[masklinn]

> I do think that this error could be improved by suggesting #[derive(Debug)], don't get me wrong.

That's what it's already doing:

> src/x/mod.rs:22:33: 22:34 note: `T` cannot be formatted using `:?`; if it is defined in your crate, add `#[derive(Debug)]` or manually implement it

and it's wrong, the error is a missing trait bound not a missing interface implementation

[pcwalton]

Oh, I see. That's just a straight-up compiler bug as far as I'm concerned. Doesn't have much to do with error message philosophy, really. Let's fix it :)