diff options
| -rw-r--r-- | compiler/rustc_middle/src/ty/relate.rs | 11 | ||||
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/mod.rs | 60 |
2 files changed, 57 insertions, 14 deletions
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs index 3bbe6a23b66..8bcae3d9ab7 100644 --- a/compiler/rustc_middle/src/ty/relate.rs +++ b/compiler/rustc_middle/src/ty/relate.rs @@ -589,17 +589,6 @@ pub fn structurally_relate_consts<'tcx, R: TypeRelation<'tcx>>( debug!("{}.structurally_relate_consts(a = {:?}, b = {:?})", relation.tag(), a, b); let tcx = relation.tcx(); - // HACK(const_generics): We still need to eagerly evaluate consts when - // relating them because during `normalize_param_env_or_error`, - // we may relate an evaluated constant in a obligation against - // an unnormalized (i.e. unevaluated) const in the param-env. - // FIXME(generic_const_exprs): Once we always lazily unify unevaluated constants - // these `eval` calls can be removed. - if !tcx.features().generic_const_exprs { - a = a.eval(tcx, relation.param_env()); - b = b.eval(tcx, relation.param_env()); - } - if tcx.features().generic_const_exprs { a = tcx.expand_abstract_consts(a); b = tcx.expand_abstract_consts(b); diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs index 4b38687eebe..f7389bda159 100644 --- a/compiler/rustc_trait_selection/src/traits/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/mod.rs @@ -32,7 +32,7 @@ use rustc_errors::ErrorGuaranteed; use rustc_middle::query::Providers; use rustc_middle::ty::fold::TypeFoldable; use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt}; -use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeSuperVisitable}; +use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFolder, TypeSuperVisitable}; use rustc_middle::ty::{InternalSubsts, SubstsRef}; use rustc_span::def_id::DefId; use rustc_span::Span; @@ -272,8 +272,62 @@ pub fn normalize_param_env_or_error<'tcx>( // parameter environments once for every fn as it goes, // and errors will get reported then; so outside of type inference we // can be sure that no errors should occur. - let mut predicates: Vec<_> = - util::elaborate(tcx, unnormalized_env.caller_bounds().into_iter()).collect(); + let mut predicates: Vec<_> = util::elaborate( + tcx, + unnormalized_env.caller_bounds().into_iter().map(|predicate| { + if tcx.features().generic_const_exprs { + return predicate; + } + + struct ConstNormalizer<'tcx>(TyCtxt<'tcx>); + + impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ConstNormalizer<'tcx> { + fn interner(&self) -> TyCtxt<'tcx> { + self.0 + } + + fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> { + // While it is pretty sus to be evaluating things with an empty param env, it + // should actually be okay since without `feature(generic_const_exprs)` the only + // const arguments that have a non-empty param env are array repeat counts. These + // do not appear in the type system though. + c.eval(self.0, ty::ParamEnv::empty()) + } + } + + // This whole normalization step is a hack to work around the fact that + // `normalize_param_env_or_error` is fundamentally broken from using an + // unnormalized param env with a trait solver that expects the param env + // to be normalized. + // + // When normalizing the param env we can end up evaluating obligations + // that have been normalized but can only be proven via a where clause + // which is still in its unnormalized form. example: + // + // Attempting to prove `T: Trait<<u8 as Identity>::Assoc>` in a param env + // with a `T: Trait<<u8 as Identity>::Assoc>` where clause will fail because + // we first normalize obligations before proving them so we end up proving + // `T: Trait<u8>`. Since lazy normalization is not implemented equating `u8` + // with `<u8 as Identity>::Assoc` fails outright so we incorrectly believe that + // we cannot prove `T: Trait<u8>`. + // + // The same thing is true for const generics- attempting to prove + // `T: Trait<ConstKind::Unevaluated(...)>` with the same thing as a where clauses + // will fail. After normalization we may be attempting to prove `T: Trait<4>` with + // the unnormalized where clause `T: Trait<ConstKind::Unevaluated(...)>`. In order + // for the obligation to hold `4` must be equal to `ConstKind::Unevaluated(...)` + // but as we do not have lazy norm implemented, equating the two consts fails outright. + // + // Ideally we would not normalize consts here at all but it is required for backwards + // compatibility. Eventually when lazy norm is implemented this can just be removed. + // We do not normalize types here as there is no backwards compatibility requirement + // for us to do so. + // + // FIXME(-Ztrait-solver=next): remove this hack since we have deferred projection equality + predicate.fold_with(&mut ConstNormalizer(tcx)) + }), + ) + .collect(); debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates); |