error[E0277]: the trait bound `<T as Config>::C: std::default::Default` is not satisfied
   --> $DIR/default.rs:7:2
    |
7   |     c: T::C,
    |     ^ the trait `std::default::Default` is not implemented for `<T as Config>::C`
    |
note: required by `std::default::Default::default`
   --> $DIR/default.rs:116:5
    |
116 |     fn default() -> Self;
    |     ^^^^^^^^^^^^^^^^^^^^^
