Fix regression spotted at #3027

Author: GKFX

bindgen-tests/tests/expectations/tests/issue-3027.rs

@@ -0,0 +1,6 @@
+// bindgen-flags: --enable-cxx-namespaces
+
+namespace regression {
+    template<unsigned N> class A { char c[N]; };
+    class C { A<3> a; };
+}

bindgen-tests/tests/headers/issue-3027.hpp

@@ -102,7 +102,11 @@ pub(crate) fn blob(
         ty
     } else if ffi_safe && ctx.options().rust_features().min_const_generics {
         ctx.generated_opaque_array();
-        syn::parse_quote! { __BindgenOpaqueArray<#ty, #data_len> }
+        if ctx.options().enable_cxx_namespaces {
+            syn::parse_quote! { root::__BindgenOpaqueArray<#ty, #data_len> }
+        } else {
+            syn::parse_quote! { __BindgenOpaqueArray<#ty, #data_len> }
+        }
     } else {
         // This is not FFI safe as an argument; the struct above is
         // preferable.