| /////////////////////////////////////////////////////////////////////////// |
| // # Type combining |
| // |
| // There are four type combiners: equate, sub, lub, and glb. Each |
| // implements the trait `Combine` and contains methods for combining |
| // two instances of various things and yielding a new instance. These |
| // combiner methods always yield a `Result<T>`. There is a lot of |
| // common code for these operations, implemented as default methods on |
| // the `Combine` trait. |
| // |
| // Each operation may have side-effects on the inference context, |
| // though these can be unrolled using snapshots. On success, the |
| // LUB/GLB operations return the appropriate bound. The Eq and Sub |
| // operations generally return the first operand. |
| // |
| // ## Contravariance |
| // |
| // When you are relating two things which have a contravariant |
| // relationship, you should use `contratys()` or `contraregions()`, |
| // rather than inversing the order of arguments! This is necessary |
| // because the order of arguments is not relevant for LUB and GLB. It |
| // is also useful to track which value is the "expected" value in |
| // terms of error reporting. |
| |
| use super::equate::Equate; |
| use super::glb::Glb; |
| use super::lub::Lub; |
| use super::sub::Sub; |
| use super::type_variable::TypeVariableValue; |
| use super::unify_key::replace_if_possible; |
| use super::unify_key::{ConstVarValue, ConstVariableValue}; |
| use super::unify_key::{ConstVariableOrigin, ConstVariableOriginKind}; |
| 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::traits::ObligationCause; |
| use rustc_middle::ty::error::TypeError; |
| use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation}; |
| use rustc_middle::ty::subst::SubstsRef; |
| use rustc_middle::ty::{self, InferConst, ToPredicate, Ty, TyCtxt, TypeFoldable}; |
| use rustc_middle::ty::{IntType, UintType}; |
| use rustc_span::{Span, DUMMY_SP}; |
| |
| #[derive(Clone)] |
| pub struct CombineFields<'infcx, 'tcx> { |
| pub infcx: &'infcx InferCtxt<'infcx, 'tcx>, |
| pub trace: TypeTrace<'tcx>, |
| pub cause: Option<ty::relate::Cause>, |
| pub param_env: ty::ParamEnv<'tcx>, |
| pub obligations: PredicateObligations<'tcx>, |
| } |
| |
| #[derive(Copy, Clone, Debug)] |
| pub enum RelationDir { |
| SubtypeOf, |
| SupertypeOf, |
| EqTo, |
| } |
| |
| impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> { |
| pub fn super_combine_tys<R>( |
| &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<R>( |
| &self, |
| relation: &mut R, |
| a: &'tcx ty::Const<'tcx>, |
| b: &'tcx ty::Const<'tcx>, |
| ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> |
| where |
| R: ConstEquateRelation<'tcx>, |
| { |
| debug!("{}.consts({:?}, {:?})", relation.tag(), a, b); |
| if a == b { |
| return Ok(a); |
| } |
| |
| let a = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table(), a); |
| let b = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table(), b); |
| |
| let a_is_expected = relation.a_is_expected(); |
| |
| match (a.val, b.val) { |
| ( |
| ty::ConstKind::Infer(InferConst::Var(a_vid)), |
| ty::ConstKind::Infer(InferConst::Var(b_vid)), |
| ) => { |
| self.inner |
| .borrow_mut() |
| .const_unification_table() |
| .unify_var_var(a_vid, b_vid) |
| .map_err(|e| const_unification_error(a_is_expected, e))?; |
| 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: |
| /// |
| /// ```rust |
| /// #![feature(const_generics)] |
| /// |
| /// fn bind<const N: usize>(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 `src/test/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: &'tcx ty::Const<'tcx>, |
| vid_is_expected: bool, |
| ) -> RelateResult<'tcx, &'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() |
| .unify_var_value( |
| target_vid, |
| ConstVarValue { |
| origin: ConstVariableOrigin { |
| kind: ConstVariableOriginKind::ConstInference, |
| span: DUMMY_SP, |
| }, |
| val: ConstVariableValue::Known { value }, |
| }, |
| ) |
| .map(|()| value) |
| .map_err(|e| const_unification_error(vid_is_expected, e)) |
| } |
| |
| 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. |
| 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()); |
| |
| debug!("instantiate(a_ty={:?} dir={:?} b_vid={:?})", a_ty, dir, b_vid); |
| |
| // 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!( |
| "instantiate(a_ty={:?}, dir={:?}, b_vid={:?}, generalized b_ty={:?})", |
| a_ty, dir, b_vid, b_ty |
| ); |
| self.infcx.inner.borrow_mut().type_variables().instantiate(b_vid, b_ty); |
| |
| if needs_wf { |
| self.obligations.push(Obligation::new( |
| self.trace.cause.clone(), |
| self.param_env, |
| ty::PredicateKind::WellFormed(b_ty.into()).to_predicate(self.infcx.tcx), |
| )); |
| } |
| |
| // 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, 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" |
| fn generalize( |
| &self, |
| ty: Ty<'tcx>, |
| for_vid: ty::TyVid, |
| dir: RelationDir, |
| ) -> RelateResult<'tcx, Generalization<'tcx>> { |
| debug!("generalize(ty={:?}, for_vid={:?}, dir={:?}", ty, for_vid, dir); |
| // 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, |
| }; |
| |
| debug!("generalize: ambient_variance = {:?}", 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, |
| }; |
| |
| debug!("generalize: for_universe = {:?}", for_universe); |
| debug!("generalize: 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 = match generalize.relate(ty, ty) { |
| Ok(ty) => ty, |
| Err(e) => { |
| debug!("generalize: failure {:?}", e); |
| return Err(e); |
| } |
| }; |
| let needs_wf = generalize.needs_wf; |
| debug!("generalize: success {{ {:?}, {:?} }}", ty, needs_wf); |
| Ok(Generalization { ty, needs_wf }) |
| } |
| |
| pub fn add_const_equate_obligation( |
| &mut self, |
| a_is_expected: bool, |
| a: &'tcx ty::Const<'tcx>, |
| b: &'tcx 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.trace.cause.clone(), |
| self.param_env, |
| predicate.to_predicate(self.tcx()), |
| )); |
| } |
| } |
| |
| struct Generalizer<'cx, 'tcx> { |
| infcx: &'cx InferCtxt<'cx, '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>, RelateResult<'tcx, 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. |
| 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<A, B> where A: Iterator<Item = B> { |
| /// 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<?A, ?B>`, |
| /// then after generalization we will wind up with a type like |
| /// `Foo<?C, ?D>`. When we enforce that `Foo<?A, ?B> <: Foo<?C, |
| /// ?D>` (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<?C, ?D>)` |
| /// holds, which in turn implies that `?C::Item == ?D`. So once |
| /// `?C` is constrained, that should suffice to restrict `?D`. |
| needs_wf: bool, |
| } |
| |
| impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> { |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.infcx.tcx |
| } |
| fn param_env(&self) -> ty::ParamEnv<'tcx> { |
| self.param_env |
| } |
| |
| fn tag(&self) -> &'static str { |
| "Generalizer" |
| } |
| |
| fn a_is_expected(&self) -> bool { |
| true |
| } |
| |
| fn binders<T>( |
| &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, None, a_subst, b_subst) |
| } else { |
| let opt_variances = self.tcx().variances_of(item_def_id); |
| relate::relate_substs(self, Some(&opt_variances), a_subst, b_subst) |
| } |
| } |
| |
| fn relate_with_variance<T: Relate<'tcx>>( |
| &mut self, |
| variance: ty::Variance, |
| 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 result.clone(); |
| } |
| 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, false, origin); |
| let u = self.tcx().mk_ty_var(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) |
| } |
| _ => relate::super_relate_tys(self, t, t), |
| }; |
| |
| self.cache.insert(t, result.clone()); |
| return 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::ReEmpty(_) |
| | 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: &'tcx ty::Const<'tcx>, |
| c2: &'tcx ty::Const<'tcx>, |
| ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> { |
| assert_eq!(c, c2); // we are abusing TypeRelation here; both LHS and RHS ought to be == |
| |
| match c.val { |
| 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_var(new_var_id, c.ty)) |
| } |
| } |
| } |
| } |
| ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) |
| if self.tcx().lazy_normalization() => |
| { |
| assert_eq!(promoted, None); |
| let substs = self.relate_with_variance(ty::Variance::Invariant, substs, substs)?; |
| Ok(self.tcx().mk_const(ty::Const { |
| ty: c.ty, |
| val: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }), |
| })) |
| } |
| _ => 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: &'tcx ty::Const<'tcx>, b: &'tcx ty::Const<'tcx>); |
| } |
| |
| pub trait RelateResultCompare<'tcx, T> { |
| fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T> |
| where |
| F: FnOnce() -> TypeError<'tcx>; |
| } |
| |
| impl<'tcx, T: Clone + PartialEq> RelateResultCompare<'tcx, T> for RelateResult<'tcx, T> { |
| fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T> |
| where |
| F: FnOnce() -> TypeError<'tcx>, |
| { |
| self.clone().and_then(|s| if s == t { self.clone() } else { Err(f()) }) |
| } |
| } |
| |
| pub fn const_unification_error<'tcx>( |
| a_is_expected: bool, |
| (a, b): (&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>), |
| ) -> TypeError<'tcx> { |
| TypeError::ConstMismatch(ty::relate::expected_found_bool(a_is_expected, a, b)) |
| } |
| |
| fn int_unification_error<'tcx>( |
| a_is_expected: bool, |
| v: (ty::IntVarValue, ty::IntVarValue), |
| ) -> TypeError<'tcx> { |
| let (a, b) = v; |
| TypeError::IntMismatch(ty::relate::expected_found_bool(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(ty::relate::expected_found_bool(a_is_expected, a, b)) |
| } |
| |
| struct ConstInferUnifier<'cx, 'tcx> { |
| infcx: &'cx InferCtxt<'cx, '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 TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> { |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.infcx.tcx |
| } |
| |
| fn param_env(&self) -> ty::ParamEnv<'tcx> { |
| self.param_env |
| } |
| |
| fn tag(&self) -> &'static str { |
| "ConstInferUnifier" |
| } |
| |
| fn a_is_expected(&self) -> bool { |
| true |
| } |
| |
| fn relate_with_variance<T: Relate<'tcx>>( |
| &mut self, |
| _variance: ty::Variance, |
| a: T, |
| b: T, |
| ) -> RelateResult<'tcx, T> { |
| // We don't care about variance here. |
| self.relate(a, b) |
| } |
| |
| fn binders<T>( |
| &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 tys(&mut self, t: Ty<'tcx>, _t: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { |
| debug_assert_eq!(t, _t); |
| debug!("ConstInferUnifier: 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, |
| false, |
| origin, |
| ); |
| let u = self.tcx().mk_ty_var(new_var_id); |
| debug!( |
| "ConstInferUnifier: replacing original vid={:?} with new={:?}", |
| vid, u |
| ); |
| Ok(u) |
| } |
| } |
| } |
| 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::ReEmpty(_) |
| | 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)) |
| } |
| } |
| |
| fn consts( |
| &mut self, |
| c: &'tcx ty::Const<'tcx>, |
| _c: &'tcx ty::Const<'tcx>, |
| ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> { |
| debug_assert_eq!(c, _c); |
| debug!("ConstInferUnifier: c={:?}", c); |
| |
| match c.val { |
| ty::ConstKind::Infer(InferConst::Var(vid)) => { |
| let mut inner = self.infcx.inner.borrow_mut(); |
| let variable_table = &mut inner.const_unification_table(); |
| |
| // 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 variable_table.unioned(self.target_vid, vid) { |
| return Err(TypeError::CyclicConst(c)); |
| } |
| |
| let var_value = variable_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 = variable_table.new_key(ConstVarValue { |
| origin: var_value.origin, |
| val: ConstVariableValue::Unknown { universe: self.for_universe }, |
| }); |
| Ok(self.tcx().mk_const_var(new_var_id, c.ty)) |
| } |
| } |
| } |
| } |
| ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) |
| if self.tcx().lazy_normalization() => |
| { |
| assert_eq!(promoted, None); |
| let substs = self.relate_with_variance(ty::Variance::Invariant, substs, substs)?; |
| Ok(self.tcx().mk_const(ty::Const { |
| ty: c.ty, |
| val: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }), |
| })) |
| } |
| _ => relate::super_relate_consts(self, c, c), |
| } |
| } |
| } |
