cue: proto support

[cueckoo]

Originally opened by @mpvl in cuelang/cue#5

Tracking issue for adding protobuf support to CUE:

• import command reads text and binary proto instance
• import command reads proto definitions
• export command supports the converse
• core libs

[cueckoo]

Original reply by @JohnAZoidberg in cuelang/cue#5 (comment)

What's the status of encoding Cue values as Protobuf?
I'd like to describe my data in cue and dump is as binary using Protobuf.
Should I go through JSON and convert that to Proto3?

[cueckoo]

Original reply by @mpvl in cuelang/cue#5 (comment)

It is not implemented so far. Should be straightforward, but stabilizing the new evaluator has priority.

But open to contributions.

[cueckoo]

Original reply by @mvdan in cuelang/cue#5 (comment)

In case you're not aware, the new protobuf module has low-level primitive packages for encoding and decoding, for example for arbitrary data in protowire: https://pkg.go.dev/google.golang.org/protobuf@v1.26.0/encoding/protowire

https://pkg.go.dev/google.golang.org/protobuf@v1.26.0/encoding/prototext is message-based instead of token-based, though, so it's unclear if you could use it at all without a schema.

[andreidum]

Original reply by @mpvl in cuelang/cue#5 (comment)

It is not implemented so far. Should be straightforward, but stabilizing the new evaluator has priority.

Hello, is there any update/estimate on the timelines for this request?

[randomizedcoder]

With regards to Protobuf support, the documentation has been improved since 2021, but still does not make it clear that Cue can't generate protobuf files form Cue. Cue can import .proto to .cue, but cannot go the other way.
https://cuelang.org/docs/concept/how-cue-works-with-protocol-buffers/

References:
cue-lang/cuelang.org#371
#581
#983

Instead of cue, we have settled for the protobuf validation via:
https://github.com/bufbuild/protovalidate