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};
34 use arrayvec::ArrayVec;
35 use rustc_data_structures::fx::FxHashMap;
38 use crate::traits::{Obligation, PredicateObligations};
41 use rustc_hir::def_id::DefId;
42 use rustc_middle::traits::ObligationCause;
43 use rustc_middle::ty::error::TypeError;
44 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
45 use rustc_middle::ty::subst::SubstsRef;
46 use rustc_middle::ty::{self, InferConst, ToPredicate, Ty, TyCtxt, TypeFoldable};
47 use rustc_middle::ty::{IntType, UintType};
48 use rustc_span::DUMMY_SP;
50 /// Small-storage-optimized implementation of a map
51 /// made specifically for caching results.
53 /// Stores elements in a small array up to a certain length
54 /// and switches to `HashMap` when that length is exceeded.
56 Array(ArrayVec<[(K, V); 8]>),
60 impl<K: Eq + Hash, V> MiniMap<K, V> {
61 /// Creates an empty `MiniMap`.
62 pub fn new() -> Self {
63 MiniMap::Array(ArrayVec::new())
66 /// Inserts or updates value in the map.
67 pub fn insert(&mut self, key: K, value: V) {
69 MiniMap::Array(array) => {
70 for pair in array.iter_mut() {
76 if let Err(error) = array.try_push((key, value)) {
77 let mut map: FxHashMap<K, V> = array.drain(..).collect();
78 let (key, value) = error.element();
79 map.insert(key, value);
80 *self = MiniMap::Map(map);
83 MiniMap::Map(map) => {
84 map.insert(key, value);
89 /// Return value by key if any.
90 pub fn get(&self, key: &K) -> Option<&V> {
92 MiniMap::Array(array) => {
100 MiniMap::Map(map) => {
108 pub struct CombineFields<'infcx, 'tcx> {
109 pub infcx: &'infcx InferCtxt<'infcx, 'tcx>,
110 pub trace: TypeTrace<'tcx>,
111 pub cause: Option<ty::relate::Cause>,
112 pub param_env: ty::ParamEnv<'tcx>,
113 pub obligations: PredicateObligations<'tcx>,
116 #[derive(Copy, Clone, Debug)]
117 pub enum RelationDir {
123 impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
124 pub fn super_combine_tys<R>(
129 ) -> RelateResult<'tcx, Ty<'tcx>>
131 R: TypeRelation<'tcx>,
133 let a_is_expected = relation.a_is_expected();
135 match (a.kind(), b.kind()) {
136 // Relate integral variables to other types
137 (&ty::Infer(ty::IntVar(a_id)), &ty::Infer(ty::IntVar(b_id))) => {
140 .int_unification_table()
141 .unify_var_var(a_id, b_id)
142 .map_err(|e| int_unification_error(a_is_expected, e))?;
145 (&ty::Infer(ty::IntVar(v_id)), &ty::Int(v)) => {
146 self.unify_integral_variable(a_is_expected, v_id, IntType(v))
148 (&ty::Int(v), &ty::Infer(ty::IntVar(v_id))) => {
149 self.unify_integral_variable(!a_is_expected, v_id, IntType(v))
151 (&ty::Infer(ty::IntVar(v_id)), &ty::Uint(v)) => {
152 self.unify_integral_variable(a_is_expected, v_id, UintType(v))
154 (&ty::Uint(v), &ty::Infer(ty::IntVar(v_id))) => {
155 self.unify_integral_variable(!a_is_expected, v_id, UintType(v))
158 // Relate floating-point variables to other types
159 (&ty::Infer(ty::FloatVar(a_id)), &ty::Infer(ty::FloatVar(b_id))) => {
162 .float_unification_table()
163 .unify_var_var(a_id, b_id)
164 .map_err(|e| float_unification_error(relation.a_is_expected(), e))?;
167 (&ty::Infer(ty::FloatVar(v_id)), &ty::Float(v)) => {
168 self.unify_float_variable(a_is_expected, v_id, v)
170 (&ty::Float(v), &ty::Infer(ty::FloatVar(v_id))) => {
171 self.unify_float_variable(!a_is_expected, v_id, v)
174 // All other cases of inference are errors
175 (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
176 Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b)))
179 _ => ty::relate::super_relate_tys(relation, a, b),
183 pub fn super_combine_consts<R>(
186 a: &'tcx ty::Const<'tcx>,
187 b: &'tcx ty::Const<'tcx>,
188 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>>
190 R: ConstEquateRelation<'tcx>,
192 debug!("{}.consts({:?}, {:?})", relation.tag(), a, b);
197 let a = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table(), a);
198 let b = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table(), b);
200 let a_is_expected = relation.a_is_expected();
202 match (a.val, b.val) {
204 ty::ConstKind::Infer(InferConst::Var(a_vid)),
205 ty::ConstKind::Infer(InferConst::Var(b_vid)),
209 .const_unification_table()
210 .unify_var_var(a_vid, b_vid)
211 .map_err(|e| const_unification_error(a_is_expected, e))?;
215 // All other cases of inference with other variables are errors.
216 (ty::ConstKind::Infer(InferConst::Var(_)), ty::ConstKind::Infer(_))
217 | (ty::ConstKind::Infer(_), ty::ConstKind::Infer(InferConst::Var(_))) => {
218 bug!("tried to combine ConstKind::Infer/ConstKind::Infer(InferConst::Var)")
221 (ty::ConstKind::Infer(InferConst::Var(vid)), _) => {
222 return self.unify_const_variable(a_is_expected, vid, b);
225 (_, ty::ConstKind::Infer(InferConst::Var(vid))) => {
226 return self.unify_const_variable(!a_is_expected, vid, a);
228 (ty::ConstKind::Unevaluated(..), _) if self.tcx.lazy_normalization() => {
229 // FIXME(#59490): Need to remove the leak check to accommodate
230 // escaping bound variables here.
231 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
232 relation.const_equate_obligation(a, b);
236 (_, ty::ConstKind::Unevaluated(..)) if self.tcx.lazy_normalization() => {
237 // FIXME(#59490): Need to remove the leak check to accommodate
238 // escaping bound variables here.
239 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
240 relation.const_equate_obligation(a, b);
247 ty::relate::super_relate_consts(relation, a, b)
250 pub fn unify_const_variable(
252 vid_is_expected: bool,
253 vid: ty::ConstVid<'tcx>,
254 value: &'tcx ty::Const<'tcx>,
255 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
258 .const_unification_table()
262 origin: ConstVariableOrigin {
263 kind: ConstVariableOriginKind::ConstInference,
266 val: ConstVariableValue::Known { value },
269 .map_err(|e| const_unification_error(vid_is_expected, e))?;
273 fn unify_integral_variable(
275 vid_is_expected: bool,
277 val: ty::IntVarValue,
278 ) -> RelateResult<'tcx, Ty<'tcx>> {
281 .int_unification_table()
282 .unify_var_value(vid, Some(val))
283 .map_err(|e| int_unification_error(vid_is_expected, e))?;
285 IntType(v) => Ok(self.tcx.mk_mach_int(v)),
286 UintType(v) => Ok(self.tcx.mk_mach_uint(v)),
290 fn unify_float_variable(
292 vid_is_expected: bool,
295 ) -> RelateResult<'tcx, Ty<'tcx>> {
298 .float_unification_table()
299 .unify_var_value(vid, Some(ty::FloatVarValue(val)))
300 .map_err(|e| float_unification_error(vid_is_expected, e))?;
301 Ok(self.tcx.mk_mach_float(val))
305 impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
306 pub fn tcx(&self) -> TyCtxt<'tcx> {
310 pub fn equate<'a>(&'a mut self, a_is_expected: bool) -> Equate<'a, 'infcx, 'tcx> {
311 Equate::new(self, a_is_expected)
314 pub fn sub<'a>(&'a mut self, a_is_expected: bool) -> Sub<'a, 'infcx, 'tcx> {
315 Sub::new(self, a_is_expected)
318 pub fn lub<'a>(&'a mut self, a_is_expected: bool) -> Lub<'a, 'infcx, 'tcx> {
319 Lub::new(self, a_is_expected)
322 pub fn glb<'a>(&'a mut self, a_is_expected: bool) -> Glb<'a, 'infcx, 'tcx> {
323 Glb::new(self, a_is_expected)
326 /// Here, `dir` is either `EqTo`, `SubtypeOf`, or `SupertypeOf`.
327 /// The idea is that we should ensure that the type `a_ty` is equal
328 /// to, a subtype of, or a supertype of (respectively) the type
329 /// to which `b_vid` is bound.
331 /// Since `b_vid` has not yet been instantiated with a type, we
332 /// will first instantiate `b_vid` with a *generalized* version
333 /// of `a_ty`. Generalization introduces other inference
334 /// variables wherever subtyping could occur.
341 ) -> RelateResult<'tcx, ()> {
342 use self::RelationDir::*;
344 // Get the actual variable that b_vid has been inferred to
345 debug_assert!(self.infcx.inner.borrow_mut().type_variables().probe(b_vid).is_unknown());
347 debug!("instantiate(a_ty={:?} dir={:?} b_vid={:?})", a_ty, dir, b_vid);
349 // Generalize type of `a_ty` appropriately depending on the
350 // direction. As an example, assume:
352 // - `a_ty == &'x ?1`, where `'x` is some free region and `?1` is an
353 // inference variable,
354 // - and `dir` == `SubtypeOf`.
356 // Then the generalized form `b_ty` would be `&'?2 ?3`, where
357 // `'?2` and `?3` are fresh region/type inference
358 // variables. (Down below, we will relate `a_ty <: b_ty`,
359 // adding constraints like `'x: '?2` and `?1 <: ?3`.)
360 let Generalization { ty: b_ty, needs_wf } = self.generalize(a_ty, b_vid, dir)?;
362 "instantiate(a_ty={:?}, dir={:?}, b_vid={:?}, generalized b_ty={:?})",
363 a_ty, dir, b_vid, b_ty
365 self.infcx.inner.borrow_mut().type_variables().instantiate(b_vid, b_ty);
368 self.obligations.push(Obligation::new(
369 self.trace.cause.clone(),
371 ty::PredicateAtom::WellFormed(b_ty.into()).to_predicate(self.infcx.tcx),
375 // Finally, relate `b_ty` to `a_ty`, as described in previous comment.
377 // FIXME(#16847): This code is non-ideal because all these subtype
378 // relations wind up attributed to the same spans. We need
379 // to associate causes/spans with each of the relations in
380 // the stack to get this right.
382 EqTo => self.equate(a_is_expected).relate(a_ty, b_ty),
383 SubtypeOf => self.sub(a_is_expected).relate(a_ty, b_ty),
385 self.sub(a_is_expected).relate_with_variance(ty::Contravariant, a_ty, b_ty)
392 /// Attempts to generalize `ty` for the type variable `for_vid`.
393 /// This checks for cycle -- that is, whether the type `ty`
394 /// references `for_vid`. The `dir` is the "direction" for which we
395 /// a performing the generalization (i.e., are we producing a type
396 /// that can be used as a supertype etc).
400 /// - `for_vid` is a "root vid"
406 ) -> RelateResult<'tcx, Generalization<'tcx>> {
407 debug!("generalize(ty={:?}, for_vid={:?}, dir={:?}", ty, for_vid, dir);
408 // Determine the ambient variance within which `ty` appears.
409 // The surrounding equation is:
413 // where `op` is either `==`, `<:`, or `:>`. This maps quite
415 let ambient_variance = match dir {
416 RelationDir::EqTo => ty::Invariant,
417 RelationDir::SubtypeOf => ty::Covariant,
418 RelationDir::SupertypeOf => ty::Contravariant,
421 debug!("generalize: ambient_variance = {:?}", ambient_variance);
423 let for_universe = match self.infcx.inner.borrow_mut().type_variables().probe(for_vid) {
424 v @ TypeVariableValue::Known { .. } => {
425 panic!("instantiating {:?} which has a known value {:?}", for_vid, v,)
427 TypeVariableValue::Unknown { universe } => universe,
430 debug!("generalize: for_universe = {:?}", for_universe);
431 debug!("generalize: trace = {:?}", self.trace);
433 let mut generalize = Generalizer {
435 cause: &self.trace.cause,
436 for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables().sub_root_var(for_vid),
441 param_env: self.param_env,
442 cache: MiniMap::new(),
445 let ty = match generalize.relate(ty, ty) {
448 debug!("generalize: failure {:?}", e);
452 let needs_wf = generalize.needs_wf;
453 debug!("generalize: success {{ {:?}, {:?} }}", ty, needs_wf);
454 Ok(Generalization { ty, needs_wf })
457 pub fn add_const_equate_obligation(
460 a: &'tcx ty::Const<'tcx>,
461 b: &'tcx ty::Const<'tcx>,
463 let predicate = if a_is_expected {
464 ty::PredicateAtom::ConstEquate(a, b)
466 ty::PredicateAtom::ConstEquate(b, a)
468 self.obligations.push(Obligation::new(
469 self.trace.cause.clone(),
471 predicate.to_predicate(self.tcx()),
476 struct Generalizer<'cx, 'tcx> {
477 infcx: &'cx InferCtxt<'cx, 'tcx>,
479 /// The span, used when creating new type variables and things.
480 cause: &'cx ObligationCause<'tcx>,
482 /// The vid of the type variable that is in the process of being
483 /// instantiated; if we find this within the type we are folding,
484 /// that means we would have created a cyclic type.
485 for_vid_sub_root: ty::TyVid,
487 /// The universe of the type variable that is in the process of
488 /// being instantiated. Any fresh variables that we create in this
489 /// process should be in that same universe.
490 for_universe: ty::UniverseIndex,
492 /// Track the variance as we descend into the type.
493 ambient_variance: ty::Variance,
495 /// See the field `needs_wf` in `Generalization`.
498 /// The root type that we are generalizing. Used when reporting cycles.
501 param_env: ty::ParamEnv<'tcx>,
503 cache: MiniMap<Ty<'tcx>, RelateResult<'tcx, Ty<'tcx>>>,
506 /// Result from a generalization operation. This includes
507 /// not only the generalized type, but also a bool flag
508 /// indicating whether further WF checks are needed.
509 struct Generalization<'tcx> {
512 /// If true, then the generalized type may not be well-formed,
513 /// even if the source type is well-formed, so we should add an
514 /// additional check to enforce that it is. This arises in
515 /// particular around 'bivariant' type parameters that are only
516 /// constrained by a where-clause. As an example, imagine a type:
518 /// struct Foo<A, B> where A: Iterator<Item = B> {
522 /// here, `A` will be covariant, but `B` is
523 /// unconstrained. However, whatever it is, for `Foo` to be WF, it
524 /// must be equal to `A::Item`. If we have an input `Foo<?A, ?B>`,
525 /// then after generalization we will wind up with a type like
526 /// `Foo<?C, ?D>`. When we enforce that `Foo<?A, ?B> <: Foo<?C,
527 /// ?D>` (or `>:`), we will wind up with the requirement that `?A
528 /// <: ?C`, but no particular relationship between `?B` and `?D`
529 /// (after all, we do not know the variance of the normalized form
530 /// of `A::Item` with respect to `A`). If we do nothing else, this
531 /// may mean that `?D` goes unconstrained (as in #41677). So, in
532 /// this scenario where we create a new type variable in a
533 /// bivariant context, we set the `needs_wf` flag to true. This
534 /// will force the calling code to check that `WF(Foo<?C, ?D>)`
535 /// holds, which in turn implies that `?C::Item == ?D`. So once
536 /// `?C` is constrained, that should suffice to restrict `?D`.
540 impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
541 fn tcx(&self) -> TyCtxt<'tcx> {
544 fn param_env(&self) -> ty::ParamEnv<'tcx> {
548 fn tag(&self) -> &'static str {
552 fn a_is_expected(&self) -> bool {
560 ) -> RelateResult<'tcx, ty::Binder<T>>
564 Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?))
567 fn relate_item_substs(
570 a_subst: SubstsRef<'tcx>,
571 b_subst: SubstsRef<'tcx>,
572 ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
573 if self.ambient_variance == ty::Variance::Invariant {
574 // Avoid fetching the variance if we are in an invariant
575 // context; no need, and it can induce dependency cycles
577 relate::relate_substs(self, None, a_subst, b_subst)
579 let opt_variances = self.tcx().variances_of(item_def_id);
580 relate::relate_substs(self, Some(&opt_variances), a_subst, b_subst)
584 fn relate_with_variance<T: Relate<'tcx>>(
586 variance: ty::Variance,
589 ) -> RelateResult<'tcx, T> {
590 let old_ambient_variance = self.ambient_variance;
591 self.ambient_variance = self.ambient_variance.xform(variance);
593 let result = self.relate(a, b);
594 self.ambient_variance = old_ambient_variance;
598 fn tys(&mut self, t: Ty<'tcx>, t2: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
599 assert_eq!(t, t2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
601 if let Some(result) = self.cache.get(&t) {
602 return result.clone();
604 debug!("generalize: t={:?}", t);
606 // Check to see whether the type we are generalizing references
607 // any other type variable related to `vid` via
608 // subtyping. This is basically our "occurs check", preventing
609 // us from creating infinitely sized types.
610 let result = match *t.kind() {
611 ty::Infer(ty::TyVar(vid)) => {
612 let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
613 let sub_vid = self.infcx.inner.borrow_mut().type_variables().sub_root_var(vid);
614 if sub_vid == self.for_vid_sub_root {
615 // If sub-roots are equal, then `for_vid` and
616 // `vid` are related via subtyping.
617 Err(TypeError::CyclicTy(self.root_ty))
619 let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
621 TypeVariableValue::Known { value: u } => {
622 debug!("generalize: known value {:?}", u);
625 TypeVariableValue::Unknown { universe } => {
626 match self.ambient_variance {
627 // Invariant: no need to make a fresh type variable.
629 if self.for_universe.can_name(universe) {
634 // Bivariant: make a fresh var, but we
635 // may need a WF predicate. See
636 // comment on `needs_wf` field for
638 ty::Bivariant => self.needs_wf = true,
640 // Co/contravariant: this will be
641 // sufficiently constrained later on.
642 ty::Covariant | ty::Contravariant => (),
646 *self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
647 let new_var_id = self
652 .new_var(self.for_universe, false, origin);
653 let u = self.tcx().mk_ty_var(new_var_id);
654 debug!("generalize: replacing original vid={:?} with new={:?}", vid, u);
660 ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => {
661 // No matter what mode we are in,
662 // integer/floating-point types must be equal to be
666 _ => relate::super_relate_tys(self, t, t),
669 self.cache.insert(t, result.clone());
676 r2: ty::Region<'tcx>,
677 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
678 assert_eq!(r, r2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
680 debug!("generalize: regions r={:?}", r);
683 // Never make variables for regions bound within the type itself,
684 // nor for erased regions.
685 ty::ReLateBound(..) | ty::ReErased => {
689 ty::RePlaceholder(..)
693 | ty::ReEarlyBound(..)
694 | ty::ReFree(..) => {
695 // see common code below
699 // If we are in an invariant context, we can re-use the region
700 // as is, unless it happens to be in some universe that we
701 // can't name. (In the case of a region *variable*, we could
702 // use it if we promoted it into our universe, but we don't
704 if let ty::Invariant = self.ambient_variance {
705 let r_universe = self.infcx.universe_of_region(r);
706 if self.for_universe.can_name(r_universe) {
711 // FIXME: This is non-ideal because we don't give a
712 // very descriptive origin for this region variable.
713 Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.cause.span), self.for_universe))
718 c: &'tcx ty::Const<'tcx>,
719 c2: &'tcx ty::Const<'tcx>,
720 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
721 assert_eq!(c, c2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
724 ty::ConstKind::Infer(InferConst::Var(vid)) => {
725 let mut inner = self.infcx.inner.borrow_mut();
726 let variable_table = &mut inner.const_unification_table();
727 let var_value = variable_table.probe_value(vid);
728 match var_value.val {
729 ConstVariableValue::Known { value: u } => self.relate(u, u),
730 ConstVariableValue::Unknown { universe } => {
731 if self.for_universe.can_name(universe) {
734 let new_var_id = variable_table.new_key(ConstVarValue {
735 origin: var_value.origin,
736 val: ConstVariableValue::Unknown { universe: self.for_universe },
738 Ok(self.tcx().mk_const_var(new_var_id, c.ty))
743 ty::ConstKind::Unevaluated(..) if self.tcx().lazy_normalization() => Ok(c),
744 _ => relate::super_relate_consts(self, c, c),
749 pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
750 /// Register an obligation that both constants must be equal to each other.
752 /// If they aren't equal then the relation doesn't hold.
753 fn const_equate_obligation(&mut self, a: &'tcx ty::Const<'tcx>, b: &'tcx ty::Const<'tcx>);
756 pub trait RelateResultCompare<'tcx, T> {
757 fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T>
759 F: FnOnce() -> TypeError<'tcx>;
762 impl<'tcx, T: Clone + PartialEq> RelateResultCompare<'tcx, T> for RelateResult<'tcx, T> {
763 fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T>
765 F: FnOnce() -> TypeError<'tcx>,
767 self.clone().and_then(|s| if s == t { self.clone() } else { Err(f()) })
771 pub fn const_unification_error<'tcx>(
773 (a, b): (&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>),
774 ) -> TypeError<'tcx> {
775 TypeError::ConstMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))
778 fn int_unification_error<'tcx>(
780 v: (ty::IntVarValue, ty::IntVarValue),
781 ) -> TypeError<'tcx> {
783 TypeError::IntMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))
786 fn float_unification_error<'tcx>(
788 v: (ty::FloatVarValue, ty::FloatVarValue),
789 ) -> TypeError<'tcx> {
790 let (ty::FloatVarValue(a), ty::FloatVarValue(b)) = v;
791 TypeError::FloatMismatch(ty::relate::expected_found_bool(a_is_expected, a, b))