Victor, I think you misunderstood the issue. The problem is not that a decoding error is raised. The problem is that the incremental decoder no longer raises where it raised before.

I think that both behavior may be correct, and that it is better to not rely on ability of the incremental decoder with final=False to detect an invalid encoded data, but I see now that it is possible to fix for the original issue more carefully, without changing that behavior. PR 14304 does this.

It also change the UTF-16 incremental decoder with the surrogatepass error handler to return a non-empty data when decode a low surrogate with final=False. It is not necessary, but it makes all UTF-* decoders consistent and makes tests simpler.