bjoernager/rust
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add a deep fast_reject routine

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This commit is contained in:
lcnr 2022-05-24 09:15:19 +02:00
parent b8d0cd8de0
commit a76277c6c4
3 changed files with 240 additions and 55 deletions
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33
compiler/rustc_trait_selection/src/traits/coherence.rs
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@ -20,7 +20,7 @@ use rustc_hir::CRATE_HIR_ID;
use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::{util, TraitEngine};
use rustc_middle::traits::specialization_graph::OverlapMode;
use rustc_middle::ty::fast_reject::{self, TreatParams};
use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
use rustc_middle::ty::fold::TypeFoldable;
use rustc_middle::ty::subst::Subst;
use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt};
@ -79,26 +79,21 @@ where
// Before doing expensive operations like entering an inference context, do
// a quick check via fast_reject to tell if the impl headers could possibly
// unify.
let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer };
let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
// Check if any of the input types definitely do not unify.
if iter::zip(
impl1_ref.iter().flat_map(|tref| tref.substs.types()),
impl2_ref.iter().flat_map(|tref| tref.substs.types()),
)
.any(|(ty1, ty2)| {
let t1 = fast_reject::simplify_type(tcx, ty1, TreatParams::AsInfer);
let t2 = fast_reject::simplify_type(tcx, ty2, TreatParams::AsInfer);
if let (Some(t1), Some(t2)) = (t1, t2) {
// Simplified successfully
t1 != t2
} else {
// Types might unify
false
let may_overlap = match (impl1_ref, impl2_ref) {
(Some(a), Some(b)) => iter::zip(a.substs, b.substs)
.all(|(arg1, arg2)| drcx.generic_args_may_unify(arg1, arg2)),
(None, None) => {
let self_ty1 = tcx.type_of(impl1_def_id);
let self_ty2 = tcx.type_of(impl2_def_id);
drcx.types_may_unify(self_ty1, self_ty2)
}
}) {
_ => bug!("unexpected impls: {impl1_def_id:?} {impl2_def_id:?}"),
};
if !may_overlap {
// Some types involved are definitely different, so the impls couldn't possibly overlap.
debug!("overlapping_impls: fast_reject early-exit");
return no_overlap();
@ -519,7 +514,7 @@ pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanChe
/// 3. Before this local type, no generic type parameter of the impl must
/// be reachable through fundamental types.
/// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
/// - while `impl<T> Trait<LocalType for Box<T>` results in an error, as `T` is
/// - while `impl<T> Trait<LocalType> for Box<T>` results in an error, as `T` is
/// reachable through the fundamental type `Box`.
/// 4. Every type in the local key parameter not known in C, going
/// through the parameter's type tree, must appear only as a subtree of