Simpler test.

Author: cjgillot

tests/ui/where-clauses/cfg-attr-issue-138010-3.rs

@@ -0,0 +1,14 @@
+//@ check-pass
+
+#![feature(associated_type_defaults, where_clause_attrs)]
+#![allow(deprecated_where_clause_location)]
+
+trait A {
+    type F<T>
+    where
+        #[cfg(false)]
+        T: TraitB,
+    = T;
+}
+
+fn main() {}