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::{InferCtxt, MiscVariable, TypeTrace};
31 use crate::traits::{Obligation, PredicateObligations};
32 use rustc_data_structures::sso::SsoHashMap;
33 use rustc_hir::def_id::DefId;
34 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
35 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
36 use rustc_middle::traits::ObligationCause;
37 use rustc_middle::ty::error::{ExpectedFound, TypeError};
38 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
39 use rustc_middle::ty::subst::SubstsRef;
40 use rustc_middle::ty::{self, InferConst, ToPredicate, Ty, TyCtxt, TypeFoldable};
41 use rustc_middle::ty::{IntType, UintType};
42 use rustc_span::{Span, DUMMY_SP};
45 pub struct CombineFields<'infcx, 'tcx> {
46 pub infcx: &'infcx InferCtxt<'infcx, 'tcx>,
47 pub trace: TypeTrace<'tcx>,
48 pub cause: Option<ty::relate::Cause>,
49 pub param_env: ty::ParamEnv<'tcx>,
50 pub obligations: PredicateObligations<'tcx>,
51 /// Whether we should define opaque types
52 /// or just treat them opaquely.
53 /// Currently only used to prevent predicate
54 /// matching from matching anything against opaque
56 pub define_opaque_types: bool,
59 #[derive(Copy, Clone, Debug)]
60 pub enum RelationDir {
66 impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
67 pub fn super_combine_tys<R>(
72 ) -> RelateResult<'tcx, Ty<'tcx>>
74 R: TypeRelation<'tcx>,
76 let a_is_expected = relation.a_is_expected();
78 match (a.kind(), b.kind()) {
79 // Relate integral variables to other types
80 (&ty::Infer(ty::IntVar(a_id)), &ty::Infer(ty::IntVar(b_id))) => {
83 .int_unification_table()
84 .unify_var_var(a_id, b_id)
85 .map_err(|e| int_unification_error(a_is_expected, e))?;
88 (&ty::Infer(ty::IntVar(v_id)), &ty::Int(v)) => {
89 self.unify_integral_variable(a_is_expected, v_id, IntType(v))
91 (&ty::Int(v), &ty::Infer(ty::IntVar(v_id))) => {
92 self.unify_integral_variable(!a_is_expected, v_id, IntType(v))
94 (&ty::Infer(ty::IntVar(v_id)), &ty::Uint(v)) => {
95 self.unify_integral_variable(a_is_expected, v_id, UintType(v))
97 (&ty::Uint(v), &ty::Infer(ty::IntVar(v_id))) => {
98 self.unify_integral_variable(!a_is_expected, v_id, UintType(v))
101 // Relate floating-point variables to other types
102 (&ty::Infer(ty::FloatVar(a_id)), &ty::Infer(ty::FloatVar(b_id))) => {
105 .float_unification_table()
106 .unify_var_var(a_id, b_id)
107 .map_err(|e| float_unification_error(relation.a_is_expected(), e))?;
110 (&ty::Infer(ty::FloatVar(v_id)), &ty::Float(v)) => {
111 self.unify_float_variable(a_is_expected, v_id, v)
113 (&ty::Float(v), &ty::Infer(ty::FloatVar(v_id))) => {
114 self.unify_float_variable(!a_is_expected, v_id, v)
117 // All other cases of inference are errors
118 (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
119 Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b)))
122 _ => ty::relate::super_relate_tys(relation, a, b),
126 pub fn super_combine_consts<R>(
131 ) -> RelateResult<'tcx, ty::Const<'tcx>>
133 R: ConstEquateRelation<'tcx>,
135 debug!("{}.consts({:?}, {:?})", relation.tag(), a, b);
140 let a = self.shallow_resolve(a);
141 let b = self.shallow_resolve(b);
143 let a_is_expected = relation.a_is_expected();
145 match (a.val(), b.val()) {
147 ty::ConstKind::Infer(InferConst::Var(a_vid)),
148 ty::ConstKind::Infer(InferConst::Var(b_vid)),
152 .const_unification_table()
153 .unify_var_var(a_vid, b_vid)
154 .map_err(|e| const_unification_error(a_is_expected, e))?;
158 // All other cases of inference with other variables are errors.
159 (ty::ConstKind::Infer(InferConst::Var(_)), ty::ConstKind::Infer(_))
160 | (ty::ConstKind::Infer(_), ty::ConstKind::Infer(InferConst::Var(_))) => {
161 bug!("tried to combine ConstKind::Infer/ConstKind::Infer(InferConst::Var)")
164 (ty::ConstKind::Infer(InferConst::Var(vid)), _) => {
165 return self.unify_const_variable(relation.param_env(), vid, b, a_is_expected);
168 (_, ty::ConstKind::Infer(InferConst::Var(vid))) => {
169 return self.unify_const_variable(relation.param_env(), vid, a, !a_is_expected);
171 (ty::ConstKind::Unevaluated(..), _) if self.tcx.lazy_normalization() => {
172 // FIXME(#59490): Need to remove the leak check to accommodate
173 // escaping bound variables here.
174 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
175 relation.const_equate_obligation(a, b);
179 (_, ty::ConstKind::Unevaluated(..)) if self.tcx.lazy_normalization() => {
180 // FIXME(#59490): Need to remove the leak check to accommodate
181 // escaping bound variables here.
182 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
183 relation.const_equate_obligation(a, b);
190 ty::relate::super_relate_consts(relation, a, b)
193 /// Unifies the const variable `target_vid` with the given constant.
195 /// This also tests if the given const `ct` contains an inference variable which was previously
196 /// unioned with `target_vid`. If this is the case, inferring `target_vid` to `ct`
197 /// would result in an infinite type as we continuously replace an inference variable
198 /// in `ct` with `ct` itself.
200 /// This is especially important as unevaluated consts use their parents generics.
201 /// They therefore often contain unused substs, making these errors far more likely.
203 /// A good example of this is the following:
205 /// ```compile_fail,E0308
206 /// #![feature(generic_const_exprs)]
208 /// fn bind<const N: usize>(value: [u8; N]) -> [u8; 3 + 4] {
213 /// let mut arr = Default::default();
218 /// Here `3 + 4` ends up as `ConstKind::Unevaluated` which uses the generics
219 /// of `fn bind` (meaning that its substs contain `N`).
221 /// `bind(arr)` now infers that the type of `arr` must be `[u8; N]`.
222 /// The assignment `arr = bind(arr)` now tries to equate `N` with `3 + 4`.
224 /// As `3 + 4` contains `N` in its substs, this must not succeed.
226 /// See `src/test/ui/const-generics/occurs-check/` for more examples where this is relevant.
227 #[instrument(level = "debug", skip(self))]
228 fn unify_const_variable(
230 param_env: ty::ParamEnv<'tcx>,
231 target_vid: ty::ConstVid<'tcx>,
233 vid_is_expected: bool,
234 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
235 let (for_universe, span) = {
236 let mut inner = self.inner.borrow_mut();
237 let variable_table = &mut inner.const_unification_table();
238 let var_value = variable_table.probe_value(target_vid);
239 match var_value.val {
240 ConstVariableValue::Known { value } => {
241 bug!("instantiating {:?} which has a known value {:?}", target_vid, value)
243 ConstVariableValue::Unknown { universe } => (universe, var_value.origin.span),
246 let value = ConstInferUnifier { infcx: self, span, param_env, for_universe, target_vid }
251 .const_unification_table()
255 origin: ConstVariableOrigin {
256 kind: ConstVariableOriginKind::ConstInference,
259 val: ConstVariableValue::Known { value },
263 .map_err(|e| const_unification_error(vid_is_expected, e))
266 fn unify_integral_variable(
268 vid_is_expected: bool,
270 val: ty::IntVarValue,
271 ) -> RelateResult<'tcx, Ty<'tcx>> {
274 .int_unification_table()
275 .unify_var_value(vid, Some(val))
276 .map_err(|e| int_unification_error(vid_is_expected, e))?;
278 IntType(v) => Ok(self.tcx.mk_mach_int(v)),
279 UintType(v) => Ok(self.tcx.mk_mach_uint(v)),
283 fn unify_float_variable(
285 vid_is_expected: bool,
288 ) -> RelateResult<'tcx, Ty<'tcx>> {
291 .float_unification_table()
292 .unify_var_value(vid, Some(ty::FloatVarValue(val)))
293 .map_err(|e| float_unification_error(vid_is_expected, e))?;
294 Ok(self.tcx.mk_mach_float(val))
298 impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
299 pub fn tcx(&self) -> TyCtxt<'tcx> {
303 pub fn equate<'a>(&'a mut self, a_is_expected: bool) -> Equate<'a, 'infcx, 'tcx> {
304 Equate::new(self, a_is_expected)
307 pub fn sub<'a>(&'a mut self, a_is_expected: bool) -> Sub<'a, 'infcx, 'tcx> {
308 Sub::new(self, a_is_expected)
311 pub fn lub<'a>(&'a mut self, a_is_expected: bool) -> Lub<'a, 'infcx, 'tcx> {
312 Lub::new(self, a_is_expected)
315 pub fn glb<'a>(&'a mut self, a_is_expected: bool) -> Glb<'a, 'infcx, 'tcx> {
316 Glb::new(self, a_is_expected)
319 /// Here, `dir` is either `EqTo`, `SubtypeOf`, or `SupertypeOf`.
320 /// The idea is that we should ensure that the type `a_ty` is equal
321 /// to, a subtype of, or a supertype of (respectively) the type
322 /// to which `b_vid` is bound.
324 /// Since `b_vid` has not yet been instantiated with a type, we
325 /// will first instantiate `b_vid` with a *generalized* version
326 /// of `a_ty`. Generalization introduces other inference
327 /// variables wherever subtyping could occur.
328 #[instrument(skip(self), level = "debug")]
335 ) -> RelateResult<'tcx, ()> {
336 use self::RelationDir::*;
338 // Get the actual variable that b_vid has been inferred to
339 debug_assert!(self.infcx.inner.borrow_mut().type_variables().probe(b_vid).is_unknown());
341 // Generalize type of `a_ty` appropriately depending on the
342 // direction. As an example, assume:
344 // - `a_ty == &'x ?1`, where `'x` is some free region and `?1` is an
345 // inference variable,
346 // - and `dir` == `SubtypeOf`.
348 // Then the generalized form `b_ty` would be `&'?2 ?3`, where
349 // `'?2` and `?3` are fresh region/type inference
350 // variables. (Down below, we will relate `a_ty <: b_ty`,
351 // adding constraints like `'x: '?2` and `?1 <: ?3`.)
352 let Generalization { ty: b_ty, needs_wf } = self.generalize(a_ty, b_vid, dir)?;
354 self.infcx.inner.borrow_mut().type_variables().instantiate(b_vid, b_ty);
357 self.obligations.push(Obligation::new(
358 self.trace.cause.clone(),
360 ty::Binder::dummy(ty::PredicateKind::WellFormed(b_ty.into()))
361 .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),
374 SupertypeOf => self.sub(a_is_expected).relate_with_variance(
376 ty::VarianceDiagInfo::default(),
385 /// Attempts to generalize `ty` for the type variable `for_vid`.
386 /// This checks for cycle -- that is, whether the type `ty`
387 /// references `for_vid`. The `dir` is the "direction" for which we
388 /// a performing the generalization (i.e., are we producing a type
389 /// that can be used as a supertype etc).
393 /// - `for_vid` is a "root vid"
394 #[instrument(skip(self), level = "trace")]
400 ) -> RelateResult<'tcx, Generalization<'tcx>> {
401 // Determine the ambient variance within which `ty` appears.
402 // The surrounding equation is:
406 // where `op` is either `==`, `<:`, or `:>`. This maps quite
408 let ambient_variance = match dir {
409 RelationDir::EqTo => ty::Invariant,
410 RelationDir::SubtypeOf => ty::Covariant,
411 RelationDir::SupertypeOf => ty::Contravariant,
414 trace!(?ambient_variance);
416 let for_universe = match self.infcx.inner.borrow_mut().type_variables().probe(for_vid) {
417 v @ TypeVariableValue::Known { .. } => {
418 bug!("instantiating {:?} which has a known value {:?}", for_vid, v,)
420 TypeVariableValue::Unknown { universe } => universe,
423 trace!(?for_universe);
426 let mut generalize = Generalizer {
428 cause: &self.trace.cause,
429 for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables().sub_root_var(for_vid),
434 param_env: self.param_env,
435 cache: SsoHashMap::new(),
438 let ty = match generalize.relate(ty, ty) {
441 debug!(?e, "failure");
445 let needs_wf = generalize.needs_wf;
446 trace!(?ty, ?needs_wf, "success");
447 Ok(Generalization { ty, needs_wf })
450 pub fn add_const_equate_obligation(
456 let predicate = if a_is_expected {
457 ty::PredicateKind::ConstEquate(a, b)
459 ty::PredicateKind::ConstEquate(b, a)
461 self.obligations.push(Obligation::new(
462 self.trace.cause.clone(),
464 ty::Binder::dummy(predicate).to_predicate(self.tcx()),
469 struct Generalizer<'cx, 'tcx> {
470 infcx: &'cx InferCtxt<'cx, 'tcx>,
472 /// The span, used when creating new type variables and things.
473 cause: &'cx ObligationCause<'tcx>,
475 /// The vid of the type variable that is in the process of being
476 /// instantiated; if we find this within the type we are folding,
477 /// that means we would have created a cyclic type.
478 for_vid_sub_root: ty::TyVid,
480 /// The universe of the type variable that is in the process of
481 /// being instantiated. Any fresh variables that we create in this
482 /// process should be in that same universe.
483 for_universe: ty::UniverseIndex,
485 /// Track the variance as we descend into the type.
486 ambient_variance: ty::Variance,
488 /// See the field `needs_wf` in `Generalization`.
491 /// The root type that we are generalizing. Used when reporting cycles.
494 param_env: ty::ParamEnv<'tcx>,
496 cache: SsoHashMap<Ty<'tcx>, RelateResult<'tcx, Ty<'tcx>>>,
499 /// Result from a generalization operation. This includes
500 /// not only the generalized type, but also a bool flag
501 /// indicating whether further WF checks are needed.
502 struct Generalization<'tcx> {
505 /// If true, then the generalized type may not be well-formed,
506 /// even if the source type is well-formed, so we should add an
507 /// additional check to enforce that it is. This arises in
508 /// particular around 'bivariant' type parameters that are only
509 /// constrained by a where-clause. As an example, imagine a type:
511 /// struct Foo<A, B> where A: Iterator<Item = B> {
515 /// here, `A` will be covariant, but `B` is
516 /// unconstrained. However, whatever it is, for `Foo` to be WF, it
517 /// must be equal to `A::Item`. If we have an input `Foo<?A, ?B>`,
518 /// then after generalization we will wind up with a type like
519 /// `Foo<?C, ?D>`. When we enforce that `Foo<?A, ?B> <: Foo<?C,
520 /// ?D>` (or `>:`), we will wind up with the requirement that `?A
521 /// <: ?C`, but no particular relationship between `?B` and `?D`
522 /// (after all, we do not know the variance of the normalized form
523 /// of `A::Item` with respect to `A`). If we do nothing else, this
524 /// may mean that `?D` goes unconstrained (as in #41677). So, in
525 /// this scenario where we create a new type variable in a
526 /// bivariant context, we set the `needs_wf` flag to true. This
527 /// will force the calling code to check that `WF(Foo<?C, ?D>)`
528 /// holds, which in turn implies that `?C::Item == ?D`. So once
529 /// `?C` is constrained, that should suffice to restrict `?D`.
533 impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
534 fn tcx(&self) -> TyCtxt<'tcx> {
537 fn param_env(&self) -> ty::ParamEnv<'tcx> {
541 fn tag(&self) -> &'static str {
545 fn a_is_expected(&self) -> bool {
551 a: ty::Binder<'tcx, T>,
552 b: ty::Binder<'tcx, T>,
553 ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
557 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
560 fn relate_item_substs(
563 a_subst: SubstsRef<'tcx>,
564 b_subst: SubstsRef<'tcx>,
565 ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
566 if self.ambient_variance == ty::Variance::Invariant {
567 // Avoid fetching the variance if we are in an invariant
568 // context; no need, and it can induce dependency cycles
570 relate::relate_substs(self, a_subst, b_subst)
572 let tcx = self.tcx();
573 let opt_variances = tcx.variances_of(item_def_id);
574 relate::relate_substs_with_variances(
584 fn relate_with_variance<T: Relate<'tcx>>(
586 variance: ty::Variance,
587 _info: ty::VarianceDiagInfo<'tcx>,
590 ) -> RelateResult<'tcx, T> {
591 let old_ambient_variance = self.ambient_variance;
592 self.ambient_variance = self.ambient_variance.xform(variance);
594 let result = self.relate(a, b);
595 self.ambient_variance = old_ambient_variance;
599 fn tys(&mut self, t: Ty<'tcx>, t2: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
600 assert_eq!(t, t2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
602 if let Some(result) = self.cache.get(&t) {
603 return result.clone();
605 debug!("generalize: t={:?}", t);
607 // Check to see whether the type we are generalizing references
608 // any other type variable related to `vid` via
609 // subtyping. This is basically our "occurs check", preventing
610 // us from creating infinitely sized types.
611 let result = match *t.kind() {
612 ty::Infer(ty::TyVar(vid)) => {
613 let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
614 let sub_vid = self.infcx.inner.borrow_mut().type_variables().sub_root_var(vid);
615 if sub_vid == self.for_vid_sub_root {
616 // If sub-roots are equal, then `for_vid` and
617 // `vid` are related via subtyping.
618 Err(TypeError::CyclicTy(self.root_ty))
620 let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
622 TypeVariableValue::Known { value: u } => {
623 debug!("generalize: known value {:?}", u);
626 TypeVariableValue::Unknown { universe } => {
627 match self.ambient_variance {
628 // Invariant: no need to make a fresh type variable.
630 if self.for_universe.can_name(universe) {
635 // Bivariant: make a fresh var, but we
636 // may need a WF predicate. See
637 // comment on `needs_wf` field for
639 ty::Bivariant => self.needs_wf = true,
641 // Co/contravariant: this will be
642 // sufficiently constrained later on.
643 ty::Covariant | ty::Contravariant => (),
647 *self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
648 let new_var_id = self
653 .new_var(self.for_universe, origin);
654 let u = self.tcx().mk_ty_var(new_var_id);
656 // Record that we replaced `vid` with `new_var_id` as part of a generalization
657 // operation. This is needed to detect cyclic types. To see why, see the
658 // docs in the `type_variables` module.
659 self.infcx.inner.borrow_mut().type_variables().sub(vid, new_var_id);
660 debug!("generalize: replacing original vid={:?} with new={:?}", vid, u);
666 ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => {
667 // No matter what mode we are in,
668 // integer/floating-point types must be equal to be
672 _ => relate::super_relate_tys(self, t, t),
675 self.cache.insert(t, result.clone());
682 r2: ty::Region<'tcx>,
683 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
684 assert_eq!(r, r2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
686 debug!("generalize: regions r={:?}", r);
689 // Never make variables for regions bound within the type itself,
690 // nor for erased regions.
691 ty::ReLateBound(..) | ty::ReErased => {
695 ty::RePlaceholder(..)
699 | ty::ReEarlyBound(..)
700 | ty::ReFree(..) => {
701 // see common code below
705 // If we are in an invariant context, we can re-use the region
706 // as is, unless it happens to be in some universe that we
707 // can't name. (In the case of a region *variable*, we could
708 // use it if we promoted it into our universe, but we don't
710 if let ty::Invariant = self.ambient_variance {
711 let r_universe = self.infcx.universe_of_region(r);
712 if self.for_universe.can_name(r_universe) {
717 // FIXME: This is non-ideal because we don't give a
718 // very descriptive origin for this region variable.
719 Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.cause.span), self.for_universe))
726 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
727 assert_eq!(c, c2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
730 ty::ConstKind::Infer(InferConst::Var(vid)) => {
731 let mut inner = self.infcx.inner.borrow_mut();
732 let variable_table = &mut inner.const_unification_table();
733 let var_value = variable_table.probe_value(vid);
734 match var_value.val {
735 ConstVariableValue::Known { value: u } => {
739 ConstVariableValue::Unknown { universe } => {
740 if self.for_universe.can_name(universe) {
743 let new_var_id = variable_table.new_key(ConstVarValue {
744 origin: var_value.origin,
745 val: ConstVariableValue::Unknown { universe: self.for_universe },
747 Ok(self.tcx().mk_const_var(new_var_id, c.ty()))
752 ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
753 if self.tcx().lazy_normalization() =>
755 assert_eq!(promoted, None);
756 let substs = self.relate_with_variance(
757 ty::Variance::Invariant,
758 ty::VarianceDiagInfo::default(),
762 Ok(self.tcx().mk_const(ty::ConstS {
764 val: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),
767 _ => relate::super_relate_consts(self, c, c),
772 pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
773 /// Register an obligation that both constants must be equal to each other.
775 /// If they aren't equal then the relation doesn't hold.
776 fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>);
779 pub fn const_unification_error<'tcx>(
781 (a, b): (ty::Const<'tcx>, ty::Const<'tcx>),
782 ) -> TypeError<'tcx> {
783 TypeError::ConstMismatch(ExpectedFound::new(a_is_expected, a, b))
786 fn int_unification_error<'tcx>(
788 v: (ty::IntVarValue, ty::IntVarValue),
789 ) -> TypeError<'tcx> {
791 TypeError::IntMismatch(ExpectedFound::new(a_is_expected, a, b))
794 fn float_unification_error<'tcx>(
796 v: (ty::FloatVarValue, ty::FloatVarValue),
797 ) -> TypeError<'tcx> {
798 let (ty::FloatVarValue(a), ty::FloatVarValue(b)) = v;
799 TypeError::FloatMismatch(ExpectedFound::new(a_is_expected, a, b))
802 struct ConstInferUnifier<'cx, 'tcx> {
803 infcx: &'cx InferCtxt<'cx, 'tcx>,
807 param_env: ty::ParamEnv<'tcx>,
809 for_universe: ty::UniverseIndex,
811 /// The vid of the const variable that is in the process of being
812 /// instantiated; if we find this within the const we are folding,
813 /// that means we would have created a cyclic const.
814 target_vid: ty::ConstVid<'tcx>,
817 // We use `TypeRelation` here to propagate `RelateResult` upwards.
819 // Both inputs are expected to be the same.
820 impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
821 fn tcx(&self) -> TyCtxt<'tcx> {
825 fn param_env(&self) -> ty::ParamEnv<'tcx> {
829 fn tag(&self) -> &'static str {
833 fn a_is_expected(&self) -> bool {
837 fn relate_with_variance<T: Relate<'tcx>>(
839 _variance: ty::Variance,
840 _info: ty::VarianceDiagInfo<'tcx>,
843 ) -> RelateResult<'tcx, T> {
844 // We don't care about variance here.
850 a: ty::Binder<'tcx, T>,
851 b: ty::Binder<'tcx, T>,
852 ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
856 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
859 #[tracing::instrument(level = "debug", skip(self))]
860 fn tys(&mut self, t: Ty<'tcx>, _t: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
861 debug_assert_eq!(t, _t);
862 debug!("ConstInferUnifier: t={:?}", t);
865 &ty::Infer(ty::TyVar(vid)) => {
866 let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
867 let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
869 TypeVariableValue::Known { value: u } => {
870 debug!("ConstOccursChecker: known value {:?}", u);
873 TypeVariableValue::Unknown { universe } => {
874 if self.for_universe.can_name(universe) {
879 *self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
880 let new_var_id = self
885 .new_var(self.for_universe, origin);
886 let u = self.tcx().mk_ty_var(new_var_id);
888 "ConstInferUnifier: replacing original vid={:?} with new={:?}",
895 ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => Ok(t),
896 _ => relate::super_relate_tys(self, t, t),
903 _r: ty::Region<'tcx>,
904 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
905 debug_assert_eq!(r, _r);
906 debug!("ConstInferUnifier: r={:?}", r);
909 // Never make variables for regions bound within the type itself,
910 // nor for erased regions.
911 ty::ReLateBound(..) | ty::ReErased => {
915 ty::RePlaceholder(..)
919 | ty::ReEarlyBound(..)
920 | ty::ReFree(..) => {
921 // see common code below
925 let r_universe = self.infcx.universe_of_region(r);
926 if self.for_universe.can_name(r_universe) {
929 // FIXME: This is non-ideal because we don't give a
930 // very descriptive origin for this region variable.
931 Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.span), self.for_universe))
935 #[tracing::instrument(level = "debug", skip(self))]
940 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
941 debug_assert_eq!(c, _c);
942 debug!("ConstInferUnifier: c={:?}", c);
945 ty::ConstKind::Infer(InferConst::Var(vid)) => {
946 // Check if the current unification would end up
947 // unifying `target_vid` with a const which contains
948 // an inference variable which is unioned with `target_vid`.
950 // Not doing so can easily result in stack overflows.
955 .const_unification_table()
956 .unioned(self.target_vid, vid)
958 return Err(TypeError::CyclicConst(c));
962 self.infcx.inner.borrow_mut().const_unification_table().probe_value(vid);
963 match var_value.val {
964 ConstVariableValue::Known { value: u } => self.consts(u, u),
965 ConstVariableValue::Unknown { universe } => {
966 if self.for_universe.can_name(universe) {
970 self.infcx.inner.borrow_mut().const_unification_table().new_key(
972 origin: var_value.origin,
973 val: ConstVariableValue::Unknown {
974 universe: self.for_universe,
978 Ok(self.tcx().mk_const_var(new_var_id, c.ty()))
983 ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
984 if self.tcx().lazy_normalization() =>
986 assert_eq!(promoted, None);
987 let substs = self.relate_with_variance(
988 ty::Variance::Invariant,
989 ty::VarianceDiagInfo::default(),
993 Ok(self.tcx().mk_const(ty::ConstS {
995 val: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),
998 _ => relate::super_relate_consts(self, c, c),