compiler/rustc_ty_utils/src/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 tracing::debug;
  12
  13 #[instrument(level = "debug", skip(tcx))]
  14 fn resolve_instance<'tcx>(
  15     tcx: TyCtxt<'tcx>,
  16     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
  17 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  18     let (param_env, (did, substs)) = key.into_parts();
  19     if let Some(did) = did.as_local() {
  20         if let Some(param_did) = tcx.opt_const_param_of(did) {
  21             return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
  22         }
  23     }
  24
  25     inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::unknown(did), substs)))
  26 }
  27
  28 fn resolve_instance_of_const_arg<'tcx>(
  29     tcx: TyCtxt<'tcx>,
  30     key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
  31 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  32     let (param_env, (did, const_param_did, substs)) = key.into_parts();
  33     inner_resolve_instance(
  34         tcx,
  35         param_env.and((
  36             ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
  37             substs,
  38         )),
  39     )
  40 }
  41
  42 #[instrument(level = "debug", skip(tcx))]
  43 fn inner_resolve_instance<'tcx>(
  44     tcx: TyCtxt<'tcx>,
  45     key: ty::ParamEnvAnd<'tcx, (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>)>,
  46 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  47     let (param_env, (def, substs)) = key.into_parts();
  48
  49     let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
  50         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
  51         let item = tcx.associated_item(def.did);
  52         resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
  53     } else {
  54         let ty = tcx.type_of(def.def_id_for_type_of());
  55         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, ty);
  56
  57         let def = match *item_type.kind() {
  58             ty::FnDef(..)
  59                 if {
  60                     let f = item_type.fn_sig(tcx);
  61                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
  62                 } =>
  63             {
  64                 debug!(" => intrinsic");
  65                 ty::InstanceDef::Intrinsic(def.did)
  66             }
  67             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
  68                 let ty = substs.type_at(0);
  69
  70                 if ty.needs_drop(tcx, param_env) {
  71                     debug!(" => nontrivial drop glue");
  72                     match *ty.kind() {
  73                         ty::Closure(..)
  74                         | ty::Generator(..)
  75                         | ty::Tuple(..)
  76                         | ty::Adt(..)
  77                         | ty::Dynamic(..)
  78                         | ty::Array(..)
  79                         | ty::Slice(..) => {}
  80                         // Drop shims can only be built from ADTs.
  81                         _ => return Ok(None),
  82                     }
  83
  84                     ty::InstanceDef::DropGlue(def_id, Some(ty))
  85                 } else {
  86                     debug!(" => trivial drop glue");
  87                     ty::InstanceDef::DropGlue(def_id, None)
  88                 }
  89             }
  90             _ => {
  91                 debug!(" => free item");
  92                 ty::InstanceDef::Item(def)
  93             }
  94         };
  95         Ok(Some(Instance { def, substs }))
  96     };
  97     debug!("inner_resolve_instance: result={:?}", result);
  98     result
  99 }
 100
 101 fn resolve_associated_item<'tcx>(
 102     tcx: TyCtxt<'tcx>,
 103     trait_item: &ty::AssocItem,
 104     param_env: ty::ParamEnv<'tcx>,
 105     trait_id: DefId,
 106     rcvr_substs: SubstsRef<'tcx>,
 107 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 108     let def_id = trait_item.def_id;
 109     debug!(
 110         "resolve_associated_item(trait_item={:?}, \
 111             param_env={:?}, \
 112             trait_id={:?}, \
 113             rcvr_substs={:?})",
 114         def_id, param_env, trait_id, rcvr_substs
 115     );
 116
 117     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 118     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)))?;
 119
 120     // Now that we know which impl is being used, we can dispatch to
 121     // the actual function:
 122     Ok(match vtbl {
 123         traits::ImplSource::UserDefined(impl_data) => {
 124             debug!(
 125                 "resolving ImplSource::UserDefined: {:?}, {:?}, {:?}, {:?}",
 126                 param_env, trait_item, rcvr_substs, impl_data
 127             );
 128             assert!(!rcvr_substs.needs_infer());
 129             assert!(!trait_ref.needs_infer());
 130
 131             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 132             let trait_def = tcx.trait_def(trait_def_id);
 133             let leaf_def = trait_def
 134                 .ancestors(tcx, impl_data.impl_def_id)?
 135                 .leaf_def(tcx, trait_item.ident, trait_item.kind)
 136                 .unwrap_or_else(|| {
 137                     bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
 138                 });
 139
 140             let substs = tcx.infer_ctxt().enter(|infcx| {
 141                 let param_env = param_env.with_reveal_all_normalized(tcx);
 142                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 143                 let substs = translate_substs(
 144                     &infcx,
 145                     param_env,
 146                     impl_data.impl_def_id,
 147                     substs,
 148                     leaf_def.defining_node,
 149                 );
 150                 infcx.tcx.erase_regions(substs)
 151             });
 152
 153             // Since this is a trait item, we need to see if the item is either a trait default item
 154             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 155             // NOTE: This should be kept in sync with the similar code in
 156             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 157             let eligible = if leaf_def.is_final() {
 158                 // Non-specializable items are always projectable.
 159                 true
 160             } else {
 161                 // Only reveal a specializable default if we're past type-checking
 162                 // and the obligation is monomorphic, otherwise passes such as
 163                 // transmute checking and polymorphic MIR optimizations could
 164                 // get a result which isn't correct for all monomorphizations.
 165                 if param_env.reveal() == Reveal::All {
 166                     !trait_ref.still_further_specializable()
 167                 } else {
 168                     false
 169                 }
 170             };
 171
 172             if !eligible {
 173                 return Ok(None);
 174             }
 175
 176             let substs = tcx.erase_regions(substs);
 177
 178             // Check if we just resolved an associated `const` declaration from
 179             // a `trait` to an associated `const` definition in an `impl`, where
 180             // the definition in the `impl` has the wrong type (for which an
 181             // error has already been/will be emitted elsewhere).
 182             //
 183             // NB: this may be expensive, we try to skip it in all the cases where
 184             // we know the error would've been caught (e.g. in an upstream crate).
 185             //
 186             // A better approach might be to just introduce a query (returning
 187             // `Result<(), ErrorReported>`) for the check that `rustc_typeck`
 188             // performs (i.e. that the definition's type in the `impl` matches
 189             // the declaration in the `trait`), so that we can cheaply check
 190             // here if it failed, instead of approximating it.
 191             if trait_item.kind == ty::AssocKind::Const
 192                 && trait_item.def_id != leaf_def.item.def_id
 193                 && leaf_def.item.def_id.is_local()
 194             {
 195                 let normalized_type_of = |def_id, substs| {
 196                     tcx.subst_and_normalize_erasing_regions(substs, param_env, tcx.type_of(def_id))
 197                 };
 198
 199                 let original_ty = normalized_type_of(trait_item.def_id, rcvr_substs);
 200                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 201
 202                 if original_ty != resolved_ty {
 203                     let msg = format!(
 204                         "Instance::resolve: inconsistent associated `const` type: \
 205                          was `{}: {}` but resolved to `{}: {}`",
 206                         tcx.def_path_str_with_substs(trait_item.def_id, rcvr_substs),
 207                         original_ty,
 208                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 209                         resolved_ty,
 210                     );
 211                     let span = tcx.def_span(leaf_def.item.def_id);
 212                     tcx.sess.delay_span_bug(span, &msg);
 213
 214                     return Err(ErrorReported);
 215                 }
 216             }
 217
 218             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 219         }
 220         traits::ImplSource::Generator(generator_data) => Some(Instance {
 221             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 222                 generator_data.generator_def_id,
 223             )),
 224             substs: generator_data.substs,
 225         }),
 226         traits::ImplSource::Closure(closure_data) => {
 227             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 228             Some(Instance::resolve_closure(
 229                 tcx,
 230                 closure_data.closure_def_id,
 231                 closure_data.substs,
 232                 trait_closure_kind,
 233             ))
 234         }
 235         traits::ImplSource::FnPointer(ref data) => match data.fn_ty.kind() {
 236             ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
 237                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 238                 substs: rcvr_substs,
 239             }),
 240             _ => None,
 241         },
 242         traits::ImplSource::Object(ref data) => {
 243             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 244             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 245         }
 246         traits::ImplSource::Builtin(..) => {
 247             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 248                 // FIXME(eddyb) use lang items for methods instead of names.
 249                 let name = tcx.item_name(def_id);
 250                 if name == sym::clone {
 251                     let self_ty = trait_ref.self_ty();
 252
 253                     let is_copy = self_ty.is_copy_modulo_regions(tcx.at(DUMMY_SP), param_env);
 254                     match self_ty.kind() {
 255                         _ if is_copy => (),
 256                         ty::Array(..) | ty::Closure(..) | ty::Tuple(..) => {}
 257                         _ => return Ok(None),
 258                     };
 259
 260                     Some(Instance {
 261                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 262                         substs: rcvr_substs,
 263                     })
 264                 } else {
 265                     assert_eq!(name, sym::clone_from);
 266
 267                     // Use the default `fn clone_from` from `trait Clone`.
 268                     let substs = tcx.erase_regions(rcvr_substs);
 269                     Some(ty::Instance::new(def_id, substs))
 270                 }
 271             } else {
 272                 None
 273             }
 274         }
 275         traits::ImplSource::AutoImpl(..)
 276         | traits::ImplSource::Param(..)
 277         | traits::ImplSource::TraitAlias(..)
 278         | traits::ImplSource::DiscriminantKind(..)
 279         | traits::ImplSource::Pointee(..) => None,
 280     })
 281 }
 282
 283 pub fn provide(providers: &mut ty::query::Providers) {
 284     *providers =
 285         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 286 }