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::{ExpectedFound, 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>(
128 ) -> RelateResult<'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 continuously 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(generic_const_exprs)]
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>,
230 vid_is_expected: bool,
231 ) -> RelateResult<'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::Binder::dummy(ty::PredicateKind::WellFormed(b_ty.into()))
362 .to_predicate(self.infcx.tcx),
366 // Finally, relate `b_ty` to `a_ty`, as described in previous comment.
368 // FIXME(#16847): This code is non-ideal because all these subtype
369 // relations wind up attributed to the same spans. We need
370 // to associate causes/spans with each of the relations in
371 // the stack to get this right.
373 EqTo => self.equate(a_is_expected).relate(a_ty, b_ty),
374 SubtypeOf => self.sub(a_is_expected).relate(a_ty, b_ty),
375 SupertypeOf => self.sub(a_is_expected).relate_with_variance(
377 ty::VarianceDiagInfo::default(),
386 /// Attempts to generalize `ty` for the type variable `for_vid`.
387 /// This checks for cycle -- that is, whether the type `ty`
388 /// references `for_vid`. The `dir` is the "direction" for which we
389 /// a performing the generalization (i.e., are we producing a type
390 /// that can be used as a supertype etc).
394 /// - `for_vid` is a "root vid"
400 ) -> RelateResult<'tcx, Generalization<'tcx>> {
401 debug!("generalize(ty={:?}, for_vid={:?}, dir={:?}", ty, for_vid, dir);
402 // Determine the ambient variance within which `ty` appears.
403 // The surrounding equation is:
407 // where `op` is either `==`, `<:`, or `:>`. This maps quite
409 let ambient_variance = match dir {
410 RelationDir::EqTo => ty::Invariant,
411 RelationDir::SubtypeOf => ty::Covariant,
412 RelationDir::SupertypeOf => ty::Contravariant,
415 debug!("generalize: ambient_variance = {:?}", ambient_variance);
417 let for_universe = match self.infcx.inner.borrow_mut().type_variables().probe(for_vid) {
418 v @ TypeVariableValue::Known { .. } => {
419 bug!("instantiating {:?} which has a known value {:?}", for_vid, v,)
421 TypeVariableValue::Unknown { universe } => universe,
424 debug!("generalize: for_universe = {:?}", for_universe);
425 debug!("generalize: trace = {:?}", self.trace);
427 let mut generalize = Generalizer {
429 cause: &self.trace.cause,
430 for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables().sub_root_var(for_vid),
435 param_env: self.param_env,
436 cache: SsoHashMap::new(),
439 let ty = match generalize.relate(ty, ty) {
442 debug!("generalize: failure {:?}", e);
446 let needs_wf = generalize.needs_wf;
447 debug!("generalize: success {{ {:?}, {:?} }}", ty, needs_wf);
448 Ok(Generalization { ty, needs_wf })
451 pub fn add_const_equate_obligation(
457 let predicate = if a_is_expected {
458 ty::PredicateKind::ConstEquate(a, b)
460 ty::PredicateKind::ConstEquate(b, a)
462 self.obligations.push(Obligation::new(
463 self.trace.cause.clone(),
465 ty::Binder::dummy(predicate).to_predicate(self.tcx()),
470 struct Generalizer<'cx, 'tcx> {
471 infcx: &'cx InferCtxt<'cx, 'tcx>,
473 /// The span, used when creating new type variables and things.
474 cause: &'cx ObligationCause<'tcx>,
476 /// The vid of the type variable that is in the process of being
477 /// instantiated; if we find this within the type we are folding,
478 /// that means we would have created a cyclic type.
479 for_vid_sub_root: ty::TyVid,
481 /// The universe of the type variable that is in the process of
482 /// being instantiated. Any fresh variables that we create in this
483 /// process should be in that same universe.
484 for_universe: ty::UniverseIndex,
486 /// Track the variance as we descend into the type.
487 ambient_variance: ty::Variance,
489 /// See the field `needs_wf` in `Generalization`.
492 /// The root type that we are generalizing. Used when reporting cycles.
495 param_env: ty::ParamEnv<'tcx>,
497 cache: SsoHashMap<Ty<'tcx>, RelateResult<'tcx, Ty<'tcx>>>,
500 /// Result from a generalization operation. This includes
501 /// not only the generalized type, but also a bool flag
502 /// indicating whether further WF checks are needed.
503 struct Generalization<'tcx> {
506 /// If true, then the generalized type may not be well-formed,
507 /// even if the source type is well-formed, so we should add an
508 /// additional check to enforce that it is. This arises in
509 /// particular around 'bivariant' type parameters that are only
510 /// constrained by a where-clause. As an example, imagine a type:
512 /// struct Foo<A, B> where A: Iterator<Item = B> {
516 /// here, `A` will be covariant, but `B` is
517 /// unconstrained. However, whatever it is, for `Foo` to be WF, it
518 /// must be equal to `A::Item`. If we have an input `Foo<?A, ?B>`,
519 /// then after generalization we will wind up with a type like
520 /// `Foo<?C, ?D>`. When we enforce that `Foo<?A, ?B> <: Foo<?C,
521 /// ?D>` (or `>:`), we will wind up with the requirement that `?A
522 /// <: ?C`, but no particular relationship between `?B` and `?D`
523 /// (after all, we do not know the variance of the normalized form
524 /// of `A::Item` with respect to `A`). If we do nothing else, this
525 /// may mean that `?D` goes unconstrained (as in #41677). So, in
526 /// this scenario where we create a new type variable in a
527 /// bivariant context, we set the `needs_wf` flag to true. This
528 /// will force the calling code to check that `WF(Foo<?C, ?D>)`
529 /// holds, which in turn implies that `?C::Item == ?D`. So once
530 /// `?C` is constrained, that should suffice to restrict `?D`.
534 impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
535 fn tcx(&self) -> TyCtxt<'tcx> {
538 fn param_env(&self) -> ty::ParamEnv<'tcx> {
542 fn tag(&self) -> &'static str {
546 fn a_is_expected(&self) -> bool {
552 a: ty::Binder<'tcx, T>,
553 b: ty::Binder<'tcx, T>,
554 ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
558 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
561 fn relate_item_substs(
564 a_subst: SubstsRef<'tcx>,
565 b_subst: SubstsRef<'tcx>,
566 ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
567 if self.ambient_variance == ty::Variance::Invariant {
568 // Avoid fetching the variance if we are in an invariant
569 // context; no need, and it can induce dependency cycles
571 relate::relate_substs(self, None, a_subst, b_subst)
573 let tcx = self.tcx();
574 let opt_variances = tcx.variances_of(item_def_id);
575 relate::relate_substs(self, Some((item_def_id, &opt_variances)), a_subst, b_subst)
579 fn relate_with_variance<T: Relate<'tcx>>(
581 variance: ty::Variance,
582 _info: ty::VarianceDiagInfo<'tcx>,
585 ) -> RelateResult<'tcx, T> {
586 let old_ambient_variance = self.ambient_variance;
587 self.ambient_variance = self.ambient_variance.xform(variance);
589 let result = self.relate(a, b);
590 self.ambient_variance = old_ambient_variance;
594 fn tys(&mut self, t: Ty<'tcx>, t2: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
595 assert_eq!(t, t2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
597 if let Some(result) = self.cache.get(&t) {
598 return result.clone();
600 debug!("generalize: t={:?}", t);
602 // Check to see whether the type we are generalizing references
603 // any other type variable related to `vid` via
604 // subtyping. This is basically our "occurs check", preventing
605 // us from creating infinitely sized types.
606 let result = match *t.kind() {
607 ty::Infer(ty::TyVar(vid)) => {
608 let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
609 let sub_vid = self.infcx.inner.borrow_mut().type_variables().sub_root_var(vid);
610 if sub_vid == self.for_vid_sub_root {
611 // If sub-roots are equal, then `for_vid` and
612 // `vid` are related via subtyping.
613 Err(TypeError::CyclicTy(self.root_ty))
615 let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
617 TypeVariableValue::Known { value: u } => {
618 debug!("generalize: known value {:?}", u);
621 TypeVariableValue::Unknown { universe } => {
622 match self.ambient_variance {
623 // Invariant: no need to make a fresh type variable.
625 if self.for_universe.can_name(universe) {
630 // Bivariant: make a fresh var, but we
631 // may need a WF predicate. See
632 // comment on `needs_wf` field for
634 ty::Bivariant => self.needs_wf = true,
636 // Co/contravariant: this will be
637 // sufficiently constrained later on.
638 ty::Covariant | ty::Contravariant => (),
642 *self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
643 let new_var_id = self
648 .new_var(self.for_universe, origin);
649 let u = self.tcx().mk_ty_var(new_var_id);
651 // Record that we replaced `vid` with `new_var_id` as part of a generalization
652 // operation. This is needed to detect cyclic types. To see why, see the
653 // docs in the `type_variables` module.
654 self.infcx.inner.borrow_mut().type_variables().sub(vid, new_var_id);
655 debug!("generalize: replacing original vid={:?} with new={:?}", vid, u);
661 ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => {
662 // No matter what mode we are in,
663 // integer/floating-point types must be equal to be
667 _ => relate::super_relate_tys(self, t, t),
670 self.cache.insert(t, result.clone());
677 r2: ty::Region<'tcx>,
678 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
679 assert_eq!(r, r2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
681 debug!("generalize: regions r={:?}", r);
684 // Never make variables for regions bound within the type itself,
685 // nor for erased regions.
686 ty::ReLateBound(..) | ty::ReErased => {
690 ty::RePlaceholder(..)
694 | ty::ReEarlyBound(..)
695 | ty::ReFree(..) => {
696 // see common code below
700 // If we are in an invariant context, we can re-use the region
701 // as is, unless it happens to be in some universe that we
702 // can't name. (In the case of a region *variable*, we could
703 // use it if we promoted it into our universe, but we don't
705 if let ty::Invariant = self.ambient_variance {
706 let r_universe = self.infcx.universe_of_region(r);
707 if self.for_universe.can_name(r_universe) {
712 // FIXME: This is non-ideal because we don't give a
713 // very descriptive origin for this region variable.
714 Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.cause.span), self.for_universe))
721 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
722 assert_eq!(c, c2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
725 ty::ConstKind::Infer(InferConst::Var(vid)) => {
726 let mut inner = self.infcx.inner.borrow_mut();
727 let variable_table = &mut inner.const_unification_table();
728 let var_value = variable_table.probe_value(vid);
729 match var_value.val {
730 ConstVariableValue::Known { value: u } => {
734 ConstVariableValue::Unknown { universe } => {
735 if self.for_universe.can_name(universe) {
738 let new_var_id = variable_table.new_key(ConstVarValue {
739 origin: var_value.origin,
740 val: ConstVariableValue::Unknown { universe: self.for_universe },
742 Ok(self.tcx().mk_const_var(new_var_id, c.ty()))
747 ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
748 if self.tcx().lazy_normalization() =>
750 assert_eq!(promoted, None);
751 let substs = self.relate_with_variance(
752 ty::Variance::Invariant,
753 ty::VarianceDiagInfo::default(),
757 Ok(self.tcx().mk_const(ty::ConstS {
759 val: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),
762 _ => relate::super_relate_consts(self, c, c),
767 pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
768 /// Register an obligation that both constants must be equal to each other.
770 /// If they aren't equal then the relation doesn't hold.
771 fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>);
774 pub trait RelateResultCompare<'tcx, T> {
775 fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T>
777 F: FnOnce() -> TypeError<'tcx>;
780 impl<'tcx, T: Clone + PartialEq> RelateResultCompare<'tcx, T> for RelateResult<'tcx, T> {
781 fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T>
783 F: FnOnce() -> TypeError<'tcx>,
785 self.clone().and_then(|s| if s == t { self.clone() } else { Err(f()) })
789 pub fn const_unification_error<'tcx>(
791 (a, b): (ty::Const<'tcx>, ty::Const<'tcx>),
792 ) -> TypeError<'tcx> {
793 TypeError::ConstMismatch(ExpectedFound::new(a_is_expected, a, b))
796 fn int_unification_error<'tcx>(
798 v: (ty::IntVarValue, ty::IntVarValue),
799 ) -> TypeError<'tcx> {
801 TypeError::IntMismatch(ExpectedFound::new(a_is_expected, a, b))
804 fn float_unification_error<'tcx>(
806 v: (ty::FloatVarValue, ty::FloatVarValue),
807 ) -> TypeError<'tcx> {
808 let (ty::FloatVarValue(a), ty::FloatVarValue(b)) = v;
809 TypeError::FloatMismatch(ExpectedFound::new(a_is_expected, a, b))
812 struct ConstInferUnifier<'cx, 'tcx> {
813 infcx: &'cx InferCtxt<'cx, 'tcx>,
817 param_env: ty::ParamEnv<'tcx>,
819 for_universe: ty::UniverseIndex,
821 /// The vid of the const variable that is in the process of being
822 /// instantiated; if we find this within the const we are folding,
823 /// that means we would have created a cyclic const.
824 target_vid: ty::ConstVid<'tcx>,
827 // We use `TypeRelation` here to propagate `RelateResult` upwards.
829 // Both inputs are expected to be the same.
830 impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
831 fn tcx(&self) -> TyCtxt<'tcx> {
835 fn param_env(&self) -> ty::ParamEnv<'tcx> {
839 fn tag(&self) -> &'static str {
843 fn a_is_expected(&self) -> bool {
847 fn relate_with_variance<T: Relate<'tcx>>(
849 _variance: ty::Variance,
850 _info: ty::VarianceDiagInfo<'tcx>,
853 ) -> RelateResult<'tcx, T> {
854 // We don't care about variance here.
860 a: ty::Binder<'tcx, T>,
861 b: ty::Binder<'tcx, T>,
862 ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
866 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
869 #[tracing::instrument(level = "debug", skip(self))]
870 fn tys(&mut self, t: Ty<'tcx>, _t: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
871 debug_assert_eq!(t, _t);
872 debug!("ConstInferUnifier: t={:?}", t);
875 &ty::Infer(ty::TyVar(vid)) => {
876 let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
877 let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
879 TypeVariableValue::Known { value: u } => {
880 debug!("ConstOccursChecker: known value {:?}", u);
883 TypeVariableValue::Unknown { universe } => {
884 if self.for_universe.can_name(universe) {
889 *self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
890 let new_var_id = self
895 .new_var(self.for_universe, origin);
896 let u = self.tcx().mk_ty_var(new_var_id);
898 "ConstInferUnifier: replacing original vid={:?} with new={:?}",
905 ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => Ok(t),
906 _ => relate::super_relate_tys(self, t, t),
913 _r: ty::Region<'tcx>,
914 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
915 debug_assert_eq!(r, _r);
916 debug!("ConstInferUnifier: r={:?}", r);
919 // Never make variables for regions bound within the type itself,
920 // nor for erased regions.
921 ty::ReLateBound(..) | ty::ReErased => {
925 ty::RePlaceholder(..)
929 | ty::ReEarlyBound(..)
930 | ty::ReFree(..) => {
931 // see common code below
935 let r_universe = self.infcx.universe_of_region(r);
936 if self.for_universe.can_name(r_universe) {
939 // FIXME: This is non-ideal because we don't give a
940 // very descriptive origin for this region variable.
941 Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.span), self.for_universe))
945 #[tracing::instrument(level = "debug", skip(self))]
950 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
951 debug_assert_eq!(c, _c);
952 debug!("ConstInferUnifier: c={:?}", c);
955 ty::ConstKind::Infer(InferConst::Var(vid)) => {
956 // Check if the current unification would end up
957 // unifying `target_vid` with a const which contains
958 // an inference variable which is unioned with `target_vid`.
960 // Not doing so can easily result in stack overflows.
965 .const_unification_table()
966 .unioned(self.target_vid, vid)
968 return Err(TypeError::CyclicConst(c));
972 self.infcx.inner.borrow_mut().const_unification_table().probe_value(vid);
973 match var_value.val {
974 ConstVariableValue::Known { value: u } => self.consts(u, u),
975 ConstVariableValue::Unknown { universe } => {
976 if self.for_universe.can_name(universe) {
980 self.infcx.inner.borrow_mut().const_unification_table().new_key(
982 origin: var_value.origin,
983 val: ConstVariableValue::Unknown {
984 universe: self.for_universe,
988 Ok(self.tcx().mk_const_var(new_var_id, c.ty()))
993 ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
994 if self.tcx().lazy_normalization() =>
996 assert_eq!(promoted, None);
997 let substs = self.relate_with_variance(
998 ty::Variance::Invariant,
999 ty::VarianceDiagInfo::default(),
1003 Ok(self.tcx().mk_const(ty::ConstS {
1005 val: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),
1008 _ => relate::super_relate_consts(self, c, c),