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

@@ -4,15 +4,15 @@ 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::{
     self, OpaqueHiddenType, OpaqueTypeKey, ToPredicate, Ty, TyCtxt, TypeFoldable,
 };
 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

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -13,11 +13,8 @@ use rustc_middle::ty::{self, adjustment::PointerCast, Instance, InstanceDef, Ty,
 use rustc_middle::ty::{Binder, TraitPredicate, TraitRef, TypeVisitable};
 use rustc_mir_dataflow::{self, Analysis};
 use rustc_span::{sym, Span, Symbol};
-use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
-use rustc_trait_selection::traits::{
-    self, ObligationCauseCode, SelectionContext, TraitEngine, TraitEngineExt,
-};
+use rustc_trait_selection::traits::{self, ObligationCauseCode, ObligationCtxt, SelectionContext};
 
 use std::mem;
 use std::ops::Deref;
@@ -747,35 +744,26 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     // "non-const" check. This is required for correctness here.
                     {
                         let infcx = tcx.infer_ctxt().build();
-                        let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
+                        let ocx = ObligationCtxt::new(&infcx);
+
                         let predicates = tcx.predicates_of(callee).instantiate(tcx, substs);
                         let hir_id = tcx
                             .hir()
                             .local_def_id_to_hir_id(self.body.source.def_id().expect_local());
-                        let cause = || {
-                            ObligationCause::new(
-                                terminator.source_info.span,
-                                hir_id,
-                                ObligationCauseCode::ItemObligation(callee),
-                            )
-                        };
-                        let normalized = infcx.partially_normalize_associated_types_in(
-                            cause(),
-                            param_env,
-                            predicates,
+                        let cause = ObligationCause::new(
+                            terminator.source_info.span,
+                            hir_id,
+                            ObligationCauseCode::ItemObligation(callee),
                         );
-
-                        for p in normalized.obligations {
-                            fulfill_cx.register_predicate_obligation(&infcx, p);
-                        }
-                        for obligation in traits::predicates_for_generics(
-                            |_, _| cause(),
+                        let normalized_predicates =
+                            ocx.normalize(cause.clone(), param_env, predicates);
+                        ocx.register_obligations(traits::predicates_for_generics(
+                            |_, _| cause.clone(),
                             self.param_env,
-                            normalized.value,
-                        ) {
-                            fulfill_cx.register_predicate_obligation(&infcx, obligation);
-                        }
-                        let errors = fulfill_cx.select_all_or_error(&infcx);
+                            normalized_predicates,
+                        ));
+
+                        let errors = ocx.select_all_or_error();
                         if !errors.is_empty() {
                             infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
                         }

compiler/rustc_hir_typeck/src/op.rs

@@ -19,7 +19,7 @@ use rustc_span::symbol::{sym, Ident};
 use rustc_span::Span;
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt as _;
-use rustc_trait_selection::traits::{FulfillmentError, TraitEngine, TraitEngineExt};
+use rustc_trait_selection::traits::FulfillmentError;
 use rustc_type_ir::sty::TyKind::*;
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
@@ -785,9 +785,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     other_ty_expr,
                     expected,
                 );
-                let mut fulfill = <dyn TraitEngine<'_>>::new(self.tcx);
-                fulfill.register_predicate_obligation(self, obligation);
-                Err(fulfill.select_where_possible(&self.infcx))
+                Err(rustc_trait_selection::traits::fully_solve_obligation(self, obligation))
             }
         }
     }

compiler/rustc_lint/src/for_loops_over_fallibles.rs

@@ -3,11 +3,9 @@ use crate::{LateContext, LateLintPass, LintContext};
 use hir::{Expr, Pat};
 use rustc_errors::{Applicability, DelayDm};
 use rustc_hir as hir;
-use rustc_infer::traits::TraitEngine;
 use rustc_infer::{infer::TyCtxtInferExt, traits::ObligationCause};
 use rustc_middle::ty::{self, List};
 use rustc_span::{sym, Span};
-use rustc_trait_selection::traits::TraitEngineExt;
 
 declare_lint! {
     /// The `for_loops_over_fallibles` lint checks for `for` loops over `Option` or `Result` values.
@@ -160,24 +158,19 @@ fn suggest_question_mark<'tcx>(
 
     let ty = substs.type_at(0);
     let infcx = cx.tcx.infer_ctxt().build();
-    let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
-
     let cause = ObligationCause::new(
         span,
         body_id.hir_id,
         rustc_infer::traits::ObligationCauseCode::MiscObligation,
     );
-    fulfill_cx.register_bound(
+    let errors = rustc_trait_selection::traits::fully_solve_bound(
         &infcx,
+        cause,
         ty::ParamEnv::empty(),
         // Erase any region vids from the type, which may not be resolved
         infcx.tcx.erase_regions(ty),
         into_iterator_did,
-        cause,
     );
 
-    // Select all, including ambiguous predicates
-    let errors = fulfill_cx.select_all_or_error(&infcx);
-
     errors.is_empty()
 }

compiler/rustc_trait_selection/src/traits/outlives_bounds.rs

@@ -1,7 +1,7 @@
 use crate::infer::InferCtxt;
 use crate::traits::query::type_op::{self, TypeOp, TypeOpOutput};
 use crate::traits::query::NoSolution;
-use crate::traits::{ObligationCause, TraitEngine, TraitEngineExt};
+use crate::traits::ObligationCause;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::HirId;
@@ -74,20 +74,20 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
             debug!(?constraints);
             // Instantiation may have produced new inference variables and constraints on those
             // variables. Process these constraints.
-            let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(self.tcx);
             let cause = ObligationCause::misc(span, body_id);
-            for &constraint in &constraints.outlives {
-                let obligation = self.query_outlives_constraint_to_obligation(
-                    constraint,
-                    cause.clone(),
-                    param_env,
-                );
-                fulfill_cx.register_predicate_obligation(self, obligation);
-            }
+            let errors = super::fully_solve_obligations(
+                self,
+                constraints.outlives.iter().map(|constraint| {
+                    self.query_outlives_constraint_to_obligation(
+                        *constraint,
+                        cause.clone(),
+                        param_env,
+                    )
+                }),
+            );
             if !constraints.member_constraints.is_empty() {
                 span_bug!(span, "{:#?}", constraints.member_constraints);
             }
-            let errors = fulfill_cx.select_all_or_error(self);
             if !errors.is_empty() {
                 self.tcx.sess.delay_span_bug(
                     span,