src/librustc/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::mir::interpret::{get_slice_bytes, ConstValue};
   8 use crate::traits;
   9 use crate::ty::error::{ExpectedFound, TypeError};
  10 use crate::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
  11 use crate::ty::{self, Ty, TyCtxt, TypeFoldable};
  12 use rustc_hir as ast;
  13 use rustc_hir::def_id::DefId;
  14 use rustc_target::spec::abi;
  15 use std::iter;
  16 use std::rc::Rc;
  17
  18 pub type RelateResult<'tcx, T> = Result<T, TypeError<'tcx>>;
  19
  20 #[derive(Clone, Debug)]
  21 pub enum Cause {
  22     ExistentialRegionBound, // relating an existential region bound
  23 }
  24
  25 pub trait TypeRelation<'tcx>: Sized {
  26     fn tcx(&self) -> TyCtxt<'tcx>;
  27
  28     fn param_env(&self) -> ty::ParamEnv<'tcx>;
  29
  30     /// Returns a static string we can use for printouts.
  31     fn tag(&self) -> &'static str;
  32
  33     /// Returns `true` if the value `a` is the "expected" type in the
  34     /// relation. Just affects error messages.
  35     fn a_is_expected(&self) -> bool;
  36
  37     fn with_cause<F, R>(&mut self, _cause: Cause, f: F) -> R
  38     where
  39         F: FnOnce(&mut Self) -> R,
  40     {
  41         f(self)
  42     }
  43
  44     /// Generic relation routine suitable for most anything.
  45     fn relate<T: Relate<'tcx>>(&mut self, a: &T, b: &T) -> RelateResult<'tcx, T> {
  46         Relate::relate(self, a, b)
  47     }
  48
  49     /// Relate the two substitutions for the given item. The default
  50     /// is to look up the variance for the item and proceed
  51     /// accordingly.
  52     fn relate_item_substs(
  53         &mut self,
  54         item_def_id: DefId,
  55         a_subst: SubstsRef<'tcx>,
  56         b_subst: SubstsRef<'tcx>,
  57     ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
  58         debug!(
  59             "relate_item_substs(item_def_id={:?}, a_subst={:?}, b_subst={:?})",
  60             item_def_id, a_subst, b_subst
  61         );
  62
  63         let opt_variances = self.tcx().variances_of(item_def_id);
  64         relate_substs(self, Some(opt_variances), a_subst, b_subst)
  65     }
  66
  67     /// Switch variance for the purpose of relating `a` and `b`.
  68     fn relate_with_variance<T: Relate<'tcx>>(
  69         &mut self,
  70         variance: ty::Variance,
  71         a: &T,
  72         b: &T,
  73     ) -> RelateResult<'tcx, T>;
  74
  75     // Overridable relations. You shouldn't typically call these
  76     // directly, instead call `relate()`, which in turn calls
  77     // these. This is both more uniform but also allows us to add
  78     // additional hooks for other types in the future if needed
  79     // without making older code, which called `relate`, obsolete.
  80
  81     fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>>;
  82
  83     fn regions(
  84         &mut self,
  85         a: ty::Region<'tcx>,
  86         b: ty::Region<'tcx>,
  87     ) -> RelateResult<'tcx, ty::Region<'tcx>>;
  88
  89     fn consts(
  90         &mut self,
  91         a: &'tcx ty::Const<'tcx>,
  92         b: &'tcx ty::Const<'tcx>,
  93     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>>;
  94
  95     fn binders<T>(
  96         &mut self,
  97         a: &ty::Binder<T>,
  98         b: &ty::Binder<T>,
  99     ) -> RelateResult<'tcx, ty::Binder<T>>
 100     where
 101         T: Relate<'tcx>;
 102 }
 103
 104 pub trait Relate<'tcx>: TypeFoldable<'tcx> {
 105     fn relate<R: TypeRelation<'tcx>>(
 106         relation: &mut R,
 107         a: &Self,
 108         b: &Self,
 109     ) -> RelateResult<'tcx, Self>;
 110 }
 111
 112 ///////////////////////////////////////////////////////////////////////////
 113 // Relate impls
 114
 115 impl<'tcx> Relate<'tcx> for ty::TypeAndMut<'tcx> {
 116     fn relate<R: TypeRelation<'tcx>>(
 117         relation: &mut R,
 118         a: &ty::TypeAndMut<'tcx>,
 119         b: &ty::TypeAndMut<'tcx>,
 120     ) -> RelateResult<'tcx, ty::TypeAndMut<'tcx>> {
 121         debug!("{}.mts({:?}, {:?})", relation.tag(), a, b);
 122         if a.mutbl != b.mutbl {
 123             Err(TypeError::Mutability)
 124         } else {
 125             let mutbl = a.mutbl;
 126             let variance = match mutbl {
 127                 ast::Mutability::Not => ty::Covariant,
 128                 ast::Mutability::Mut => ty::Invariant,
 129             };
 130             let ty = relation.relate_with_variance(variance, &a.ty, &b.ty)?;
 131             Ok(ty::TypeAndMut { ty, mutbl })
 132         }
 133     }
 134 }
 135
 136 pub fn relate_substs<R: TypeRelation<'tcx>>(
 137     relation: &mut R,
 138     variances: Option<&[ty::Variance]>,
 139     a_subst: SubstsRef<'tcx>,
 140     b_subst: SubstsRef<'tcx>,
 141 ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
 142     let tcx = relation.tcx();
 143
 144     let params = a_subst.iter().zip(b_subst).enumerate().map(|(i, (a, b))| {
 145         let variance = variances.map_or(ty::Invariant, |v| v[i]);
 146         relation.relate_with_variance(variance, a, b)
 147     });
 148
 149     Ok(tcx.mk_substs(params)?)
 150 }
 151
 152 impl<'tcx> Relate<'tcx> for ty::FnSig<'tcx> {
 153     fn relate<R: TypeRelation<'tcx>>(
 154         relation: &mut R,
 155         a: &ty::FnSig<'tcx>,
 156         b: &ty::FnSig<'tcx>,
 157     ) -> RelateResult<'tcx, ty::FnSig<'tcx>> {
 158         let tcx = relation.tcx();
 159
 160         if a.c_variadic != b.c_variadic {
 161             return Err(TypeError::VariadicMismatch(expected_found(
 162                 relation,
 163                 &a.c_variadic,
 164                 &b.c_variadic,
 165             )));
 166         }
 167         let unsafety = relation.relate(&a.unsafety, &b.unsafety)?;
 168         let abi = relation.relate(&a.abi, &b.abi)?;
 169
 170         if a.inputs().len() != b.inputs().len() {
 171             return Err(TypeError::ArgCount);
 172         }
 173
 174         let inputs_and_output = a
 175             .inputs()
 176             .iter()
 177             .cloned()
 178             .zip(b.inputs().iter().cloned())
 179             .map(|x| (x, false))
 180             .chain(iter::once(((a.output(), b.output()), true)))
 181             .map(|((a, b), is_output)| {
 182                 if is_output {
 183                     relation.relate(&a, &b)
 184                 } else {
 185                     relation.relate_with_variance(ty::Contravariant, &a, &b)
 186                 }
 187             });
 188         Ok(ty::FnSig {
 189             inputs_and_output: tcx.mk_type_list(inputs_and_output)?,
 190             c_variadic: a.c_variadic,
 191             unsafety,
 192             abi,
 193         })
 194     }
 195 }
 196
 197 impl<'tcx> Relate<'tcx> for ast::Unsafety {
 198     fn relate<R: TypeRelation<'tcx>>(
 199         relation: &mut R,
 200         a: &ast::Unsafety,
 201         b: &ast::Unsafety,
 202     ) -> RelateResult<'tcx, ast::Unsafety> {
 203         if a != b {
 204             Err(TypeError::UnsafetyMismatch(expected_found(relation, a, b)))
 205         } else {
 206             Ok(*a)
 207         }
 208     }
 209 }
 210
 211 impl<'tcx> Relate<'tcx> for abi::Abi {
 212     fn relate<R: TypeRelation<'tcx>>(
 213         relation: &mut R,
 214         a: &abi::Abi,
 215         b: &abi::Abi,
 216     ) -> RelateResult<'tcx, abi::Abi> {
 217         if a == b { Ok(*a) } else { Err(TypeError::AbiMismatch(expected_found(relation, a, b))) }
 218     }
 219 }
 220
 221 impl<'tcx> Relate<'tcx> for ty::ProjectionTy<'tcx> {
 222     fn relate<R: TypeRelation<'tcx>>(
 223         relation: &mut R,
 224         a: &ty::ProjectionTy<'tcx>,
 225         b: &ty::ProjectionTy<'tcx>,
 226     ) -> RelateResult<'tcx, ty::ProjectionTy<'tcx>> {
 227         if a.item_def_id != b.item_def_id {
 228             Err(TypeError::ProjectionMismatched(expected_found(
 229                 relation,
 230                 &a.item_def_id,
 231                 &b.item_def_id,
 232             )))
 233         } else {
 234             let substs = relation.relate(&a.substs, &b.substs)?;
 235             Ok(ty::ProjectionTy { item_def_id: a.item_def_id, substs: &substs })
 236         }
 237     }
 238 }
 239
 240 impl<'tcx> Relate<'tcx> for ty::ExistentialProjection<'tcx> {
 241     fn relate<R: TypeRelation<'tcx>>(
 242         relation: &mut R,
 243         a: &ty::ExistentialProjection<'tcx>,
 244         b: &ty::ExistentialProjection<'tcx>,
 245     ) -> RelateResult<'tcx, ty::ExistentialProjection<'tcx>> {
 246         if a.item_def_id != b.item_def_id {
 247             Err(TypeError::ProjectionMismatched(expected_found(
 248                 relation,
 249                 &a.item_def_id,
 250                 &b.item_def_id,
 251             )))
 252         } else {
 253             let ty = relation.relate(&a.ty, &b.ty)?;
 254             let substs = relation.relate(&a.substs, &b.substs)?;
 255             Ok(ty::ExistentialProjection { item_def_id: a.item_def_id, substs, ty })
 256         }
 257     }
 258 }
 259
 260 impl<'tcx> Relate<'tcx> for Vec<ty::PolyExistentialProjection<'tcx>> {
 261     fn relate<R: TypeRelation<'tcx>>(
 262         relation: &mut R,
 263         a: &Vec<ty::PolyExistentialProjection<'tcx>>,
 264         b: &Vec<ty::PolyExistentialProjection<'tcx>>,
 265     ) -> RelateResult<'tcx, Vec<ty::PolyExistentialProjection<'tcx>>> {
 266         // To be compatible, `a` and `b` must be for precisely the
 267         // same set of traits and item names. We always require that
 268         // projection bounds lists are sorted by trait-def-id and item-name,
 269         // so we can just iterate through the lists pairwise, so long as they are the
 270         // same length.
 271         if a.len() != b.len() {
 272             Err(TypeError::ProjectionBoundsLength(expected_found(relation, &a.len(), &b.len())))
 273         } else {
 274             a.iter().zip(b).map(|(a, b)| relation.relate(a, b)).collect()
 275         }
 276     }
 277 }
 278
 279 impl<'tcx> Relate<'tcx> for ty::TraitRef<'tcx> {
 280     fn relate<R: TypeRelation<'tcx>>(
 281         relation: &mut R,
 282         a: &ty::TraitRef<'tcx>,
 283         b: &ty::TraitRef<'tcx>,
 284     ) -> RelateResult<'tcx, ty::TraitRef<'tcx>> {
 285         // Different traits cannot be related.
 286         if a.def_id != b.def_id {
 287             Err(TypeError::Traits(expected_found(relation, &a.def_id, &b.def_id)))
 288         } else {
 289             let substs = relate_substs(relation, None, a.substs, b.substs)?;
 290             Ok(ty::TraitRef { def_id: a.def_id, substs })
 291         }
 292     }
 293 }
 294
 295 impl<'tcx> Relate<'tcx> for ty::ExistentialTraitRef<'tcx> {
 296     fn relate<R: TypeRelation<'tcx>>(
 297         relation: &mut R,
 298         a: &ty::ExistentialTraitRef<'tcx>,
 299         b: &ty::ExistentialTraitRef<'tcx>,
 300     ) -> RelateResult<'tcx, ty::ExistentialTraitRef<'tcx>> {
 301         // Different traits cannot be related.
 302         if a.def_id != b.def_id {
 303             Err(TypeError::Traits(expected_found(relation, &a.def_id, &b.def_id)))
 304         } else {
 305             let substs = relate_substs(relation, None, a.substs, b.substs)?;
 306             Ok(ty::ExistentialTraitRef { def_id: a.def_id, substs })
 307         }
 308     }
 309 }
 310
 311 #[derive(Debug, Clone, TypeFoldable)]
 312 struct GeneratorWitness<'tcx>(&'tcx ty::List<Ty<'tcx>>);
 313
 314 impl<'tcx> Relate<'tcx> for GeneratorWitness<'tcx> {
 315     fn relate<R: TypeRelation<'tcx>>(
 316         relation: &mut R,
 317         a: &GeneratorWitness<'tcx>,
 318         b: &GeneratorWitness<'tcx>,
 319     ) -> RelateResult<'tcx, GeneratorWitness<'tcx>> {
 320         assert_eq!(a.0.len(), b.0.len());
 321         let tcx = relation.tcx();
 322         let types = tcx.mk_type_list(a.0.iter().zip(b.0).map(|(a, b)| relation.relate(a, b)))?;
 323         Ok(GeneratorWitness(types))
 324     }
 325 }
 326
 327 impl<'tcx> Relate<'tcx> for Ty<'tcx> {
 328     fn relate<R: TypeRelation<'tcx>>(
 329         relation: &mut R,
 330         a: &Ty<'tcx>,
 331         b: &Ty<'tcx>,
 332     ) -> RelateResult<'tcx, Ty<'tcx>> {
 333         relation.tys(a, b)
 334     }
 335 }
 336
 337 /// The main "type relation" routine. Note that this does not handle
 338 /// inference artifacts, so you should filter those out before calling
 339 /// it.
 340 pub fn super_relate_tys<R: TypeRelation<'tcx>>(
 341     relation: &mut R,
 342     a: Ty<'tcx>,
 343     b: Ty<'tcx>,
 344 ) -> RelateResult<'tcx, Ty<'tcx>> {
 345     let tcx = relation.tcx();
 346     debug!("super_relate_tys: a={:?} b={:?}", a, b);
 347     match (&a.kind, &b.kind) {
 348         (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
 349             // The caller should handle these cases!
 350             bug!("var types encountered in super_relate_tys")
 351         }
 352
 353         (ty::Bound(..), _) | (_, ty::Bound(..)) => {
 354             bug!("bound types encountered in super_relate_tys")
 355         }
 356
 357         (&ty::Error, _) | (_, &ty::Error) => Ok(tcx.types.err),
 358
 359         (&ty::Never, _)
 360         | (&ty::Char, _)
 361         | (&ty::Bool, _)
 362         | (&ty::Int(_), _)
 363         | (&ty::Uint(_), _)
 364         | (&ty::Float(_), _)
 365         | (&ty::Str, _)
 366             if a == b =>
 367         {
 368             Ok(a)
 369         }
 370
 371         (&ty::Param(ref a_p), &ty::Param(ref b_p)) if a_p.index == b_p.index => Ok(a),
 372
 373         (ty::Placeholder(p1), ty::Placeholder(p2)) if p1 == p2 => Ok(a),
 374
 375         (&ty::Adt(a_def, a_substs), &ty::Adt(b_def, b_substs)) if a_def == b_def => {
 376             let substs = relation.relate_item_substs(a_def.did, a_substs, b_substs)?;
 377             Ok(tcx.mk_adt(a_def, substs))
 378         }
 379
 380         (&ty::Foreign(a_id), &ty::Foreign(b_id)) if a_id == b_id => Ok(tcx.mk_foreign(a_id)),
 381
 382         (&ty::Dynamic(ref a_obj, ref a_region), &ty::Dynamic(ref b_obj, ref b_region)) => {
 383             let region_bound = relation.with_cause(Cause::ExistentialRegionBound, |relation| {
 384                 relation.relate_with_variance(ty::Contravariant, a_region, b_region)
 385             })?;
 386             Ok(tcx.mk_dynamic(relation.relate(a_obj, b_obj)?, region_bound))
 387         }
 388
 389         (&ty::Generator(a_id, a_substs, movability), &ty::Generator(b_id, b_substs, _))
 390             if a_id == b_id =>
 391         {
 392             // All Generator types with the same id represent
 393             // the (anonymous) type of the same generator expression. So
 394             // all of their regions should be equated.
 395             let substs = relation.relate(&a_substs, &b_substs)?;
 396             Ok(tcx.mk_generator(a_id, substs, movability))
 397         }
 398
 399         (&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => {
 400             // Wrap our types with a temporary GeneratorWitness struct
 401             // inside the binder so we can related them
 402             let a_types = a_types.map_bound(GeneratorWitness);
 403             let b_types = b_types.map_bound(GeneratorWitness);
 404             // Then remove the GeneratorWitness for the result
 405             let types = relation.relate(&a_types, &b_types)?.map_bound(|witness| witness.0);
 406             Ok(tcx.mk_generator_witness(types))
 407         }
 408
 409         (&ty::Closure(a_id, a_substs), &ty::Closure(b_id, b_substs)) if a_id == b_id => {
 410             // All Closure types with the same id represent
 411             // the (anonymous) type of the same closure expression. So
 412             // all of their regions should be equated.
 413             let substs = relation.relate(&a_substs, &b_substs)?;
 414             Ok(tcx.mk_closure(a_id, &substs))
 415         }
 416
 417         (&ty::RawPtr(ref a_mt), &ty::RawPtr(ref b_mt)) => {
 418             let mt = relation.relate(a_mt, b_mt)?;
 419             Ok(tcx.mk_ptr(mt))
 420         }
 421
 422         (&ty::Ref(a_r, a_ty, a_mutbl), &ty::Ref(b_r, b_ty, b_mutbl)) => {
 423             let r = relation.relate_with_variance(ty::Contravariant, &a_r, &b_r)?;
 424             let a_mt = ty::TypeAndMut { ty: a_ty, mutbl: a_mutbl };
 425             let b_mt = ty::TypeAndMut { ty: b_ty, mutbl: b_mutbl };
 426             let mt = relation.relate(&a_mt, &b_mt)?;
 427             Ok(tcx.mk_ref(r, mt))
 428         }
 429
 430         (&ty::Array(a_t, sz_a), &ty::Array(b_t, sz_b)) => {
 431             let t = relation.relate(&a_t, &b_t)?;
 432             match relation.relate(&sz_a, &sz_b) {
 433                 Ok(sz) => Ok(tcx.mk_ty(ty::Array(t, sz))),
 434                 Err(err) => {
 435                     // Check whether the lengths are both concrete/known values,
 436                     // but are unequal, for better diagnostics.
 437                     let sz_a = sz_a.try_eval_usize(tcx, relation.param_env());
 438                     let sz_b = sz_b.try_eval_usize(tcx, relation.param_env());
 439                     match (sz_a, sz_b) {
 440                         (Some(sz_a_val), Some(sz_b_val)) => Err(TypeError::FixedArraySize(
 441                             expected_found(relation, &sz_a_val, &sz_b_val),
 442                         )),
 443                         _ => return Err(err),
 444                     }
 445                 }
 446             }
 447         }
 448
 449         (&ty::Slice(a_t), &ty::Slice(b_t)) => {
 450             let t = relation.relate(&a_t, &b_t)?;
 451             Ok(tcx.mk_slice(t))
 452         }
 453
 454         (&ty::Tuple(as_), &ty::Tuple(bs)) => {
 455             if as_.len() == bs.len() {
 456                 Ok(tcx.mk_tup(
 457                     as_.iter()
 458                         .zip(bs)
 459                         .map(|(a, b)| relation.relate(&a.expect_ty(), &b.expect_ty())),
 460                 )?)
 461             } else if !(as_.is_empty() || bs.is_empty()) {
 462                 Err(TypeError::TupleSize(expected_found(relation, &as_.len(), &bs.len())))
 463             } else {
 464                 Err(TypeError::Sorts(expected_found(relation, &a, &b)))
 465             }
 466         }
 467
 468         (&ty::FnDef(a_def_id, a_substs), &ty::FnDef(b_def_id, b_substs))
 469             if a_def_id == b_def_id =>
 470         {
 471             let substs = relation.relate_item_substs(a_def_id, a_substs, b_substs)?;
 472             Ok(tcx.mk_fn_def(a_def_id, substs))
 473         }
 474
 475         (&ty::FnPtr(a_fty), &ty::FnPtr(b_fty)) => {
 476             let fty = relation.relate(&a_fty, &b_fty)?;
 477             Ok(tcx.mk_fn_ptr(fty))
 478         }
 479
 480         (ty::UnnormalizedProjection(a_data), ty::UnnormalizedProjection(b_data)) => {
 481             let projection_ty = relation.relate(a_data, b_data)?;
 482             Ok(tcx.mk_ty(ty::UnnormalizedProjection(projection_ty)))
 483         }
 484
 485         // these two are already handled downstream in case of lazy normalization
 486         (ty::Projection(a_data), ty::Projection(b_data)) => {
 487             let projection_ty = relation.relate(a_data, b_data)?;
 488             Ok(tcx.mk_projection(projection_ty.item_def_id, projection_ty.substs))
 489         }
 490
 491         (&ty::Opaque(a_def_id, a_substs), &ty::Opaque(b_def_id, b_substs))
 492             if a_def_id == b_def_id =>
 493         {
 494             let substs = relate_substs(relation, None, a_substs, b_substs)?;
 495             Ok(tcx.mk_opaque(a_def_id, substs))
 496         }
 497
 498         _ => Err(TypeError::Sorts(expected_found(relation, &a, &b))),
 499     }
 500 }
 501
 502 /// The main "const relation" routine. Note that this does not handle
 503 /// inference artifacts, so you should filter those out before calling
 504 /// it.
 505 pub fn super_relate_consts<R: TypeRelation<'tcx>>(
 506     relation: &mut R,
 507     a: &'tcx ty::Const<'tcx>,
 508     b: &'tcx ty::Const<'tcx>,
 509 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
 510     let tcx = relation.tcx();
 511
 512     let eagerly_eval = |x: &'tcx ty::Const<'tcx>| {
 513         if !x.val.has_local_value() {
 514             return x.eval(tcx, relation.param_env()).val;
 515         }
 516         x.val
 517     };
 518
 519     // Currently, the values that can be unified are primitive types,
 520     // and those that derive both `PartialEq` and `Eq`, corresponding
 521     // to `structural_match` types.
 522     let new_const_val = match (eagerly_eval(a), eagerly_eval(b)) {
 523         (ty::ConstKind::Infer(_), _) | (_, ty::ConstKind::Infer(_)) => {
 524             // The caller should handle these cases!
 525             bug!("var types encountered in super_relate_consts: {:?} {:?}", a, b)
 526         }
 527         (ty::ConstKind::Param(a_p), ty::ConstKind::Param(b_p)) if a_p.index == b_p.index => {
 528             return Ok(a);
 529         }
 530         (ty::ConstKind::Placeholder(p1), ty::ConstKind::Placeholder(p2)) if p1 == p2 => {
 531             return Ok(a);
 532         }
 533         (ty::ConstKind::Value(a_val), ty::ConstKind::Value(b_val)) => {
 534             let new_val = match (a_val, b_val) {
 535                 (ConstValue::Scalar(a_val), ConstValue::Scalar(b_val)) if a.ty == b.ty => {
 536                     if a_val == b_val {
 537                         Ok(ConstValue::Scalar(a_val))
 538                     } else if let ty::FnPtr(_) = a.ty.kind {
 539                         let alloc_map = tcx.alloc_map.lock();
 540                         let a_instance = alloc_map.unwrap_fn(a_val.assert_ptr().alloc_id);
 541                         let b_instance = alloc_map.unwrap_fn(b_val.assert_ptr().alloc_id);
 542                         if a_instance == b_instance {
 543                             Ok(ConstValue::Scalar(a_val))
 544                         } else {
 545                             Err(TypeError::ConstMismatch(expected_found(relation, &a, &b)))
 546                         }
 547                     } else {
 548                         Err(TypeError::ConstMismatch(expected_found(relation, &a, &b)))
 549                     }
 550                 }
 551
 552                 (a_val @ ConstValue::Slice { .. }, b_val @ ConstValue::Slice { .. }) => {
 553                     let a_bytes = get_slice_bytes(&tcx, a_val);
 554                     let b_bytes = get_slice_bytes(&tcx, b_val);
 555                     if a_bytes == b_bytes {
 556                         Ok(a_val)
 557                     } else {
 558                         Err(TypeError::ConstMismatch(expected_found(relation, &a, &b)))
 559                     }
 560                 }
 561
 562                 // FIXME(const_generics): handle `ConstValue::ByRef`.
 563                 _ => Err(TypeError::ConstMismatch(expected_found(relation, &a, &b))),
 564             };
 565
 566             new_val.map(ty::ConstKind::Value)
 567         }
 568
 569         // FIXME(const_generics): this is wrong, as it is a projection
 570         (
 571             ty::ConstKind::Unevaluated(a_def_id, a_substs, a_promoted),
 572             ty::ConstKind::Unevaluated(b_def_id, b_substs, b_promoted),
 573         ) if a_def_id == b_def_id && a_promoted == b_promoted => {
 574             let substs =
 575                 relation.relate_with_variance(ty::Variance::Invariant, &a_substs, &b_substs)?;
 576             Ok(ty::ConstKind::Unevaluated(a_def_id, &substs, a_promoted))
 577         }
 578         _ => Err(TypeError::ConstMismatch(expected_found(relation, &a, &b))),
 579     };
 580     new_const_val.map(|val| tcx.mk_const(ty::Const { val, ty: a.ty }))
 581 }
 582
 583 impl<'tcx> Relate<'tcx> for &'tcx ty::List<ty::ExistentialPredicate<'tcx>> {
 584     fn relate<R: TypeRelation<'tcx>>(
 585         relation: &mut R,
 586         a: &Self,
 587         b: &Self,
 588     ) -> RelateResult<'tcx, Self> {
 589         if a.len() != b.len() {
 590             return Err(TypeError::ExistentialMismatch(expected_found(relation, a, b)));
 591         }
 592
 593         let tcx = relation.tcx();
 594         let v = a.iter().zip(b.iter()).map(|(ep_a, ep_b)| {
 595             use crate::ty::ExistentialPredicate::*;
 596             match (*ep_a, *ep_b) {
 597                 (Trait(ref a), Trait(ref b)) => Ok(Trait(relation.relate(a, b)?)),
 598                 (Projection(ref a), Projection(ref b)) => Ok(Projection(relation.relate(a, b)?)),
 599                 (AutoTrait(ref a), AutoTrait(ref b)) if a == b => Ok(AutoTrait(*a)),
 600                 _ => Err(TypeError::ExistentialMismatch(expected_found(relation, a, b))),
 601             }
 602         });
 603         Ok(tcx.mk_existential_predicates(v)?)
 604     }
 605 }
 606
 607 impl<'tcx> Relate<'tcx> for ty::ClosureSubsts<'tcx> {
 608     fn relate<R: TypeRelation<'tcx>>(
 609         relation: &mut R,
 610         a: &ty::ClosureSubsts<'tcx>,
 611         b: &ty::ClosureSubsts<'tcx>,
 612     ) -> RelateResult<'tcx, ty::ClosureSubsts<'tcx>> {
 613         let substs = relate_substs(relation, None, a.substs, b.substs)?;
 614         Ok(ty::ClosureSubsts { substs })
 615     }
 616 }
 617
 618 impl<'tcx> Relate<'tcx> for ty::GeneratorSubsts<'tcx> {
 619     fn relate<R: TypeRelation<'tcx>>(
 620         relation: &mut R,
 621         a: &ty::GeneratorSubsts<'tcx>,
 622         b: &ty::GeneratorSubsts<'tcx>,
 623     ) -> RelateResult<'tcx, ty::GeneratorSubsts<'tcx>> {
 624         let substs = relate_substs(relation, None, a.substs, b.substs)?;
 625         Ok(ty::GeneratorSubsts { substs })
 626     }
 627 }
 628
 629 impl<'tcx> Relate<'tcx> for SubstsRef<'tcx> {
 630     fn relate<R: TypeRelation<'tcx>>(
 631         relation: &mut R,
 632         a: &SubstsRef<'tcx>,
 633         b: &SubstsRef<'tcx>,
 634     ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
 635         relate_substs(relation, None, a, b)
 636     }
 637 }
 638
 639 impl<'tcx> Relate<'tcx> for ty::Region<'tcx> {
 640     fn relate<R: TypeRelation<'tcx>>(
 641         relation: &mut R,
 642         a: &ty::Region<'tcx>,
 643         b: &ty::Region<'tcx>,
 644     ) -> RelateResult<'tcx, ty::Region<'tcx>> {
 645         relation.regions(*a, *b)
 646     }
 647 }
 648
 649 impl<'tcx> Relate<'tcx> for &'tcx ty::Const<'tcx> {
 650     fn relate<R: TypeRelation<'tcx>>(
 651         relation: &mut R,
 652         a: &&'tcx ty::Const<'tcx>,
 653         b: &&'tcx ty::Const<'tcx>,
 654     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
 655         relation.consts(*a, *b)
 656     }
 657 }
 658
 659 impl<'tcx, T: Relate<'tcx>> Relate<'tcx> for ty::Binder<T> {
 660     fn relate<R: TypeRelation<'tcx>>(
 661         relation: &mut R,
 662         a: &ty::Binder<T>,
 663         b: &ty::Binder<T>,
 664     ) -> RelateResult<'tcx, ty::Binder<T>> {
 665         relation.binders(a, b)
 666     }
 667 }
 668
 669 impl<'tcx, T: Relate<'tcx>> Relate<'tcx> for Rc<T> {
 670     fn relate<R: TypeRelation<'tcx>>(
 671         relation: &mut R,
 672         a: &Rc<T>,
 673         b: &Rc<T>,
 674     ) -> RelateResult<'tcx, Rc<T>> {
 675         let a: &T = a;
 676         let b: &T = b;
 677         Ok(Rc::new(relation.relate(a, b)?))
 678     }
 679 }
 680
 681 impl<'tcx, T: Relate<'tcx>> Relate<'tcx> for Box<T> {
 682     fn relate<R: TypeRelation<'tcx>>(
 683         relation: &mut R,
 684         a: &Box<T>,
 685         b: &Box<T>,
 686     ) -> RelateResult<'tcx, Box<T>> {
 687         let a: &T = a;
 688         let b: &T = b;
 689         Ok(Box::new(relation.relate(a, b)?))
 690     }
 691 }
 692
 693 impl<'tcx> Relate<'tcx> for GenericArg<'tcx> {
 694     fn relate<R: TypeRelation<'tcx>>(
 695         relation: &mut R,
 696         a: &GenericArg<'tcx>,
 697         b: &GenericArg<'tcx>,
 698     ) -> RelateResult<'tcx, GenericArg<'tcx>> {
 699         match (a.unpack(), b.unpack()) {
 700             (GenericArgKind::Lifetime(a_lt), GenericArgKind::Lifetime(b_lt)) => {
 701                 Ok(relation.relate(&a_lt, &b_lt)?.into())
 702             }
 703             (GenericArgKind::Type(a_ty), GenericArgKind::Type(b_ty)) => {
 704                 Ok(relation.relate(&a_ty, &b_ty)?.into())
 705             }
 706             (GenericArgKind::Const(a_ct), GenericArgKind::Const(b_ct)) => {
 707                 Ok(relation.relate(&a_ct, &b_ct)?.into())
 708             }
 709             (GenericArgKind::Lifetime(unpacked), x) => {
 710                 bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
 711             }
 712             (GenericArgKind::Type(unpacked), x) => {
 713                 bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
 714             }
 715             (GenericArgKind::Const(unpacked), x) => {
 716                 bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
 717             }
 718         }
 719     }
 720 }
 721
 722 impl<'tcx> Relate<'tcx> for ty::TraitPredicate<'tcx> {
 723     fn relate<R: TypeRelation<'tcx>>(
 724         relation: &mut R,
 725         a: &ty::TraitPredicate<'tcx>,
 726         b: &ty::TraitPredicate<'tcx>,
 727     ) -> RelateResult<'tcx, ty::TraitPredicate<'tcx>> {
 728         Ok(ty::TraitPredicate { trait_ref: relation.relate(&a.trait_ref, &b.trait_ref)? })
 729     }
 730 }
 731
 732 impl<'tcx> Relate<'tcx> for ty::ProjectionPredicate<'tcx> {
 733     fn relate<R: TypeRelation<'tcx>>(
 734         relation: &mut R,
 735         a: &ty::ProjectionPredicate<'tcx>,
 736         b: &ty::ProjectionPredicate<'tcx>,
 737     ) -> RelateResult<'tcx, ty::ProjectionPredicate<'tcx>> {
 738         Ok(ty::ProjectionPredicate {
 739             projection_ty: relation.relate(&a.projection_ty, &b.projection_ty)?,
 740             ty: relation.relate(&a.ty, &b.ty)?,
 741         })
 742     }
 743 }
 744
 745 impl<'tcx> Relate<'tcx> for traits::WhereClause<'tcx> {
 746     fn relate<R: TypeRelation<'tcx>>(
 747         relation: &mut R,
 748         a: &traits::WhereClause<'tcx>,
 749         b: &traits::WhereClause<'tcx>,
 750     ) -> RelateResult<'tcx, traits::WhereClause<'tcx>> {
 751         use crate::traits::WhereClause::*;
 752         match (a, b) {
 753             (Implemented(a_pred), Implemented(b_pred)) => {
 754                 Ok(Implemented(relation.relate(a_pred, b_pred)?))
 755             }
 756
 757             (ProjectionEq(a_pred), ProjectionEq(b_pred)) => {
 758                 Ok(ProjectionEq(relation.relate(a_pred, b_pred)?))
 759             }
 760
 761             (RegionOutlives(a_pred), RegionOutlives(b_pred)) => {
 762                 Ok(RegionOutlives(ty::OutlivesPredicate(
 763                     relation.relate(&a_pred.0, &b_pred.0)?,
 764                     relation.relate(&a_pred.1, &b_pred.1)?,
 765                 )))
 766             }
 767
 768             (TypeOutlives(a_pred), TypeOutlives(b_pred)) => {
 769                 Ok(TypeOutlives(ty::OutlivesPredicate(
 770                     relation.relate(&a_pred.0, &b_pred.0)?,
 771                     relation.relate(&a_pred.1, &b_pred.1)?,
 772                 )))
 773             }
 774
 775             _ => Err(TypeError::Mismatch),
 776         }
 777     }
 778 }
 779
 780 impl<'tcx> Relate<'tcx> for traits::WellFormed<'tcx> {
 781     fn relate<R: TypeRelation<'tcx>>(
 782         relation: &mut R,
 783         a: &traits::WellFormed<'tcx>,
 784         b: &traits::WellFormed<'tcx>,
 785     ) -> RelateResult<'tcx, traits::WellFormed<'tcx>> {
 786         use crate::traits::WellFormed::*;
 787         match (a, b) {
 788             (Trait(a_pred), Trait(b_pred)) => Ok(Trait(relation.relate(a_pred, b_pred)?)),
 789             (Ty(a_ty), Ty(b_ty)) => Ok(Ty(relation.relate(a_ty, b_ty)?)),
 790             _ => Err(TypeError::Mismatch),
 791         }
 792     }
 793 }
 794
 795 impl<'tcx> Relate<'tcx> for traits::FromEnv<'tcx> {
 796     fn relate<R: TypeRelation<'tcx>>(
 797         relation: &mut R,
 798         a: &traits::FromEnv<'tcx>,
 799         b: &traits::FromEnv<'tcx>,
 800     ) -> RelateResult<'tcx, traits::FromEnv<'tcx>> {
 801         use crate::traits::FromEnv::*;
 802         match (a, b) {
 803             (Trait(a_pred), Trait(b_pred)) => Ok(Trait(relation.relate(a_pred, b_pred)?)),
 804             (Ty(a_ty), Ty(b_ty)) => Ok(Ty(relation.relate(a_ty, b_ty)?)),
 805             _ => Err(TypeError::Mismatch),
 806         }
 807     }
 808 }
 809
 810 impl<'tcx> Relate<'tcx> for traits::DomainGoal<'tcx> {
 811     fn relate<R: TypeRelation<'tcx>>(
 812         relation: &mut R,
 813         a: &traits::DomainGoal<'tcx>,
 814         b: &traits::DomainGoal<'tcx>,
 815     ) -> RelateResult<'tcx, traits::DomainGoal<'tcx>> {
 816         use crate::traits::DomainGoal::*;
 817         match (a, b) {
 818             (Holds(a_wc), Holds(b_wc)) => Ok(Holds(relation.relate(a_wc, b_wc)?)),
 819             (WellFormed(a_wf), WellFormed(b_wf)) => Ok(WellFormed(relation.relate(a_wf, b_wf)?)),
 820             (FromEnv(a_fe), FromEnv(b_fe)) => Ok(FromEnv(relation.relate(a_fe, b_fe)?)),
 821
 822             (Normalize(a_pred), Normalize(b_pred)) => {
 823                 Ok(Normalize(relation.relate(a_pred, b_pred)?))
 824             }
 825
 826             _ => Err(TypeError::Mismatch),
 827         }
 828     }
 829 }
 830
 831 impl<'tcx> Relate<'tcx> for traits::Goal<'tcx> {
 832     fn relate<R: TypeRelation<'tcx>>(
 833         relation: &mut R,
 834         a: &traits::Goal<'tcx>,
 835         b: &traits::Goal<'tcx>,
 836     ) -> RelateResult<'tcx, traits::Goal<'tcx>> {
 837         use crate::traits::GoalKind::*;
 838         match (a, b) {
 839             (Implies(a_clauses, a_goal), Implies(b_clauses, b_goal)) => {
 840                 let clauses = relation.relate(a_clauses, b_clauses)?;
 841                 let goal = relation.relate(a_goal, b_goal)?;
 842                 Ok(relation.tcx().mk_goal(Implies(clauses, goal)))
 843             }
 844
 845             (And(a_left, a_right), And(b_left, b_right)) => {
 846                 let left = relation.relate(a_left, b_left)?;
 847                 let right = relation.relate(a_right, b_right)?;
 848                 Ok(relation.tcx().mk_goal(And(left, right)))
 849             }
 850
 851             (Not(a_goal), Not(b_goal)) => {
 852                 let goal = relation.relate(a_goal, b_goal)?;
 853                 Ok(relation.tcx().mk_goal(Not(goal)))
 854             }
 855
 856             (DomainGoal(a_goal), DomainGoal(b_goal)) => {
 857                 let goal = relation.relate(a_goal, b_goal)?;
 858                 Ok(relation.tcx().mk_goal(DomainGoal(goal)))
 859             }
 860
 861             (Quantified(a_qkind, a_goal), Quantified(b_qkind, b_goal)) if a_qkind == b_qkind => {
 862                 let goal = relation.relate(a_goal, b_goal)?;
 863                 Ok(relation.tcx().mk_goal(Quantified(*a_qkind, goal)))
 864             }
 865
 866             (CannotProve, CannotProve) => Ok(*a),
 867
 868             _ => Err(TypeError::Mismatch),
 869         }
 870     }
 871 }
 872
 873 impl<'tcx> Relate<'tcx> for traits::Goals<'tcx> {
 874     fn relate<R: TypeRelation<'tcx>>(
 875         relation: &mut R,
 876         a: &traits::Goals<'tcx>,
 877         b: &traits::Goals<'tcx>,
 878     ) -> RelateResult<'tcx, traits::Goals<'tcx>> {
 879         if a.len() != b.len() {
 880             return Err(TypeError::Mismatch);
 881         }
 882
 883         let tcx = relation.tcx();
 884         let goals = a.iter().zip(b.iter()).map(|(a, b)| relation.relate(a, b));
 885         Ok(tcx.mk_goals(goals)?)
 886     }
 887 }
 888
 889 impl<'tcx> Relate<'tcx> for traits::Clause<'tcx> {
 890     fn relate<R: TypeRelation<'tcx>>(
 891         relation: &mut R,
 892         a: &traits::Clause<'tcx>,
 893         b: &traits::Clause<'tcx>,
 894     ) -> RelateResult<'tcx, traits::Clause<'tcx>> {
 895         use crate::traits::Clause::*;
 896         match (a, b) {
 897             (Implies(a_clause), Implies(b_clause)) => {
 898                 let clause = relation.relate(a_clause, b_clause)?;
 899                 Ok(Implies(clause))
 900             }
 901
 902             (ForAll(a_clause), ForAll(b_clause)) => {
 903                 let clause = relation.relate(a_clause, b_clause)?;
 904                 Ok(ForAll(clause))
 905             }
 906
 907             _ => Err(TypeError::Mismatch),
 908         }
 909     }
 910 }
 911
 912 impl<'tcx> Relate<'tcx> for traits::Clauses<'tcx> {
 913     fn relate<R: TypeRelation<'tcx>>(
 914         relation: &mut R,
 915         a: &traits::Clauses<'tcx>,
 916         b: &traits::Clauses<'tcx>,
 917     ) -> RelateResult<'tcx, traits::Clauses<'tcx>> {
 918         if a.len() != b.len() {
 919             return Err(TypeError::Mismatch);
 920         }
 921
 922         let tcx = relation.tcx();
 923         let clauses = a.iter().zip(b.iter()).map(|(a, b)| relation.relate(a, b));
 924         Ok(tcx.mk_clauses(clauses)?)
 925     }
 926 }
 927
 928 impl<'tcx> Relate<'tcx> for traits::ProgramClause<'tcx> {
 929     fn relate<R: TypeRelation<'tcx>>(
 930         relation: &mut R,
 931         a: &traits::ProgramClause<'tcx>,
 932         b: &traits::ProgramClause<'tcx>,
 933     ) -> RelateResult<'tcx, traits::ProgramClause<'tcx>> {
 934         Ok(traits::ProgramClause {
 935             goal: relation.relate(&a.goal, &b.goal)?,
 936             hypotheses: relation.relate(&a.hypotheses, &b.hypotheses)?,
 937             category: traits::ProgramClauseCategory::Other,
 938         })
 939     }
 940 }
 941
 942 impl<'tcx> Relate<'tcx> for traits::Environment<'tcx> {
 943     fn relate<R: TypeRelation<'tcx>>(
 944         relation: &mut R,
 945         a: &traits::Environment<'tcx>,
 946         b: &traits::Environment<'tcx>,
 947     ) -> RelateResult<'tcx, traits::Environment<'tcx>> {
 948         Ok(traits::Environment { clauses: relation.relate(&a.clauses, &b.clauses)? })
 949     }
 950 }
 951
 952 impl<'tcx, G> Relate<'tcx> for traits::InEnvironment<'tcx, G>
 953 where
 954     G: Relate<'tcx>,
 955 {
 956     fn relate<R: TypeRelation<'tcx>>(
 957         relation: &mut R,
 958         a: &traits::InEnvironment<'tcx, G>,
 959         b: &traits::InEnvironment<'tcx, G>,
 960     ) -> RelateResult<'tcx, traits::InEnvironment<'tcx, G>> {
 961         Ok(traits::InEnvironment {
 962             environment: relation.relate(&a.environment, &b.environment)?,
 963             goal: relation.relate(&a.goal, &b.goal)?,
 964         })
 965     }
 966 }
 967
 968 ///////////////////////////////////////////////////////////////////////////
 969 // Error handling
 970
 971 pub fn expected_found<R, T>(relation: &mut R, a: &T, b: &T) -> ExpectedFound<T>
 972 where
 973     R: TypeRelation<'tcx>,
 974     T: Clone,
 975 {
 976     expected_found_bool(relation.a_is_expected(), a, b)
 977 }
 978
 979 pub fn expected_found_bool<T>(a_is_expected: bool, a: &T, b: &T) -> ExpectedFound<T>
 980 where
 981     T: Clone,
 982 {
 983     let a = a.clone();
 984     let b = b.clone();
 985     if a_is_expected {
 986         ExpectedFound { expected: a, found: b }
 987     } else {
 988         ExpectedFound { expected: b, found: a }
 989     }
 990 }