Handle non-type args in TraitRefPrintSugared

The issue was that `TraitRefPrintSugared` called `type_at(1)`
which panics when the argument is not a type (e.g., an inference variable).

This can happen when there are prior errors in user code, such as
incorrect trait parameters with paren sugar syntax.

The fix uses `get(1).and_then(|arg| arg.as_type())` to safely
check if the argument is a type before accessing it, falling back
to the default printing path if not.

Author: yimiliya

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -3313,7 +3313,8 @@ define_print_and_forward_display! {
     TraitRefPrintSugared<'tcx> {
         if !with_reduced_queries()
             && p.tcx().trait_def(self.0.def_id).paren_sugar
-            && let ty::Tuple(args) = self.0.args.type_at(1).kind()
+            && let Some(ty) = self.0.args.get(1).and_then(|arg| arg.as_type())
+            && let ty::Tuple(args) = ty.kind()
         {
             write!(p, "{}(", p.tcx().item_name(self.0.def_id))?;
             for (i, arg) in args.iter().enumerate() {

tests/ui/unboxed-closures/issue-153853-ice-paren-sugar.rs

@@ -0,0 +1,10 @@
+// Test for issue #153853: ICE when using paren sugar with inferred types
+#![feature(unboxed_closures)]
+#[rustc_paren_sugar]
+trait Tr<'a, 'b, T> {
+    fn method() {}
+}
+
+fn main() {
+    <u8 as Tr(&u8)>::method;
+}