message: RFC: update to mention that salsa::requires is removed
diff: dependency information.
  * The various traits are changed to make `salsa::Database` dyn-safe. Invoking
  methods on the runtime must now go through a `salsa::Runtime` trait.
  + * The `salsa::requires` functionality is removed.
  * Upsides of the proposal:
  * Potentially improved recompilation time. Minimal code is regenerated.
  * Removing the `DatabaseData` unsafe code hack that was required by slots.
  so we were sure the value would not be deallocated; one can still imagine
  supporting this feature, but it would require some fancier unsafe code
  reasoning, although it would be more efficient.)
  + * The `salsa::requires` functionality is removed.
  ## Motivation
  @@ -122,6 +124,20 @@ have two "similar but different" ways of generating plumbing, and I'm not
  convinced that it's worth it. Moreover, it would require some form of opt-in so
  that would be a measure of user complexity as well.
  +### All query functions must take a dyn database
  +
  +You used to be able to implement queries by using `impl MyDatabase`, like so:
  +
  +```rust,ignore
  +fn my_query(db: &impl MyDatabase, ...) { .. }
  +```
  +
  +but you must now use `dyn MyDatabase`:
  +
  +```rust,ignore
  +fn my_query(db: &dyn MyDatabase, ...) { .. }
  +```
  +
  ### The query method on `salsa::Database` moves to a helper method
  As a consequence of the previous point, the existing `query` and `query_mut`
  @@ -167,6 +183,18 @@ 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.
  +### The `salsa::requires` function is removed
  +
  +We currently offer a feature for "private" dependencies between query groups
  +called `#[salsa::requires(ExtraDatabase)]`. This then requires query
  +functions to be written like:
  +
  +```rust,ignore
  +fn query_fn(db: &impl Database + ExtraDatabase, ...) { }
  +```
  +
  +This format is not compatible with `dyn`, so this feature is removed.
  +
  ## Reference guide
  ### Example
  