On Thu, Nov 11, 2021 at 3:45 PM Isaac Morland <isaac.morland@gmail.com> wrote: > There is however one kind of change at least that I think can be made safely: adding a new character in between existing characters. That shouldn't affect any existing indexes.
Only if you can guarantee that said character is not present already. I don't think we update the end of the acceptable code point range every time that Unicode adds new stuff, so probably those things are subject to some default rule unless and until someone installs something more specific. Therefore I doubt that even this case is truly safe.
Wouldn't an existing index only have characters that were already part of the collation? Attempting to use one not covered by the collation I would have expected to cause an error at insert time. But definitely I agree I wouldn't feel confident about the safety of any change.