message: Remove a redundant ref
  Summary: The ref causes it to deref, and then the compiler implicitly adds a ref. Much easier to not do that.
diff: @@ -427,7 +427,7 @@ impl<'v, 'a> ParametersCollect<'v, 'a> {
  if let Some(err) = err {
  return Err(err);
  }
  - for ((index, def), ref slot) in params
  + for ((index, def), slot) in params
  .kinds
  .iter()
  .enumerate()
  