Rollup merge of #141541 - compiler-errors:nits, r=lcnr

Random nits

Two completely random commits that I didn't know where to integrate into another PR.

* Don't use the full type relation machinery to equate two regions (it's overkill).
* Add a comment that `select_in_new_trait_solver` shouldn't be used directly.

r? lcnr or reassign

Author: GuillaumeGomez

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -23,7 +23,7 @@ use crate::infer::canonical::{
     QueryOutlivesConstraint, QueryRegionConstraints, QueryResponse,
 };
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
-use crate::infer::{DefineOpaqueTypes, InferCtxt, InferOk, InferResult};
+use crate::infer::{DefineOpaqueTypes, InferCtxt, InferOk, InferResult, SubregionOrigin};
 use crate::traits::query::NoSolution;
 use crate::traits::{
     Obligation, ObligationCause, PredicateObligation, PredicateObligations, ScrubbedTraitError,
@@ -593,10 +593,10 @@ impl<'tcx> InferCtxt<'tcx> {
                     // no action needed
                 }
                 (GenericArgKind::Lifetime(v1), GenericArgKind::Lifetime(v2)) => {
-                    obligations.extend(
-                        self.at(cause, param_env)
-                            .eq(DefineOpaqueTypes::Yes, v1, v2)?
-                            .into_obligations(),
+                    self.inner.borrow_mut().unwrap_region_constraints().make_eqregion(
+                        SubregionOrigin::RelateRegionParamBound(cause.span, None),
+                        v1,
+                        v2,
                     );
                 }
                 (GenericArgKind::Const(v1), GenericArgKind::Const(v2)) => {

compiler/rustc_trait_selection/src/solve/select.rs

@@ -15,6 +15,7 @@ use crate::solve::inspect::{self, ProofTreeInferCtxtExt};
 
 #[extension(pub trait InferCtxtSelectExt<'tcx>)]
 impl<'tcx> InferCtxt<'tcx> {
+    /// Do not use this directly. This is called from [`crate::traits::SelectionContext::select`].
     fn select_in_new_trait_solver(
         &self,
         obligation: &TraitObligation<'tcx>,