events: Keep data of unknown relations

[zecakeh]

So I thought that being able to catch the data of unknown relations would be as simple as adding an untagged variant, thanks to the latest release, but it seems like it doesn't work.

For some reason the relation field of RelatesToJsonRepr is None with an unknown rel_type (see tests)… I'm putting the code here to make sure this is a serde issue rather than me not seeing something with our code. Maybe it's an issue with having a flatten above…

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Preview: https://pr-1581--ruma-docs.surge.sh

[zecakeh]

So it turns out untagged doesn't work in our cases for deserialization. I ended up using JsonValue instead of Box<RawJsonValue> for deserializing relations of the room::message module though.

[zecakeh]

Rebased on main to solve CI issue.

[jplatte]

Re. usage of serde_json::Value, can you explain why it's necessary? Haven't actually found the place it's used yet from skimming. It's quite bad perf-wise so I'd like to avoid it where possible.

[zecakeh]

Re. usage of serde_json::Value, can you explain why it's necessary? Haven't actually found the place it's used yet from skimming. It's quite bad perf-wise so I'd like to avoid it where possible.

I don't know if it is necessary per se, but I can't find another way to deserialize it and keep custom relation data. The untagged variant attribute doesn't work and neither does deserializing m.relates_to in a Box<RawJsonValue>, for some reason.

[zecakeh]

Rebased on main

[jplatte]

Haven't reviewed thoroughly, but AFAICT we have new tests, and the JsonObject deserialization only happens for custom relations, not for known ones. Based on that, I'm happy to merge.

[zecakeh]

Alright I finally found a way to do it without JsonValue. I got some inspiration from the description of serde-rs/serde#2403 (the PR that added the untagged attributes to enum variants): separate the enum between a tagged enum for known relations an untagged one to get the custom relation if the tagged ones don't match, and it works.

My guess is that this doesn't work with the attribute because the rel_type field is consumed trying to match the tagged variants, so we can't get it in the custom variant and deserialization fails.

[jplatte]

Hm, this isn't much better than serde_json::Value I think (does internal buffering). I have a different idea..

[jplatte]

Can we make this a boxed RawJsonValue and try different deserializers on that?

[jplatte]

If you don't feel like it though we can also merge now and I'll try to revisit myself.

[zecakeh]

I have been trying to do that in different ways, and for some reason whenever I try to deserialize something into a Box<RawJsonValue>, it always triggers this error on types that are not RoomMessageEventContent (so the extensible events types):

Error("invalid type: newtype struct, expected any valid JSON value", line: 1, column: 296)

[jplatte]

Sounds like we're using internal buffering elsewhere. I guess that makes sense. Let's merge.

[jplatte]

Nice!