Alternative names (aliases) for a protobuf field

[Charith Ellawala]

Hello,

I am wondering whether it is possible to create aliases for protobuf fields so that the CEL parser automatically treats an expression like `obj.non_existent_attribute` as `obj.actual_attribute` instead. 

The users of my application usually deal with the JSON representation of protobufs. One of the quirks arising from that is that a protobuf definition like `string some_field = 1` is represented as `someField` in the JSON representation. So when they want to refer to that field in a CEL expression, they would write `obj.someField` but CEL can't resolve that because `obj` is declared as a protobuf type in the Env and CEL expects the field to be referenced like `obj.some_field`.

I hope that makes sense. I could't find an way to achieve the above in cel-go but I feel like I am missing something obvious. Any help is much appreciated.

Thank you.

[Tristan Swadell]

Hi Charith,

Unfortunately, you're not missing something obvious. One approach is to introduce a new `ref.TypeProvider` which can map from the camelCase `json` tag on the protobuf field to the snake_case name of the field. Your approach can be very robust and read the Go metadata information, or it can also be fairly simple and just recase from camelCase to snake_case when attempting to find a field name and that might just be enough to make things work.

Hopefully this helps!

-Tristan

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[Charith Ellawala]

Hi Tristan,

I somehow overlooked the `ref.TypeProvider.FindFieldType` method so thank you very much for that tip. I think it would work for my use case. 

BTW, the cel-go library is amazing in its extensibility. Thanks to you and the rest of the team for maintaining such a brilliant open source project.

Charith.