Don't ignore additional entries in UntypedReflectDeserializerVisitor

[SkiFire13]

Objective

Currently when UntypedReflectDeserializerVisitor deserializes a Box<dyn Reflect> it only considers the first entry of the map, silently ignoring any additional entries. For example the following RON data:

{
    "f32": 1.23,
    "u32": 1,
}

is successfully deserialized as a f32, completly ignoring the "u32": 1 part.

Solution

UntypedReflectDeserializerVisitor was changed to check if any other key could be deserialized, and in that case returns an error.

---

Changelog

UntypedReflectDeserializer now errors on malformed inputs instead of silently disgarding additional data.

Migration Guide

If you were deserializing Box<dyn Reflect> values with multiple entries (i.e. entries other than "type": { /* fields */ }) you should remove them or deserialization will fail.

[MrGVSV]

@SkiFire13 Alice is right that this could be a potentially breaking change. It was not an intended behavior but there may be users who happen to have a map with more than one entry (perhaps generated via a tool and left by accident).

Could you add a Migration Guide section to the PR just indicating that affected users simply need to remove the second entry? This will help with the Migration Guide automation when putting together the release notes.

[SkiFire13]

I've added a Migration Guide section. I feel like the wording could be clearer though, let me know if you have any idea on how to improve it.

[MrGVSV]

I've added a Migration Guide section. I feel like the wording could be clearer though, let me know if you have any idea on how to improve it.

I think the wording is okay (or at least good enough to build off when putting together the full guide haha). Thanks for adding it!

[SkiFire13]

Rebased to solve the merge conflicts.

[alice-i-cecile]

@SkiFire13 can you rebase this? CI isn't detectingsome of the runs, and I think that a trivial rebase should fix it up.

[SkiFire13]

I rebased but I'm not sure why CI decided to cancel the build-wasm job.

[alice-i-cecile]

Fingers crossed let's go...