1 ///////////////////////////////////////////////////////////////////////////
4 // There are four type combiners: equate, sub, lub, and glb. Each
5 // implements the trait `Combine` and contains methods for combining
6 // two instances of various things and yielding a new instance. These
7 // combiner methods always yield a `Result<T>`. There is a lot of
8 // common code for these operations, implemented as default methods on
9 // the `Combine` trait.
11 // Each operation may have side-effects on the inference context,
12 // though these can be unrolled using snapshots. On success, the
13 // LUB/GLB operations return the appropriate bound. The Eq and Sub
14 // operations generally return the first operand.
18 // When you are relating two things which have a contravariant
19 // relationship, you should use `contratys()` or `contraregions()`,
20 // rather than inversing the order of arguments! This is necessary
21 // because the order of arguments is not relevant for LUB and GLB. It
22 // is also useful to track which value is the "expected" value in
23 // terms of error reporting.
25 use super::equate::Equate;
29 use super::type_variable::TypeVariableValue;
30 use super::unify_key::replace_if_possible;
31 use super::unify_key::{ConstVarValue, ConstVariableValue};
32 use super::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
33 use super::{InferCtxt, MiscVariable, TypeTrace};
35 use crate::traits::{Obligation, PredicateObligations};
37 use rustc_data_structures::sso::SsoHashMap;
38 use rustc_hir::def_id::DefId;
39 use rustc_middle::traits::ObligationCause;
40 use rustc_middle::ty::error::TypeError;
41 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
42 use rustc_middle::ty::subst::SubstsRef;
43 use rustc_middle::ty::{self, InferConst, ToPredicate, Ty, TyCtxt, TypeFoldable};
44 use rustc_middle::ty::{IntType, UintType};
45 use rustc_span::{Span, DUMMY_SP};
48 pub struct CombineFields<'infcx, 'tcx> {
49 pub infcx: &'infcx InferCtxt<'infcx, 'tcx>,
50 pub trace: TypeTrace<'tcx>,
51 pub cause: Option<ty::relate::Cause>,
52 pub param_env: ty::ParamEnv<'tcx>,
53 pub obligations: PredicateObligations<'tcx>,
56 #[derive(Copy, Clone, Debug)]
57 pub enum RelationDir {
63 impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
64 pub fn super_combine_tys<R>(
69 ) -> RelateResult<'tcx, Ty<'tcx>>
71 R: TypeRelation<'tcx>,
73 let a_is_expected = relation.a_is_expected();
75 match (a.kind(), b.kind()) {
76 // Relate integral variables to other types
77 (&ty::Infer(ty::IntVar(a_id)), &ty::Infer(ty::IntVar(b_id))) => {
80 .int_unification_table()
81 .unify_var_var(a_id, b_id)
82 .map_err(|e| int_unification_error(a_is_expected, e))?;
85 (&ty::Infer(ty::IntVar(v_id)), &ty::Int(v)) => {
86 self.unify_integral_variable(a_is_expected, v_id, IntType(v))
88 (&ty::Int(v), &ty::Infer(ty::IntVar(v_id))) => {
89 self.unify_integral_variable(!a_is_expected, v_id, IntType(v))
91 (&ty::Infer(ty::IntVar(v_id)), &ty::Uint(v)) => {
92 self.unify_integral_variable(a_is_expected, v_id, UintType(v))
94 (&ty::Uint(v), &ty::Infer(ty::IntVar(v_id))) => {
95 self.unify_integral_variable(!a_is_expected, v_id, UintType(v))
98 // Relate floating-point variables to other types
99 (&ty::Infer(ty::FloatVar(a_id)), &ty::Infer(ty::FloatVar(b_id))) => {
102 .float_unification_table()
103 .unify_var_var(a_id, b_id)
104 .map_err(|e| float_unification_error(relation.a_is_expected(), e))?;
107 (&ty::Infer(ty::FloatVar(v_id)), &ty::Float(v)) => {
108 self.unify_float_variable(a_is_expected, v_id, v)
110 (&ty::Float(v), &ty::Infer(ty::FloatVar(v_id))) => {
111 self.unify_float_variable(!a_is_expected, v_id, v)
114 // All other cases of inference are errors
115 (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
116 Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b)))
119 _ => ty::relate::super_relate_tys(relation, a, b),
123 pub fn super_combine_consts<R>(
126 a: &'tcx ty::Const<'tcx>,
127 b: &'tcx ty::Const<'tcx>,
128 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>>
130 R: ConstEquateRelation<'tcx>,
132 debug!("{}.consts({:?}, {:?})", relation.tag(), a, b);
137 let a = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table(), a);
138 let b = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table(), b);
140 let a_is_expected = relation.a_is_expected();
142 match (a.val, b.val) {
144 ty::ConstKind::Infer(InferConst::Var(a_vid)),
145 ty::ConstKind::Infer(InferConst::Var(b_vid)),
149 .const_unification_table()
150 .unify_var_var(a_vid, b_vid)
151 .map_err(|e| const_unification_error(a_is_expected, e))?;
155 // All other cases of inference with other variables are errors.
156 (ty::ConstKind::Infer(InferConst::Var(_)), ty::ConstKind::Infer(_))
157 | (ty::ConstKind::Infer(_), ty::ConstKind::Infer(InferConst::Var(_))) => {
158 bug!("tried to combine ConstKind::Infer/ConstKind::Infer(InferConst::Var)")
161 (ty::ConstKind::Infer(InferConst::Var(vid)), _) => {
162 return self.unify_const_variable(relation.param_env(), vid, b, a_is_expected);
165 (_, ty::ConstKind::Infer(InferConst::Var(vid))) => {
166 return self.unify_const_variable(relation.param_env(), vid, a, !a_is_expected);
168 (ty::ConstKind::Unevaluated(..), _) if self.tcx.lazy_normalization() => {
169 // FIXME(#59490): Need to remove the leak check to accommodate
170 // escaping bound variables here.
171 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
172 relation.const_equate_obligation(a, b);
176 (_, ty::ConstKind::Unevaluated(..)) if self.tcx.lazy_normalization() => {
177 // FIXME(#59490): Need to remove the leak check to accommodate
178 // escaping bound variables here.
179 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
180 relation.const_equate_obligation(a, b);
187 ty::relate::super_relate_consts(relation, a, b)
190 /// Unifies the const variable `target_vid` with the given constant.
192 /// This also tests if the given const `ct` contains an inference variable which was previously
193 /// unioned with `target_vid`. If this is the case, inferring `target_vid` to `ct`
194 /// would result in an infinite type as we continously replace an inference variable
195 /// in `ct` with `ct` itself.
197 /// This is especially important as unevaluated consts use their parents generics.
198 /// They therefore often contain unused substs, making these errors far more likely.
200 /// A good example of this is the following:
203 /// #![feature(const_generics)]
205 /// fn bind<const N: usize>(value: [u8; N]) -> [u8; 3 + 4] {
210 /// let mut arr = Default::default();
215 /// Here `3 + 4` ends up as `ConstKind::Unevaluated` which uses the generics
216 /// of `fn bind` (meaning that its substs contain `N`).
218 /// `bind(arr)` now infers that the type of `arr` must be `[u8; N]`.
219 /// The assignment `arr = bind(arr)` now tries to equate `N` with `3 + 4`.
221 /// As `3 + 4` contains `N` in its substs, this must not succeed.
223 /// See `src/test/ui/const-generics/occurs-check/` for more examples where this is relevant.
224 #[instrument(level = "debug", skip(self))]
225 fn unify_const_variable(
227 param_env: ty::ParamEnv<'tcx>,
228 target_vid: ty::ConstVid<'tcx>,
229 ct: &'tcx ty::Const<'tcx>,
230 vid_is_expected: bool,
231 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
232 let (for_universe, span) = {
233 let mut inner = self.inner.borrow_mut();
234 let variable_table = &mut inner.const_unification_table();
235 let var_value = variable_table.probe_value(target_vid);
236 match var_value.val {
237 ConstVariableValue::Known { value } => {
238 bug!("instantiating {:?} which has a known value {:?}", target_vid, value)
240 ConstVariableValue::Unknown { universe } => (universe, var_value.origin.span),
243 let value = ConstInferUnifier { infcx: self, span, param_env, for_universe, target_vid }
248 .const_unification_table()
252 origin: ConstVariableOrigin {
253 kind: ConstVariableOriginKind::ConstInference,
256 val: ConstVariableValue::Known { value },
260 .map_err(|e| const_unification_error(vid_is_expected, e))
263 fn unify_integral_variable(
265 vid_is_expected: bool,
267 val: ty::IntVarValue,
268 ) -> RelateResult<'tcx, Ty<'tcx>> {
271 .int_unification_table()
272 .unify_var_value(vid, Some(val))
273 .map_err(|e| int_unification_error(vid_is_expected, e))?;
275 IntType(v) => Ok(self.tcx.mk_mach_int(v)),
276 UintType(v) => Ok(self.tcx.mk_mach_uint(v)),
280 fn unify_float_variable(
282 vid_is_expected: bool,
285 ) -> RelateResult<'tcx, Ty<'tcx>> {
288 .float_unification_table()
289 .unify_var_value(vid, Some(ty::FloatVarValue(val)))
290 .map_err(|e| float_unification_error(vid_is_expected, e))?;
291 Ok(self.tcx.mk_mach_float(val))
295 impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
296 pub fn tcx(&self) -> TyCtxt<'tcx> {
300 pub fn equate<'a>(&'a mut self, a_is_expected: bool) -> Equate<'a, 'infcx, 'tcx> {
301 Equate::new(self, a_is_expected)
304 pub fn sub<'a>(&'a mut self, a_is_expected: bool) -> Sub<'a, 'infcx, 'tcx> {
305 Sub::new(self, a_is_expected)
308 pub fn lub<'a>(&'a mut self, a_is_expected: bool) -> Lub<'a, 'infcx, 'tcx> {
309 Lub::new(self, a_is_expected)
312 pub fn glb<'a>(&'a mut self, a_is_expected: bool) -> Glb<'a, 'infcx, 'tcx> {
313 Glb::new(self, a_is_expected)
316 /// Here, `dir` is either `EqTo`, `SubtypeOf`, or `SupertypeOf`.
317 /// The idea is that we should ensure that the type `a_ty` is equal
318 /// to, a subtype of, or a supertype of (respectively) the type
319 /// to which `b_vid` is bound.
321 /// Since `b_vid` has not yet been instantiated with a type, we
322 /// will first instantiate `b_vid` with a *generalized* version
323 /// of `a_ty`. Generalization introduces other inference
324 /// variables wherever subtyping could occur.
331 ) -> RelateResult<'tcx, ()> {
332 use self::RelationDir::*;
334 // Get the actual variable that b_vid has been inferred to
335 debug_assert!(self.infcx.inner.borrow_mut().type_variables().probe(b_vid).is_unknown());
337 debug!("instantiate(a_ty={:?} dir={:?} b_vid={:?})", a_ty, dir, b_vid);
339 // Generalize type of `a_ty` appropriately depending on the
340 // direction. As an example, assume:
342 // - `a_ty == &'x ?1`, where `'x` is some free region and `?1` is an
343 // inference variable,
344 // - and `dir` == `SubtypeOf`.
346 // Then the generalized form `b_ty` would be `&'?2 ?3`, where
347 // `'?2` and `?3` are fresh region/type inference
348 // variables. (Down below, we will relate `a_ty <: b_ty`,
349 // adding constraints like `'x: '?2` and `?1 <: ?3`.)
350 let Generalization { ty: b_ty, needs_wf } = self.generalize(a_ty, b_vid, dir)?;
352 "instantiate(a_ty={:?}, dir={:?}, b_vid={:?}, generalized b_ty={:?})",
353 a_ty, dir, b_vid, b_ty
355 self.infcx.inner.borrow_mut().type_variables().instantiate(b_vid, b_ty);
358 self.obligations.push(Obligation::new(
359 self.trace.cause.clone(),
361 ty::PredicateKind::WellFormed(b_ty.into()).to_predicate(self.infcx.tcx),
365 // Finally, relate `b_ty` to `a_ty`, as described in previous comment.
367 // FIXME(#16847): This code is non-ideal because all these subtype
368 // relations wind up attributed to the same spans. We need
369 // to associate causes/spans with each of the relations in
370 // the stack to get this right.
372 EqTo => self.equate(a_is_expected).relate(a_ty, b_ty),
373 SubtypeOf => self.sub(a_is_expected).relate(a_ty, b_ty),
375 self.sub(a_is_expected).relate_with_variance(ty::Contravariant, a_ty, b_ty)
382 /// Attempts to generalize `ty` for the type variable `for_vid`.
383 /// This checks for cycle -- that is, whether the type `ty`
384 /// references `for_vid`. The `dir` is the "direction" for which we
385 /// a performing the generalization (i.e., are we producing a type
386 /// that can be used as a supertype etc).
390 /// - `for_vid` is a "root vid"
396 ) -> RelateResult<'tcx, Generalization<'tcx>> {
397 debug!("generalize(ty={:?}, for_vid={:?}, dir={:?}", ty, for_vid, dir);
398 // Determine the ambient variance within which `ty` appears.
399 // The surrounding equation is:
403 // where `op` is either `==`, `<:`, or `:>`. This maps quite
405 let ambient_variance = match dir {
406 RelationDir::EqTo => ty::Invariant,
407 RelationDir::SubtypeOf => ty::Covariant,
408 RelationDir::SupertypeOf => ty::Contravariant,
411 debug!("generalize: ambient_variance = {:?}", ambient_variance);
413 let for_universe = match self.infcx.inner.borrow_mut().type_variables().probe(for_vid) {
414 v @ TypeVariableValue::Known { .. } => {
415 bug!("instantiating {:?} which has a known value {:?}", for_vid, v,)
417 TypeVariableValue::Unknown { universe } => universe,
420 debug!("generalize: for_universe = {:?}", for_universe);
421 debug!("generalize: trace = {:?}", self.trace);
423 let mut generalize = Generalizer {
425 cause: &self.trace.cause,
426 for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables().sub_root_var(for_vid),
431 param_env: self.param_env,
432 cache: SsoHashMap::new(),
435 let ty = match generalize.relate(ty, ty) {
438 debug!("generalize: failure {:?}", e);
442 let needs_wf = generalize.needs_wf;
443 debug!("generalize: success {{ {:?}, {:?} }}", ty, needs_wf);
444 Ok(Generalization { ty, needs_wf })
447 pub fn add_const_equate_obligation(
450 a: &'tcx ty::Const<'tcx>,
451 b: &'tcx ty::Const<'tcx>,
453 let predicate = if a_is_expected {
454 ty::PredicateKind::ConstEquate(a, b)
456 ty::PredicateKind::ConstEquate(b, a)
458 self.obligations.push(Obligation::new(
459 self.trace.cause.clone(),
461 predicate.to_predicate(self.tcx()),
466 struct Generalizer<'cx, 'tcx> {
467 infcx: &'cx InferCtxt<'cx, 'tcx>,
469 /// The span, used when creating new type variables and things.
470 cause: &'cx ObligationCause<'tcx>,
472 /// The vid of the type variable that is in the process of being
473 /// instantiated; if we find this within the type we are folding,
474 /// that means we would have created a cyclic type.
475 for_vid_sub_root: ty::TyVid,
477 /// The universe of the type variable that is in the process of
478 /// being instantiated. Any fresh variables that we create in this
479 /// process should be in that same universe.
480 for_universe: ty::UniverseIndex,
482 /// Track the variance as we descend into the type.
483 ambient_variance: ty::Variance,
485 /// See the field `needs_wf` in `Generalization`.
488 /// The root type that we are generalizing. Used when reporting cycles.
491 param_env: ty::ParamEnv<'tcx>,
493 cache: SsoHashMap<Ty<'tcx>, RelateResult<'tcx, Ty<'tcx>>>,
496 /// Result from a generalization operation. This includes
497 /// not only the generalized type, but also a bool flag
498 /// indicating whether further WF checks are needed.
499 struct Generalization<'tcx> {
502 /// If true, then the generalized type may not be well-formed,
503 /// even if the source type is well-formed, so we should add an
504 /// additional check to enforce that it is. This arises in
505 /// particular around 'bivariant' type parameters that are only
506 /// constrained by a where-clause. As an example, imagine a type:
508 /// struct Foo<A, B> where A: Iterator<Item = B> {
512 /// here, `A` will be covariant, but `B` is
513 /// unconstrained. However, whatever it is, for `Foo` to be WF, it
514 /// must be equal to `A::Item`. If we have an input `Foo<?A, ?B>`,
515 /// then after generalization we will wind up with a type like
516 /// `Foo<?C, ?D>`. When we enforce that `Foo<?A, ?B> <: Foo<?C,
517 /// ?D>` (or `>:`), we will wind up with the requirement that `?A
518 /// <: ?C`, but no particular relationship between `?B` and `?D`
519 /// (after all, we do not know the variance of the normalized form
520 /// of `A::Item` with respect to `A`). If we do nothing else, this
521 /// may mean that `?D` goes unconstrained (as in #41677). So, in
522 /// this scenario where we create a new type variable in a
523 /// bivariant context, we set the `needs_wf` flag to true. This
524 /// will force the calling code to check that `WF(Foo<?C, ?D>)`
525 /// holds, which in turn implies that `?C::Item == ?D`. So once
526 /// `?C` is constrained, that should suffice to restrict `?D`.
530 impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
531 fn tcx(&self) -> TyCtxt<'tcx> {
534 fn param_env(&self) -> ty::ParamEnv<'tcx> {
538 fn tag(&self) -> &'static str {
542 fn a_is_expected(&self) -> bool {
550 ) -> RelateResult<'tcx, ty::Binder<T>>
554 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
557 fn relate_item_substs(
560 a_subst: SubstsRef<'tcx>,
561 b_subst: SubstsRef<'tcx>,
562 ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
563 if self.ambient_variance == ty::Variance::Invariant {
564 // Avoid fetching the variance if we are in an invariant
565 // context; no need, and it can induce dependency cycles
567 relate::relate_substs(self, None, a_subst, b_subst)
569 let opt_variances = self.tcx().variances_of(item_def_id);
570 relate::relate_substs(self, Some(&opt_variances), a_subst, b_subst)
574 fn relate_with_variance<T: Relate<'tcx>>(
576 variance: ty::Variance,
579 ) -> RelateResult<'tcx, T> {
580 let old_ambient_variance = self.ambient_variance;
581 self.ambient_variance = self.ambient_variance.xform(variance);
583 let result = self.relate(a, b);
584 self.ambient_variance = old_ambient_variance;
588 fn tys(&mut self, t: Ty<'tcx>, t2: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
589 assert_eq!(t, t2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
591 if let Some(result) = self.cache.get(&t) {
592 return result.clone();
594 debug!("generalize: t={:?}", t);
596 // Check to see whether the type we are generalizing references
597 // any other type variable related to `vid` via
598 // subtyping. This is basically our "occurs check", preventing
599 // us from creating infinitely sized types.
600 let result = match *t.kind() {
601 ty::Infer(ty::TyVar(vid)) => {
602 let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
603 let sub_vid = self.infcx.inner.borrow_mut().type_variables().sub_root_var(vid);
604 if sub_vid == self.for_vid_sub_root {
605 // If sub-roots are equal, then `for_vid` and
606 // `vid` are related via subtyping.
607 Err(TypeError::CyclicTy(self.root_ty))
609 let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
611 TypeVariableValue::Known { value: u } => {
612 debug!("generalize: known value {:?}", u);
615 TypeVariableValue::Unknown { universe } => {
616 match self.ambient_variance {
617 // Invariant: no need to make a fresh type variable.
619 if self.for_universe.can_name(universe) {
624 // Bivariant: make a fresh var, but we
625 // may need a WF predicate. See
626 // comment on `needs_wf` field for
628 ty::Bivariant => self.needs_wf = true,
630 // Co/contravariant: this will be
631 // sufficiently constrained later on.
632 ty::Covariant | ty::Contravariant => (),
636 *self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
637 let new_var_id = self
642 .new_var(self.for_universe, false, origin);
643 let u = self.tcx().mk_ty_var(new_var_id);
644 debug!("generalize: replacing original vid={:?} with new={:?}", vid, u);
650 ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => {
651 // No matter what mode we are in,
652 // integer/floating-point types must be equal to be
656 _ => relate::super_relate_tys(self, t, t),
659 self.cache.insert(t, result.clone());
666 r2: ty::Region<'tcx>,
667 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
668 assert_eq!(r, r2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
670 debug!("generalize: regions r={:?}", r);
673 // Never make variables for regions bound within the type itself,
674 // nor for erased regions.
675 ty::ReLateBound(..) | ty::ReErased => {
679 ty::RePlaceholder(..)
683 | ty::ReEarlyBound(..)
684 | ty::ReFree(..) => {
685 // see common code below
689 // If we are in an invariant context, we can re-use the region
690 // as is, unless it happens to be in some universe that we
691 // can't name. (In the case of a region *variable*, we could
692 // use it if we promoted it into our universe, but we don't
694 if let ty::Invariant = self.ambient_variance {
695 let r_universe = self.infcx.universe_of_region(r);
696 if self.for_universe.can_name(r_universe) {
701 // FIXME: This is non-ideal because we don't give a
702 // very descriptive origin for this region variable.
703 Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.cause.span), self.for_universe))
708 c: &'tcx ty::Const<'tcx>,
709 c2: &'tcx ty::Const<'tcx>,
710 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
711 assert_eq!(c, c2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
714 ty::ConstKind::Infer(InferConst::Var(vid)) => {
715 let mut inner = self.infcx.inner.borrow_mut();
716 let variable_table = &mut inner.const_unification_table();
717 let var_value = variable_table.probe_value(vid);
718 match var_value.val {
719 ConstVariableValue::Known { value: u } => {
723 ConstVariableValue::Unknown { universe } => {
724 if self.for_universe.can_name(universe) {
727 let new_var_id = variable_table.new_key(ConstVarValue {
728 origin: var_value.origin,
729 val: ConstVariableValue::Unknown { universe: self.for_universe },
731 Ok(self.tcx().mk_const_var(new_var_id, c.ty))
736 ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
737 if self.tcx().lazy_normalization() =>
739 assert_eq!(promoted, None);
740 let substs = self.relate_with_variance(ty::Variance::Invariant, substs, substs)?;
741 Ok(self.tcx().mk_const(ty::Const {
743 val: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),
746 _ => relate::super_relate_consts(self, c, c),
751 pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
752 /// Register an obligation that both constants must be equal to each other.
754 /// If they aren't equal then the relation doesn't hold.
755 fn const_equate_obligation(&mut self, a: &'tcx ty::Const<'tcx>, b: &'tcx ty::Const<'tcx>);
758 pub trait RelateResultCompare<'tcx, T> {
759 fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T>
761 F: FnOnce() -> TypeError<'tcx>;
764 impl<'tcx, T: Clone + PartialEq> RelateResultCompare<'tcx, T> for RelateResult<'tcx, T> {
765 fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T>
767 F: FnOnce() -> TypeError<'tcx>,
769 self.clone().and_then(|s| if s == t { self.clone() } else { Err(f()) })
773 pub fn const_unification_error<'tcx>(
775 (a, b): (&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>),
776 ) -> TypeError<'tcx> {
777 TypeError::ConstMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))
780 fn int_unification_error<'tcx>(
782 v: (ty::IntVarValue, ty::IntVarValue),
783 ) -> TypeError<'tcx> {
785 TypeError::IntMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))
788 fn float_unification_error<'tcx>(
790 v: (ty::FloatVarValue, ty::FloatVarValue),
791 ) -> TypeError<'tcx> {
792 let (ty::FloatVarValue(a), ty::FloatVarValue(b)) = v;
793 TypeError::FloatMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))
796 struct ConstInferUnifier<'cx, 'tcx> {
797 infcx: &'cx InferCtxt<'cx, 'tcx>,
801 param_env: ty::ParamEnv<'tcx>,
803 for_universe: ty::UniverseIndex,
805 /// The vid of the const variable that is in the process of being
806 /// instantiated; if we find this within the const we are folding,
807 /// that means we would have created a cyclic const.
808 target_vid: ty::ConstVid<'tcx>,
811 // We use `TypeRelation` here to propagate `RelateResult` upwards.
813 // Both inputs are expected to be the same.
814 impl TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
815 fn tcx(&self) -> TyCtxt<'tcx> {
819 fn param_env(&self) -> ty::ParamEnv<'tcx> {
823 fn tag(&self) -> &'static str {
827 fn a_is_expected(&self) -> bool {
831 fn relate_with_variance<T: Relate<'tcx>>(
833 _variance: ty::Variance,
836 ) -> RelateResult<'tcx, T> {
837 // We don't care about variance here.
845 ) -> RelateResult<'tcx, ty::Binder<T>>
849 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
852 fn tys(&mut self, t: Ty<'tcx>, _t: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
853 debug_assert_eq!(t, _t);
854 debug!("ConstInferUnifier: t={:?}", t);
857 &ty::Infer(ty::TyVar(vid)) => {
858 let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
859 let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
861 TypeVariableValue::Known { value: u } => {
862 debug!("ConstOccursChecker: known value {:?}", u);
865 TypeVariableValue::Unknown { universe } => {
866 if self.for_universe.can_name(universe) {
871 *self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
872 let new_var_id = self.infcx.inner.borrow_mut().type_variables().new_var(
877 let u = self.tcx().mk_ty_var(new_var_id);
879 "ConstInferUnifier: replacing original vid={:?} with new={:?}",
886 ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => Ok(t),
887 _ => relate::super_relate_tys(self, t, t),
894 _r: ty::Region<'tcx>,
895 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
896 debug_assert_eq!(r, _r);
897 debug!("ConstInferUnifier: r={:?}", r);
900 // Never make variables for regions bound within the type itself,
901 // nor for erased regions.
902 ty::ReLateBound(..) | ty::ReErased => {
906 ty::RePlaceholder(..)
910 | ty::ReEarlyBound(..)
911 | ty::ReFree(..) => {
912 // see common code below
916 let r_universe = self.infcx.universe_of_region(r);
917 if self.for_universe.can_name(r_universe) {
920 // FIXME: This is non-ideal because we don't give a
921 // very descriptive origin for this region variable.
922 Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.span), self.for_universe))
928 c: &'tcx ty::Const<'tcx>,
929 _c: &'tcx ty::Const<'tcx>,
930 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
931 debug_assert_eq!(c, _c);
932 debug!("ConstInferUnifier: c={:?}", c);
935 ty::ConstKind::Infer(InferConst::Var(vid)) => {
936 let mut inner = self.infcx.inner.borrow_mut();
937 let variable_table = &mut inner.const_unification_table();
939 // Check if the current unification would end up
940 // unifying `target_vid` with a const which contains
941 // an inference variable which is unioned with `target_vid`.
943 // Not doing so can easily result in stack overflows.
944 if variable_table.unioned(self.target_vid, vid) {
945 return Err(TypeError::CyclicConst(c));
948 let var_value = variable_table.probe_value(vid);
949 match var_value.val {
950 ConstVariableValue::Known { value: u } => self.consts(u, u),
951 ConstVariableValue::Unknown { universe } => {
952 if self.for_universe.can_name(universe) {
955 let new_var_id = variable_table.new_key(ConstVarValue {
956 origin: var_value.origin,
957 val: ConstVariableValue::Unknown { universe: self.for_universe },
959 Ok(self.tcx().mk_const_var(new_var_id, c.ty))
964 ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
965 if self.tcx().lazy_normalization() =>
967 assert_eq!(promoted, None);
968 let substs = self.relate_with_variance(ty::Variance::Invariant, substs, substs)?;
969 Ok(self.tcx().mk_const(ty::Const {
971 val: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),
974 _ => relate::super_relate_consts(self, c, c),