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Auto merge of rust-lang#121864 - compiler-errors:type-relating-varian…
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…ces, r=aliemjay

Don't grab variances in `TypeRelating` relation if we're invariant

Since `Invariant.xform(var) = Invariant` always, so just copy what the generalizer relation does.

Fixes rust-lang#110106
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bors committed Mar 2, 2024
2 parents 4cdd205 + 003b920 commit 2e3581b
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22 changes: 21 additions & 1 deletion compiler/rustc_infer/src/infer/relate/type_relating.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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,
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
//@ check-pass

#![feature(inherent_associated_types)]
//~^ WARN the feature `inherent_associated_types` is incomplete

struct D<T> {
a: T
}

impl<T: Default> D<T> {
type Item = T;

fn next() -> Self::Item {
Self::Item::default()
}
}


fn main() {
}
Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
warning: the feature `inherent_associated_types` is incomplete and may not be safe to use and/or cause compiler crashes
--> $DIR/variance-computation-requires-equality.rs:3:12
|
LL | #![feature(inherent_associated_types)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #8995 <https://github.com/rust-lang/rust/issues/8995> for more information
= note: `#[warn(incomplete_features)]` on by default

warning: 1 warning emitted

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