Structurally resolve before builtin_index in EUV

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -1741,7 +1741,11 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
  }
 
  PatKind::Slice(before, ref slice, after) => {
- let Some(element_ty) = place_with_id.place.ty().builtin_index() else {
+ let Some(element_ty) = self
+ .cx
+ .try_structurally_resolve_type(pat.span, place_with_id.place.ty())
+ .builtin_index()
+ else {
  debug!("explicit index of non-indexable type {:?}", place_with_id);
  return Err(self
  .cx

tests/ui/traits/next-solver/typeck/index-of-projection.rs

@@ -0,0 +1,13 @@
+//@ compile-flags: -Znext-solver
+//@ check-pass
+
+// Fixes a regression in `rustc_attr` where we weren't normalizing the
+// output type of a index operator performing a `Ty::builtin_index` call,
+// leading to an ICE.
+
+fn main() {
+ let mut vec = [1, 2, 3];
+ let x = || {
+ let [..] = &vec[..];
+ };
+}