bjoernager/rust
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Auto merge of #85481 - lcnr:const-equate, r=matthewjasper

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deal with `const_evaluatable_checked` in `ConstEquate`

Failing to evaluate two constants which do not contain inference variables should not result in ambiguity.
This commit is contained in:
bors 2021-05-25 13:53:48 +00:00
commit ff2c947c00
7 changed files with 80 additions and 6 deletions
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24
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -557,6 +557,23 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
ty::PredicateKind::ConstEquate(c1, c2) => {
debug!(?c1, ?c2, "evaluate_predicate_recursively: equating consts");
if self.tcx().features().const_evaluatable_checked {
// FIXME: we probably should only try to unify abstract constants
// if the constants depend on generic parameters.
//
// Let's just see where this breaks :shrug:
if let (ty::ConstKind::Unevaluated(a), ty::ConstKind::Unevaluated(b)) =
(c1.val, c2.val)
{
if self
.tcx()
.try_unify_abstract_consts(((a.def, a.substs), (b.def, b.substs)))
{
return Ok(EvaluatedToOk);
}
}
}
let evaluate = |c: &'tcx ty::Const<'tcx>| {
if let ty::ConstKind::Unevaluated(unevaluated) = c.val {
self.infcx
@ -591,7 +608,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
)
}
(Err(ErrorHandled::TooGeneric), _) | (_, Err(ErrorHandled::TooGeneric)) => {
Ok(EvaluatedToAmbig)
if c1.has_infer_types_or_consts() || c2.has_infer_types_or_consts() {
Ok(EvaluatedToAmbig)
} else {
// Two different constants using generic parameters ~> error.
Ok(EvaluatedToErr)
}
}
}
}