message: RFC: adjust because DatabaseKeyIndex are not part of public API
diff: @@ -167,23 +167,6 @@ those calls, this has not been tested, and in any case the runtime effects are
  not expected to be high, since all the calls will always go to the same
  function.
  -### Database keys will become indices
  -
  -There are currently some parts of the API that take a `DB::DatabaseKey`, most
  -notably cycle recovery and reporting. Those will now take a `salsa::DatabaseKey`
  -struct that is a kind of integer index. There will be methods on
  -`salsa::Database` that permit one to generate debug output from such a key:
  -
  -```rust
  -trait Database {
  - fn debug_fmt_database_key(
  - &self,
  - key: DatabaseKey,
  - fmt: &mut std::fmt::Formatter<'_>,
  - ) -> std::fmt::Result<()>;
  -}
  -```
  -
  ## Reference guide
  ### Example
  @@ -223,7 +206,7 @@ impl salsa::Database for DatabaseStruct {
  }
  ```
  -### Identifying queries
  +### Identifying queries using the `DatabaseKeyIndex`
  We introduce the following struct that represents a database key using a series
  of indices:
  @@ -268,6 +251,11 @@ slots already take this approach today. In principle, we could extend the
  tracing GC to permit compressing and perhaps even rewriting indices, but it's
  not clear that this is a problem in practice.
  +The `DatabaseKeyIndex` also supports a `debug` method that returns a value with
  +a human readable `debug!` output, so that you can do `debug!("{:?}",
  +index.debug(db))`. This works by generating a `fmt_debug` method that is
  +supported by the various query groups.
  +
  ### The various query traits are not generic over a database
  Today, the `Query`, `QueryFunction`, and `QueryGroup` traits are generic over
  