Rollup merge of #103868 - compiler-errors:trait-engine-less, r=jackh726

Use `TraitEngine` (by itself) less

Replace `TraitEngine` in favor of `ObligationCtxt` or `fully_solve_*`, improving code readability.

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -23,7 +23,6 @@ use rustc_span::hygiene::DesugaringKind;
 use rustc_span::symbol::sym;
 use rustc_span::{BytePos, Span, Symbol};
 use rustc_trait_selection::infer::InferCtxtExt;
-use rustc_trait_selection::traits::TraitEngineExt as _;
 
 use crate::borrow_set::TwoPhaseActivation;
 use crate::borrowck_errors;
@@ -613,24 +612,20 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         else { return; };
         // Try to find predicates on *generic params* that would allow copying `ty`
         let infcx = tcx.infer_ctxt().build();
-        let mut fulfill_cx = <dyn rustc_infer::traits::TraitEngine<'_>>::new(infcx.tcx);
-
         let copy_did = infcx.tcx.lang_items().copy_trait().unwrap();
         let cause = ObligationCause::new(
             span,
             self.mir_hir_id(),
             rustc_infer::traits::ObligationCauseCode::MiscObligation,
         );
-        fulfill_cx.register_bound(
+        let errors = rustc_trait_selection::traits::fully_solve_bound(
             &infcx,
+            cause,
             self.param_env,
             // Erase any region vids from the type, which may not be resolved
             infcx.tcx.erase_regions(ty),
             copy_did,
-            cause,
         );
-        // Select all, including ambiguous predicates
-        let errors = fulfill_cx.select_all_or_error(&infcx);
 
         // Only emit suggestion if all required predicates are on generic
         let predicates: Result<Vec<_>, _> = errors

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -4,7 +4,7 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_hir::OpaqueTyOrigin;
 use rustc_infer::infer::TyCtxtInferExt as _;
 use rustc_infer::infer::{DefiningAnchor, InferCtxt};
-use rustc_infer::traits::{Obligation, ObligationCause, TraitEngine};
+use rustc_infer::traits::{Obligation, ObligationCause};
 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{
@@ -12,7 +12,7 @@ use rustc_middle::ty::{
 };
 use rustc_span::Span;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
-use rustc_trait_selection::traits::TraitEngineExt as _;
+use rustc_trait_selection::traits::ObligationCtxt;
 
 use super::RegionInferenceContext;
 
@@ -252,48 +252,45 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         // type-alias-impl-trait/issue-67844-nested-opaque.rs
         let infcx =
             self.tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).build();
+        let ocx = ObligationCtxt::new(&infcx);
         // Require the hidden type to be well-formed with only the generics of the opaque type.
         // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
         // hidden type is well formed even without those bounds.
         let predicate = ty::Binder::dummy(ty::PredicateKind::WellFormed(definition_ty.into()))
             .to_predicate(infcx.tcx);
-        let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
 
         let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id.to_def_id());
 
         // Require that the hidden type actually fulfills all the bounds of the opaque type, even without
         // the bounds that the function supplies.
         let opaque_ty = self.tcx.mk_opaque(def_id.to_def_id(), id_substs);
-        match infcx
-            .at(&ObligationCause::misc(instantiated_ty.span, body_id), param_env)
-            .eq(opaque_ty, definition_ty)
-        {
-            Ok(infer_ok) => {
-                for obligation in infer_ok.obligations {
-                    fulfillment_cx.register_predicate_obligation(&infcx, obligation);
-                }
-            }
-            Err(err) => {
-                infcx
-                    .err_ctxt()
-                    .report_mismatched_types(
-                        &ObligationCause::misc(instantiated_ty.span, body_id),
-                        opaque_ty,
-                        definition_ty,
-                        err,
-                    )
-                    .emit();
-            }
+        if let Err(err) = ocx.eq(
+            &ObligationCause::misc(instantiated_ty.span, body_id),
+            param_env,
+            opaque_ty,
+            definition_ty,
+        ) {
+            infcx
+                .err_ctxt()
+                .report_mismatched_types(
+                    &ObligationCause::misc(instantiated_ty.span, body_id),
+                    opaque_ty,
+                    definition_ty,
+                    err,
+                )
+                .emit();
         }
 
-        fulfillment_cx.register_predicate_obligation(
-            &infcx,
-            Obligation::misc(instantiated_ty.span, body_id, param_env, predicate),
-        );
+        ocx.register_obligation(Obligation::misc(
+            instantiated_ty.span,
+            body_id,
+            param_env,
+            predicate,
+        ));
 
         // Check that all obligations are satisfied by the implementation's
         // version.
-        let errors = fulfillment_cx.select_all_or_error(&infcx);
+        let errors = ocx.select_all_or_error();
 
         // This is still required for many(half of the tests in ui/type-alias-impl-trait)
         // tests to pass