feat: Debug for Value and Key to be optional

[dzmitry-lahoda]

error[E0277]: `User` doesn't implement `Debug`
  --> examples/borsh.rs:12:22
   |
12 | impl redb::Value for User {
   |                      ^^^^ `User` cannot be formatted using `{:?}`
   |
   = help: the trait `Debug` is not implemented for `User`
   = note: add `#[derive(Debug)]` to `User` or manually `impl Debug for User`
note: required by a bound in `Value`
  --> /home/dz/github.com/cberner/redb/src/types.rs:74:18
   |
74 | pub trait Value: Debug {
   |                  ^^^^^ required by this bound in `Value`
help: consider annotating `User` with `#[derive(Debug)]`
   |
8  | #[derive(Debug)]
   |

error[E0277]: `Id` doesn't implement `Debug`
  --> examples/borsh.rs:50:22
   |
50 | impl redb::Value for Id {
   |                      ^^ `Id` cannot be formatted using `{:?}`
   |
   = help: the trait `Debug` is not implemented for `Id`
   = note: add `#[derive(Debug)]` to `Id` or manually `impl Debug for Id`
note: required by a bound in `Value`
  --> /home/dz/github.com/cberner/redb/src/types.rs:74:18
   |

I would like to avoid Debug in our production code, only in test, so Debug for sure does not slows performance.

Debug is optional feature.

[cberner]

If you're worried about performance, you should be able to use cfg in your Debug implementation to make it a no-op in production. Is there a reason that doesn't work?

[dzmitry-lahoda]

I guess yes, this is workaround. So it will not allow to read behavior out of struct definition.

[dzmitry-lahoda]

Also, workaround does not guarant redb does not creates some temporal structures which are compiled away without being created just for Debug.

[dzmitry-lahoda]

Debug is poor man json serde kind of, it should be optional feat of redb, like redb could have optional support of some serde kinds of for example.

[cberner]

I decided not to add support in redb for serde. You can find the reasoning in past issues, such as this one: #805