compiler/rustc_ty_utils/src/instance.rs

   1 use rustc_errors::ErrorGuaranteed;
   2 use rustc_hir::def_id::{DefId, LocalDefId};
   3 use rustc_infer::infer::TyCtxtInferExt;
   4 use rustc_middle::traits::CodegenObligationError;
   5 use rustc_middle::ty::subst::SubstsRef;
   6 use rustc_middle::ty::{
   7     self, Binder, Instance, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVisitor,
   8 };
   9 use rustc_span::{sym, DUMMY_SP};
  10 use rustc_trait_selection::traits;
  11 use traits::{translate_substs, Reveal};
  12
  13 use rustc_data_structures::sso::SsoHashSet;
  14 use std::collections::btree_map::Entry;
  15 use std::collections::BTreeMap;
  16 use std::ops::ControlFlow;
  17
  18 use tracing::debug;
  19
  20 // FIXME(#86795): `BoundVarsCollector` here should **NOT** be used
  21 // outside of `resolve_associated_item`. It's just to address #64494,
  22 // #83765, and #85848 which are creating bound types/regions that lose
  23 // their `Binder` *unintentionally*.
  24 // It's ideal to remove `BoundVarsCollector` and just use
  25 // `ty::Binder::*` methods but we use this stopgap until we figure out
  26 // the "real" fix.
  27 struct BoundVarsCollector<'tcx> {
  28     binder_index: ty::DebruijnIndex,
  29     vars: BTreeMap<u32, ty::BoundVariableKind>,
  30     // We may encounter the same variable at different levels of binding, so
  31     // this can't just be `Ty`
  32     visited: SsoHashSet<(ty::DebruijnIndex, Ty<'tcx>)>,
  33 }
  34
  35 impl<'tcx> BoundVarsCollector<'tcx> {
  36     fn new() -> Self {
  37         BoundVarsCollector {
  38             binder_index: ty::INNERMOST,
  39             vars: BTreeMap::new(),
  40             visited: SsoHashSet::default(),
  41         }
  42     }
  43
  44     fn into_vars(self, tcx: TyCtxt<'tcx>) -> &'tcx ty::List<ty::BoundVariableKind> {
  45         let max = self.vars.iter().map(|(k, _)| *k).max().unwrap_or(0);
  46         for i in 0..max {
  47             if let None = self.vars.get(&i) {
  48                 panic!("Unknown variable: {:?}", i);
  49             }
  50         }
  51
  52         tcx.mk_bound_variable_kinds(self.vars.into_iter().map(|(_, v)| v))
  53     }
  54 }
  55
  56 impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
  57     type BreakTy = ();
  58
  59     fn visit_binder<T: TypeFoldable<'tcx>>(
  60         &mut self,
  61         t: &Binder<'tcx, T>,
  62     ) -> ControlFlow<Self::BreakTy> {
  63         self.binder_index.shift_in(1);
  64         let result = t.super_visit_with(self);
  65         self.binder_index.shift_out(1);
  66         result
  67     }
  68
  69     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
  70         if t.outer_exclusive_binder() < self.binder_index
  71             || !self.visited.insert((self.binder_index, t))
  72         {
  73             return ControlFlow::CONTINUE;
  74         }
  75         match *t.kind() {
  76             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
  77                 match self.vars.entry(bound_ty.var.as_u32()) {
  78                     Entry::Vacant(entry) => {
  79                         entry.insert(ty::BoundVariableKind::Ty(bound_ty.kind));
  80                     }
  81                     Entry::Occupied(entry) => match entry.get() {
  82                         ty::BoundVariableKind::Ty(_) => {}
  83                         _ => bug!("Conflicting bound vars"),
  84                     },
  85                 }
  86             }
  87
  88             _ => (),
  89         };
  90
  91         t.super_visit_with(self)
  92     }
  93
  94     fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
  95         match *r {
  96             ty::ReLateBound(index, br) if index == self.binder_index => {
  97                 match self.vars.entry(br.var.as_u32()) {
  98                     Entry::Vacant(entry) => {
  99                         entry.insert(ty::BoundVariableKind::Region(br.kind));
 100                     }
 101                     Entry::Occupied(entry) => match entry.get() {
 102                         ty::BoundVariableKind::Region(_) => {}
 103                         _ => bug!("Conflicting bound vars"),
 104                     },
 105                 }
 106             }
 107
 108             _ => (),
 109         };
 110
 111         r.super_visit_with(self)
 112     }
 113 }
 114
 115 fn resolve_instance<'tcx>(
 116     tcx: TyCtxt<'tcx>,
 117     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
 118 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
 119     let (param_env, (did, substs)) = key.into_parts();
 120     if let Some(did) = did.as_local() {
 121         if let Some(param_did) = tcx.opt_const_param_of(did) {
 122             return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
 123         }
 124     }
 125
 126     inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::unknown(did), substs)))
 127 }
 128
 129 fn resolve_instance_of_const_arg<'tcx>(
 130     tcx: TyCtxt<'tcx>,
 131     key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
 132 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
 133     let (param_env, (did, const_param_did, substs)) = key.into_parts();
 134     inner_resolve_instance(
 135         tcx,
 136         param_env.and((
 137             ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
 138             substs,
 139         )),
 140     )
 141 }
 142
 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>>, ErrorGuaranteed> {
 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         resolve_associated_item(tcx, def.did, param_env, trait_def_id, substs)
 152     } else {
 153         let ty = tcx.type_of(def.def_id_for_type_of());
 154         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, ty);
 155
 156         let def = match *item_type.kind() {
 157             ty::FnDef(def_id, ..) if tcx.is_intrinsic(def_id) => {
 158                 debug!(" => intrinsic");
 159                 ty::InstanceDef::Intrinsic(def.did)
 160             }
 161             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
 162                 let ty = substs.type_at(0);
 163
 164                 if ty.needs_drop(tcx, param_env) {
 165                     debug!(" => nontrivial drop glue");
 166                     match *ty.kind() {
 167                         ty::Closure(..)
 168                         | ty::Generator(..)
 169                         | ty::Tuple(..)
 170                         | ty::Adt(..)
 171                         | ty::Dynamic(..)
 172                         | ty::Array(..)
 173                         | ty::Slice(..) => {}
 174                         // Drop shims can only be built from ADTs.
 175                         _ => return Ok(None),
 176                     }
 177
 178                     ty::InstanceDef::DropGlue(def_id, Some(ty))
 179                 } else {
 180                     debug!(" => trivial drop glue");
 181                     ty::InstanceDef::DropGlue(def_id, None)
 182                 }
 183             }
 184             _ => {
 185                 debug!(" => free item");
 186                 ty::InstanceDef::Item(def)
 187             }
 188         };
 189         Ok(Some(Instance { def, substs }))
 190     };
 191     debug!("inner_resolve_instance: result={:?}", result);
 192     result
 193 }
 194
 195 fn resolve_associated_item<'tcx>(
 196     tcx: TyCtxt<'tcx>,
 197     trait_item_id: DefId,
 198     param_env: ty::ParamEnv<'tcx>,
 199     trait_id: DefId,
 200     rcvr_substs: SubstsRef<'tcx>,
 201 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
 202     debug!(?trait_item_id, ?param_env, ?trait_id, ?rcvr_substs, "resolve_associated_item");
 203
 204     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 205
 206     // See FIXME on `BoundVarsCollector`.
 207     let mut bound_vars_collector = BoundVarsCollector::new();
 208     trait_ref.visit_with(&mut bound_vars_collector);
 209     let trait_binder = ty::Binder::bind_with_vars(trait_ref, bound_vars_collector.into_vars(tcx));
 210     let vtbl = match tcx.codegen_fulfill_obligation((param_env, trait_binder)) {
 211         Ok(vtbl) => vtbl,
 212         Err(CodegenObligationError::Ambiguity) => {
 213             let reported = tcx.sess.delay_span_bug(
 214                 tcx.def_span(trait_item_id),
 215                 &format!(
 216                     "encountered ambiguity selecting `{:?}` during codegen, presuming due to \
 217                      overflow or prior type error",
 218                     trait_binder
 219                 ),
 220             );
 221             return Err(reported);
 222         }
 223         Err(CodegenObligationError::Unimplemented) => return Ok(None),
 224         Err(CodegenObligationError::FulfillmentError) => return Ok(None),
 225     };
 226
 227     // Now that we know which impl is being used, we can dispatch to
 228     // the actual function:
 229     Ok(match vtbl {
 230         traits::ImplSource::UserDefined(impl_data) => {
 231             debug!(
 232                 "resolving ImplSource::UserDefined: {:?}, {:?}, {:?}, {:?}",
 233                 param_env, trait_item_id, rcvr_substs, impl_data
 234             );
 235             assert!(!rcvr_substs.needs_infer());
 236             assert!(!trait_ref.needs_infer());
 237
 238             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 239             let trait_def = tcx.trait_def(trait_def_id);
 240             let leaf_def = trait_def
 241                 .ancestors(tcx, impl_data.impl_def_id)?
 242                 .leaf_def(tcx, trait_item_id)
 243                 .unwrap_or_else(|| {
 244                     bug!("{:?} not found in {:?}", trait_item_id, impl_data.impl_def_id);
 245                 });
 246
 247             let substs = tcx.infer_ctxt().enter(|infcx| {
 248                 let param_env = param_env.with_reveal_all_normalized(tcx);
 249                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 250                 let substs = translate_substs(
 251                     &infcx,
 252                     param_env,
 253                     impl_data.impl_def_id,
 254                     substs,
 255                     leaf_def.defining_node,
 256                 );
 257                 infcx.tcx.erase_regions(substs)
 258             });
 259
 260             // Since this is a trait item, we need to see if the item is either a trait default item
 261             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 262             // NOTE: This should be kept in sync with the similar code in
 263             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 264             let eligible = if leaf_def.is_final() {
 265                 // Non-specializable items are always projectable.
 266                 true
 267             } else {
 268                 // Only reveal a specializable default if we're past type-checking
 269                 // and the obligation is monomorphic, otherwise passes such as
 270                 // transmute checking and polymorphic MIR optimizations could
 271                 // get a result which isn't correct for all monomorphizations.
 272                 if param_env.reveal() == Reveal::All {
 273                     !trait_ref.still_further_specializable()
 274                 } else {
 275                     false
 276                 }
 277             };
 278
 279             if !eligible {
 280                 return Ok(None);
 281             }
 282
 283             let substs = tcx.erase_regions(substs);
 284
 285             // Check if we just resolved an associated `const` declaration from
 286             // a `trait` to an associated `const` definition in an `impl`, where
 287             // the definition in the `impl` has the wrong type (for which an
 288             // error has already been/will be emitted elsewhere).
 289             //
 290             // NB: this may be expensive, we try to skip it in all the cases where
 291             // we know the error would've been caught (e.g. in an upstream crate).
 292             //
 293             // A better approach might be to just introduce a query (returning
 294             // `Result<(), ErrorGuaranteed>`) for the check that `rustc_typeck`
 295             // performs (i.e. that the definition's type in the `impl` matches
 296             // the declaration in the `trait`), so that we can cheaply check
 297             // here if it failed, instead of approximating it.
 298             if leaf_def.item.kind == ty::AssocKind::Const
 299                 && trait_item_id != leaf_def.item.def_id
 300                 && leaf_def.item.def_id.is_local()
 301             {
 302                 let normalized_type_of = |def_id, substs| {
 303                     tcx.subst_and_normalize_erasing_regions(substs, param_env, tcx.type_of(def_id))
 304                 };
 305
 306                 let original_ty = normalized_type_of(trait_item_id, rcvr_substs);
 307                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 308
 309                 if original_ty != resolved_ty {
 310                     let msg = format!(
 311                         "Instance::resolve: inconsistent associated `const` type: \
 312                          was `{}: {}` but resolved to `{}: {}`",
 313                         tcx.def_path_str_with_substs(trait_item_id, rcvr_substs),
 314                         original_ty,
 315                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 316                         resolved_ty,
 317                     );
 318                     let span = tcx.def_span(leaf_def.item.def_id);
 319                     let reported = tcx.sess.delay_span_bug(span, &msg);
 320
 321                     return Err(reported);
 322                 }
 323             }
 324
 325             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 326         }
 327         traits::ImplSource::Generator(generator_data) => Some(Instance {
 328             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 329                 generator_data.generator_def_id,
 330             )),
 331             substs: generator_data.substs,
 332         }),
 333         traits::ImplSource::Closure(closure_data) => {
 334             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 335             Some(Instance::resolve_closure(
 336                 tcx,
 337                 closure_data.closure_def_id,
 338                 closure_data.substs,
 339                 trait_closure_kind,
 340             ))
 341         }
 342         traits::ImplSource::FnPointer(ref data) => match data.fn_ty.kind() {
 343             ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
 344                 def: ty::InstanceDef::FnPtrShim(trait_item_id, data.fn_ty),
 345                 substs: rcvr_substs,
 346             }),
 347             _ => None,
 348         },
 349         traits::ImplSource::Object(ref data) => {
 350             if let Some(index) = traits::get_vtable_index_of_object_method(tcx, data, trait_item_id)
 351             {
 352                 Some(Instance {
 353                     def: ty::InstanceDef::Virtual(trait_item_id, index),
 354                     substs: rcvr_substs,
 355                 })
 356             } else {
 357                 None
 358             }
 359         }
 360         traits::ImplSource::Builtin(..) => {
 361             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 362                 // FIXME(eddyb) use lang items for methods instead of names.
 363                 let name = tcx.item_name(trait_item_id);
 364                 if name == sym::clone {
 365                     let self_ty = trait_ref.self_ty();
 366
 367                     let is_copy = self_ty.is_copy_modulo_regions(tcx.at(DUMMY_SP), param_env);
 368                     match self_ty.kind() {
 369                         _ if is_copy => (),
 370                         ty::Closure(..) | ty::Tuple(..) => {}
 371                         _ => return Ok(None),
 372                     };
 373
 374                     Some(Instance {
 375                         def: ty::InstanceDef::CloneShim(trait_item_id, self_ty),
 376                         substs: rcvr_substs,
 377                     })
 378                 } else {
 379                     assert_eq!(name, sym::clone_from);
 380
 381                     // Use the default `fn clone_from` from `trait Clone`.
 382                     let substs = tcx.erase_regions(rcvr_substs);
 383                     Some(ty::Instance::new(trait_item_id, substs))
 384                 }
 385             } else {
 386                 None
 387             }
 388         }
 389         traits::ImplSource::AutoImpl(..)
 390         | traits::ImplSource::Param(..)
 391         | traits::ImplSource::TraitAlias(..)
 392         | traits::ImplSource::DiscriminantKind(..)
 393         | traits::ImplSource::Pointee(..)
 394         | traits::ImplSource::TraitUpcasting(_)
 395         | traits::ImplSource::ConstDestruct(_) => None,
 396     })
 397 }
 398
 399 pub fn provide(providers: &mut ty::query::Providers) {
 400     *providers =
 401         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 402 }