Update book

book/src/tutorial/debug.md

@@ -18,23 +18,7 @@ eprintln!("Expression = {:?}", expr.debug(db));
 
 and get back the output you expect.
 
-## Implementing the `DebugWithDb` trait
-
-For now, unfortunately, you have to implement the `DebugWithDb` trait manually, as we do not provide a derive.
-This is tedious but not difficult. Here is an example of implementing the trait for `Expression`:
-
-```rust
-{{#include ../../../calc-example/calc/src/ir.rs:expression_debug_impl}}
-```
-
-Some things to note:
-
-- The `data` method gives access to the full enum from the database.
-- The [`Formatter`] methods (e.g., [`debug_tuple`]) can be used to provide consistent output.
-- When printing the value of a field, use `.field(&a.debug(db))` for fields that are themselves interned or entities, and use `.field(&a)` for fields that just implement the ordinary `Debug` trait.
-
-[`debug_tuple`]: https://doc.rust-lang.org/std/fmt/struct.Formatter.html#method.debug_tuple
-[`formatter`]: https://doc.rust-lang.org/std/fmt/struct.Formatter.html#
+The `DebugWithDb` trait is automatically derived for all `#[input]`, `#[interned]` and `#[tracked]` structs.
 
 ## Forwarding to the ordinary `Debug` trait