Deserializing `Decimal`s from Postgres using the `db-postgres` feature can lead to invalid `Decimal` instances about rust-decimal

[paupino]

Thank you for raising this - it's a very interesting edge case. I've created a fix for this which effectively bounds the scale at 28. While there are some legitimate cases for a scale of 29 - it can cause undefined behavior so we typically avoid anything above 28. Consequently, after bounding it - things work "as expected" (assuming rounding to fit into the decimal type is desired).

[Tony-Samuels]

I've seen bugs raised around this behaviour before but thought it was fixed by this MR.

I'm able to reproduce it via your repo though, so there's probably a second issue there too. It's not a regression since that change, as I can reproduce it directly on the fix commit.

FYI: If anyone else hits issues starting the docker container, switch the image from postgres to postgres:12-bullseye.

[klevente]

Hey @Tony-Samuels, thanks for the swift reply! If you need any more repro steps or anything else, please let me know. Unfortunately I'm not that well-versed in decimal handling, but I'll try looking into the code as well to see what might be going wrong.

[klevente]

Thanks @paupino, really appreciate the fix! I think for this case, rounding is acceptable for now, until a configuration option or feature flag gets added where the user can control whether they'd like rounding or not - for me, rounding is perfectly fine.