Guard `AliasTy` creation against passing the wrong number of substs

9 files changed, 35 insertions, 38 deletions

diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index c8c10385f0c..babf2ef1af4 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -1146,7 +1146,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
             debug!(?substs_trait_ref_and_assoc_item);
 
-            ty::AliasTy { def_id: assoc_item.def_id, substs: substs_trait_ref_and_assoc_item }
+            self.tcx().mk_alias_ty(assoc_item.def_id, substs_trait_ref_and_assoc_item)
         });
 
         if !speculative {
diff --git a/compiler/rustc_hir_analysis/src/check/compare_method.rs b/compiler/rustc_hir_analysis/src/check/compare_method.rs
index ba7d31cea2e..4f4e9a89fc7 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_method.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_method.rs
@@ -1746,10 +1746,7 @@ pub fn check_type_bounds<'tcx>(
             _ => predicates.push(
                 ty::Binder::bind_with_vars(
                     ty::ProjectionPredicate {
-                        projection_ty: ty::AliasTy {
-                            def_id: trait_ty.def_id,
-                            substs: rebased_substs,
-                        },
+                        projection_ty: tcx.mk_alias_ty(trait_ty.def_id, rebased_substs),
                         term: impl_ty_value.into(),
                     },
                     bound_vars,
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 41cd6bf314e..0103f58d061 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -557,10 +557,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                         .chain(projection_ty.substs.iter().skip(1)),
                                 );
 
-                                let quiet_projection_ty = ty::AliasTy {
-                                    substs: substs_with_infer_self,
-                                    def_id: projection_ty.def_id,
-                                };
+                                let quiet_projection_ty =
+                                    tcx.mk_alias_ty(projection_ty.def_id, substs_with_infer_self);
 
                                 let term = pred.skip_binder().term;
 
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index dc333b4702f..ad097b39d10 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -18,7 +18,7 @@ use crate::thir::Thir;
 use crate::traits;
 use crate::ty::query::{self, TyCtxtAt};
 use crate::ty::{
-    self, AdtDef, AdtDefData, AdtKind, AliasTy, Binder, BindingMode, BoundVar, CanonicalPolyFnSig,
+    self, AdtDef, AdtDefData, AdtKind, Binder, BindingMode, BoundVar, CanonicalPolyFnSig,
     ClosureSizeProfileData, Const, ConstS, DefIdTree, FloatTy, FloatVar, FloatVid,
     GenericParamDefKind, InferTy, IntTy, IntVar, IntVid, List, ParamConst, ParamTy,
     PolyExistentialPredicate, PolyFnSig, Predicate, PredicateKind, Region, RegionKind, ReprOptions,
@@ -2591,12 +2591,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn mk_projection(self, item_def_id: DefId, substs: SubstsRef<'tcx>) -> Ty<'tcx> {
-        debug_assert_eq!(
-            self.generics_of(item_def_id).count(),
-            substs.len(),
-            "wrong number of generic parameters for {item_def_id:?}: {substs:?}",
-        );
-        self.mk_ty(Alias(ty::Projection, AliasTy { def_id: item_def_id, substs }))
+        self.mk_ty(Alias(ty::Projection, self.mk_alias_ty(item_def_id, substs)))
     }
 
     #[inline]
@@ -2867,6 +2862,23 @@ impl<'tcx> TyCtxt<'tcx> {
         ty::TraitRef::new(trait_def_id, substs)
     }
 
+    pub fn mk_alias_ty(
+        self,
+        def_id: DefId,
+        substs: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
+    ) -> ty::AliasTy<'tcx> {
+        let substs = substs.into_iter().map(Into::into);
+        let n = self.generics_of(def_id).count();
+        debug_assert_eq!(
+            (n, Some(n)),
+            substs.size_hint(),
+            "wrong number of generic parameters for {def_id:?}: {:?} \nDid you accidentally include the self-type in the params list?",
+            substs.collect::<Vec<_>>(),
+        );
+        let substs = self.mk_substs(substs);
+        ty::AliasTy { def_id, substs }
+    }
+
     pub fn mk_bound_variable_kinds<
         I: InternAs<ty::BoundVariableKind, &'tcx List<ty::BoundVariableKind>>,
     >(
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index 1eac8859ca9..c463980bed5 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -280,7 +280,7 @@ impl<'tcx> Relate<'tcx> for ty::AliasTy<'tcx> {
             Err(TypeError::ProjectionMismatched(expected_found(relation, a.def_id, b.def_id)))
         } else {
             let substs = relation.relate(a.substs, b.substs)?;
-            Ok(ty::AliasTy { def_id: a.def_id, substs: &substs })
+            Ok(relation.tcx().mk_alias_ty(a.def_id, substs))
         }
     }
 }
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 27de48c1f83..092e68a4bf7 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -1449,10 +1449,8 @@ impl<'tcx> ExistentialProjection<'tcx> {
         debug_assert!(!self_ty.has_escaping_bound_vars());
 
         ty::ProjectionPredicate {
-            projection_ty: ty::AliasTy {
-                def_id: self.def_id,
-                substs: tcx.mk_substs_trait(self_ty, self.substs),
-            },
+            projection_ty: tcx
+                .mk_alias_ty(self.def_id, [self_ty.into()].into_iter().chain(self.substs)),
             term: self.term,
         }
     }
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 55a05df763f..f2ee0387888 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -3265,9 +3265,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 // in. For example, this would be what `Iterator::Item` is here.
                 let ty_var = self.infcx.next_ty_var(origin);
                 // This corresponds to `<ExprTy as Iterator>::Item = _`.
-                let trait_ref = ty::Binder::dummy(ty::PredicateKind::Clause(
+                let projection = ty::Binder::dummy(ty::PredicateKind::Clause(
                     ty::Clause::Projection(ty::ProjectionPredicate {
-                        projection_ty: ty::AliasTy { substs, def_id: proj.def_id },
+                        projection_ty: tcx.mk_alias_ty(proj.def_id, substs),
                         term: ty_var.into(),
                     }),
                 ));
@@ -3277,7 +3277,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     span,
                     expr.hir_id,
                     param_env,
-                    trait_ref,
+                    projection,
                 ));
                 if ocx.select_where_possible().is_empty() {
                     // `ty_var` now holds the type that `Item` is for `ExprTy`.
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index ca9ee04c58c..445d783aabc 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -1867,10 +1867,7 @@ fn confirm_generator_candidate<'cx, 'tcx>(
         };
 
         ty::ProjectionPredicate {
-            projection_ty: ty::AliasTy {
-                substs: trait_ref.substs,
-                def_id: obligation.predicate.def_id,
-            },
+            projection_ty: tcx.mk_alias_ty(obligation.predicate.def_id, trait_ref.substs),
             term: ty.into(),
         }
     });
@@ -1909,10 +1906,7 @@ fn confirm_future_candidate<'cx, 'tcx>(
         debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id).name, sym::Output);
 
         ty::ProjectionPredicate {
-            projection_ty: ty::AliasTy {
-                substs: trait_ref.substs,
-                def_id: obligation.predicate.def_id,
-            },
+            projection_ty: tcx.mk_alias_ty(obligation.predicate.def_id, trait_ref.substs),
             term: return_ty.into(),
         }
     });
@@ -1965,10 +1959,8 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
         bug!("unexpected builtin trait with associated type: {:?}", obligation.predicate);
     };
 
-    let predicate = ty::ProjectionPredicate {
-        projection_ty: ty::AliasTy { substs, def_id: item_def_id },
-        term,
-    };
+    let predicate =
+        ty::ProjectionPredicate { projection_ty: tcx.mk_alias_ty(item_def_id, substs), term };
 
     confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false)
         .with_addl_obligations(obligations)
@@ -2037,7 +2029,7 @@ fn confirm_callable_candidate<'cx, 'tcx>(
         flag,
     )
     .map_bound(|(trait_ref, ret_type)| ty::ProjectionPredicate {
-        projection_ty: ty::AliasTy { substs: trait_ref.substs, def_id: fn_once_output_def_id },
+        projection_ty: tcx.mk_alias_ty(fn_once_output_def_id, trait_ref.substs),
         term: ret_type.into(),
     });
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index 829d4f60986..c54d901e9b1 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -536,7 +536,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             let ty = traits::normalize_projection_type(
                 self,
                 param_env,
-                ty::AliasTy { def_id: tcx.lang_items().deref_target()?, substs: trait_ref.substs },
+                tcx.mk_alias_ty(tcx.lang_items().deref_target()?, trait_ref.substs),
                 cause.clone(),
                 0,
                 // We're *intentionally* throwing these away,