Use TraitEngine in more places, restrict visibility of FulfillmentCtxt constructor

compiler/rustc_hir_typeck/src/coercion.rs

@@ -62,6 +62,7 @@ use rustc_span::{self, BytePos, DesugaringKind, Span};
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::infer::InferCtxtExt as _;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
+use rustc_trait_selection::traits::TraitEngineExt as _;
 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
 
 use smallvec::{smallvec, SmallVec};
@@ -1038,7 +1039,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let Ok(ok) = coerce.coerce(source, target) else {
                 return false;
             };
-            let mut fcx = traits::FulfillmentContext::new_in_snapshot();
+            let mut fcx = <dyn TraitEngine<'tcx>>::new_in_snapshot(self.tcx);
             fcx.register_predicate_obligations(self, ok.obligations);
             fcx.select_where_possible(&self).is_empty()
         })

compiler/rustc_trait_selection/src/autoderef.rs

@@ -1,6 +1,6 @@
 use crate::errors::AutoDerefReachedRecursionLimit;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
-use crate::traits::{self, TraitEngine};
+use crate::traits::{self, TraitEngine, TraitEngineExt};
 use rustc_hir as hir;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt};
@@ -139,7 +139,7 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
             return None;
         }
 
-        let mut fulfillcx = traits::FulfillmentContext::new_in_snapshot();
+        let mut fulfillcx = <dyn TraitEngine<'tcx>>::new_in_snapshot(tcx);
         let normalized_ty = fulfillcx.normalize_projection_type(
             &self.infcx,
             self.param_env,

compiler/rustc_trait_selection/src/traits/chalk_fulfill.rs

@@ -19,7 +19,7 @@ pub struct FulfillmentContext<'tcx> {
 }
 
 impl FulfillmentContext<'_> {
-    pub(crate) fn new() -> Self {
+    pub(super) fn new() -> Self {
         FulfillmentContext {
             obligations: FxIndexSet::default(),
             relationships: FxHashMap::default(),

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

@@ -3,13 +3,14 @@ pub mod on_unimplemented;
 pub mod suggestions;
 
 use super::{
-    FulfillmentContext, FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes,
-    Obligation, ObligationCause, ObligationCauseCode, OutputTypeParameterMismatch, Overflow,
-    PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
+    FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes, Obligation, ObligationCause,
+    ObligationCauseCode, OutputTypeParameterMismatch, Overflow, PredicateObligation,
+    SelectionContext, SelectionError, TraitNotObjectSafe,
 };
 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::infer::{self, InferCtxt, TyCtxtInferExt};
+use crate::traits::engine::TraitEngineExt as _;
 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
 use crate::traits::query::normalize::AtExt as _;
 use crate::traits::specialize::to_pretty_impl_header;
@@ -352,7 +353,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                     })
                     .to_predicate(self.tcx),
                 );
-                let mut fulfill_cx = FulfillmentContext::new_in_snapshot();
+                let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new_in_snapshot(self.tcx);
                 fulfill_cx.register_predicate_obligation(self, obligation);
                 if fulfill_cx.select_all_or_error(self).is_empty() {
                     return Ok((

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -85,15 +85,15 @@ static_assert_size!(PendingPredicateObligation<'_>, 72);
 
 impl<'a, 'tcx> FulfillmentContext<'tcx> {
     /// Creates a new fulfillment context.
-    pub fn new() -> FulfillmentContext<'tcx> {
+    pub(super) fn new() -> FulfillmentContext<'tcx> {
         FulfillmentContext {
             predicates: ObligationForest::new(),
             relationships: FxHashMap::default(),
             usable_in_snapshot: false,
         }
     }
 
-    pub fn new_in_snapshot() -> FulfillmentContext<'tcx> {
+    pub(super) fn new_in_snapshot() -> FulfillmentContext<'tcx> {
         FulfillmentContext {
             predicates: ObligationForest::new(),
             relationships: FxHashMap::default(),

src/test/ui/chalkify/trait-objects.stderr

@@ -22,6 +22,10 @@ LL |     f(2);
    |     ^^^^ expected an `Fn<(i32,)>` closure, found `dyn Fn(i32) -> i32`
    |
    = help: the trait `Fn<(i32,)>` is not implemented for `dyn Fn(i32) -> i32`
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   |
+LL | fn main() where dyn Fn(i32) -> i32: Fn<(i32,)> {
+   |           ++++++++++++++++++++++++++++++++++++
 
 error: aborting due to 3 previous errors