safely transmute<&List<Ty<'tcx>>, &List<GenericArg<'tcx>>>

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2298,7 +2298,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 // Closure arguments are wrapped in a tuple, so we need to get the first
                 // from that.
                 if let ty::Tuple(elems) = argument_ty.kind() {
-                    let argument_ty = elems.first()?.expect_ty();
+                    let &argument_ty = elems.first()?;
                     if let ty::Ref(_, _, _) = argument_ty.kind() {
                         return Some(AnnotatedBorrowFnSignature::Closure {
                             argument_ty,

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -480,7 +480,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         let search_stack: &mut Vec<(Ty<'tcx>, &hir::Ty<'_>)> = &mut vec![(ty, hir_ty)];
 
         while let Some((ty, hir_ty)) = search_stack.pop() {
-            match (&ty.kind(), &hir_ty.kind) {
+            match (ty.kind(), &hir_ty.kind) {
                 // Check if the `ty` is `&'X ..` where `'X`
                 // is the region we are looking for -- if so, and we have a `&T`
                 // on the RHS, then we want to highlight the `&` like so:
@@ -532,9 +532,8 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                 // The following cases don't have lifetimes, so we
                 // just worry about trying to match up the rustc type
                 // with the HIR types:
-                (ty::Tuple(elem_tys), hir::TyKind::Tup(elem_hir_tys)) => {
-                    search_stack
-                        .extend(iter::zip(elem_tys.iter().map(|k| k.expect_ty()), *elem_hir_tys));
+                (&ty::Tuple(elem_tys), hir::TyKind::Tup(elem_hir_tys)) => {
+                    search_stack.extend(iter::zip(elem_tys, *elem_hir_tys));
                 }
 
                 (ty::Slice(elem_ty), hir::TyKind::Slice(elem_hir_ty))

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -832,9 +832,10 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                     return match substs
                         .as_closure()
                         .tupled_upvars_ty()
-                        .tuple_element_ty(field.index())
+                        .tuple_fields()
+                        .get(field.index())
                     {
-                        Some(ty) => Ok(ty),
+                        Some(&ty) => Ok(ty),
                         None => Err(FieldAccessError::OutOfRange {
                             field_count: substs.as_closure().upvar_tys().count(),
                         }),
@@ -852,7 +853,7 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                 }
                 ty::Tuple(tys) => {
                     return match tys.get(field.index()) {
-                        Some(&ty) => Ok(ty.expect_ty()),
+                        Some(&ty) => Ok(ty),
                         None => Err(FieldAccessError::OutOfRange { field_count: tys.len() }),
                     };
                 }

compiler/rustc_borrowck/src/universal_regions.rs

@@ -641,15 +641,13 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                 let (&output, tuplized_inputs) =
                     inputs_and_output.skip_binder().split_last().unwrap();
                 assert_eq!(tuplized_inputs.len(), 1, "multiple closure inputs");
-                let ty::Tuple(inputs) = tuplized_inputs[0].kind() else {
+                let &ty::Tuple(inputs) = tuplized_inputs[0].kind() else {
                     bug!("closure inputs not a tuple: {:?}", tuplized_inputs[0]);
                 };
 
                 ty::Binder::bind_with_vars(
                     tcx.mk_type_list(
-                        iter::once(closure_ty)
-                            .chain(inputs.iter().map(|k| k.expect_ty()))
-                            .chain(iter::once(output)),
+                        iter::once(closure_ty).chain(inputs).chain(iter::once(output)),
                     ),
                     bound_vars,
                 )

compiler/rustc_codegen_cranelift/src/abi/mod.rs

@@ -117,7 +117,7 @@ impl<'tcx> FunctionCx<'_, '_, 'tcx> {
             .unzip();
         let return_layout = self.layout_of(return_ty);
         let return_tys = if let ty::Tuple(tup) = return_ty.kind() {
-            tup.types().map(|ty| AbiParam::new(self.clif_type(ty).unwrap())).collect()
+            tup.iter().map(|ty| AbiParam::new(self.clif_type(ty).unwrap())).collect()
         } else {
             vec![AbiParam::new(self.clif_type(return_ty).unwrap())]
         };
@@ -199,7 +199,7 @@ pub(crate) fn codegen_fn_prelude<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, start_
                 };
 
                 let mut params = Vec::new();
-                for (i, _arg_ty) in tupled_arg_tys.types().enumerate() {
+                for (i, _arg_ty) in tupled_arg_tys.iter().enumerate() {
                     let arg_abi = arg_abis_iter.next().unwrap();
                     let param =
                         cvalue_for_param(fx, Some(local), Some(i), arg_abi, &mut block_params_iter);

compiler/rustc_codegen_cranelift/src/common.rs

@@ -90,10 +90,9 @@ fn clif_pair_type_from_ty<'tcx>(
     ty: Ty<'tcx>,
 ) -> Option<(types::Type, types::Type)> {
     Some(match ty.kind() {
-        ty::Tuple(substs) if substs.len() == 2 => {
-            let mut types = substs.types();
-            let a = clif_type_from_ty(tcx, types.next().unwrap())?;
-            let b = clif_type_from_ty(tcx, types.next().unwrap())?;
+        ty::Tuple(types) if types.len() == 2 => {
+            let a = clif_type_from_ty(tcx, types[0])?;
+            let b = clif_type_from_ty(tcx, types[1])?;
             if a.is_vector() || b.is_vector() {
                 return None;
             }

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -752,9 +752,8 @@ pub fn type_metadata<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>) -> &'ll
                 prepare_enum_metadata(cx, t, def.did, unique_type_id, vec![]).finalize(cx)
             }
         },
-        ty::Tuple(elements) => {
-            let tys: Vec<_> = elements.iter().map(|k| k.expect_ty()).collect();
-            prepare_tuple_metadata(cx, t, &tys, unique_type_id, NO_SCOPE_METADATA).finalize(cx)
+        ty::Tuple(tys) => {
+            prepare_tuple_metadata(cx, t, tys, unique_type_id, NO_SCOPE_METADATA).finalize(cx)
         }
         // Type parameters from polymorphized functions.
         ty::Param(_) => MetadataCreationResult::new(param_type_metadata(cx, t), false),

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -86,7 +86,7 @@ fn push_debuginfo_type_name<'tcx>(
             }
 
             for component_type in component_types {
-                push_debuginfo_type_name(tcx, component_type.expect_ty(), true, output, visited);
+                push_debuginfo_type_name(tcx, component_type, true, output, visited);
                 push_arg_separator(cpp_like_debuginfo, output);
             }
             if !component_types.is_empty() {

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -69,7 +69,7 @@ use rustc_middle::ty::{
     self,
     error::TypeError,
     subst::{GenericArgKind, Subst, SubstsRef},
-    Binder, Region, Ty, TyCtxt, TypeFoldable,
+    Binder, List, Region, Ty, TyCtxt, TypeFoldable,
 };
 use rustc_span::{sym, BytePos, DesugaringKind, MultiSpan, Pos, Span};
 use rustc_target::spec::abi;
@@ -1361,7 +1361,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 let mut values =
                     (DiagnosticStyledString::normal("("), DiagnosticStyledString::normal("("));
                 let len = substs1.len();
-                for (i, (left, right)) in substs1.types().zip(substs2.types()).enumerate() {
+                for (i, (left, right)) in substs1.iter().zip(substs2).enumerate() {
                     let (x1, x2) = self.cmp(left, right);
                     (values.0).0.extend(x1.0);
                     (values.1).0.extend(x2.0);
@@ -2042,8 +2042,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         // If a tuple of length one was expected and the found expression has
                         // parentheses around it, perhaps the user meant to write `(expr,)` to
                         // build a tuple (issue #86100)
-                        (ty::Tuple(_), _) => {
-                            self.emit_tuple_wrap_err(&mut err, span, found, expected)
+                        (ty::Tuple(fields), _) => {
+                            self.emit_tuple_wrap_err(&mut err, span, found, fields)
                         }
                         // If a character was expected and the found expression is a string literal
                         // containing a single character, perhaps the user meant to write `'c'` to
@@ -2111,12 +2111,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         err: &mut DiagnosticBuilder<'tcx>,
         span: Span,
         found: Ty<'tcx>,
-        expected: Ty<'tcx>,
+        expected_fields: &List<Ty<'tcx>>,
     ) {
-        let [expected_tup_elem] = &expected.tuple_fields().collect::<Vec<_>>()[..]
-            else { return };
+        let [expected_tup_elem] = expected_fields[..] else { return };
 
-        if !same_type_modulo_infer(*expected_tup_elem, found) {
+        if !same_type_modulo_infer(expected_tup_elem, found) {
             return;
         }
 

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -254,7 +254,9 @@ fn closure_args(fn_sig: &ty::PolyFnSig<'_>) -> String {
         .skip_binder()
         .iter()
         .next()
-        .map(|args| args.tuple_fields().map(|arg| arg.to_string()).collect::<Vec<_>>().join(", "))
+        .map(|args| {
+            args.tuple_fields().iter().map(|arg| arg.to_string()).collect::<Vec<_>>().join(", ")
+        })
         .unwrap_or_default()
 }
 

compiler/rustc_lint/src/builtin.rs

@@ -2621,7 +2621,7 @@ impl<'tcx> LateLintPass<'tcx> for InvalidValue {
                 }
                 Tuple(..) => {
                     // Proceed recursively, check all fields.
-                    ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
+                    ty.tuple_fields().iter().find_map(|field| ty_find_init_error(tcx, field, init))
                 }
                 // Conservative fallback.
                 _ => None,
@@ -2934,7 +2934,7 @@ impl ClashingExternDeclarations {
                                 )
                         }
                         (Tuple(a_substs), Tuple(b_substs)) => {
-                            a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
+                            a_substs.iter().eq_by(b_substs.iter(), |a_ty, b_ty| {
                                 structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
                             })
                         }

compiler/rustc_lint/src/unused.rs

@@ -246,7 +246,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                     } else {
                         vec![]
                     };
-                    for (i, ty) in tys.iter().map(|k| k.expect_ty()).enumerate() {
+                    for (i, ty) in tys.iter().enumerate() {
                         let descr_post = &format!(" in tuple element {}", i);
                         let span = *spans.get(i).unwrap_or(&span);
                         if check_must_use_ty(cx, ty, expr, span, descr_pre, descr_post, plural_len)

compiler/rustc_middle/src/mir/pretty.rs

@@ -427,7 +427,7 @@ fn use_verbose<'tcx>(ty: Ty<'tcx>, fn_def: bool) -> bool {
         ty::Int(_) | ty::Uint(_) | ty::Bool | ty::Char | ty::Float(_) => false,
         // Unit type
         ty::Tuple(g_args) if g_args.is_empty() => false,
-        ty::Tuple(g_args) => g_args.iter().any(|g_arg| use_verbose(g_arg.expect_ty(), fn_def)),
+        ty::Tuple(g_args) => g_args.iter().any(|g_arg| use_verbose(g_arg, fn_def)),
         ty::Array(ty, _) => use_verbose(ty, fn_def),
         ty::FnDef(..) => fn_def,
         _ => true,

compiler/rustc_middle/src/mir/tcx.rs

@@ -46,7 +46,7 @@ impl<'tcx> PlaceTy<'tcx> {
                 let field_def = &variant_def.fields[f.index()];
                 field_def.ty(tcx, substs)
             }
-            ty::Tuple(ref tys) => tys[f.index()].expect_ty(),
+            ty::Tuple(tys) => tys[f.index()],
             _ => bug!("extracting field of non-tuple non-adt: {:?}", self),
         };
         debug!("field_ty self: {:?} f: {:?} yields: {:?}", self, f, answer);

compiler/rustc_middle/src/ty/context.rs

@@ -101,7 +101,6 @@ pub struct CtxtInterners<'tcx> {
     // Specifically use a speedy hash algorithm for these hash sets, since
     // they're accessed quite often.
     type_: InternedSet<'tcx, TyS<'tcx>>,
-    type_list: InternedSet<'tcx, List<Ty<'tcx>>>,
     substs: InternedSet<'tcx, InternalSubsts<'tcx>>,
     canonical_var_infos: InternedSet<'tcx, List<CanonicalVarInfo<'tcx>>>,
     region: InternedSet<'tcx, RegionKind>,
@@ -129,7 +128,6 @@ impl<'tcx> CtxtInterners<'tcx> {
         CtxtInterners {
             arena,
             type_: Default::default(),
-            type_list: Default::default(),
             substs: Default::default(),
             region: Default::default(),
             poly_existential_predicates: Default::default(),
@@ -1657,6 +1655,8 @@ macro_rules! nop_lift {
             type Lifted = $lifted;
             fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
                 if tcx.interners.$set.contains_pointer_to(&InternedInSet(self.0.0)) {
+                    // SAFETY: `self` is interned and therefore valid
+                    // for the entire lifetime of the `TyCtxt`.
                     Some(unsafe { mem::transmute(self) })
                 } else {
                     None
@@ -1666,6 +1666,25 @@ macro_rules! nop_lift {
     };
 }
 
+// Can't use the macros as we have reuse the `substs` here.
+//
+// See `intern_type_list` for more info.
+impl<'a, 'tcx> Lift<'tcx> for &'a List<Ty<'a>> {
+    type Lifted = &'tcx List<Ty<'tcx>>;
+    fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
+        if self.is_empty() {
+            return Some(List::empty());
+        }
+        if tcx.interners.substs.contains_pointer_to(&InternedInSet(self.as_substs())) {
+            // SAFETY: `self` is interned and therefore valid
+            // for the entire lifetime of the `TyCtxt`.
+            Some(unsafe { mem::transmute::<&'a List<Ty<'a>>, &'tcx List<Ty<'tcx>>>(self) })
+        } else {
+            None
+        }
+    }
+}
+
 macro_rules! nop_list_lift {
     ($set:ident; $ty:ty => $lifted:ty) => {
         impl<'a, 'tcx> Lift<'tcx> for &'a List<$ty> {
@@ -1690,7 +1709,6 @@ nop_lift! {const_; Const<'a> => Const<'tcx>}
 nop_lift_old! {const_allocation; &'a Allocation => &'tcx Allocation}
 nop_lift! {predicate; Predicate<'a> => Predicate<'tcx>}
 
-nop_list_lift! {type_list; Ty<'a> => Ty<'tcx>}
 nop_list_lift! {poly_existential_predicates; ty::Binder<'a, ExistentialPredicate<'a>> => ty::Binder<'tcx, ExistentialPredicate<'tcx>>}
 nop_list_lift! {predicates; Predicate<'a> => Predicate<'tcx>}
 nop_list_lift! {canonical_var_infos; CanonicalVarInfo<'a> => CanonicalVarInfo<'tcx>}
@@ -2189,7 +2207,6 @@ macro_rules! slice_interners {
 }
 
 slice_interners!(
-    type_list: _intern_type_list(Ty<'tcx>),
     substs: _intern_substs(GenericArg<'tcx>),
     canonical_var_infos: _intern_canonical_var_infos(CanonicalVarInfo<'tcx>),
     poly_existential_predicates:
@@ -2259,7 +2276,7 @@ impl<'tcx> TyCtxt<'tcx> {
     ) -> PolyFnSig<'tcx> {
         sig.map_bound(|s| {
             let params_iter = match s.inputs()[0].kind() {
-                ty::Tuple(params) => params.into_iter().map(|k| k.expect_ty()),
+                ty::Tuple(params) => params.into_iter(),
                 _ => bug!(),
             };
             self.mk_fn_sig(params_iter, s.output(), s.c_variadic, unsafety, abi::Abi::Rust)
@@ -2421,15 +2438,11 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn intern_tup(self, ts: &[Ty<'tcx>]) -> Ty<'tcx> {
-        let kinds: Vec<_> = ts.iter().map(|&t| GenericArg::from(t)).collect();
-        self.mk_ty(Tuple(self.intern_substs(&kinds)))
+        self.mk_ty(Tuple(self.intern_type_list(&ts)))
     }
 
     pub fn mk_tup<I: InternAs<[Ty<'tcx>], Ty<'tcx>>>(self, iter: I) -> I::Output {
-        iter.intern_with(|ts| {
-            let kinds: Vec<_> = ts.iter().map(|&t| GenericArg::from(t)).collect();
-            self.mk_ty(Tuple(self.intern_substs(&kinds)))
-        })
+        iter.intern_with(|ts| self.mk_ty(Tuple(self.intern_type_list(&ts))))
     }
 
     #[inline]
@@ -2611,7 +2624,19 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     pub fn intern_type_list(self, ts: &[Ty<'tcx>]) -> &'tcx List<Ty<'tcx>> {
-        if ts.is_empty() { List::empty() } else { self._intern_type_list(ts) }
+        if ts.is_empty() {
+            List::empty()
+        } else {
+            // Actually intern type lists as lists of `GenericArg`s.
+            //
+            // Transmuting from `Ty<'tcx>` to `GenericArg<'tcx>` is sound
+            // as explained in ty_slice_as_generic_arg`. With this,
+            // we guarantee that even when transmuting between `List<Ty<'tcx>>`
+            // and `List<GenericArg<'tcx>>`, the uniqueness requirement for
+            // lists is upheld.
+            let substs = self._intern_substs(ty::subst::ty_slice_as_generic_args(ts));
+            substs.try_as_type_list().unwrap()
+        }
     }
 
     pub fn intern_substs(self, ts: &[GenericArg<'tcx>]) -> &'tcx List<GenericArg<'tcx>> {

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -116,9 +116,10 @@ impl<'tcx> Ty<'tcx> {
                 }
                 _ => true,
             }),
-            Projection(ProjectionTy { substs: args, .. }) | Adt(_, args) | Tuple(args) => {
+            Projection(ProjectionTy { substs: args, .. }) | Adt(_, args) => {
                 args.iter().all(generic_arg_is_suggestible)
             }
+            Tuple(args) => args.iter().all(|ty| ty.is_suggestable()),
             Slice(ty) | RawPtr(TypeAndMut { ty, .. }) | Ref(_, ty, _) => ty.is_suggestable(),
             Array(ty, c) => ty.is_suggestable() && const_is_suggestable(c.val()),
             _ => true,

compiler/rustc_middle/src/ty/flags.rs

@@ -201,8 +201,8 @@ impl FlagComputation {
                 self.add_ty(ty);
             }
 
-            &ty::Tuple(ref substs) => {
-                self.add_substs(substs);
+            &ty::Tuple(types) => {
+                self.add_tys(types);
             }
 
             &ty::FnDef(_, substs) => {

compiler/rustc_middle/src/ty/impls_ty.rs

@@ -61,6 +61,36 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for ty::subst::GenericArg<'t
     }
 }
 
+impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for ty::subst::GenericArgKind<'tcx> {
+    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
+        match self {
+            // WARNING: We dedup cache the `HashStable` results for `List`
+            // while ignoring types and freely transmute
+            // between `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>`.
+            // See `fn intern_type_list` for more details.
+            //
+            // We therefore hash types without adding a hash for their discriminant.
+            //
+            // In order to make it very unlikely for the sequence of bytes being hashed for
+            // a `GenericArgKind::Type` to be the same as the sequence of bytes being
+            // hashed for one of the other variants, we hash a `0xFF` byte before hashing
+            // their discriminant (since the discriminant of `TyKind` is unlikely to ever start
+            // with 0xFF).
+            ty::subst::GenericArgKind::Type(ty) => ty.hash_stable(hcx, hasher),
+            ty::subst::GenericArgKind::Const(ct) => {
+                0xFFu8.hash_stable(hcx, hasher);
+                mem::discriminant(self).hash_stable(hcx, hasher);
+                ct.hash_stable(hcx, hasher);
+            }
+            ty::subst::GenericArgKind::Lifetime(lt) => {
+                0xFFu8.hash_stable(hcx, hasher);
+                mem::discriminant(self).hash_stable(hcx, hasher);
+                lt.hash_stable(hcx, hasher);
+            }
+        }
+    }
+}
+
 impl<'a> HashStable<StableHashingContext<'a>> for ty::RegionKind {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         mem::discriminant(self).hash_stable(hcx, hasher);