Fix const normalization for generic const items with trait assoc consts

Author: lapla-cogito

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -376,10 +376,14 @@ impl<'a, 'tcx> QueryNormalizer<'a, 'tcx> {
         // `tcx.normalize_canonicalized_projection` may normalize to a type that
         // still has unevaluated consts, so keep normalizing here if that's the case.
         // Similarly, `tcx.normalize_canonicalized_free_alias` will only unwrap one layer
-        // of type and we need to continue folding it to reveal the TAIT behind it.
+        // of type/const and we need to continue folding it to reveal the TAIT behind it
+        // or further normalize nested unevaluated consts.
         if res != term.to_term(tcx)
-            && (res.as_type().map_or(false, |t| t.has_type_flags(ty::TypeFlags::HAS_CT_PROJECTION))
-                || term.kind(tcx) == ty::AliasTermKind::FreeTy)
+            && (res.has_type_flags(ty::TypeFlags::HAS_CT_PROJECTION)
+                || matches!(
+                    term.kind(tcx),
+                    ty::AliasTermKind::FreeTy | ty::AliasTermKind::FreeConst
+                ))
         {
             res.try_fold_with(self)
         } else {

tests/ui/generic-const-items/type-const-nested-assoc-const.rs

@@ -0,0 +1,18 @@
+//@ check-pass
+
+#![feature(generic_const_items, min_generic_const_args)]
+#![allow(incomplete_features)]
+
+type const CT<T: ?Sized>: usize = { <T as Trait>::N };
+
+trait Trait {
+    type const N: usize;
+}
+
+impl<T: ?Sized> Trait for T {
+    type const N = 0;
+}
+
+fn f(_x: [(); CT::<()>]) {}
+
+fn main() {}