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

3 files changed, 22 insertions, 12 deletions

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,
         }
     }