Use TraitEngine in more places that don't specifically need FulfillmentCtxt::new_in_snapshot

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -205,7 +205,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
             // At this point, we already have all of the bounds we need. FulfillmentContext is used
             // to store all of the necessary region/lifetime bounds in the InferContext, as well as
             // an additional sanity check.
-            let mut fulfill = FulfillmentContext::new();
+            let mut fulfill = <dyn TraitEngine<'tcx>>::new(tcx);
             fulfill.register_bound(&infcx, full_env, ty, trait_did, ObligationCause::dummy());
             let errors = fulfill.select_all_or_error(&infcx);
 

compiler/rustc_trait_selection/src/traits/codegen.rs

@@ -5,7 +5,7 @@
 
 use crate::infer::{DefiningAnchor, TyCtxtInferExt};
 use crate::traits::{
-    FulfillmentContext, ImplSource, Obligation, ObligationCause, SelectionContext, TraitEngine,
+    ImplSource, Obligation, ObligationCause, SelectionContext, TraitEngine, TraitEngineExt,
     Unimplemented,
 };
 use rustc_middle::traits::CodegenObligationError;
@@ -55,7 +55,7 @@ pub fn codegen_fulfill_obligation<'tcx>(
         // Currently, we use a fulfillment context to completely resolve
         // all nested obligations. This is because they can inform the
         // inference of the impl's type parameters.
-        let mut fulfill_cx = FulfillmentContext::new();
+        let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(tcx);
         let impl_source = selection.map(|predicate| {
             fulfill_cx.register_predicate_obligation(&infcx, predicate);
         });

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -11,7 +11,7 @@ use crate::traits::util::impl_subject_and_oblig;
 use crate::traits::SkipLeakCheck;
 use crate::traits::{
     self, FulfillmentContext, Normalized, Obligation, ObligationCause, PredicateObligation,
-    PredicateObligations, SelectionContext,
+    PredicateObligations, SelectionContext, TraitEngineExt,
 };
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::Diagnostic;
@@ -385,7 +385,7 @@ fn resolve_negative_obligation<'cx, 'tcx>(
         return false;
     };
 
-    let mut fulfillment_cx = FulfillmentContext::new();
+    let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
     fulfillment_cx.register_predicate_obligation(infcx, o);
 
     let errors = fulfillment_cx.select_all_or_error(infcx);

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -163,7 +163,7 @@ pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
         // The handling of regions in this area of the code is terrible,
         // see issue #29149. We should be able to improve on this with
         // NLL.
-        let mut fulfill_cx = FulfillmentContext::new();
+        let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
 
         // We can use a dummy node-id here because we won't pay any mind
         // to region obligations that arise (there shouldn't really be any

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

@@ -14,7 +14,9 @@ use specialization_graph::GraphExt;
 
 use crate::infer::{InferCtxt, InferOk, TyCtxtInferExt};
 use crate::traits::select::IntercrateAmbiguityCause;
-use crate::traits::{self, coherence, FutureCompatOverlapErrorKind, ObligationCause, TraitEngine};
+use crate::traits::{
+    self, coherence, FutureCompatOverlapErrorKind, ObligationCause, TraitEngine, TraitEngineExt,
+};
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_errors::{struct_span_err, EmissionGuarantee, LintDiagnosticBuilder};
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -24,8 +26,8 @@ use rustc_session::lint::builtin::COHERENCE_LEAK_CHECK;
 use rustc_session::lint::builtin::ORDER_DEPENDENT_TRAIT_OBJECTS;
 use rustc_span::{Span, DUMMY_SP};
 
-use super::util;
-use super::{FulfillmentContext, SelectionContext};
+use super::SelectionContext;
+use super::{util, FulfillmentContext};
 
 /// Information pertinent to an overlapping impl error.
 #[derive(Debug)]
@@ -207,7 +209,7 @@ fn fulfill_implication<'a, 'tcx>(
     // (which are packed up in penv)
 
     infcx.save_and_restore_in_snapshot_flag(|infcx| {
-        let mut fulfill_cx = FulfillmentContext::new();
+        let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
         for oblig in obligations.chain(more_obligations) {
             fulfill_cx.register_predicate_obligation(&infcx, oblig);
         }

compiler/rustc_trait_selection/src/traits/structural_match.rs

@@ -1,6 +1,6 @@
 use crate::infer::{InferCtxt, TyCtxtInferExt};
 use crate::traits::ObligationCause;
-use crate::traits::{self, TraitEngine};
+use crate::traits::{TraitEngine, TraitEngineExt};
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
@@ -78,7 +78,7 @@ fn type_marked_structural<'tcx>(
     adt_ty: Ty<'tcx>,
     cause: ObligationCause<'tcx>,
 ) -> bool {
-    let mut fulfillment_cx = traits::FulfillmentContext::new();
+    let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
     // require `#[derive(PartialEq)]`
     let structural_peq_def_id =
         infcx.tcx.require_lang_item(LangItem::StructuralPeq, Some(cause.span));