New trait solver is a property of inference context

compiler/rustc_trait_selection/src/solve/eval_ctxt.rs

@@ -187,6 +187,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
             let (ref infcx, input, var_values) = tcx
                 .infer_ctxt()
                 .intercrate(intercrate)
+                .with_next_trait_solver(true)
                 .with_opaque_type_inference(canonical_input.value.anchor)
                 .build_with_canonical(DUMMY_SP, &canonical_input);
 

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1047,7 +1047,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 // (which may fail).
                                 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
                             }
-                            TraitSolver::Chalk | TraitSolver::Next => {
+                            TraitSolver::Chalk | TraitSolver::Next | TraitSolver::NextCoherence => {
                                 // FIXME: we'll need a better message which takes into account
                                 // which bounds actually failed to hold.
                                 self.tcx.sess.struct_span_err(

compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs

@@ -78,7 +78,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
             _ => obligation.param_env.without_const(),
         };
 
-        if self.tcx.trait_solver_next() {
+        if self.next_trait_solver() {
             self.probe(|snapshot| {
                 let mut fulfill_cx = crate::solve::FulfillmentCtxt::new();
                 fulfill_cx.register_predicate_obligation(self, obligation.clone());

compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs

@@ -146,7 +146,7 @@ where
         infcx: &InferCtxt<'tcx>,
         span: Span,
     ) -> Result<TypeOpOutput<'tcx, Self>, ErrorGuaranteed> {
-        if infcx.tcx.trait_solver_next() {
+        if infcx.next_trait_solver() {
             return Ok(scrape_region_constraints(
                 infcx,
                 |ocx| QueryTypeOp::perform_locally_in_new_solver(ocx, self),

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -539,7 +539,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         self.evaluation_probe(|this| {
             let goal =
                 this.infcx.resolve_vars_if_possible((obligation.predicate, obligation.param_env));
-            let mut result = if this.tcx().trait_solver_next() {
+            let mut result = if this.infcx.next_trait_solver() {
                 this.evaluate_predicates_recursively_in_new_solver([obligation.clone()])?
             } else {
                 this.evaluate_predicate_recursively(
@@ -593,7 +593,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     where
         I: IntoIterator<Item = PredicateObligation<'tcx>> + std::fmt::Debug,
     {
-        if self.tcx().trait_solver_next() {
+        if self.infcx.next_trait_solver() {
             self.evaluate_predicates_recursively_in_new_solver(predicates)
         } else {
             let mut result = EvaluatedToOk;

compiler/rustc_trait_selection/src/traits/structural_normalize.rs

@@ -21,7 +21,7 @@ impl<'tcx> StructurallyNormalizeExt<'tcx> for At<'_, 'tcx> {
     ) -> Result<Ty<'tcx>, Vec<FulfillmentError<'tcx>>> {
         assert!(!ty.is_ty_var(), "should have resolved vars before calling");
 
-        if self.infcx.tcx.trait_solver_next() {
+        if self.infcx.next_trait_solver() {
             while let ty::Alias(ty::Projection, projection_ty) = *ty.kind() {
                 let new_infer_ty = self.infcx.next_ty_var(TypeVariableOrigin {
                     kind: TypeVariableOriginKind::NormalizeProjectionType,