fn provide(providers: &mut ty::query::Providers) {
 282     *providers =
 283         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 284 }