Support for trait's associated const

[aliXsed]

The following code, when compiled, throws the "missing C in an implementation" error:

use mockall::predicate::*;
use mockall::*;

trait A {
    type T;
    const C: &'static str;

    fn foo(t: Self::T) -> bool;
}

mock! {
    S {}

    trait A {
        type T = isize;
        const C: &'static str = "Mock";

        fn foo(t: isize) -> bool;
    }
}

fn main() {
    println!("Hello, world!");
    let foo_ctx = MockS::foo_context();
    foo_ctx.expect().times(1).return_const(true);
    MockS::foo(0);
    foo_ctx.checkpoint();
}

[aliXsed]

Hi @asomers,

Thank you for this very useful library. I have had the above issue that seems to be caused by the lack of support for trait consts. However, in the case you know a workaround already, I will appreciate it if you can let us know.

Best regards,
Alex

[asomers]

I don't think this is something I've tried yet, so it doesn't surprise me that it doesn't work. But I doubt it's difficult to add. What happens if you do this:

mock! {
    S {
        const C: &'static str = "foo";
    }

    trait A {
        type T = isize;
        const C: &'static str = "Mock";

        fn foo(t: isize) -> bool;
    }
}

[aliXsed]

I get a different vague build error:

error: Unsupported in this context
--> src/main.rs:16:5
|
16 | trait A {
| ^^^^^

[asomers]

Yep, that means I have some work to do. Unfortunately, I can't suggest any workaround. However, you'll get a better error message if you build Mockall with the "nightly" feature.