bjoernager/rust
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Don't grab variances if we're invariant

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This commit is contained in:
Michael Goulet 2024-03-01 17:49:21 +00:00
parent 6db96de66c
commit 003b920591
3 changed files with 52 additions and 1 deletions
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22
compiler/rustc_infer/src/infer/relate/type_relating.rs
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@ -5,7 +5,9 @@ use crate::infer::{
};
use crate::traits::{Obligation, PredicateObligations};
use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation};
use rustc_middle::ty::relate::{
relate_args_invariantly, relate_args_with_variances, Relate, RelateResult, TypeRelation,
};
use rustc_middle::ty::TyVar;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_span::Span;
@ -36,6 +38,24 @@ impl<'tcx> TypeRelation<'tcx> for TypeRelating<'_, '_, 'tcx> {
self.fields.infcx.tcx
}
fn relate_item_args(
&mut self,
item_def_id: rustc_hir::def_id::DefId,
a_arg: ty::GenericArgsRef<'tcx>,
b_arg: ty::GenericArgsRef<'tcx>,
) -> RelateResult<'tcx, ty::GenericArgsRef<'tcx>> {
if self.ambient_variance == ty::Variance::Invariant {
// Avoid fetching the variance if we are in an invariant
// context; no need, and it can induce dependency cycles
// (e.g., #41849).
relate_args_invariantly(self, a_arg, b_arg)
} else {
let tcx = self.tcx();
let opt_variances = tcx.variances_of(item_def_id);
relate_args_with_variances(self, item_def_id, opt_variances, a_arg, b_arg, false)
}
}
fn relate_with_variance<T: Relate<'tcx>>(
&mut self,
variance: ty::Variance,