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 let a = self.tcx.expose_default_const_substs(a);
133 let b = self.tcx.expose_default_const_substs(b);
134 debug!("{}.consts({:?}, {:?})", relation.tag(), a, b);
139 let a = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table(), a);
140 let b = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table(), b);
142 let a_is_expected = relation.a_is_expected();
144 match (a.val, b.val) {
146 ty::ConstKind::Infer(InferConst::Var(a_vid)),
147 ty::ConstKind::Infer(InferConst::Var(b_vid)),
151 .const_unification_table()
152 .unify_var_var(a_vid, b_vid)
153 .map_err(|e| const_unification_error(a_is_expected, e))?;
157 // All other cases of inference with other variables are errors.
158 (ty::ConstKind::Infer(InferConst::Var(_)), ty::ConstKind::Infer(_))
159 | (ty::ConstKind::Infer(_), ty::ConstKind::Infer(InferConst::Var(_))) => {
160 bug!("tried to combine ConstKind::Infer/ConstKind::Infer(InferConst::Var)")
163 (ty::ConstKind::Infer(InferConst::Var(vid)), _) => {
164 return self.unify_const_variable(relation.param_env(), vid, b, a_is_expected);
167 (_, ty::ConstKind::Infer(InferConst::Var(vid))) => {
168 return self.unify_const_variable(relation.param_env(), vid, a, !a_is_expected);
170 (ty::ConstKind::Unevaluated(..), _) if self.tcx.lazy_normalization() => {
171 // FIXME(#59490): Need to remove the leak check to accommodate
172 // escaping bound variables here.
173 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
174 relation.const_equate_obligation(a, b);
178 (_, ty::ConstKind::Unevaluated(..)) if self.tcx.lazy_normalization() => {
179 // FIXME(#59490): Need to remove the leak check to accommodate
180 // escaping bound variables here.
181 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
182 relation.const_equate_obligation(a, b);
189 ty::relate::super_relate_consts(relation, a, b)
192 /// Unifies the const variable `target_vid` with the given constant.
194 /// This also tests if the given const `ct` contains an inference variable which was previously
195 /// unioned with `target_vid`. If this is the case, inferring `target_vid` to `ct`
196 /// would result in an infinite type as we continuously replace an inference variable
197 /// in `ct` with `ct` itself.
199 /// This is especially important as unevaluated consts use their parents generics.
200 /// They therefore often contain unused substs, making these errors far more likely.
202 /// A good example of this is the following:
205 /// #![feature(generic_const_exprs)]
207 /// fn bind<const N: usize>(value: [u8; N]) -> [u8; 3 + 4] {
212 /// let mut arr = Default::default();
217 /// Here `3 + 4` ends up as `ConstKind::Unevaluated` which uses the generics
218 /// of `fn bind` (meaning that its substs contain `N`).
220 /// `bind(arr)` now infers that the type of `arr` must be `[u8; N]`.
221 /// The assignment `arr = bind(arr)` now tries to equate `N` with `3 + 4`.
223 /// As `3 + 4` contains `N` in its substs, this must not succeed.
225 /// See `src/test/ui/const-generics/occurs-check/` for more examples where this is relevant.
226 #[instrument(level = "debug", skip(self))]
227 fn unify_const_variable(
229 param_env: ty::ParamEnv<'tcx>,
230 target_vid: ty::ConstVid<'tcx>,
231 ct: &'tcx ty::Const<'tcx>,
232 vid_is_expected: bool,
233 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
234 let (for_universe, span) = {
235 let mut inner = self.inner.borrow_mut();
236 let variable_table = &mut inner.const_unification_table();
237 let var_value = variable_table.probe_value(target_vid);
238 match var_value.val {
239 ConstVariableValue::Known { value } => {
240 bug!("instantiating {:?} which has a known value {:?}", target_vid, value)
242 ConstVariableValue::Unknown { universe } => (universe, var_value.origin.span),
245 let value = ConstInferUnifier { infcx: self, span, param_env, for_universe, target_vid }
250 .const_unification_table()
254 origin: ConstVariableOrigin {
255 kind: ConstVariableOriginKind::ConstInference,
258 val: ConstVariableValue::Known { value },
262 .map_err(|e| const_unification_error(vid_is_expected, e))
265 fn unify_integral_variable(
267 vid_is_expected: bool,
269 val: ty::IntVarValue,
270 ) -> RelateResult<'tcx, Ty<'tcx>> {
273 .int_unification_table()
274 .unify_var_value(vid, Some(val))
275 .map_err(|e| int_unification_error(vid_is_expected, e))?;
277 IntType(v) => Ok(self.tcx.mk_mach_int(v)),
278 UintType(v) => Ok(self.tcx.mk_mach_uint(v)),
282 fn unify_float_variable(
284 vid_is_expected: bool,
287 ) -> RelateResult<'tcx, Ty<'tcx>> {
290 .float_unification_table()
291 .unify_var_value(vid, Some(ty::FloatVarValue(val)))
292 .map_err(|e| float_unification_error(vid_is_expected, e))?;
293 Ok(self.tcx.mk_mach_float(val))
297 impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
298 pub fn tcx(&self) -> TyCtxt<'tcx> {
302 pub fn equate<'a>(&'a mut self, a_is_expected: bool) -> Equate<'a, 'infcx, 'tcx> {
303 Equate::new(self, a_is_expected)
306 pub fn sub<'a>(&'a mut self, a_is_expected: bool) -> Sub<'a, 'infcx, 'tcx> {
307 Sub::new(self, a_is_expected)
310 pub fn lub<'a>(&'a mut self, a_is_expected: bool) -> Lub<'a, 'infcx, 'tcx> {
311 Lub::new(self, a_is_expected)
314 pub fn glb<'a>(&'a mut self, a_is_expected: bool) -> Glb<'a, 'infcx, 'tcx> {
315 Glb::new(self, a_is_expected)
318 /// Here, `dir` is either `EqTo`, `SubtypeOf`, or `SupertypeOf`.
319 /// The idea is that we should ensure that the type `a_ty` is equal
320 /// to, a subtype of, or a supertype of (respectively) the type
321 /// to which `b_vid` is bound.
323 /// Since `b_vid` has not yet been instantiated with a type, we
324 /// will first instantiate `b_vid` with a *generalized* version
325 /// of `a_ty`. Generalization introduces other inference
326 /// variables wherever subtyping could occur.
333 ) -> RelateResult<'tcx, ()> {
334 use self::RelationDir::*;
336 // Get the actual variable that b_vid has been inferred to
337 debug_assert!(self.infcx.inner.borrow_mut().type_variables().probe(b_vid).is_unknown());
339 debug!("instantiate(a_ty={:?} dir={:?} b_vid={:?})", a_ty, dir, b_vid);
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 "instantiate(a_ty={:?}, dir={:?}, b_vid={:?}, generalized b_ty={:?})",
355 a_ty, dir, b_vid, b_ty
357 self.infcx.inner.borrow_mut().type_variables().instantiate(b_vid, b_ty);
360 self.obligations.push(Obligation::new(
361 self.trace.cause.clone(),
363 ty::PredicateKind::WellFormed(b_ty.into()).to_predicate(self.infcx.tcx),
367 // Finally, relate `b_ty` to `a_ty`, as described in previous comment.
369 // FIXME(#16847): This code is non-ideal because all these subtype
370 // relations wind up attributed to the same spans. We need
371 // to associate causes/spans with each of the relations in
372 // the stack to get this right.
374 EqTo => self.equate(a_is_expected).relate(a_ty, b_ty),
375 SubtypeOf => self.sub(a_is_expected).relate(a_ty, b_ty),
376 SupertypeOf => self.sub(a_is_expected).relate_with_variance(
378 ty::VarianceDiagInfo::default(),
387 /// Attempts to generalize `ty` for the type variable `for_vid`.
388 /// This checks for cycle -- that is, whether the type `ty`
389 /// references `for_vid`. The `dir` is the "direction" for which we
390 /// a performing the generalization (i.e., are we producing a type
391 /// that can be used as a supertype etc).
395 /// - `for_vid` is a "root vid"
401 ) -> RelateResult<'tcx, Generalization<'tcx>> {
402 debug!("generalize(ty={:?}, for_vid={:?}, dir={:?}", ty, for_vid, dir);
403 // Determine the ambient variance within which `ty` appears.
404 // The surrounding equation is:
408 // where `op` is either `==`, `<:`, or `:>`. This maps quite
410 let ambient_variance = match dir {
411 RelationDir::EqTo => ty::Invariant,
412 RelationDir::SubtypeOf => ty::Covariant,
413 RelationDir::SupertypeOf => ty::Contravariant,
416 debug!("generalize: ambient_variance = {:?}", ambient_variance);
418 let for_universe = match self.infcx.inner.borrow_mut().type_variables().probe(for_vid) {
419 v @ TypeVariableValue::Known { .. } => {
420 bug!("instantiating {:?} which has a known value {:?}", for_vid, v,)
422 TypeVariableValue::Unknown { universe } => universe,
425 debug!("generalize: for_universe = {:?}", for_universe);
426 debug!("generalize: trace = {:?}", self.trace);
428 let mut generalize = Generalizer {
430 cause: &self.trace.cause,
431 for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables().sub_root_var(for_vid),
436 param_env: self.param_env,
437 cache: SsoHashMap::new(),
440 let ty = match generalize.relate(ty, ty) {
443 debug!("generalize: failure {:?}", e);
447 let needs_wf = generalize.needs_wf;
448 debug!("generalize: success {{ {:?}, {:?} }}", ty, needs_wf);
449 Ok(Generalization { ty, needs_wf })
452 pub fn add_const_equate_obligation(
455 a: &'tcx ty::Const<'tcx>,
456 b: &'tcx ty::Const<'tcx>,
458 let predicate = if a_is_expected {
459 ty::PredicateKind::ConstEquate(a, b)
461 ty::PredicateKind::ConstEquate(b, a)
463 self.obligations.push(Obligation::new(
464 self.trace.cause.clone(),
466 predicate.to_predicate(self.tcx()),
471 struct Generalizer<'cx, 'tcx> {
472 infcx: &'cx InferCtxt<'cx, 'tcx>,
474 /// The span, used when creating new type variables and things.
475 cause: &'cx ObligationCause<'tcx>,
477 /// The vid of the type variable that is in the process of being
478 /// instantiated; if we find this within the type we are folding,
479 /// that means we would have created a cyclic type.
480 for_vid_sub_root: ty::TyVid,
482 /// The universe of the type variable that is in the process of
483 /// being instantiated. Any fresh variables that we create in this
484 /// process should be in that same universe.
485 for_universe: ty::UniverseIndex,
487 /// Track the variance as we descend into the type.
488 ambient_variance: ty::Variance,
490 /// See the field `needs_wf` in `Generalization`.
493 /// The root type that we are generalizing. Used when reporting cycles.
496 param_env: ty::ParamEnv<'tcx>,
498 cache: SsoHashMap<Ty<'tcx>, RelateResult<'tcx, Ty<'tcx>>>,
501 /// Result from a generalization operation. This includes
502 /// not only the generalized type, but also a bool flag
503 /// indicating whether further WF checks are needed.
504 struct Generalization<'tcx> {
507 /// If true, then the generalized type may not be well-formed,
508 /// even if the source type is well-formed, so we should add an
509 /// additional check to enforce that it is. This arises in
510 /// particular around 'bivariant' type parameters that are only
511 /// constrained by a where-clause. As an example, imagine a type:
513 /// struct Foo<A, B> where A: Iterator<Item = B> {
517 /// here, `A` will be covariant, but `B` is
518 /// unconstrained. However, whatever it is, for `Foo` to be WF, it
519 /// must be equal to `A::Item`. If we have an input `Foo<?A, ?B>`,
520 /// then after generalization we will wind up with a type like
521 /// `Foo<?C, ?D>`. When we enforce that `Foo<?A, ?B> <: Foo<?C,
522 /// ?D>` (or `>:`), we will wind up with the requirement that `?A
523 /// <: ?C`, but no particular relationship between `?B` and `?D`
524 /// (after all, we do not know the variance of the normalized form
525 /// of `A::Item` with respect to `A`). If we do nothing else, this
526 /// may mean that `?D` goes unconstrained (as in #41677). So, in
527 /// this scenario where we create a new type variable in a
528 /// bivariant context, we set the `needs_wf` flag to true. This
529 /// will force the calling code to check that `WF(Foo<?C, ?D>)`
530 /// holds, which in turn implies that `?C::Item == ?D`. So once
531 /// `?C` is constrained, that should suffice to restrict `?D`.
535 impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
536 fn tcx(&self) -> TyCtxt<'tcx> {
539 fn param_env(&self) -> ty::ParamEnv<'tcx> {
543 fn tag(&self) -> &'static str {
547 fn a_is_expected(&self) -> bool {
553 a: ty::Binder<'tcx, T>,
554 b: ty::Binder<'tcx, T>,
555 ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
559 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
562 fn relate_item_substs(
565 a_subst: SubstsRef<'tcx>,
566 b_subst: SubstsRef<'tcx>,
567 ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
568 if self.ambient_variance == ty::Variance::Invariant {
569 // Avoid fetching the variance if we are in an invariant
570 // context; no need, and it can induce dependency cycles
572 relate::relate_substs(self, None, a_subst, b_subst)
574 let opt_variances = self.tcx().variances_of(item_def_id);
575 relate::relate_substs(self, Some(&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))
719 c: &'tcx ty::Const<'tcx>,
720 c2: &'tcx ty::Const<'tcx>,
721 ) -> RelateResult<'tcx, &'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(uv) if self.tcx().lazy_normalization() => {
748 assert_eq!(uv.promoted, None);
749 let substs = uv.substs(self.tcx());
750 let substs = self.relate_with_variance(
751 ty::Variance::Invariant,
752 ty::VarianceDiagInfo::default(),
756 Ok(self.tcx().mk_const(ty::Const {
758 val: ty::ConstKind::Unevaluated(ty::Unevaluated::new(uv.def, substs)),
761 _ => relate::super_relate_consts(self, c, c),
766 pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
767 /// Register an obligation that both constants must be equal to each other.
769 /// If they aren't equal then the relation doesn't hold.
770 fn const_equate_obligation(&mut self, a: &'tcx ty::Const<'tcx>, b: &'tcx ty::Const<'tcx>);
773 pub trait RelateResultCompare<'tcx, T> {
774 fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T>
776 F: FnOnce() -> TypeError<'tcx>;
779 impl<'tcx, T: Clone + PartialEq> RelateResultCompare<'tcx, T> for RelateResult<'tcx, T> {
780 fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T>
782 F: FnOnce() -> TypeError<'tcx>,
784 self.clone().and_then(|s| if s == t { self.clone() } else { Err(f()) })
788 pub fn const_unification_error<'tcx>(
790 (a, b): (&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>),
791 ) -> TypeError<'tcx> {
792 TypeError::ConstMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))
795 fn int_unification_error<'tcx>(
797 v: (ty::IntVarValue, ty::IntVarValue),
798 ) -> TypeError<'tcx> {
800 TypeError::IntMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))
803 fn float_unification_error<'tcx>(
805 v: (ty::FloatVarValue, ty::FloatVarValue),
806 ) -> TypeError<'tcx> {
807 let (ty::FloatVarValue(a), ty::FloatVarValue(b)) = v;
808 TypeError::FloatMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))
811 struct ConstInferUnifier<'cx, 'tcx> {
812 infcx: &'cx InferCtxt<'cx, 'tcx>,
816 param_env: ty::ParamEnv<'tcx>,
818 for_universe: ty::UniverseIndex,
820 /// The vid of the const variable that is in the process of being
821 /// instantiated; if we find this within the const we are folding,
822 /// that means we would have created a cyclic const.
823 target_vid: ty::ConstVid<'tcx>,
826 // We use `TypeRelation` here to propagate `RelateResult` upwards.
828 // Both inputs are expected to be the same.
829 impl TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
830 fn tcx(&self) -> TyCtxt<'tcx> {
834 fn param_env(&self) -> ty::ParamEnv<'tcx> {
838 fn tag(&self) -> &'static str {
842 fn a_is_expected(&self) -> bool {
846 fn relate_with_variance<T: Relate<'tcx>>(
848 _variance: ty::Variance,
849 _info: ty::VarianceDiagInfo<'tcx>,
852 ) -> RelateResult<'tcx, T> {
853 // We don't care about variance here.
859 a: ty::Binder<'tcx, T>,
860 b: ty::Binder<'tcx, T>,
861 ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
865 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
868 fn tys(&mut self, t: Ty<'tcx>, _t: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
869 debug_assert_eq!(t, _t);
870 debug!("ConstInferUnifier: t={:?}", t);
873 &ty::Infer(ty::TyVar(vid)) => {
874 let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
875 let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
877 TypeVariableValue::Known { value: u } => {
878 debug!("ConstOccursChecker: known value {:?}", u);
881 TypeVariableValue::Unknown { universe } => {
882 if self.for_universe.can_name(universe) {
887 *self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
888 let new_var_id = self
893 .new_var(self.for_universe, origin);
894 let u = self.tcx().mk_ty_var(new_var_id);
896 "ConstInferUnifier: replacing original vid={:?} with new={:?}",
903 ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => Ok(t),
904 _ => relate::super_relate_tys(self, t, t),
911 _r: ty::Region<'tcx>,
912 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
913 debug_assert_eq!(r, _r);
914 debug!("ConstInferUnifier: r={:?}", r);
917 // Never make variables for regions bound within the type itself,
918 // nor for erased regions.
919 ty::ReLateBound(..) | ty::ReErased => {
923 ty::RePlaceholder(..)
927 | ty::ReEarlyBound(..)
928 | ty::ReFree(..) => {
929 // see common code below
933 let r_universe = self.infcx.universe_of_region(r);
934 if self.for_universe.can_name(r_universe) {
937 // FIXME: This is non-ideal because we don't give a
938 // very descriptive origin for this region variable.
939 Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.span), self.for_universe))
945 c: &'tcx ty::Const<'tcx>,
946 _c: &'tcx ty::Const<'tcx>,
947 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
948 debug_assert_eq!(c, _c);
949 debug!("ConstInferUnifier: c={:?}", c);
952 ty::ConstKind::Infer(InferConst::Var(vid)) => {
953 let mut inner = self.infcx.inner.borrow_mut();
954 let variable_table = &mut inner.const_unification_table();
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.
961 if variable_table.unioned(self.target_vid, vid) {
962 return Err(TypeError::CyclicConst(c));
965 let var_value = variable_table.probe_value(vid);
966 match var_value.val {
967 ConstVariableValue::Known { value: u } => self.consts(u, u),
968 ConstVariableValue::Unknown { universe } => {
969 if self.for_universe.can_name(universe) {
972 let new_var_id = variable_table.new_key(ConstVarValue {
973 origin: var_value.origin,
974 val: ConstVariableValue::Unknown { universe: self.for_universe },
976 Ok(self.tcx().mk_const_var(new_var_id, c.ty))
981 ty::ConstKind::Unevaluated(uv) if self.tcx().lazy_normalization() => {
982 assert_eq!(uv.promoted, None);
983 let substs = uv.substs(self.tcx());
984 let substs = self.relate_with_variance(
985 ty::Variance::Invariant,
986 ty::VarianceDiagInfo::default(),
990 Ok(self.tcx().mk_const(ty::Const {
992 val: ty::ConstKind::Unevaluated(ty::Unevaluated::new(uv.def, substs)),
995 _ => relate::super_relate_consts(self, c, c),