to_document(): numbers now serialized to serde_json::private::number?

[Theodlz]

Versions/Environment

1. What version of Rust are you using? rustc 1.89.0-nightly (be19eda0d 2025-06-22)
2. What operating system are you using? MacOS
3. What versions of the driver and its dependencies are you using? (Run
   cargo pkgid mongodb & cargo pkgid bson) mongodb==3.3.0, bson==2.15.0
4. What version of MongoDB are you using? (Check with the MongoDB shell using db.version()) 8.0.11
5. What is your MongoDB topology (standalone, replica set, sharded cluster, serverless)? standalone

Describe the bug

With mongodb==3.2.5 which used bson==2.14.0, when I called mongodb::bson::to_document on a serde Value that contains numerical values (e.g. {"$round": ["$candidate.magpsf", 2]}), the resulting Document looks very much like it's input serde_json Value, which btw I created from a string, read with serde_json::from_str::<serde_json::Value>(string_value). But now, instead all numerical values (like the 2 in that example I provided) are instead a Document of their own that looks like Document({"$serde_json::private::Number": String("2")}).

I guess I'm trying to understand where something changed for that to happen, and why? It makes it a lot harder to read documents created from serde_json::Values. Perhaps this change happened in serde_json and not here? I haven't figured that out yet.

[Theodlz]

Quick update: I reverted all updates to the Cargo.toml file in my projet (I had run a cargo upgrade earlier, and that's when newer versions seem to change the output of mongodb::bson::to_document). Errors naturally go away, and then I tried upgrading serde_json, serde, and mongodb to latest. To my surprise, ... then that change doesn't show up... Now I'm wondering if that difference in output comes from yet another crate that one of the above relies on...

[Theodlz]

Ok turns out that it's rsgen-avro, which when updated to versions above (and excluding). 0.16.1 which breaks this??? I can't wrap my head around why, but something must upgrade a dependency that mongodb, bson, or other relies on, and that breaks something there. Downgroading to rsgen-avro 0.16.1 or removing it from my Cargo.toml makes all these issues go away.

[isabelatkinson]

Hey @Theodlz - I expect this is not related to BSON itself given the differences in rsgen-avro versions you've found. If you want us to look into this further, can you please provide a minimal reproduction of the behavior? Thanks!

[Theodlz]

I think we can close that issue for now. I still haven't identified a root cause of it and I doubt lots of folks rely on rsgen-avro, so probably not worth spending time on this!