Add marshal_strict feature

[artemreyt]

Hello! We in gowaves use this plug-in to marshal messages for producing signatures futher and compare them to signed messages which would be marshalled by other languages implementations. The problem is that many other implementations of protobuf (for e.g. Java) marshal fields in the strict order by their numbers declared in .proto file. Consequently, the most rational way to use such marshal scheme in all languages we use in our project.

marshal feature doesn't satisfy this requirement and mustn't do as it should behave indentically to proto.Marshal() which doesn't satisfy respectively. To be more precise the difference is that oneOfs fields are marshalled before others(#22) and in the example below ethereum_transaction would be marshalled before proofs:

message SignedTransaction {
    oneof transaction {
        Transaction waves_transaction = 1;
        bytes ethereum_transaction = 3;
    }
    repeated bytes proofs = 2;
}

But we would like ethereum_transaction to be marshalled after proofs.

We came with implementation of the new feature marshal_strict that solves this problem and can be useful in similar cases.

[vmg]

Hey! Sorry for the delay on reviewing this. Code looks good but I'm confused about the varint with a new encoding. Can you clarify?

[vmg]

I don't understand why you need a specific name for encodeVarint. The implementation is identical to the previous, so why name it differently?

[artemreyt]

As i commented on 56 line in order to generate helpers for marshal and marshal_strict features independently.
E.g. if we want to use both marshal and marshal_strict features then encodeVarint implementation would be generated twice that will lead to compilation error.

[vmg]

Sorry for the delay getting back to this, you caught me in holiday. We need to do better than that for this feature: let's check during codegen whether both marshal and marshal_strict are being requested and handle that case by generating the encodeVarint helpers only once.

[artemreyt]

Sorry for long delay! Returned to this PR. Watch please, added duplicate checker for helper functions to avoid duplicates among helper functions names which are generated by different features in the same file.

[artemreyt]

Hello! @vmg , we would be really grateful if you looked the last changes! Thank you!

[fenollp]

How about replacing the default marshal feature with this one? Does this take more space on the wire or is less optimized in time or space somehow? Thanks

[artemreyt]

How about replacing the default marshal feature with this one? Does this take more space on the wire or is less optimized in time or space somehow? Thanks

I'm afraid it can break something in projects which are using current order.

[vmg]

Looking at this PR today!