Rapid proto message generator

[aaronc]

Summary

Create a configurable generator that works with https://pkg.go.dev/pgregory.net/rapid to generate random protobuf messages for testing.

Problem Definition

Property-based testing and fuzz testing allow us to automatically generate test input to cover a wider variety of cases than hard-coded input. Rapid allows us to create generators which can be used in both property-based and fuzz testing. Protobuf messages are a common source of input in the SDK and have a well-defined format. It would help testing in many places to have a good high-quality reusable generator.

Specific use cases right now are:

• as a basis for testing Implement protoreflect based amino JSON encoder #10993
• for use in ORM and/or collections for testing complex write/iterate/read scenarios (ORM currently has its own custom set of rapid generators for this)
• maybe for testing sign mode textual

Proposal

Create a configurable generator using rapid in codec/v2 that uses the protoreflect API to generate random protobuf input. This can serve as a starting point: https://github.com/cosmos/cosmos-proto/blob/main/internal/fuzz/message.go.

It should be possible to:

• configure the file and type registries
• limit the set of messages which are generated
• use accepts_interface/implements_interface annotations to sensibly populate Anys
• use generics to specify the root message to be generated (ex. ProtoGenerator[MsgSend])

[aaronc]

@fdymylja I've also done some work here that could be useful: https://github.com/cosmos/cosmos-proto/pull/83/files#diff-ecc40b4ba1c58b2392970c1555ce6fe8646eb5a79a0ebc5464e01ac9a43d0bf4.