Deny defaults for higher-ranked generic parameters

tests/ui/parser/generic-param-default-in-binder.rs

@@ -0,0 +1,10 @@
+// Check that defaults for generic parameters in `for<...>` binders are
+// syntactically valid. See also PR #119042.
+
+// check-pass
+
+macro_rules! a { ($ty:ty) => {} }
+
+a! { for<T = &i32> fn() }
+
+fn main() {}