Use builin_index instead of hand-rolling it

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1048,8 +1048,7 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) -> Result<(),
                             match ty.kind() {
                                 ty::Adt(adt_def, ..) => adt_def.did().is_local(),
                                 // Arrays and slices use the inner type's `ConstParamTy`.
-                                ty::Array(ty, ..) => ty_is_local(*ty),
-                                ty::Slice(ty) => ty_is_local(*ty),
+                                ty::Array(ty, ..) | ty::Slice(ty) => ty_is_local(*ty),
                                 // `&` references use the inner type's `ConstParamTy`.
                                 // `&mut` are not supported.
                                 ty::Ref(_, ty, ast::Mutability::Not) => ty_is_local(*ty),

compiler/rustc_hir_typeck/src/expr.rs

@@ -1793,10 +1793,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let element_ty = if !args.is_empty() {
             let coerce_to = expected
                 .to_option(self)
-                .and_then(|uty| match *self.try_structurally_resolve_type(expr.span, uty).kind() {
-                    ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
-                    _ => None,
-                })
+                .and_then(|uty| self.try_structurally_resolve_type(expr.span, uty).builtin_index())
                 .unwrap_or_else(|| self.next_ty_var(expr.span));
             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
             assert_eq!(self.diverges.get(), Diverges::Maybe);
@@ -1874,10 +1871,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         let uty = match expected {
-            ExpectHasType(uty) => match *uty.kind() {
-                ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
-                _ => None,
-            },
+            ExpectHasType(uty) => uty.builtin_index(),
             _ => None,
         };
 

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -249,12 +249,12 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
                 ty::Ref(_, rty, _) => reveal_and_alloc(cx, once(*rty)),
                 _ => bug!("Unexpected type for `Ref` constructor: {ty:?}"),
             },
-            Slice(slice) => match *ty.kind() {
-                ty::Slice(ty) | ty::Array(ty, _) => {
+            Slice(slice) => match ty.builtin_index() {
+                Some(ty) => {
                     let arity = slice.arity();
                     reveal_and_alloc(cx, (0..arity).map(|_| ty))
                 }
-                _ => bug!("bad slice pattern {:?} {:?}", ctor, ty),
+                None => bug!("bad slice pattern {:?} {:?}", ctor, ty),
             },
             DerefPattern(pointee_ty) => reveal_and_alloc(cx, once(pointee_ty.inner())),
             Bool(..) | IntRange(..) | F16Range(..) | F32Range(..) | F64Range(..)

src/tools/clippy/clippy_lints/src/index_refutable_slice.rs

@@ -12,7 +12,6 @@ use rustc_hir::HirId;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::nested_filter;
-use rustc_middle::ty;
 use rustc_session::impl_lint_pass;
 use rustc_span::Span;
 use rustc_span::symbol::Ident;
@@ -109,11 +108,11 @@ fn find_slice_values(cx: &LateContext<'_>, pat: &hir::Pat<'_>) -> FxIndexMap<Hir
             }
 
             let bound_ty = cx.typeck_results().node_type(pat.hir_id);
-            if let ty::Slice(inner_ty) | ty::Array(inner_ty, _) = bound_ty.peel_refs().kind() {
+            if let Some(inner_ty) = bound_ty.peel_refs().builtin_index() {
                 // The values need to use the `ref` keyword if they can't be copied.
                 // This will need to be adjusted if the lint want to support mutable access in the future
                 let src_is_ref = bound_ty.is_ref() && by_ref == hir::ByRef::No;
-                let needs_ref = !(src_is_ref || is_copy(cx, *inner_ty));
+                let needs_ref = !(src_is_ref || is_copy(cx, inner_ty));
 
                 let slice_info = slices
                     .entry(value_hir_id)

src/tools/clippy/clippy_lints/src/tuple_array_conversions.rs

@@ -66,7 +66,7 @@ impl LateLintPass<'_> for TupleArrayConversions {
 }
 
 fn check_array<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, elements: &'tcx [Expr<'tcx>]) {
-    let (ty::Array(ty, _) | ty::Slice(ty)) = cx.typeck_results().expr_ty(expr).kind() else {
+    let Some(ty) = cx.typeck_results().expr_ty(expr).builtin_index() else {
         unreachable!("`expr` must be an array or slice due to `ExprKind::Array`");
     };
 
@@ -85,7 +85,7 @@ fn check_array<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, elements: &
             ExprKind::Path(_) => Some(elements.iter().collect()),
             _ => None,
         })
-        && all_bindings_are_for_conv(cx, &[*ty], expr, elements, &locals, ToType::Array)
+        && all_bindings_are_for_conv(cx, &[ty], expr, elements, &locals, ToType::Array)
         && !is_from_proc_macro(cx, expr)
     {
         span_lint_and_help(

src/tools/clippy/clippy_utils/src/consts.rs

@@ -235,9 +235,7 @@ impl Constant<'_> {
                 _ => None,
             },
             (Self::Vec(l), Self::Vec(r)) => {
-                let (ty::Array(cmp_type, _) | ty::Slice(cmp_type)) = *cmp_type.kind() else {
-                    return None;
-                };
+                let cmp_type = cmp_type.builtin_index()?;
                 iter::zip(l, r)
                     .map(|(li, ri)| Self::partial_cmp(tcx, cmp_type, li, ri))
                     .find(|r| r.is_none_or(|o| o != Ordering::Equal))