Remove many more cases of mk_substs_trait that can now use the iterator scheme`

compiler/rustc_hir_typeck/src/_match.rs

@@ -547,10 +547,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             }
                             ty::PredicateKind::Clause(ty::Clause::Projection(mut proj_pred)) => {
                                 assert_eq!(proj_pred.projection_ty.self_ty(), opaque_ty);
-                                proj_pred.projection_ty.substs = self.tcx.mk_substs_trait(
-                                    ty,
-                                    proj_pred.projection_ty.substs.iter().skip(1),
-                                );
+                                proj_pred = proj_pred.with_self_ty(self.tcx, ty);
                                 ty::PredicateKind::Clause(ty::Clause::Projection(proj_pred))
                             }
                             _ => continue,

compiler/rustc_lint/src/context.rs

@@ -1258,7 +1258,7 @@ impl<'tcx> LateContext<'tcx> {
         tcx.associated_items(trait_id)
             .find_by_name_and_kind(tcx, Ident::from_str(name), ty::AssocKind::Type, trait_id)
             .and_then(|assoc| {
-                let proj = tcx.mk_projection(assoc.def_id, tcx.mk_substs_trait(self_ty, []));
+                let proj = tcx.mk_projection(assoc.def_id, [self_ty]);
                 tcx.try_normalize_erasing_regions(self.param_env, proj).ok()
             })
     }

compiler/rustc_middle/src/ty/context.rs

@@ -2598,7 +2598,11 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     #[inline]
-    pub fn mk_projection(self, item_def_id: DefId, substs: SubstsRef<'tcx>) -> Ty<'tcx> {
+    pub fn mk_projection(
+        self,
+        item_def_id: DefId,
+        substs: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
+    ) -> Ty<'tcx> {
         self.mk_ty(Alias(ty::Projection, self.mk_alias_ty(item_def_id, substs)))
     }
 

compiler/rustc_middle/src/ty/mod.rs

@@ -1050,6 +1050,18 @@ impl<'tcx> PolyProjectionPredicate<'tcx> {
     }
 }
 
+impl<'tcx> ProjectionPredicate<'tcx> {
+    pub fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
+        Self {
+            projection_ty: tcx.mk_alias_ty(
+                self.projection_ty.def_id,
+                [self_ty.into()].into_iter().chain(self.projection_ty.substs.iter().skip(1)),
+            ),
+            ..self
+        }
+    }
+}
+
 pub trait ToPolyTraitRef<'tcx> {
     fn to_poly_trait_ref(&self) -> PolyTraitRef<'tcx>;
 }

compiler/rustc_mir_transform/src/shim.rs

@@ -336,8 +336,7 @@ impl<'tcx> CloneShimBuilder<'tcx> {
         // we must subst the self_ty because it's
         // otherwise going to be TySelf and we can't index
         // or access fields of a Place of type TySelf.
-        let substs = tcx.mk_substs_trait(self_ty, []);
-        let sig = tcx.bound_fn_sig(def_id).subst(tcx, substs);
+        let sig = tcx.bound_fn_sig(def_id).subst(tcx, &[self_ty.into()]);
         let sig = tcx.erase_late_bound_regions(sig);
         let span = tcx.def_span(def_id);
 
@@ -573,9 +572,8 @@ fn build_call_shim<'tcx>(
 
         // Create substitutions for the `Self` and `Args` generic parameters of the shim body.
         let arg_tup = tcx.mk_tup(untuple_args.iter());
-        let sig_substs = tcx.mk_substs_trait(ty, [ty::subst::GenericArg::from(arg_tup)]);
 
-        (Some(sig_substs), Some(untuple_args))
+        (Some([ty.into(), arg_tup.into()]), Some(untuple_args))
     } else {
         (None, None)
     };
@@ -586,7 +584,7 @@ fn build_call_shim<'tcx>(
 
     assert_eq!(sig_substs.is_some(), !instance.has_polymorphic_mir_body());
     let mut sig =
-        if let Some(sig_substs) = sig_substs { sig.subst(tcx, sig_substs) } else { sig.0 };
+        if let Some(sig_substs) = sig_substs { sig.subst(tcx, &sig_substs) } else { sig.0 };
 
     if let CallKind::Indirect(fnty) = call_kind {
         // `sig` determines our local decls, and thus the callee type in the `Call` terminator. This

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

@@ -2975,7 +2975,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     self.tcx.mk_projection(
                         item_def_id,
                         // Future::Output has no substs
-                        self.tcx.mk_substs_trait(trait_pred.self_ty(), []),
+                        [trait_pred.self_ty()],
                     )
                 });
                 let InferOk { value: projection_ty, .. } =

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -425,13 +425,8 @@ pub fn fully_solve_bound<'tcx>(
     bound: DefId,
 ) -> Vec<FulfillmentError<'tcx>> {
     let tcx = infcx.tcx;
-    let trait_ref = ty::TraitRef { def_id: bound, substs: tcx.mk_substs_trait(ty, []) };
-    let obligation = Obligation {
-        cause,
-        recursion_depth: 0,
-        param_env,
-        predicate: ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
-    };
+    let trait_ref = tcx.mk_trait_ref(bound, [ty]);
+    let obligation = Obligation::new(tcx, cause, param_env, ty::Binder::dummy(trait_ref));
 
     fully_solve_obligation(infcx, obligation)
 }