Rollup merge of rust-lang#113427 - compiler-errors:no-variances-of-rpitit-gat, r=spastorino

Remove `variances_of` on RPITIT GATs, remove its one use-case

It doesn't make sense to implement variances on a GAT anyways, since we don't relate GATs with variance:

https://github.com/rust-lang/rust/blob/85bf07972a1041b9e25393b803d0e006bec3eaaf/compiler/rustc_middle/src/ty/relate.rs#L569-L579

r? ``@spastorino``

Author: compiler-errors

compiler/rustc_hir_analysis/src/variance/mod.rs

@@ -7,7 +7,7 @@ use rustc_arena::DroplessArena;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, CrateVariancesMap, ImplTraitInTraitData, SubstsRef, Ty, TyCtxt};
+use rustc_middle::ty::{self, CrateVariancesMap, SubstsRef, Ty, TyCtxt};
 use rustc_middle::ty::{TypeSuperVisitable, TypeVisitable};
 use std::ops::ControlFlow;
 
@@ -59,13 +59,6 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
         DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder => {
             return variance_of_opaque(tcx, item_def_id);
         }
-        DefKind::AssocTy => {
-            if let Some(ImplTraitInTraitData::Trait { .. }) =
-                tcx.opt_rpitit_info(item_def_id.to_def_id())
-            {
-                return variance_of_opaque(tcx, item_def_id);
-            }
-        }
         _ => {}
     }
 
@@ -125,7 +118,8 @@ fn variance_of_opaque(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Varianc
                 // FIXME(-Zlower-impl-trait-in-trait-to-assoc-ty) check whether this is necessary
                 // at all for RPITITs.
                 ty::Alias(_, ty::AliasTy { def_id, substs, .. })
-                    if self.tcx.is_impl_trait_in_trait(*def_id) =>
+                    if self.tcx.is_impl_trait_in_trait(*def_id)
+                        && !self.tcx.lower_impl_trait_in_trait_to_assoc_ty() =>
                 {
                     self.visit_opaque(*def_id, substs)
                 }

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -473,17 +473,6 @@ where
                 }
             }
 
-            ty::Alias(ty::Projection, proj) if self.tcx.is_impl_trait_in_trait(proj.def_id) => {
-                // Skip lifetime parameters that are not captures.
-                let variances = self.tcx.variances_of(proj.def_id);
-
-                for (v, s) in std::iter::zip(variances, proj.substs.iter()) {
-                    if *v != ty::Variance::Bivariant {
-                        s.visit_with(self);
-                    }
-                }
-            }
-
             _ => {
                 ty.super_visit_with(self);
             }