diff options
Diffstat (limited to 'compiler/rustc_infer/src/infer/combine.rs')
| -rw-r--r-- | compiler/rustc_infer/src/infer/combine.rs | 586 |
1 files changed, 40 insertions, 546 deletions
diff --git a/compiler/rustc_infer/src/infer/combine.rs b/compiler/rustc_infer/src/infer/combine.rs index 3f385c47f19..79fc02c6c79 100644 --- a/compiler/rustc_infer/src/infer/combine.rs +++ b/compiler/rustc_infer/src/infer/combine.rs @@ -26,24 +26,17 @@ use super::equate::Equate; use super::glb::Glb; use super::lub::Lub; use super::sub::Sub; -use super::type_variable::TypeVariableValue; -use super::{DefineOpaqueTypes, InferCtxt, MiscVariable, TypeTrace}; +use super::{DefineOpaqueTypes, InferCtxt, TypeTrace}; +use crate::infer::generalize::{self, CombineDelegate, Generalization}; use crate::traits::{Obligation, PredicateObligations}; -use rustc_data_structures::sso::SsoHashMap; -use rustc_hir::def_id::DefId; use rustc_middle::infer::canonical::OriginalQueryValues; 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, AliasKind, FallibleTypeFolder, InferConst, ToPredicate, Ty, TyCtxt, TypeFoldable, - TypeSuperFoldable, TypeVisitableExt, -}; +use rustc_middle::ty::relate::{RelateResult, TypeRelation}; +use rustc_middle::ty::{self, AliasKind, InferConst, ToPredicate, Ty, TyCtxt, TypeVisitableExt}; use rustc_middle::ty::{IntType, UintType}; -use rustc_span::{Span, DUMMY_SP}; +use rustc_span::DUMMY_SP; #[derive(Clone)] pub struct CombineFields<'infcx, 'tcx> { @@ -55,13 +48,6 @@ pub struct CombineFields<'infcx, 'tcx> { pub define_opaque_types: DefineOpaqueTypes, } -#[derive(Copy, Clone, Debug)] -pub enum RelationDir { - SubtypeOf, - SupertypeOf, - EqTo, -} - impl<'tcx> InferCtxt<'tcx> { pub fn super_combine_tys<R>( &self, @@ -152,7 +138,7 @@ impl<'tcx> InferCtxt<'tcx> { Ok(a) } - _ => ty::relate::super_relate_tys(relation, a, b), + _ => ty::relate::structurally_relate_tys(relation, a, b), } } @@ -211,11 +197,11 @@ impl<'tcx> InferCtxt<'tcx> { // matching in the solver. let a_error = self.tcx.const_error(a.ty(), guar); if let ty::ConstKind::Infer(InferConst::Var(vid)) = a.kind() { - return self.unify_const_variable(vid, a_error); + return self.unify_const_variable(vid, a_error, relation.param_env()); } let b_error = self.tcx.const_error(b.ty(), guar); if let ty::ConstKind::Infer(InferConst::Var(vid)) = b.kind() { - return self.unify_const_variable(vid, b_error); + return self.unify_const_variable(vid, b_error, relation.param_env()); } return Ok(if relation.a_is_expected() { a_error } else { b_error }); @@ -237,11 +223,11 @@ impl<'tcx> InferCtxt<'tcx> { } (ty::ConstKind::Infer(InferConst::Var(vid)), _) => { - return self.unify_const_variable(vid, b); + return self.unify_const_variable(vid, b, relation.param_env()); } (_, ty::ConstKind::Infer(InferConst::Var(vid))) => { - return self.unify_const_variable(vid, a); + return self.unify_const_variable(vid, a, relation.param_env()); } (ty::ConstKind::Unevaluated(..), _) | (_, ty::ConstKind::Unevaluated(..)) if self.tcx.lazy_normalization() => @@ -252,7 +238,7 @@ impl<'tcx> InferCtxt<'tcx> { _ => {} } - ty::relate::super_relate_consts(relation, a, b) + ty::relate::structurally_relate_consts(relation, a, b) } /// Unifies the const variable `target_vid` with the given constant. @@ -294,24 +280,17 @@ impl<'tcx> InferCtxt<'tcx> { &self, target_vid: ty::ConstVid<'tcx>, ct: ty::Const<'tcx>, + param_env: ty::ParamEnv<'tcx>, ) -> 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 = ct.try_fold_with(&mut ConstInferUnifier { - infcx: self, - span, - for_universe, + let span = + self.inner.borrow_mut().const_unification_table().probe_value(target_vid).origin.span; + let Generalization { value, needs_wf: _ } = generalize::generalize( + self, + &mut CombineDelegate { infcx: self, span, param_env }, + ct, target_vid, - })?; + ty::Variance::Invariant, + )?; self.inner.borrow_mut().const_unification_table().union_value( target_vid, @@ -392,12 +371,10 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> { pub fn instantiate( &mut self, a_ty: Ty<'tcx>, - dir: RelationDir, + ambient_variance: ty::Variance, 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()); @@ -412,7 +389,18 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> { // `'?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)?; + let Generalization { value: b_ty, needs_wf } = generalize::generalize( + self.infcx, + &mut CombineDelegate { + infcx: self.infcx, + param_env: self.param_env, + span: self.trace.span(), + }, + a_ty, + b_vid, + ambient_variance, + )?; + debug!(?b_ty); self.infcx.inner.borrow_mut().type_variables().instantiate(b_vid, b_ty); @@ -431,78 +419,23 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> { // 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( + match ambient_variance { + ty::Variance::Invariant => self.equate(a_is_expected).relate(a_ty, b_ty), + ty::Variance::Covariant => self.sub(a_is_expected).relate(a_ty, b_ty), + ty::Variance::Contravariant => self.sub(a_is_expected).relate_with_variance( ty::Contravariant, ty::VarianceDiagInfo::default(), a_ty, b_ty, ), + ty::Variance::Bivariant => { + unreachable!("no code should be generalizing bivariantly (currently)") + } }?; 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 register_obligations(&mut self, obligations: PredicateObligations<'tcx>) { self.obligations.extend(obligations.into_iter()); } @@ -514,313 +447,6 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> { } } -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>, 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<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<'tcx> 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, 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<T: Relate<'tcx>>( - &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::ReError(_) => { - 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 ObligationEmittingRelation<'tcx>: TypeRelation<'tcx> { /// Register obligations that must hold in order for this relation to hold fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>); @@ -873,135 +499,3 @@ fn float_unification_error<'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, - - 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>, -} - -impl<'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for ConstInferUnifier<'_, 'tcx> { - type Error = TypeError<'tcx>; - - fn interner(&self) -> TyCtxt<'tcx> { - self.infcx.tcx - } - - #[instrument(level = "debug", skip(self), ret)] - fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, TypeError<'tcx>> { - 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); - u.try_fold_with(self) - } - 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.interner().mk_ty_var(new_var_id)) - } - } - } - ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => Ok(t), - _ => t.try_super_fold_with(self), - } - } - - #[instrument(level = "debug", skip(self), ret)] - fn try_fold_region( - &mut self, - r: ty::Region<'tcx>, - ) -> Result<ty::Region<'tcx>, TypeError<'tcx>> { - debug!("ConstInferUnifier: r={:?}", r); - - match *r { - // Never make variables for regions bound within the type itself, - // nor for erased regions. - ty::ReLateBound(..) | ty::ReErased | ty::ReError(_) => { - 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), ret)] - fn try_fold_const(&mut self, c: ty::Const<'tcx>) -> Result<ty::Const<'tcx>, TypeError<'tcx>> { - 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 } => u.try_fold_with(self), - 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.interner().mk_const(new_var_id, c.ty())) - } - } - } - } - _ => c.try_super_fold_with(self), - } - } -} |