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, Binder, Instance, Ty, TyCtxt, TypeFoldable, TypeVisitor};
   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 rustc_data_structures::sso::SsoHashSet;
  12 use std::collections::btree_map::Entry;
  13 use std::collections::BTreeMap;
  14 use std::ops::ControlFlow;
  15
  16 use tracing::debug;
  17
  18 // FIXME(#86795): `BoundVarsCollector` here should **NOT** be used
  19 // outside of `resolve_associated_item`. It's just to address #64494,
  20 // #83765, and #85848 which are creating bound types/regions that lose
  21 // their `Binder` *unintentionally*.
  22 // It's ideal to remove `BoundVarsCollector` and just use
  23 // `ty::Binder::*` methods but we use this stopgap until we figure out
  24 // the "real" fix.
  25 struct BoundVarsCollector<'tcx> {
  26     binder_index: ty::DebruijnIndex,
  27     vars: BTreeMap<u32, ty::BoundVariableKind>,
  28     // We may encounter the same variable at different levels of binding, so
  29     // this can't just be `Ty`
  30     visited: SsoHashSet<(ty::DebruijnIndex, Ty<'tcx>)>,
  31 }
  32
  33 impl<'tcx> BoundVarsCollector<'tcx> {
  34     fn new() -> Self {
  35         BoundVarsCollector {
  36             binder_index: ty::INNERMOST,
  37             vars: BTreeMap::new(),
  38             visited: SsoHashSet::default(),
  39         }
  40     }
  41
  42     fn into_vars(self, tcx: TyCtxt<'tcx>) -> &'tcx ty::List<ty::BoundVariableKind> {
  43         let max = self.vars.iter().map(|(k, _)| *k).max().unwrap_or(0);
  44         for i in 0..max {
  45             if let None = self.vars.get(&i) {
  46                 panic!("Unknown variable: {:?}", i);
  47             }
  48         }
  49
  50         tcx.mk_bound_variable_kinds(self.vars.into_iter().map(|(_, v)| v))
  51     }
  52 }
  53
  54 impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
  55     type BreakTy = ();
  56
  57     fn visit_binder<T: TypeFoldable<'tcx>>(
  58         &mut self,
  59         t: &Binder<'tcx, T>,
  60     ) -> ControlFlow<Self::BreakTy> {
  61         self.binder_index.shift_in(1);
  62         let result = t.super_visit_with(self);
  63         self.binder_index.shift_out(1);
  64         result
  65     }
  66
  67     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
  68         if t.outer_exclusive_binder() < self.binder_index
  69             || !self.visited.insert((self.binder_index, t))
  70         {
  71             return ControlFlow::CONTINUE;
  72         }
  73         match *t.kind() {
  74             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
  75                 match self.vars.entry(bound_ty.var.as_u32()) {
  76                     Entry::Vacant(entry) => {
  77                         entry.insert(ty::BoundVariableKind::Ty(bound_ty.kind));
  78                     }
  79                     Entry::Occupied(entry) => match entry.get() {
  80                         ty::BoundVariableKind::Ty(_) => {}
  81                         _ => bug!("Conflicting bound vars"),
  82                     },
  83                 }
  84             }
  85
  86             _ => (),
  87         };
  88
  89         t.super_visit_with(self)
  90     }
  91
  92     fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
  93         match r {
  94             ty::ReLateBound(index, br) if *index == self.binder_index => {
  95                 match self.vars.entry(br.var.as_u32()) {
  96                     Entry::Vacant(entry) => {
  97                         entry.insert(ty::BoundVariableKind::Region(br.kind));
  98                     }
  99                     Entry::Occupied(entry) => match entry.get() {
 100                         ty::BoundVariableKind::Region(_) => {}
 101                         _ => bug!("Conflicting bound vars"),
 102                     },
 103                 }
 104             }
 105
 106             _ => (),
 107         };
 108
 109         r.super_visit_with(self)
 110     }
 111 }
 112
 113 #[instrument(level = "debug", skip(tcx))]
 114 fn resolve_instance<'tcx>(
 115     tcx: TyCtxt<'tcx>,
 116     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
 117 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 118     let (param_env, (did, substs)) = key.into_parts();
 119     if let Some(did) = did.as_local() {
 120         if let Some(param_did) = tcx.opt_const_param_of(did) {
 121             return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
 122         }
 123     }
 124
 125     inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::unknown(did), substs)))
 126 }
 127
 128 fn resolve_instance_of_const_arg<'tcx>(
 129     tcx: TyCtxt<'tcx>,
 130     key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
 131 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 132     let (param_env, (did, const_param_did, substs)) = key.into_parts();
 133     inner_resolve_instance(
 134         tcx,
 135         param_env.and((
 136             ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
 137             substs,
 138         )),
 139     )
 140 }
 141
 142 #[instrument(level = "debug", skip(tcx))]
 143 fn inner_resolve_instance<'tcx>(
 144     tcx: TyCtxt<'tcx>,
 145     key: ty::ParamEnvAnd<'tcx, (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>)>,
 146 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 147     let (param_env, (def, substs)) = key.into_parts();
 148
 149     let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
 150         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
 151         let item = tcx.associated_item(def.did);
 152         resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
 153     } else {
 154         let ty = tcx.type_of(def.def_id_for_type_of());
 155         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, ty);
 156
 157         let def = match *item_type.kind() {
 158             ty::FnDef(..)
 159                 if {
 160                     let f = item_type.fn_sig(tcx);
 161                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
 162                 } =>
 163             {
 164                 debug!(" => intrinsic");
 165                 ty::InstanceDef::Intrinsic(def.did)
 166             }
 167             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
 168                 let ty = substs.type_at(0);
 169
 170                 if ty.needs_drop(tcx, param_env) {
 171                     debug!(" => nontrivial drop glue");
 172                     match *ty.kind() {
 173                         ty::Closure(..)
 174                         | ty::Generator(..)
 175                         | ty::Tuple(..)
 176                         | ty::Adt(..)
 177                         | ty::Dynamic(..)
 178                         | ty::Array(..)
 179                         | ty::Slice(..) => {}
 180                         // Drop shims can only be built from ADTs.
 181                         _ => return Ok(None),
 182                     }
 183
 184                     ty::InstanceDef::DropGlue(def_id, Some(ty))
 185                 } else {
 186                     debug!(" => trivial drop glue");
 187                     ty::InstanceDef::DropGlue(def_id, None)
 188                 }
 189             }
 190             _ => {
 191                 debug!(" => free item");
 192                 ty::InstanceDef::Item(def)
 193             }
 194         };
 195         Ok(Some(Instance { def, substs }))
 196     };
 197     debug!("inner_resolve_instance: result={:?}", result);
 198     result
 199 }
 200
 201 fn resolve_associated_item<'tcx>(
 202     tcx: TyCtxt<'tcx>,
 203     trait_item: &ty::AssocItem,
 204     param_env: ty::ParamEnv<'tcx>,
 205     trait_id: DefId,
 206     rcvr_substs: SubstsRef<'tcx>,
 207 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 208     let def_id = trait_item.def_id;
 209     debug!(
 210         "resolve_associated_item(trait_item={:?}, \
 211             param_env={:?}, \
 212             trait_id={:?}, \
 213             rcvr_substs={:?})",
 214         def_id, param_env, trait_id, rcvr_substs
 215     );
 216
 217     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 218
 219     // See FIXME on `BoundVarsCollector`.
 220     let mut bound_vars_collector = BoundVarsCollector::new();
 221     trait_ref.visit_with(&mut bound_vars_collector);
 222     let trait_binder = ty::Binder::bind_with_vars(trait_ref, bound_vars_collector.into_vars(tcx));
 223     let vtbl = tcx.codegen_fulfill_obligation((param_env, trait_binder))?;
 224
 225     // Now that we know which impl is being used, we can dispatch to
 226     // the actual function:
 227     Ok(match vtbl {
 228         traits::ImplSource::UserDefined(impl_data) => {
 229             debug!(
 230                 "resolving ImplSource::UserDefined: {:?}, {:?}, {:?}, {:?}",
 231                 param_env, trait_item, rcvr_substs, impl_data
 232             );
 233             assert!(!rcvr_substs.needs_infer());
 234             assert!(!trait_ref.needs_infer());
 235
 236             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 237             let trait_def = tcx.trait_def(trait_def_id);
 238             let leaf_def = trait_def
 239                 .ancestors(tcx, impl_data.impl_def_id)?
 240                 .leaf_def(tcx, trait_item.ident, trait_item.kind)
 241                 .unwrap_or_else(|| {
 242                     bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
 243                 });
 244
 245             let substs = tcx.infer_ctxt().enter(|infcx| {
 246                 let param_env = param_env.with_reveal_all_normalized(tcx);
 247                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 248                 let substs = translate_substs(
 249                     &infcx,
 250                     param_env,
 251                     impl_data.impl_def_id,
 252                     substs,
 253                     leaf_def.defining_node,
 254                 );
 255                 infcx.tcx.erase_regions(substs)
 256             });
 257
 258             // Since this is a trait item, we need to see if the item is either a trait default item
 259             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 260             // NOTE: This should be kept in sync with the similar code in
 261             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 262             let eligible = if leaf_def.is_final() {
 263                 // Non-specializable items are always projectable.
 264                 true
 265             } else {
 266                 // Only reveal a specializable default if we're past type-checking
 267                 // and the obligation is monomorphic, otherwise passes such as
 268                 // transmute checking and polymorphic MIR optimizations could
 269                 // get a result which isn't correct for all monomorphizations.
 270                 if param_env.reveal() == Reveal::All {
 271                     !trait_ref.still_further_specializable()
 272                 } else {
 273                     false
 274                 }
 275             };
 276
 277             if !eligible {
 278                 return Ok(None);
 279             }
 280
 281             let substs = tcx.erase_regions(substs);
 282
 283             // Check if we just resolved an associated `const` declaration from
 284             // a `trait` to an associated `const` definition in an `impl`, where
 285             // the definition in the `impl` has the wrong type (for which an
 286             // error has already been/will be emitted elsewhere).
 287             //
 288             // NB: this may be expensive, we try to skip it in all the cases where
 289             // we know the error would've been caught (e.g. in an upstream crate).
 290             //
 291             // A better approach might be to just introduce a query (returning
 292             // `Result<(), ErrorReported>`) for the check that `rustc_typeck`
 293             // performs (i.e. that the definition's type in the `impl` matches
 294             // the declaration in the `trait`), so that we can cheaply check
 295             // here if it failed, instead of approximating it.
 296             if trait_item.kind == ty::AssocKind::Const
 297                 && trait_item.def_id != leaf_def.item.def_id
 298                 && leaf_def.item.def_id.is_local()
 299             {
 300                 let normalized_type_of = |def_id, substs| {
 301                     tcx.subst_and_normalize_erasing_regions(substs, param_env, tcx.type_of(def_id))
 302                 };
 303
 304                 let original_ty = normalized_type_of(trait_item.def_id, rcvr_substs);
 305                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 306
 307                 if original_ty != resolved_ty {
 308                     let msg = format!(
 309                         "Instance::resolve: inconsistent associated `const` type: \
 310                          was `{}: {}` but resolved to `{}: {}`",
 311                         tcx.def_path_str_with_substs(trait_item.def_id, rcvr_substs),
 312                         original_ty,
 313                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 314                         resolved_ty,
 315                     );
 316                     let span = tcx.def_span(leaf_def.item.def_id);
 317                     tcx.sess.delay_span_bug(span, &msg);
 318
 319                     return Err(ErrorReported);
 320                 }
 321             }
 322
 323             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 324         }
 325         traits::ImplSource::Generator(generator_data) => Some(Instance {
 326             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 327                 generator_data.generator_def_id,
 328             )),
 329             substs: generator_data.substs,
 330         }),
 331         traits::ImplSource::Closure(closure_data) => {
 332             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 333             Some(Instance::resolve_closure(
 334                 tcx,
 335                 closure_data.closure_def_id,
 336                 closure_data.substs,
 337                 trait_closure_kind,
 338             ))
 339         }
 340         traits::ImplSource::FnPointer(ref data) => match data.fn_ty.kind() {
 341             ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
 342                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 343                 substs: rcvr_substs,
 344             }),
 345             _ => None,
 346         },
 347         traits::ImplSource::Object(ref data) => {
 348             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 349             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 350         }
 351         traits::ImplSource::Builtin(..) => {
 352             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 353                 // FIXME(eddyb) use lang items for methods instead of names.
 354                 let name = tcx.item_name(def_id);
 355                 if name == sym::clone {
 356                     let self_ty = trait_ref.self_ty();
 357
 358                     let is_copy = self_ty.is_copy_modulo_regions(tcx.at(DUMMY_SP), param_env);
 359                     match self_ty.kind() {
 360                         _ if is_copy => (),
 361                         ty::Array(..) | ty::Closure(..) | ty::Tuple(..) => {}
 362                         _ => return Ok(None),
 363                     };
 364
 365                     Some(Instance {
 366                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 367                         substs: rcvr_substs,
 368                     })
 369                 } else {
 370                     assert_eq!(name, sym::clone_from);
 371
 372                     // Use the default `fn clone_from` from `trait Clone`.
 373                     let substs = tcx.erase_regions(rcvr_substs);
 374                     Some(ty::Instance::new(def_id, substs))
 375                 }
 376             } else {
 377                 None
 378             }
 379         }
 380         traits::ImplSource::AutoImpl(..)
 381         | traits::ImplSource::Param(..)
 382         | traits::ImplSource::TraitAlias(..)
 383         | traits::ImplSource::DiscriminantKind(..)
 384         | traits::ImplSource::Pointee(..) => None,
 385     })
 386 }
 387
 388 pub fn provide(providers: &mut ty::query::Providers) {
 389     *providers =
 390         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 391 }