missing Handle in implementation

[asomers]

When I tried to upgrade mock_shoout from Mockers 0.13.4 to 0.20.0, every place I used #[mocked] began to fail with the error missing Handle in implementation. This appears to be unrelated to the only documented breaking change; create_mock_for now returns a tuple of mock and handle instead of a single value. Can you please tell me what I'm doing wrong? One example of the breakage looks like this:

    fn derive(){
        #[mocked]
        pub trait A {
            fn foo(&self, key: i16);
        }

        let scenario = Scenario::new();
        let _mock = scenario.create_mock_for::<A>();
    }

error[E0046]: not all trait items implemented, missing: `Handle`
   --> src/t_mockers.rs:140:9
    |
140 |         #[mocked]
    |         ^^^^^^^^^ missing `Handle` in implementation
    |
    = note: `Handle` from trait: `type Handle;`