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Rollup merge of #94057 - lcnr:simplify_type-uwu, r=nikomatsakis

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improve comments for `simplify_type`

Should now correctly describe what's going on. Experimented with checking the invariant for projections
but that ended up requiring fairly involved changes. I assume that it is not possible to get unsoundness here,
at least for now and I can pretty much guarantee that it's impossible to trigger it by accident.

r? `````@nikomatsakis````` cc #92721
This commit is contained in:
Matthias Krüger 2022-03-03 20:01:44 +01:00 • committed by GitHub
commit fec7a79088
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7 changed files with 66 additions and 60 deletions
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15
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -36,7 +36,7 @@ use rustc_infer::infer::LateBoundRegionConversionTime;
use rustc_middle::dep_graph::{DepKind, DepNodeIndex};
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::thir::abstract_const::NotConstEvaluatable;
use rustc_middle::ty::fast_reject::{self, SimplifyParams};
use rustc_middle::ty::fast_reject::{self, TreatParams};
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::relate::TypeRelation;
use rustc_middle::ty::subst::{GenericArgKind, Subst, SubstsRef};
@ -2176,8 +2176,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn fast_reject_trait_refs(
&mut self,
obligation: &TraitObligation<'_>,
impl_trait_ref: &ty::TraitRef<'_>,
obligation: &TraitObligation<'tcx>,
impl_trait_ref: &ty::TraitRef<'tcx>,
) -> bool {
// We can avoid creating type variables and doing the full
// substitution if we find that any of the input types, when
@ -2193,10 +2193,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let simplified_obligation_ty = fast_reject::simplify_type(
self.tcx(),
obligation_ty,
SimplifyParams::Yes,
TreatParams::AsBoundTypes,
);
let simplified_impl_ty = fast_reject::simplify_type(
self.tcx(),
impl_ty,
TreatParams::AsPlaceholders,
);
let simplified_impl_ty =
fast_reject::simplify_type(self.tcx(), impl_ty, SimplifyParams::No);
simplified_obligation_ty.is_some()
&& simplified_impl_ty.is_some()