compiler/rustc_middle/src/ty/relate.rs

   1 //! Generalized type relating mechanism.
   2 //!
   3 //! A type relation `R` relates a pair of values `(A, B)`. `A and B` are usually
   4 //! types or regions but can be other things. Examples of type relations are
   5 //! subtyping, type equality, etc.
   6
   7 use crate::ty::error::{ExpectedFound, TypeError};
   8 use crate::ty::{self, Expr, ImplSubject, Term, TermKind, Ty, TyCtxt, TypeFoldable};
   9 use crate::ty::{GenericArg, GenericArgKind, SubstsRef};
  10 use rustc_hir as hir;
  11 use rustc_hir::def_id::DefId;
  12 use rustc_target::spec::abi;
  13 use std::iter;
  14
  15 pub type RelateResult<'tcx, T> = Result<T, TypeError<'tcx>>;
  16
  17 #[derive(Clone, Debug)]
  18 pub enum Cause {
  19     ExistentialRegionBound, // relating an existential region bound
  20 }
  21
  22 pub trait TypeRelation<'tcx>: Sized {
  23     fn tcx(&self) -> TyCtxt<'tcx>;
  24
  25     fn param_env(&self) -> ty::ParamEnv<'tcx>;
  26
  27     /// Returns a static string we can use for printouts.
  28     fn tag(&self) -> &'static str;
  29
  30     /// Returns `true` if the value `a` is the "expected" type in the
  31     /// relation. Just affects error messages.
  32     fn a_is_expected(&self) -> bool;
  33
  34     fn with_cause<F, R>(&mut self, _cause: Cause, f: F) -> R
  35     where
  36         F: FnOnce(&mut Self) -> R,
  37     {
  38         f(self)
  39     }
  40
  41     /// Generic relation routine suitable for most anything.
  42     fn relate<T: Relate<'tcx>>(&mut self, a: T, b: T) -> RelateResult<'tcx, T> {
  43         Relate::relate(self, a, b)
  44     }
  45
  46     /// Relate the two substitutions for the given item. The default
  47     /// is to look up the variance for the item and proceed
  48     /// accordingly.
  49     fn relate_item_substs(
  50         &mut self,
  51         item_def_id: DefId,
  52         a_subst: SubstsRef<'tcx>,
  53         b_subst: SubstsRef<'tcx>,
  54     ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
  55         debug!(
  56             "relate_item_substs(item_def_id={:?}, a_subst={:?}, b_subst={:?})",
  57             item_def_id, a_subst, b_subst
  58         );
  59
  60         let tcx = self.tcx();
  61         let opt_variances = tcx.variances_of(item_def_id);
  62         relate_substs_with_variances(self, item_def_id, opt_variances, a_subst, b_subst, true)
  63     }
  64
  65     /// Switch variance for the purpose of relating `a` and `b`.
  66     fn relate_with_variance<T: Relate<'tcx>>(
  67         &mut self,
  68         variance: ty::Variance,
  69         info: ty::VarianceDiagInfo<'tcx>,
  70         a: T,
  71         b: T,
  72     ) -> RelateResult<'tcx, T>;
  73
  74     // Overridable relations. You shouldn't typically call these
  75     // directly, instead call `relate()`, which in turn calls
  76     // these. This is both more uniform but also allows us to add
  77     // additional hooks for other types in the future if needed
  78     // without making older code, which called `relate`, obsolete.
  79
  80     fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>>;
  81
  82     fn regions(
  83         &mut self,
  84         a: ty::Region<'tcx>,
  85         b: ty::Region<'tcx>,
  86     ) -> RelateResult<'tcx, ty::Region<'tcx>>;
  87
  88     fn consts(
  89         &mut self,
  90         a: ty::Const<'tcx>,
  91         b: ty::Const<'tcx>,
  92     ) -> RelateResult<'tcx, ty::Const<'tcx>>;
  93
  94     fn binders<T>(
  95         &mut self,
  96         a: ty::Binder<'tcx, T>,
  97         b: ty::Binder<'tcx, T>,
  98     ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
  99     where
 100         T: Relate<'tcx>;
 101 }
 102
 103 pub trait Relate<'tcx>: TypeFoldable<TyCtxt<'tcx>> + PartialEq + Copy {
 104     fn relate<R: TypeRelation<'tcx>>(
 105         relation: &mut R,
 106         a: Self,
 107         b: Self,
 108     ) -> RelateResult<'tcx, Self>;
 109 }
 110
 111 ///////////////////////////////////////////////////////////////////////////
 112 // Relate impls
 113
 114 pub fn relate_type_and_mut<'tcx, R: TypeRelation<'tcx>>(
 115     relation: &mut R,
 116     a: ty::TypeAndMut<'tcx>,
 117     b: ty::TypeAndMut<'tcx>,
 118     base_ty: Ty<'tcx>,
 119 ) -> RelateResult<'tcx, ty::TypeAndMut<'tcx>> {
 120     debug!("{}.mts({:?}, {:?})", relation.tag(), a, b);
 121     if a.mutbl != b.mutbl {
 122         Err(TypeError::Mutability)
 123     } else {
 124         let mutbl = a.mutbl;
 125         let (variance, info) = match mutbl {
 126             hir::Mutability::Not => (ty::Covariant, ty::VarianceDiagInfo::None),
 127             hir::Mutability::Mut => {
 128                 (ty::Invariant, ty::VarianceDiagInfo::Invariant { ty: base_ty, param_index: 0 })
 129             }
 130         };
 131         let ty = relation.relate_with_variance(variance, info, a.ty, b.ty)?;
 132         Ok(ty::TypeAndMut { ty, mutbl })
 133     }
 134 }
 135
 136 #[inline]
 137 pub fn relate_substs<'tcx, R: TypeRelation<'tcx>>(
 138     relation: &mut R,
 139     a_subst: SubstsRef<'tcx>,
 140     b_subst: SubstsRef<'tcx>,
 141 ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
 142     relation.tcx().mk_substs_from_iter(iter::zip(a_subst, b_subst).map(|(a, b)| {
 143         relation.relate_with_variance(ty::Invariant, ty::VarianceDiagInfo::default(), a, b)
 144     }))
 145 }
 146
 147 pub fn relate_substs_with_variances<'tcx, R: TypeRelation<'tcx>>(
 148     relation: &mut R,
 149     ty_def_id: DefId,
 150     variances: &[ty::Variance],
 151     a_subst: SubstsRef<'tcx>,
 152     b_subst: SubstsRef<'tcx>,
 153     fetch_ty_for_diag: bool,
 154 ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
 155     let tcx = relation.tcx();
 156
 157     let mut cached_ty = None;
 158     let params = iter::zip(a_subst, b_subst).enumerate().map(|(i, (a, b))| {
 159         let variance = variances[i];
 160         let variance_info = if variance == ty::Invariant && fetch_ty_for_diag {
 161             let ty = *cached_ty.get_or_insert_with(|| tcx.type_of(ty_def_id).subst(tcx, a_subst));
 162             ty::VarianceDiagInfo::Invariant { ty, param_index: i.try_into().unwrap() }
 163         } else {
 164             ty::VarianceDiagInfo::default()
 165         };
 166         relation.relate_with_variance(variance, variance_info, a, b)
 167     });
 168
 169     tcx.mk_substs_from_iter(params)
 170 }
 171
 172 impl<'tcx> Relate<'tcx> for ty::FnSig<'tcx> {
 173     fn relate<R: TypeRelation<'tcx>>(
 174         relation: &mut R,
 175         a: ty::FnSig<'tcx>,
 176         b: ty::FnSig<'tcx>,
 177     ) -> RelateResult<'tcx, ty::FnSig<'tcx>> {
 178         let tcx = relation.tcx();
 179
 180         if a.c_variadic != b.c_variadic {
 181             return Err(TypeError::VariadicMismatch(expected_found(
 182                 relation,
 183                 a.c_variadic,
 184                 b.c_variadic,
 185             )));
 186         }
 187         let unsafety = relation.relate(a.unsafety, b.unsafety)?;
 188         let abi = relation.relate(a.abi, b.abi)?;
 189
 190         if a.inputs().len() != b.inputs().len() {
 191             return Err(TypeError::ArgCount);
 192         }
 193
 194         let inputs_and_output = iter::zip(a.inputs(), b.inputs())
 195             .map(|(&a, &b)| ((a, b), false))
 196             .chain(iter::once(((a.output(), b.output()), true)))
 197             .map(|((a, b), is_output)| {
 198                 if is_output {
 199                     relation.relate(a, b)
 200                 } else {
 201                     relation.relate_with_variance(
 202                         ty::Contravariant,
 203                         ty::VarianceDiagInfo::default(),
 204                         a,
 205                         b,
 206                     )
 207                 }
 208             })
 209             .enumerate()
 210             .map(|(i, r)| match r {
 211                 Err(TypeError::Sorts(exp_found) | TypeError::ArgumentSorts(exp_found, _)) => {
 212                     Err(TypeError::ArgumentSorts(exp_found, i))
 213                 }
 214                 Err(TypeError::Mutability | TypeError::ArgumentMutability(_)) => {
 215                     Err(TypeError::ArgumentMutability(i))
 216                 }
 217                 r => r,
 218             });
 219         Ok(ty::FnSig {
 220             inputs_and_output: tcx.mk_type_list_from_iter(inputs_and_output)?,
 221             c_variadic: a.c_variadic,
 222             unsafety,
 223             abi,
 224         })
 225     }
 226 }
 227
 228 impl<'tcx> Relate<'tcx> for ty::BoundConstness {
 229     fn relate<R: TypeRelation<'tcx>>(
 230         relation: &mut R,
 231         a: ty::BoundConstness,
 232         b: ty::BoundConstness,
 233     ) -> RelateResult<'tcx, ty::BoundConstness> {
 234         if a != b {
 235             Err(TypeError::ConstnessMismatch(expected_found(relation, a, b)))
 236         } else {
 237             Ok(a)
 238         }
 239     }
 240 }
 241
 242 impl<'tcx> Relate<'tcx> for hir::Unsafety {
 243     fn relate<R: TypeRelation<'tcx>>(
 244         relation: &mut R,
 245         a: hir::Unsafety,
 246         b: hir::Unsafety,
 247     ) -> RelateResult<'tcx, hir::Unsafety> {
 248         if a != b {
 249             Err(TypeError::UnsafetyMismatch(expected_found(relation, a, b)))
 250         } else {
 251             Ok(a)
 252         }
 253     }
 254 }
 255
 256 impl<'tcx> Relate<'tcx> for abi::Abi {
 257     fn relate<R: TypeRelation<'tcx>>(
 258         relation: &mut R,
 259         a: abi::Abi,
 260         b: abi::Abi,
 261     ) -> RelateResult<'tcx, abi::Abi> {
 262         if a == b { Ok(a) } else { Err(TypeError::AbiMismatch(expected_found(relation, a, b))) }
 263     }
 264 }
 265
 266 impl<'tcx> Relate<'tcx> for ty::AliasTy<'tcx> {
 267     fn relate<R: TypeRelation<'tcx>>(
 268         relation: &mut R,
 269         a: ty::AliasTy<'tcx>,
 270         b: ty::AliasTy<'tcx>,
 271     ) -> RelateResult<'tcx, ty::AliasTy<'tcx>> {
 272         if a.def_id != b.def_id {
 273             Err(TypeError::ProjectionMismatched(expected_found(relation, a.def_id, b.def_id)))
 274         } else {
 275             let substs = relation.relate(a.substs, b.substs)?;
 276             Ok(relation.tcx().mk_alias_ty(a.def_id, substs))
 277         }
 278     }
 279 }
 280
 281 impl<'tcx> Relate<'tcx> for ty::ExistentialProjection<'tcx> {
 282     fn relate<R: TypeRelation<'tcx>>(
 283         relation: &mut R,
 284         a: ty::ExistentialProjection<'tcx>,
 285         b: ty::ExistentialProjection<'tcx>,
 286     ) -> RelateResult<'tcx, ty::ExistentialProjection<'tcx>> {
 287         if a.def_id != b.def_id {
 288             Err(TypeError::ProjectionMismatched(expected_found(relation, a.def_id, b.def_id)))
 289         } else {
 290             let term = relation.relate_with_variance(
 291                 ty::Invariant,
 292                 ty::VarianceDiagInfo::default(),
 293                 a.term,
 294                 b.term,
 295             )?;
 296             let substs = relation.relate_with_variance(
 297                 ty::Invariant,
 298                 ty::VarianceDiagInfo::default(),
 299                 a.substs,
 300                 b.substs,
 301             )?;
 302             Ok(ty::ExistentialProjection { def_id: a.def_id, substs, term })
 303         }
 304     }
 305 }
 306
 307 impl<'tcx> Relate<'tcx> for ty::TraitRef<'tcx> {
 308     fn relate<R: TypeRelation<'tcx>>(
 309         relation: &mut R,
 310         a: ty::TraitRef<'tcx>,
 311         b: ty::TraitRef<'tcx>,
 312     ) -> RelateResult<'tcx, ty::TraitRef<'tcx>> {
 313         // Different traits cannot be related.
 314         if a.def_id != b.def_id {
 315             Err(TypeError::Traits(expected_found(relation, a.def_id, b.def_id)))
 316         } else {
 317             let substs = relate_substs(relation, a.substs, b.substs)?;
 318             Ok(ty::TraitRef::new(relation.tcx(), a.def_id, substs))
 319         }
 320     }
 321 }
 322
 323 impl<'tcx> Relate<'tcx> for ty::ExistentialTraitRef<'tcx> {
 324     fn relate<R: TypeRelation<'tcx>>(
 325         relation: &mut R,
 326         a: ty::ExistentialTraitRef<'tcx>,
 327         b: ty::ExistentialTraitRef<'tcx>,
 328     ) -> RelateResult<'tcx, ty::ExistentialTraitRef<'tcx>> {
 329         // Different traits cannot be related.
 330         if a.def_id != b.def_id {
 331             Err(TypeError::Traits(expected_found(relation, a.def_id, b.def_id)))
 332         } else {
 333             let substs = relate_substs(relation, a.substs, b.substs)?;
 334             Ok(ty::ExistentialTraitRef { def_id: a.def_id, substs })
 335         }
 336     }
 337 }
 338
 339 #[derive(PartialEq, Copy, Debug, Clone, TypeFoldable, TypeVisitable)]
 340 struct GeneratorWitness<'tcx>(&'tcx ty::List<Ty<'tcx>>);
 341
 342 impl<'tcx> Relate<'tcx> for GeneratorWitness<'tcx> {
 343     fn relate<R: TypeRelation<'tcx>>(
 344         relation: &mut R,
 345         a: GeneratorWitness<'tcx>,
 346         b: GeneratorWitness<'tcx>,
 347     ) -> RelateResult<'tcx, GeneratorWitness<'tcx>> {
 348         assert_eq!(a.0.len(), b.0.len());
 349         let tcx = relation.tcx();
 350         let types =
 351             tcx.mk_type_list_from_iter(iter::zip(a.0, b.0).map(|(a, b)| relation.relate(a, b)))?;
 352         Ok(GeneratorWitness(types))
 353     }
 354 }
 355
 356 impl<'tcx> Relate<'tcx> for ImplSubject<'tcx> {
 357     #[inline]
 358     fn relate<R: TypeRelation<'tcx>>(
 359         relation: &mut R,
 360         a: ImplSubject<'tcx>,
 361         b: ImplSubject<'tcx>,
 362     ) -> RelateResult<'tcx, ImplSubject<'tcx>> {
 363         match (a, b) {
 364             (ImplSubject::Trait(trait_ref_a), ImplSubject::Trait(trait_ref_b)) => {
 365                 let trait_ref = ty::TraitRef::relate(relation, trait_ref_a, trait_ref_b)?;
 366                 Ok(ImplSubject::Trait(trait_ref))
 367             }
 368             (ImplSubject::Inherent(ty_a), ImplSubject::Inherent(ty_b)) => {
 369                 let ty = Ty::relate(relation, ty_a, ty_b)?;
 370                 Ok(ImplSubject::Inherent(ty))
 371             }
 372             (ImplSubject::Trait(_), ImplSubject::Inherent(_))
 373             | (ImplSubject::Inherent(_), ImplSubject::Trait(_)) => {
 374                 bug!("can not relate TraitRef and Ty");
 375             }
 376         }
 377     }
 378 }
 379
 380 impl<'tcx> Relate<'tcx> for Ty<'tcx> {
 381     #[inline]
 382     fn relate<R: TypeRelation<'tcx>>(
 383         relation: &mut R,
 384         a: Ty<'tcx>,
 385         b: Ty<'tcx>,
 386     ) -> RelateResult<'tcx, Ty<'tcx>> {
 387         relation.tys(a, b)
 388     }
 389 }
 390
 391 /// Relates `a` and `b` structurally, calling the relation for all nested values.
 392 /// Any semantic equality, e.g. of projections, and inference variables have to be
 393 /// handled by the caller.
 394 pub fn structurally_relate_tys<'tcx, R: TypeRelation<'tcx>>(
 395     relation: &mut R,
 396     a: Ty<'tcx>,
 397     b: Ty<'tcx>,
 398 ) -> RelateResult<'tcx, Ty<'tcx>> {
 399     let tcx = relation.tcx();
 400     debug!("structurally_relate_tys: a={:?} b={:?}", a, b);
 401     match (a.kind(), b.kind()) {
 402         (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
 403             // The caller should handle these cases!
 404             bug!("var types encountered in structurally_relate_tys")
 405         }
 406
 407         (ty::Bound(..), _) | (_, ty::Bound(..)) => {
 408             bug!("bound types encountered in structurally_relate_tys")
 409         }
 410
 411         (&ty::Error(guar), _) | (_, &ty::Error(guar)) => Ok(tcx.ty_error(guar)),
 412
 413         (&ty::Never, _)
 414         | (&ty::Char, _)
 415         | (&ty::Bool, _)
 416         | (&ty::Int(_), _)
 417         | (&ty::Uint(_), _)
 418         | (&ty::Float(_), _)
 419         | (&ty::Str, _)
 420             if a == b =>
 421         {
 422             Ok(a)
 423         }
 424
 425         (ty::Param(a_p), ty::Param(b_p)) if a_p.index == b_p.index => Ok(a),
 426
 427         (ty::Placeholder(p1), ty::Placeholder(p2)) if p1 == p2 => Ok(a),
 428
 429         (&ty::Adt(a_def, a_substs), &ty::Adt(b_def, b_substs)) if a_def == b_def => {
 430             let substs = relation.relate_item_substs(a_def.did(), a_substs, b_substs)?;
 431             Ok(tcx.mk_adt(a_def, substs))
 432         }
 433
 434         (&ty::Foreign(a_id), &ty::Foreign(b_id)) if a_id == b_id => Ok(tcx.mk_foreign(a_id)),
 435
 436         (&ty::Dynamic(a_obj, a_region, a_repr), &ty::Dynamic(b_obj, b_region, b_repr))
 437             if a_repr == b_repr =>
 438         {
 439             let region_bound = relation.with_cause(Cause::ExistentialRegionBound, |relation| {
 440                 relation.relate(a_region, b_region)
 441             })?;
 442             Ok(tcx.mk_dynamic(relation.relate(a_obj, b_obj)?, region_bound, a_repr))
 443         }
 444
 445         (&ty::Generator(a_id, a_substs, movability), &ty::Generator(b_id, b_substs, _))
 446             if a_id == b_id =>
 447         {
 448             // All Generator types with the same id represent
 449             // the (anonymous) type of the same generator expression. So
 450             // all of their regions should be equated.
 451             let substs = relation.relate(a_substs, b_substs)?;
 452             Ok(tcx.mk_generator(a_id, substs, movability))
 453         }
 454
 455         (&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => {
 456             // Wrap our types with a temporary GeneratorWitness struct
 457             // inside the binder so we can related them
 458             let a_types = a_types.map_bound(GeneratorWitness);
 459             let b_types = b_types.map_bound(GeneratorWitness);
 460             // Then remove the GeneratorWitness for the result
 461             let types = relation.relate(a_types, b_types)?.map_bound(|witness| witness.0);
 462             Ok(tcx.mk_generator_witness(types))
 463         }
 464
 465         (&ty::GeneratorWitnessMIR(a_id, a_substs), &ty::GeneratorWitnessMIR(b_id, b_substs))
 466             if a_id == b_id =>
 467         {
 468             // All GeneratorWitness types with the same id represent
 469             // the (anonymous) type of the same generator expression. So
 470             // all of their regions should be equated.
 471             let substs = relation.relate(a_substs, b_substs)?;
 472             Ok(tcx.mk_generator_witness_mir(a_id, substs))
 473         }
 474
 475         (&ty::Closure(a_id, a_substs), &ty::Closure(b_id, b_substs)) if a_id == b_id => {
 476             // All Closure types with the same id represent
 477             // the (anonymous) type of the same closure expression. So
 478             // all of their regions should be equated.
 479             let substs = relation.relate(a_substs, b_substs)?;
 480             Ok(tcx.mk_closure(a_id, &substs))
 481         }
 482
 483         (&ty::RawPtr(a_mt), &ty::RawPtr(b_mt)) => {
 484             let mt = relate_type_and_mut(relation, a_mt, b_mt, a)?;
 485             Ok(tcx.mk_ptr(mt))
 486         }
 487
 488         (&ty::Ref(a_r, a_ty, a_mutbl), &ty::Ref(b_r, b_ty, b_mutbl)) => {
 489             let r = relation.relate(a_r, b_r)?;
 490             let a_mt = ty::TypeAndMut { ty: a_ty, mutbl: a_mutbl };
 491             let b_mt = ty::TypeAndMut { ty: b_ty, mutbl: b_mutbl };
 492             let mt = relate_type_and_mut(relation, a_mt, b_mt, a)?;
 493             Ok(tcx.mk_ref(r, mt))
 494         }
 495
 496         (&ty::Array(a_t, sz_a), &ty::Array(b_t, sz_b)) => {
 497             let t = relation.relate(a_t, b_t)?;
 498             match relation.relate(sz_a, sz_b) {
 499                 Ok(sz) => Ok(tcx.mk_array_with_const_len(t, sz)),
 500                 Err(err) => {
 501                     // Check whether the lengths are both concrete/known values,
 502                     // but are unequal, for better diagnostics.
 503                     //
 504                     // It might seem dubious to eagerly evaluate these constants here,
 505                     // we however cannot end up with errors in `Relate` during both
 506                     // `type_of` and `predicates_of`. This means that evaluating the
 507                     // constants should not cause cycle errors here.
 508                     let sz_a = sz_a.try_eval_target_usize(tcx, relation.param_env());
 509                     let sz_b = sz_b.try_eval_target_usize(tcx, relation.param_env());
 510                     match (sz_a, sz_b) {
 511                         (Some(sz_a_val), Some(sz_b_val)) if sz_a_val != sz_b_val => Err(
 512                             TypeError::FixedArraySize(expected_found(relation, sz_a_val, sz_b_val)),
 513                         ),
 514                         _ => Err(err),
 515                     }
 516                 }
 517             }
 518         }
 519
 520         (&ty::Slice(a_t), &ty::Slice(b_t)) => {
 521             let t = relation.relate(a_t, b_t)?;
 522             Ok(tcx.mk_slice(t))
 523         }
 524
 525         (&ty::Tuple(as_), &ty::Tuple(bs)) => {
 526             if as_.len() == bs.len() {
 527                 Ok(tcx.mk_tup_from_iter(iter::zip(as_, bs).map(|(a, b)| relation.relate(a, b)))?)
 528             } else if !(as_.is_empty() || bs.is_empty()) {
 529                 Err(TypeError::TupleSize(expected_found(relation, as_.len(), bs.len())))
 530             } else {
 531                 Err(TypeError::Sorts(expected_found(relation, a, b)))
 532             }
 533         }
 534
 535         (&ty::FnDef(a_def_id, a_substs), &ty::FnDef(b_def_id, b_substs))
 536             if a_def_id == b_def_id =>
 537         {
 538             let substs = relation.relate_item_substs(a_def_id, a_substs, b_substs)?;
 539             Ok(tcx.mk_fn_def(a_def_id, substs))
 540         }
 541
 542         (&ty::FnPtr(a_fty), &ty::FnPtr(b_fty)) => {
 543             let fty = relation.relate(a_fty, b_fty)?;
 544             Ok(tcx.mk_fn_ptr(fty))
 545         }
 546
 547         // these two are already handled downstream in case of lazy normalization
 548         (&ty::Alias(ty::Projection, a_data), &ty::Alias(ty::Projection, b_data)) => {
 549             let projection_ty = relation.relate(a_data, b_data)?;
 550             Ok(tcx.mk_projection(projection_ty.def_id, projection_ty.substs))
 551         }
 552
 553         (&ty::Alias(ty::Inherent, a_data), &ty::Alias(ty::Inherent, b_data)) => {
 554             let alias_ty = relation.relate(a_data, b_data)?;
 555             Ok(tcx.mk_alias(ty::Inherent, tcx.mk_alias_ty(alias_ty.def_id, alias_ty.substs)))
 556         }
 557
 558         (
 559             &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, substs: a_substs, .. }),
 560             &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, substs: b_substs, .. }),
 561         ) if a_def_id == b_def_id => {
 562             let opt_variances = tcx.variances_of(a_def_id);
 563             let substs = relate_substs_with_variances(
 564                 relation,
 565                 a_def_id,
 566                 opt_variances,
 567                 a_substs,
 568                 b_substs,
 569                 false, // do not fetch `type_of(a_def_id)`, as it will cause a cycle
 570             )?;
 571             Ok(tcx.mk_opaque(a_def_id, substs))
 572         }
 573
 574         _ => Err(TypeError::Sorts(expected_found(relation, a, b))),
 575     }
 576 }
 577
 578 /// Relates `a` and `b` structurally, calling the relation for all nested values.
 579 /// Any semantic equality, e.g. of unevaluated consts, and inference variables have
 580 /// to be handled by the caller.
 581 ///
 582 /// FIXME: This is not totally structual, which probably should be fixed.
 583 /// See the HACKs below.
 584 pub fn structurally_relate_consts<'tcx, R: TypeRelation<'tcx>>(
 585     relation: &mut R,
 586     mut a: ty::Const<'tcx>,
 587     mut b: ty::Const<'tcx>,
 588 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
 589     debug!("{}.structurally_relate_consts(a = {:?}, b = {:?})", relation.tag(), a, b);
 590     let tcx = relation.tcx();
 591
 592     // HACK(const_generics): We still need to eagerly evaluate consts when
 593     // relating them because during `normalize_param_env_or_error`,
 594     // we may relate an evaluated constant in a obligation against
 595     // an unnormalized (i.e. unevaluated) const in the param-env.
 596     // FIXME(generic_const_exprs): Once we always lazily unify unevaluated constants
 597     // these `eval` calls can be removed.
 598     if !tcx.features().generic_const_exprs {
 599         a = a.eval(tcx, relation.param_env());
 600         b = b.eval(tcx, relation.param_env());
 601     }
 602
 603     if tcx.features().generic_const_exprs {
 604         a = tcx.expand_abstract_consts(a);
 605         b = tcx.expand_abstract_consts(b);
 606     }
 607
 608     debug!("{}.structurally_relate_consts(normed_a = {:?}, normed_b = {:?})", relation.tag(), a, b);
 609
 610     // Currently, the values that can be unified are primitive types,
 611     // and those that derive both `PartialEq` and `Eq`, corresponding
 612     // to structural-match types.
 613     let is_match = match (a.kind(), b.kind()) {
 614         (ty::ConstKind::Infer(_), _) | (_, ty::ConstKind::Infer(_)) => {
 615             // The caller should handle these cases!
 616             bug!("var types encountered in structurally_relate_consts: {:?} {:?}", a, b)
 617         }
 618
 619         (ty::ConstKind::Error(_), _) => return Ok(a),
 620         (_, ty::ConstKind::Error(_)) => return Ok(b),
 621
 622         (ty::ConstKind::Param(a_p), ty::ConstKind::Param(b_p)) => a_p.index == b_p.index,
 623         (ty::ConstKind::Placeholder(p1), ty::ConstKind::Placeholder(p2)) => p1 == p2,
 624         (ty::ConstKind::Value(a_val), ty::ConstKind::Value(b_val)) => a_val == b_val,
 625
 626         // While this is slightly incorrect, it shouldn't matter for `min_const_generics`
 627         // and is the better alternative to waiting until `generic_const_exprs` can
 628         // be stabilized.
 629         (ty::ConstKind::Unevaluated(au), ty::ConstKind::Unevaluated(bu)) if au.def == bu.def => {
 630             assert_eq!(a.ty(), b.ty());
 631             let substs = relation.relate_with_variance(
 632                 ty::Variance::Invariant,
 633                 ty::VarianceDiagInfo::default(),
 634                 au.substs,
 635                 bu.substs,
 636             )?;
 637             return Ok(tcx.mk_const(ty::UnevaluatedConst { def: au.def, substs }, a.ty()));
 638         }
 639         // Before calling relate on exprs, it is necessary to ensure that the nested consts
 640         // have identical types.
 641         (ty::ConstKind::Expr(ae), ty::ConstKind::Expr(be)) => {
 642             let r = relation;
 643
 644             // FIXME(generic_const_exprs): is it possible to relate two consts which are not identical
 645             // exprs? Should we care about that?
 646             // FIXME(generic_const_exprs): relating the `ty()`s is a little weird since it is supposed to
 647             // ICE If they mismatch. Unfortunately `ConstKind::Expr` is a little special and can be thought
 648             // of as being generic over the argument types, however this is implicit so these types don't get
 649             // related when we relate the substs of the item this const arg is for.
 650             let expr = match (ae, be) {
 651                 (Expr::Binop(a_op, al, ar), Expr::Binop(b_op, bl, br)) if a_op == b_op => {
 652                     r.relate(al.ty(), bl.ty())?;
 653                     r.relate(ar.ty(), br.ty())?;
 654                     Expr::Binop(a_op, r.consts(al, bl)?, r.consts(ar, br)?)
 655                 }
 656                 (Expr::UnOp(a_op, av), Expr::UnOp(b_op, bv)) if a_op == b_op => {
 657                     r.relate(av.ty(), bv.ty())?;
 658                     Expr::UnOp(a_op, r.consts(av, bv)?)
 659                 }
 660                 (Expr::Cast(ak, av, at), Expr::Cast(bk, bv, bt)) if ak == bk => {
 661                     r.relate(av.ty(), bv.ty())?;
 662                     Expr::Cast(ak, r.consts(av, bv)?, r.tys(at, bt)?)
 663                 }
 664                 (Expr::FunctionCall(af, aa), Expr::FunctionCall(bf, ba))
 665                     if aa.len() == ba.len() =>
 666                 {
 667                     r.relate(af.ty(), bf.ty())?;
 668                     let func = r.consts(af, bf)?;
 669                     let mut related_args = Vec::with_capacity(aa.len());
 670                     for (a_arg, b_arg) in aa.iter().zip(ba.iter()) {
 671                         related_args.push(r.consts(a_arg, b_arg)?);
 672                     }
 673                     let related_args = tcx.mk_const_list(&related_args);
 674                     Expr::FunctionCall(func, related_args)
 675                 }
 676                 _ => return Err(TypeError::ConstMismatch(expected_found(r, a, b))),
 677             };
 678             let kind = ty::ConstKind::Expr(expr);
 679             return Ok(tcx.mk_const(kind, a.ty()));
 680         }
 681         _ => false,
 682     };
 683     if is_match { Ok(a) } else { Err(TypeError::ConstMismatch(expected_found(relation, a, b))) }
 684 }
 685
 686 impl<'tcx> Relate<'tcx> for &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> {
 687     fn relate<R: TypeRelation<'tcx>>(
 688         relation: &mut R,
 689         a: Self,
 690         b: Self,
 691     ) -> RelateResult<'tcx, Self> {
 692         let tcx = relation.tcx();
 693
 694         // FIXME: this is wasteful, but want to do a perf run to see how slow it is.
 695         // We need to perform this deduplication as we sometimes generate duplicate projections
 696         // in `a`.
 697         let mut a_v: Vec<_> = a.into_iter().collect();
 698         let mut b_v: Vec<_> = b.into_iter().collect();
 699         // `skip_binder` here is okay because `stable_cmp` doesn't look at binders
 700         a_v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
 701         a_v.dedup();
 702         b_v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
 703         b_v.dedup();
 704         if a_v.len() != b_v.len() {
 705             return Err(TypeError::ExistentialMismatch(expected_found(relation, a, b)));
 706         }
 707
 708         let v = iter::zip(a_v, b_v).map(|(ep_a, ep_b)| {
 709             use crate::ty::ExistentialPredicate::*;
 710             match (ep_a.skip_binder(), ep_b.skip_binder()) {
 711                 (Trait(a), Trait(b)) => Ok(ep_a
 712                     .rebind(Trait(relation.relate(ep_a.rebind(a), ep_b.rebind(b))?.skip_binder()))),
 713                 (Projection(a), Projection(b)) => Ok(ep_a.rebind(Projection(
 714                     relation.relate(ep_a.rebind(a), ep_b.rebind(b))?.skip_binder(),
 715                 ))),
 716                 (AutoTrait(a), AutoTrait(b)) if a == b => Ok(ep_a.rebind(AutoTrait(a))),
 717                 _ => Err(TypeError::ExistentialMismatch(expected_found(relation, a, b))),
 718             }
 719         });
 720         tcx.mk_poly_existential_predicates_from_iter(v)
 721     }
 722 }
 723
 724 impl<'tcx> Relate<'tcx> for ty::ClosureSubsts<'tcx> {
 725     fn relate<R: TypeRelation<'tcx>>(
 726         relation: &mut R,
 727         a: ty::ClosureSubsts<'tcx>,
 728         b: ty::ClosureSubsts<'tcx>,
 729     ) -> RelateResult<'tcx, ty::ClosureSubsts<'tcx>> {
 730         let substs = relate_substs(relation, a.substs, b.substs)?;
 731         Ok(ty::ClosureSubsts { substs })
 732     }
 733 }
 734
 735 impl<'tcx> Relate<'tcx> for ty::GeneratorSubsts<'tcx> {
 736     fn relate<R: TypeRelation<'tcx>>(
 737         relation: &mut R,
 738         a: ty::GeneratorSubsts<'tcx>,
 739         b: ty::GeneratorSubsts<'tcx>,
 740     ) -> RelateResult<'tcx, ty::GeneratorSubsts<'tcx>> {
 741         let substs = relate_substs(relation, a.substs, b.substs)?;
 742         Ok(ty::GeneratorSubsts { substs })
 743     }
 744 }
 745
 746 impl<'tcx> Relate<'tcx> for SubstsRef<'tcx> {
 747     fn relate<R: TypeRelation<'tcx>>(
 748         relation: &mut R,
 749         a: SubstsRef<'tcx>,
 750         b: SubstsRef<'tcx>,
 751     ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
 752         relate_substs(relation, a, b)
 753     }
 754 }
 755
 756 impl<'tcx> Relate<'tcx> for ty::Region<'tcx> {
 757     fn relate<R: TypeRelation<'tcx>>(
 758         relation: &mut R,
 759         a: ty::Region<'tcx>,
 760         b: ty::Region<'tcx>,
 761     ) -> RelateResult<'tcx, ty::Region<'tcx>> {
 762         relation.regions(a, b)
 763     }
 764 }
 765
 766 impl<'tcx> Relate<'tcx> for ty::Const<'tcx> {
 767     fn relate<R: TypeRelation<'tcx>>(
 768         relation: &mut R,
 769         a: ty::Const<'tcx>,
 770         b: ty::Const<'tcx>,
 771     ) -> RelateResult<'tcx, ty::Const<'tcx>> {
 772         relation.consts(a, b)
 773     }
 774 }
 775
 776 impl<'tcx, T: Relate<'tcx>> Relate<'tcx> for ty::Binder<'tcx, T> {
 777     fn relate<R: TypeRelation<'tcx>>(
 778         relation: &mut R,
 779         a: ty::Binder<'tcx, T>,
 780         b: ty::Binder<'tcx, T>,
 781     ) -> RelateResult<'tcx, ty::Binder<'tcx, T>> {
 782         relation.binders(a, b)
 783     }
 784 }
 785
 786 impl<'tcx> Relate<'tcx> for GenericArg<'tcx> {
 787     fn relate<R: TypeRelation<'tcx>>(
 788         relation: &mut R,
 789         a: GenericArg<'tcx>,
 790         b: GenericArg<'tcx>,
 791     ) -> RelateResult<'tcx, GenericArg<'tcx>> {
 792         match (a.unpack(), b.unpack()) {
 793             (GenericArgKind::Lifetime(a_lt), GenericArgKind::Lifetime(b_lt)) => {
 794                 Ok(relation.relate(a_lt, b_lt)?.into())
 795             }
 796             (GenericArgKind::Type(a_ty), GenericArgKind::Type(b_ty)) => {
 797                 Ok(relation.relate(a_ty, b_ty)?.into())
 798             }
 799             (GenericArgKind::Const(a_ct), GenericArgKind::Const(b_ct)) => {
 800                 Ok(relation.relate(a_ct, b_ct)?.into())
 801             }
 802             (GenericArgKind::Lifetime(unpacked), x) => {
 803                 bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
 804             }
 805             (GenericArgKind::Type(unpacked), x) => {
 806                 bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
 807             }
 808             (GenericArgKind::Const(unpacked), x) => {
 809                 bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
 810             }
 811         }
 812     }
 813 }
 814
 815 impl<'tcx> Relate<'tcx> for ty::ImplPolarity {
 816     fn relate<R: TypeRelation<'tcx>>(
 817         relation: &mut R,
 818         a: ty::ImplPolarity,
 819         b: ty::ImplPolarity,
 820     ) -> RelateResult<'tcx, ty::ImplPolarity> {
 821         if a != b {
 822             Err(TypeError::PolarityMismatch(expected_found(relation, a, b)))
 823         } else {
 824             Ok(a)
 825         }
 826     }
 827 }
 828
 829 impl<'tcx> Relate<'tcx> for ty::TraitPredicate<'tcx> {
 830     fn relate<R: TypeRelation<'tcx>>(
 831         relation: &mut R,
 832         a: ty::TraitPredicate<'tcx>,
 833         b: ty::TraitPredicate<'tcx>,
 834     ) -> RelateResult<'tcx, ty::TraitPredicate<'tcx>> {
 835         Ok(ty::TraitPredicate {
 836             trait_ref: relation.relate(a.trait_ref, b.trait_ref)?,
 837             constness: relation.relate(a.constness, b.constness)?,
 838             polarity: relation.relate(a.polarity, b.polarity)?,
 839         })
 840     }
 841 }
 842
 843 impl<'tcx> Relate<'tcx> for Term<'tcx> {
 844     fn relate<R: TypeRelation<'tcx>>(
 845         relation: &mut R,
 846         a: Self,
 847         b: Self,
 848     ) -> RelateResult<'tcx, Self> {
 849         Ok(match (a.unpack(), b.unpack()) {
 850             (TermKind::Ty(a), TermKind::Ty(b)) => relation.relate(a, b)?.into(),
 851             (TermKind::Const(a), TermKind::Const(b)) => relation.relate(a, b)?.into(),
 852             _ => return Err(TypeError::Mismatch),
 853         })
 854     }
 855 }
 856
 857 impl<'tcx> Relate<'tcx> for ty::ProjectionPredicate<'tcx> {
 858     fn relate<R: TypeRelation<'tcx>>(
 859         relation: &mut R,
 860         a: ty::ProjectionPredicate<'tcx>,
 861         b: ty::ProjectionPredicate<'tcx>,
 862     ) -> RelateResult<'tcx, ty::ProjectionPredicate<'tcx>> {
 863         Ok(ty::ProjectionPredicate {
 864             projection_ty: relation.relate(a.projection_ty, b.projection_ty)?,
 865             term: relation.relate(a.term, b.term)?,
 866         })
 867     }
 868 }
 869
 870 ///////////////////////////////////////////////////////////////////////////
 871 // Error handling
 872
 873 pub fn expected_found<'tcx, R, T>(relation: &mut R, a: T, b: T) -> ExpectedFound<T>
 874 where
 875     R: TypeRelation<'tcx>,
 876 {
 877     ExpectedFound::new(relation.a_is_expected(), a, b)
 878 }