bjoernager/rust
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freshen: resolve root vars

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Without doing so we use the same candidate cache entry
for `?0: Trait<?1>` and `?0: Trait<?0>`. These goals are different
and we must not use the same entry for them.
This commit is contained in:
lcnr 2024-01-15 11:47:53 +01:00
parent 91535ad026
commit f392a870e9
4 changed files with 102 additions and 96 deletions
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25
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -40,7 +40,6 @@ use rustc_middle::dep_graph::DepNodeIndex;
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::ty::_match::MatchAgainstFreshVars;
use rustc_middle::ty::abstract_const::NotConstEvaluatable;
use rustc_middle::ty::fold::BottomUpFolder;
use rustc_middle::ty::relate::TypeRelation;
use rustc_middle::ty::GenericArgsRef;
use rustc_middle::ty::{self, EarlyBinder, PolyProjectionPredicate, ToPolyTraitRef, ToPredicate};
@ -2435,28 +2434,8 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
match self.match_impl(impl_def_id, impl_trait_header, obligation) {
Ok(args) => args,
Err(()) => {
// FIXME: A rematch may fail when a candidate cache hit occurs
// on the freshened form of the trait predicate, but the match
// fails for some reason that is not captured in the freshened
// cache key. For example, equating an impl trait ref against
// the placeholder trait ref may fail due the Generalizer relation
// raising a CyclicalTy error due to a sub_root_var relation
// for a variable being generalized...
let guar = self.infcx.dcx().span_delayed_bug(
obligation.cause.span,
format!(
"Impl {impl_def_id:?} was matchable against {obligation:?} but now is not"
),
);
let value = self.infcx.fresh_args_for_item(obligation.cause.span, impl_def_id);
let err = Ty::new_error(self.tcx(), guar);
let value = value.fold_with(&mut BottomUpFolder {
tcx: self.tcx(),
ty_op: |_| err,
lt_op: |l| l,
ct_op: |c| c,
});
Normalized { value, obligations: vec![] }
let predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
bug!("impl {impl_def_id:?} was matchable against {predicate:?} but now is not")
}
}
}