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Remap predicate/env constness before querying

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This commit is contained in:
Deadbeef 2021-12-07 16:08:59 +08:00
parent 42963f4d50
commit 2bea3b3aa3
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GPG key ID: 6D017A96D8E6C2F9
1 changed files with 24 additions and 4 deletions
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28
compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
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@ -1,3 +1,5 @@
use rustc_middle::ty;
use crate::infer::canonical::OriginalQueryValues;
use crate::infer::InferCtxt;
use crate::traits::{
@ -64,10 +66,28 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
obligation: &PredicateObligation<'tcx>,
) -> Result<EvaluationResult, OverflowError> {
let mut _orig_values = OriginalQueryValues::default();
let c_pred = self.canonicalize_query_keep_static(
obligation.param_env.and(obligation.predicate),
&mut _orig_values,
);
let (param_env, predicate) = match obligation.predicate.kind().skip_binder() {
ty::PredicateKind::Trait(mut pred) => {
let orig_pred_constness = pred.constness;
let env_constness = pred.constness.and(obligation.param_env.constness());
let predicate = if orig_pred_constness != pred.constness {
self.tcx.mk_predicate(
obligation.predicate.kind().rebind(ty::PredicateKind::Trait(pred)),
)
} else {
obligation.predicate
};
(obligation.param_env.with_constness(env_constness), predicate)
}
// constness has no effect on the given predicate.
_ => (obligation.param_env.without_const(), obligation.predicate),
};
let c_pred =
self.canonicalize_query_keep_static(param_env.and(predicate), &mut _orig_values);
// Run canonical query. If overflow occurs, rerun from scratch but this time
// in standard trait query mode so that overflow is handled appropriately
// within `SelectionContext`.