//! There are four type combiners: [Equate], [Sub], [Lub], and [Glb]. //! Each implements the trait [TypeRelation] and contains methods for //! combining two instances of various things and yielding a new instance. //! These combiner methods always yield a `Result`. To relate two //! types, you can use `infcx.at(cause, param_env)` which then allows //! you to use the relevant methods of [At](super::at::At). //! //! Combiners mostly do their specific behavior and then hand off the //! bulk of the work to [InferCtxt::super_combine_tys] and //! [InferCtxt::super_combine_consts]. //! //! Combining two types may have side-effects on the inference contexts //! which can be undone by using snapshots. You probably want to use //! either [InferCtxt::commit_if_ok] or [InferCtxt::probe]. //! //! On success, the LUB/GLB operations return the appropriate bound. The //! return value of `Equate` or `Sub` shouldn't really be used. //! //! ## Contravariance //! //! We explicitly track which argument is expected using //! [TypeRelation::a_is_expected], so when dealing with contravariance //! this should be correctly updated. use super::equate::Equate; use super::glb::Glb; use super::lub::Lub; use super::sub::Sub; use super::type_variable::TypeVariableValue; use super::{InferCtxt, MiscVariable, TypeTrace}; use crate::traits::{Obligation, PredicateObligations}; use rustc_data_structures::sso::SsoHashMap; use rustc_hir::def_id::DefId; use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue}; use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind}; use rustc_middle::traits::ObligationCause; use rustc_middle::ty::error::{ExpectedFound, TypeError}; use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation}; use rustc_middle::ty::subst::SubstsRef; use rustc_middle::ty::{self, InferConst, Ty, TyCtxt, TypeVisitable}; use rustc_middle::ty::{IntType, UintType}; use rustc_span::{Span, DUMMY_SP}; #[derive(Clone)] pub struct CombineFields<'infcx, 'tcx> { pub infcx: &'infcx InferCtxt<'tcx>, pub trace: TypeTrace<'tcx>, pub cause: Option, pub param_env: ty::ParamEnv<'tcx>, pub obligations: PredicateObligations<'tcx>, /// Whether we should define opaque types /// or just treat them opaquely. /// Currently only used to prevent predicate /// matching from matching anything against opaque /// types. pub define_opaque_types: bool, } #[derive(Copy, Clone, Debug)] pub enum RelationDir { SubtypeOf, SupertypeOf, EqTo, } impl<'tcx> InferCtxt<'tcx> { pub fn super_combine_tys( &self, relation: &mut R, a: Ty<'tcx>, b: Ty<'tcx>, ) -> RelateResult<'tcx, Ty<'tcx>> where R: TypeRelation<'tcx>, { let a_is_expected = relation.a_is_expected(); match (a.kind(), b.kind()) { // Relate integral variables to other types (&ty::Infer(ty::IntVar(a_id)), &ty::Infer(ty::IntVar(b_id))) => { self.inner .borrow_mut() .int_unification_table() .unify_var_var(a_id, b_id) .map_err(|e| int_unification_error(a_is_expected, e))?; Ok(a) } (&ty::Infer(ty::IntVar(v_id)), &ty::Int(v)) => { self.unify_integral_variable(a_is_expected, v_id, IntType(v)) } (&ty::Int(v), &ty::Infer(ty::IntVar(v_id))) => { self.unify_integral_variable(!a_is_expected, v_id, IntType(v)) } (&ty::Infer(ty::IntVar(v_id)), &ty::Uint(v)) => { self.unify_integral_variable(a_is_expected, v_id, UintType(v)) } (&ty::Uint(v), &ty::Infer(ty::IntVar(v_id))) => { self.unify_integral_variable(!a_is_expected, v_id, UintType(v)) } // Relate floating-point variables to other types (&ty::Infer(ty::FloatVar(a_id)), &ty::Infer(ty::FloatVar(b_id))) => { self.inner .borrow_mut() .float_unification_table() .unify_var_var(a_id, b_id) .map_err(|e| float_unification_error(relation.a_is_expected(), e))?; Ok(a) } (&ty::Infer(ty::FloatVar(v_id)), &ty::Float(v)) => { self.unify_float_variable(a_is_expected, v_id, v) } (&ty::Float(v), &ty::Infer(ty::FloatVar(v_id))) => { self.unify_float_variable(!a_is_expected, v_id, v) } // All other cases of inference are errors (&ty::Infer(_), _) | (_, &ty::Infer(_)) => { Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b))) } _ => ty::relate::super_relate_tys(relation, a, b), } } pub fn super_combine_consts( &self, relation: &mut R, a: ty::Const<'tcx>, b: ty::Const<'tcx>, ) -> RelateResult<'tcx, ty::Const<'tcx>> where R: ConstEquateRelation<'tcx>, { debug!("{}.consts({:?}, {:?})", relation.tag(), a, b); if a == b { return Ok(a); } let a = self.shallow_resolve(a); let b = self.shallow_resolve(b); let a_is_expected = relation.a_is_expected(); match (a.kind(), b.kind()) { ( ty::ConstKind::Infer(InferConst::Var(a_vid)), ty::ConstKind::Infer(InferConst::Var(b_vid)), ) => { self.inner.borrow_mut().const_unification_table().union(a_vid, b_vid); return Ok(a); } // All other cases of inference with other variables are errors. (ty::ConstKind::Infer(InferConst::Var(_)), ty::ConstKind::Infer(_)) | (ty::ConstKind::Infer(_), ty::ConstKind::Infer(InferConst::Var(_))) => { bug!("tried to combine ConstKind::Infer/ConstKind::Infer(InferConst::Var)") } (ty::ConstKind::Infer(InferConst::Var(vid)), _) => { return self.unify_const_variable(relation.param_env(), vid, b, a_is_expected); } (_, ty::ConstKind::Infer(InferConst::Var(vid))) => { return self.unify_const_variable(relation.param_env(), vid, a, !a_is_expected); } (ty::ConstKind::Unevaluated(..), _) if self.tcx.lazy_normalization() => { // FIXME(#59490): Need to remove the leak check to accommodate // escaping bound variables here. if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() { relation.const_equate_obligation(a, b); } return Ok(b); } (_, ty::ConstKind::Unevaluated(..)) if self.tcx.lazy_normalization() => { // FIXME(#59490): Need to remove the leak check to accommodate // escaping bound variables here. if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() { relation.const_equate_obligation(a, b); } return Ok(a); } _ => {} } ty::relate::super_relate_consts(relation, a, b) } /// Unifies the const variable `target_vid` with the given constant. /// /// This also tests if the given const `ct` contains an inference variable which was previously /// unioned with `target_vid`. If this is the case, inferring `target_vid` to `ct` /// would result in an infinite type as we continuously replace an inference variable /// in `ct` with `ct` itself. /// /// This is especially important as unevaluated consts use their parents generics. /// They therefore often contain unused substs, making these errors far more likely. /// /// A good example of this is the following: /// /// ```compile_fail,E0308 /// #![feature(generic_const_exprs)] /// /// fn bind(value: [u8; N]) -> [u8; 3 + 4] { /// todo!() /// } /// /// fn main() { /// let mut arr = Default::default(); /// arr = bind(arr); /// } /// ``` /// /// Here `3 + 4` ends up as `ConstKind::Unevaluated` which uses the generics /// of `fn bind` (meaning that its substs contain `N`). /// /// `bind(arr)` now infers that the type of `arr` must be `[u8; N]`. /// The assignment `arr = bind(arr)` now tries to equate `N` with `3 + 4`. /// /// As `3 + 4` contains `N` in its substs, this must not succeed. /// /// See `tests/ui/const-generics/occurs-check/` for more examples where this is relevant. #[instrument(level = "debug", skip(self))] fn unify_const_variable( &self, param_env: ty::ParamEnv<'tcx>, target_vid: ty::ConstVid<'tcx>, ct: ty::Const<'tcx>, vid_is_expected: bool, ) -> RelateResult<'tcx, ty::Const<'tcx>> { let (for_universe, span) = { let mut inner = self.inner.borrow_mut(); let variable_table = &mut inner.const_unification_table(); let var_value = variable_table.probe_value(target_vid); match var_value.val { ConstVariableValue::Known { value } => { bug!("instantiating {:?} which has a known value {:?}", target_vid, value) } ConstVariableValue::Unknown { universe } => (universe, var_value.origin.span), } }; let value = ConstInferUnifier { infcx: self, span, param_env, for_universe, target_vid } .relate(ct, ct)?; self.inner.borrow_mut().const_unification_table().union_value( target_vid, ConstVarValue { origin: ConstVariableOrigin { kind: ConstVariableOriginKind::ConstInference, span: DUMMY_SP, }, val: ConstVariableValue::Known { value }, }, ); Ok(value) } fn unify_integral_variable( &self, vid_is_expected: bool, vid: ty::IntVid, val: ty::IntVarValue, ) -> RelateResult<'tcx, Ty<'tcx>> { self.inner .borrow_mut() .int_unification_table() .unify_var_value(vid, Some(val)) .map_err(|e| int_unification_error(vid_is_expected, e))?; match val { IntType(v) => Ok(self.tcx.mk_mach_int(v)), UintType(v) => Ok(self.tcx.mk_mach_uint(v)), } } fn unify_float_variable( &self, vid_is_expected: bool, vid: ty::FloatVid, val: ty::FloatTy, ) -> RelateResult<'tcx, Ty<'tcx>> { self.inner .borrow_mut() .float_unification_table() .unify_var_value(vid, Some(ty::FloatVarValue(val))) .map_err(|e| float_unification_error(vid_is_expected, e))?; Ok(self.tcx.mk_mach_float(val)) } } impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> { pub fn tcx(&self) -> TyCtxt<'tcx> { self.infcx.tcx } pub fn equate<'a>(&'a mut self, a_is_expected: bool) -> Equate<'a, 'infcx, 'tcx> { Equate::new(self, a_is_expected) } pub fn sub<'a>(&'a mut self, a_is_expected: bool) -> Sub<'a, 'infcx, 'tcx> { Sub::new(self, a_is_expected) } pub fn lub<'a>(&'a mut self, a_is_expected: bool) -> Lub<'a, 'infcx, 'tcx> { Lub::new(self, a_is_expected) } pub fn glb<'a>(&'a mut self, a_is_expected: bool) -> Glb<'a, 'infcx, 'tcx> { Glb::new(self, a_is_expected) } /// Here, `dir` is either `EqTo`, `SubtypeOf`, or `SupertypeOf`. /// The idea is that we should ensure that the type `a_ty` is equal /// to, a subtype of, or a supertype of (respectively) the type /// to which `b_vid` is bound. /// /// Since `b_vid` has not yet been instantiated with a type, we /// will first instantiate `b_vid` with a *generalized* version /// of `a_ty`. Generalization introduces other inference /// variables wherever subtyping could occur. #[instrument(skip(self), level = "debug")] pub fn instantiate( &mut self, a_ty: Ty<'tcx>, dir: RelationDir, b_vid: ty::TyVid, a_is_expected: bool, ) -> RelateResult<'tcx, ()> { use self::RelationDir::*; // Get the actual variable that b_vid has been inferred to debug_assert!(self.infcx.inner.borrow_mut().type_variables().probe(b_vid).is_unknown()); // Generalize type of `a_ty` appropriately depending on the // direction. As an example, assume: // // - `a_ty == &'x ?1`, where `'x` is some free region and `?1` is an // inference variable, // - and `dir` == `SubtypeOf`. // // Then the generalized form `b_ty` would be `&'?2 ?3`, where // `'?2` and `?3` are fresh region/type inference // variables. (Down below, we will relate `a_ty <: b_ty`, // adding constraints like `'x: '?2` and `?1 <: ?3`.) let Generalization { ty: b_ty, needs_wf } = self.generalize(a_ty, b_vid, dir)?; debug!(?b_ty); self.infcx.inner.borrow_mut().type_variables().instantiate(b_vid, b_ty); if needs_wf { self.obligations.push(Obligation::new( self.tcx(), self.trace.cause.clone(), self.param_env, ty::Binder::dummy(ty::PredicateKind::WellFormed(b_ty.into())), )); } // Finally, relate `b_ty` to `a_ty`, as described in previous comment. // // FIXME(#16847): This code is non-ideal because all these subtype // relations wind up attributed to the same spans. We need // to associate causes/spans with each of the relations in // the stack to get this right. match dir { EqTo => self.equate(a_is_expected).relate(a_ty, b_ty), SubtypeOf => self.sub(a_is_expected).relate(a_ty, b_ty), SupertypeOf => self.sub(a_is_expected).relate_with_variance( ty::Contravariant, ty::VarianceDiagInfo::default(), a_ty, b_ty, ), }?; Ok(()) } /// Attempts to generalize `ty` for the type variable `for_vid`. /// This checks for cycle -- that is, whether the type `ty` /// references `for_vid`. The `dir` is the "direction" for which we /// a performing the generalization (i.e., are we producing a type /// that can be used as a supertype etc). /// /// Preconditions: /// /// - `for_vid` is a "root vid" #[instrument(skip(self), level = "trace", ret)] fn generalize( &self, ty: Ty<'tcx>, for_vid: ty::TyVid, dir: RelationDir, ) -> RelateResult<'tcx, Generalization<'tcx>> { // Determine the ambient variance within which `ty` appears. // The surrounding equation is: // // ty [op] ty2 // // where `op` is either `==`, `<:`, or `:>`. This maps quite // naturally. let ambient_variance = match dir { RelationDir::EqTo => ty::Invariant, RelationDir::SubtypeOf => ty::Covariant, RelationDir::SupertypeOf => ty::Contravariant, }; trace!(?ambient_variance); let for_universe = match self.infcx.inner.borrow_mut().type_variables().probe(for_vid) { v @ TypeVariableValue::Known { .. } => { bug!("instantiating {:?} which has a known value {:?}", for_vid, v,) } TypeVariableValue::Unknown { universe } => universe, }; trace!(?for_universe); trace!(?self.trace); let mut generalize = Generalizer { infcx: self.infcx, cause: &self.trace.cause, for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables().sub_root_var(for_vid), for_universe, ambient_variance, needs_wf: false, root_ty: ty, param_env: self.param_env, cache: SsoHashMap::new(), }; let ty = generalize.relate(ty, ty)?; let needs_wf = generalize.needs_wf; Ok(Generalization { ty, needs_wf }) } pub fn add_const_equate_obligation( &mut self, a_is_expected: bool, a: ty::Const<'tcx>, b: ty::Const<'tcx>, ) { let predicate = if a_is_expected { ty::PredicateKind::ConstEquate(a, b) } else { ty::PredicateKind::ConstEquate(b, a) }; self.obligations.push(Obligation::new( self.tcx(), self.trace.cause.clone(), self.param_env, ty::Binder::dummy(predicate), )); } pub fn mark_ambiguous(&mut self) { self.obligations.push(Obligation::new( self.tcx(), self.trace.cause.clone(), self.param_env, ty::Binder::dummy(ty::PredicateKind::Ambiguous), )); } } struct Generalizer<'cx, 'tcx> { infcx: &'cx InferCtxt<'tcx>, /// The span, used when creating new type variables and things. cause: &'cx ObligationCause<'tcx>, /// The vid of the type variable that is in the process of being /// instantiated; if we find this within the type we are folding, /// that means we would have created a cyclic type. for_vid_sub_root: ty::TyVid, /// The universe of the type variable that is in the process of /// being instantiated. Any fresh variables that we create in this /// process should be in that same universe. for_universe: ty::UniverseIndex, /// Track the variance as we descend into the type. ambient_variance: ty::Variance, /// See the field `needs_wf` in `Generalization`. needs_wf: bool, /// The root type that we are generalizing. Used when reporting cycles. root_ty: Ty<'tcx>, param_env: ty::ParamEnv<'tcx>, cache: SsoHashMap, Ty<'tcx>>, } /// Result from a generalization operation. This includes /// not only the generalized type, but also a bool flag /// indicating whether further WF checks are needed. #[derive(Debug)] struct Generalization<'tcx> { ty: Ty<'tcx>, /// If true, then the generalized type may not be well-formed, /// even if the source type is well-formed, so we should add an /// additional check to enforce that it is. This arises in /// particular around 'bivariant' type parameters that are only /// constrained by a where-clause. As an example, imagine a type: /// /// struct Foo where A: Iterator { /// data: A /// } /// /// here, `A` will be covariant, but `B` is /// unconstrained. However, whatever it is, for `Foo` to be WF, it /// must be equal to `A::Item`. If we have an input `Foo`, /// then after generalization we will wind up with a type like /// `Foo`. When we enforce that `Foo <: Foo` (or `>:`), we will wind up with the requirement that `?A /// <: ?C`, but no particular relationship between `?B` and `?D` /// (after all, we do not know the variance of the normalized form /// of `A::Item` with respect to `A`). If we do nothing else, this /// may mean that `?D` goes unconstrained (as in #41677). So, in /// this scenario where we create a new type variable in a /// bivariant context, we set the `needs_wf` flag to true. This /// will force the calling code to check that `WF(Foo)` /// holds, which in turn implies that `?C::Item == ?D`. So once /// `?C` is constrained, that should suffice to restrict `?D`. needs_wf: bool, } impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> { fn tcx(&self) -> TyCtxt<'tcx> { self.infcx.tcx } fn intercrate(&self) -> bool { self.infcx.intercrate } fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env } fn tag(&self) -> &'static str { "Generalizer" } fn a_is_expected(&self) -> bool { true } fn mark_ambiguous(&mut self) { span_bug!(self.cause.span, "opaque types are handled in `tys`"); } fn binders( &mut self, a: ty::Binder<'tcx, T>, b: ty::Binder<'tcx, T>, ) -> RelateResult<'tcx, ty::Binder<'tcx, T>> where T: Relate<'tcx>, { Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?)) } fn relate_item_substs( &mut self, item_def_id: DefId, a_subst: SubstsRef<'tcx>, b_subst: SubstsRef<'tcx>, ) -> RelateResult<'tcx, SubstsRef<'tcx>> { if self.ambient_variance == ty::Variance::Invariant { // Avoid fetching the variance if we are in an invariant // context; no need, and it can induce dependency cycles // (e.g., #41849). relate::relate_substs(self, a_subst, b_subst) } else { let tcx = self.tcx(); let opt_variances = tcx.variances_of(item_def_id); relate::relate_substs_with_variances( self, item_def_id, &opt_variances, a_subst, b_subst, true, ) } } fn relate_with_variance>( &mut self, variance: ty::Variance, _info: ty::VarianceDiagInfo<'tcx>, a: T, b: T, ) -> RelateResult<'tcx, T> { let old_ambient_variance = self.ambient_variance; self.ambient_variance = self.ambient_variance.xform(variance); let result = self.relate(a, b); self.ambient_variance = old_ambient_variance; result } fn tys(&mut self, t: Ty<'tcx>, t2: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { assert_eq!(t, t2); // we are abusing TypeRelation here; both LHS and RHS ought to be == if let Some(&result) = self.cache.get(&t) { return Ok(result); } debug!("generalize: t={:?}", t); // Check to see whether the type we are generalizing references // any other type variable related to `vid` via // subtyping. This is basically our "occurs check", preventing // us from creating infinitely sized types. let result = match *t.kind() { ty::Infer(ty::TyVar(vid)) => { let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid); let sub_vid = self.infcx.inner.borrow_mut().type_variables().sub_root_var(vid); if sub_vid == self.for_vid_sub_root { // If sub-roots are equal, then `for_vid` and // `vid` are related via subtyping. Err(TypeError::CyclicTy(self.root_ty)) } else { let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid); match probe { TypeVariableValue::Known { value: u } => { debug!("generalize: known value {:?}", u); self.relate(u, u) } TypeVariableValue::Unknown { universe } => { match self.ambient_variance { // Invariant: no need to make a fresh type variable. ty::Invariant => { if self.for_universe.can_name(universe) { return Ok(t); } } // Bivariant: make a fresh var, but we // may need a WF predicate. See // comment on `needs_wf` field for // more info. ty::Bivariant => self.needs_wf = true, // Co/contravariant: this will be // sufficiently constrained later on. ty::Covariant | ty::Contravariant => (), } let origin = *self.infcx.inner.borrow_mut().type_variables().var_origin(vid); let new_var_id = self .infcx .inner .borrow_mut() .type_variables() .new_var(self.for_universe, origin); let u = self.tcx().mk_ty_var(new_var_id); // Record that we replaced `vid` with `new_var_id` as part of a generalization // operation. This is needed to detect cyclic types. To see why, see the // docs in the `type_variables` module. self.infcx.inner.borrow_mut().type_variables().sub(vid, new_var_id); debug!("generalize: replacing original vid={:?} with new={:?}", vid, u); Ok(u) } } } } ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => { // No matter what mode we are in, // integer/floating-point types must be equal to be // relatable. Ok(t) } ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => { let s = self.relate(substs, substs)?; Ok(if s == substs { t } else { self.infcx.tcx.mk_opaque(def_id, s) }) } _ => relate::super_relate_tys(self, t, t), }?; self.cache.insert(t, result); Ok(result) } fn regions( &mut self, r: ty::Region<'tcx>, r2: ty::Region<'tcx>, ) -> RelateResult<'tcx, ty::Region<'tcx>> { assert_eq!(r, r2); // we are abusing TypeRelation here; both LHS and RHS ought to be == debug!("generalize: regions r={:?}", r); match *r { // Never make variables for regions bound within the type itself, // nor for erased regions. ty::ReLateBound(..) | ty::ReErased => { return Ok(r); } ty::RePlaceholder(..) | ty::ReVar(..) | ty::ReStatic | ty::ReEarlyBound(..) | ty::ReFree(..) => { // see common code below } } // If we are in an invariant context, we can re-use the region // as is, unless it happens to be in some universe that we // can't name. (In the case of a region *variable*, we could // use it if we promoted it into our universe, but we don't // bother.) if let ty::Invariant = self.ambient_variance { let r_universe = self.infcx.universe_of_region(r); if self.for_universe.can_name(r_universe) { return Ok(r); } } // FIXME: This is non-ideal because we don't give a // very descriptive origin for this region variable. Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.cause.span), self.for_universe)) } fn consts( &mut self, c: ty::Const<'tcx>, c2: ty::Const<'tcx>, ) -> RelateResult<'tcx, ty::Const<'tcx>> { assert_eq!(c, c2); // we are abusing TypeRelation here; both LHS and RHS ought to be == match c.kind() { ty::ConstKind::Infer(InferConst::Var(vid)) => { let mut inner = self.infcx.inner.borrow_mut(); let variable_table = &mut inner.const_unification_table(); let var_value = variable_table.probe_value(vid); match var_value.val { ConstVariableValue::Known { value: u } => { drop(inner); self.relate(u, u) } ConstVariableValue::Unknown { universe } => { if self.for_universe.can_name(universe) { Ok(c) } else { let new_var_id = variable_table.new_key(ConstVarValue { origin: var_value.origin, val: ConstVariableValue::Unknown { universe: self.for_universe }, }); Ok(self.tcx().mk_const(new_var_id, c.ty())) } } } } ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }) => { let substs = self.relate_with_variance( ty::Variance::Invariant, ty::VarianceDiagInfo::default(), substs, substs, )?; Ok(self.tcx().mk_const(ty::UnevaluatedConst { def, substs }, c.ty())) } _ => relate::super_relate_consts(self, c, c), } } } pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> { /// Register an obligation that both constants must be equal to each other. /// /// If they aren't equal then the relation doesn't hold. fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>); } fn int_unification_error<'tcx>( a_is_expected: bool, v: (ty::IntVarValue, ty::IntVarValue), ) -> TypeError<'tcx> { let (a, b) = v; TypeError::IntMismatch(ExpectedFound::new(a_is_expected, a, b)) } fn float_unification_error<'tcx>( a_is_expected: bool, v: (ty::FloatVarValue, ty::FloatVarValue), ) -> TypeError<'tcx> { let (ty::FloatVarValue(a), ty::FloatVarValue(b)) = v; TypeError::FloatMismatch(ExpectedFound::new(a_is_expected, a, b)) } struct ConstInferUnifier<'cx, 'tcx> { infcx: &'cx InferCtxt<'tcx>, span: Span, param_env: ty::ParamEnv<'tcx>, for_universe: ty::UniverseIndex, /// The vid of the const variable that is in the process of being /// instantiated; if we find this within the const we are folding, /// that means we would have created a cyclic const. target_vid: ty::ConstVid<'tcx>, } // We use `TypeRelation` here to propagate `RelateResult` upwards. // // Both inputs are expected to be the same. impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> { fn tcx(&self) -> TyCtxt<'tcx> { self.infcx.tcx } fn intercrate(&self) -> bool { assert!(!self.infcx.intercrate); false } fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env } fn tag(&self) -> &'static str { "ConstInferUnifier" } fn a_is_expected(&self) -> bool { true } fn mark_ambiguous(&mut self) { bug!() } fn relate_with_variance>( &mut self, _variance: ty::Variance, _info: ty::VarianceDiagInfo<'tcx>, a: T, b: T, ) -> RelateResult<'tcx, T> { // We don't care about variance here. self.relate(a, b) } fn binders( &mut self, a: ty::Binder<'tcx, T>, b: ty::Binder<'tcx, T>, ) -> RelateResult<'tcx, ty::Binder<'tcx, T>> where T: Relate<'tcx>, { Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?)) } #[instrument(level = "debug", skip(self), ret)] fn tys(&mut self, t: Ty<'tcx>, _t: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { debug_assert_eq!(t, _t); match t.kind() { &ty::Infer(ty::TyVar(vid)) => { let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid); let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid); match probe { TypeVariableValue::Known { value: u } => { debug!("ConstOccursChecker: known value {:?}", u); self.tys(u, u) } TypeVariableValue::Unknown { universe } => { if self.for_universe.can_name(universe) { return Ok(t); } let origin = *self.infcx.inner.borrow_mut().type_variables().var_origin(vid); let new_var_id = self .infcx .inner .borrow_mut() .type_variables() .new_var(self.for_universe, origin); Ok(self.tcx().mk_ty_var(new_var_id)) } } } ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => Ok(t), _ => relate::super_relate_tys(self, t, t), } } fn regions( &mut self, r: ty::Region<'tcx>, _r: ty::Region<'tcx>, ) -> RelateResult<'tcx, ty::Region<'tcx>> { debug_assert_eq!(r, _r); debug!("ConstInferUnifier: r={:?}", r); match *r { // Never make variables for regions bound within the type itself, // nor for erased regions. ty::ReLateBound(..) | ty::ReErased => { return Ok(r); } ty::RePlaceholder(..) | ty::ReVar(..) | ty::ReStatic | ty::ReEarlyBound(..) | ty::ReFree(..) => { // see common code below } } let r_universe = self.infcx.universe_of_region(r); if self.for_universe.can_name(r_universe) { return Ok(r); } else { // FIXME: This is non-ideal because we don't give a // very descriptive origin for this region variable. Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.span), self.for_universe)) } } #[instrument(level = "debug", skip(self))] fn consts( &mut self, c: ty::Const<'tcx>, _c: ty::Const<'tcx>, ) -> RelateResult<'tcx, ty::Const<'tcx>> { debug_assert_eq!(c, _c); match c.kind() { ty::ConstKind::Infer(InferConst::Var(vid)) => { // Check if the current unification would end up // unifying `target_vid` with a const which contains // an inference variable which is unioned with `target_vid`. // // Not doing so can easily result in stack overflows. if self .infcx .inner .borrow_mut() .const_unification_table() .unioned(self.target_vid, vid) { return Err(TypeError::CyclicConst(c)); } let var_value = self.infcx.inner.borrow_mut().const_unification_table().probe_value(vid); match var_value.val { ConstVariableValue::Known { value: u } => self.consts(u, u), ConstVariableValue::Unknown { universe } => { if self.for_universe.can_name(universe) { Ok(c) } else { let new_var_id = self.infcx.inner.borrow_mut().const_unification_table().new_key( ConstVarValue { origin: var_value.origin, val: ConstVariableValue::Unknown { universe: self.for_universe, }, }, ); Ok(self.tcx().mk_const(new_var_id, c.ty())) } } } } ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }) => { let substs = self.relate_with_variance( ty::Variance::Invariant, ty::VarianceDiagInfo::default(), substs, substs, )?; Ok(self.tcx().mk_const(ty::UnevaluatedConst { def, substs }, c.ty())) } _ => relate::super_relate_consts(self, c, c), } } }