message: squash some warnings
diff: -#[macro_use]
  extern crate salsa;
  use std::rc::Rc;
  @@ -9,11 +8,11 @@ trait NoSendSyncDatabase: salsa::Database {
  fn no_send_sync_key(&self, key: Rc<bool>) -> bool;
  }
  -fn no_send_sync_value(db: &impl NoSendSyncDatabase, key: bool) -> Rc<bool> {
  +fn no_send_sync_value(_db: &impl NoSendSyncDatabase, key: bool) -> Rc<bool> {
  Rc::new(key)
  }
  -fn no_send_sync_key(db: &impl NoSendSyncDatabase, key: Rc<bool>) -> bool {
  +fn no_send_sync_key(_db: &impl NoSendSyncDatabase, key: Rc<bool>) -> bool {
  *key
  }
  @@ -31,7 +30,7 @@ impl salsa::Database for DatabaseImpl {
  #[test]
  fn no_send_sync() {
  - let mut db = DatabaseImpl::default();
  + let db = DatabaseImpl::default();
  assert_eq!(db.no_send_sync_value(true), Rc::new(true));
  assert_eq!(db.no_send_sync_key(Rc::new(false)), false);
  