Protobuf APIV2

[marioizquierdo]

Fixes: #222, #301
Related: #299, #280, #275

Description

The protobuf library has updated from APIV1 github.com/golang/protobuf to APIV2 google.golang.org/protobuf. Now Twirp generates code using the new types.

Changes:

• Generated code no longer depends on github.com/golang/protobuf/jsonpb, it now uses google.golang.org/protobuf/protojson
• Generated code no longer depends on github.com/golang/protobuf/proto, it now uses google.golang.org/protobuf/proto
• Code generator (protoc-gen-twirp) works with the latest version of google.golang.org/protobuf
• Code generator (protoc-gen-twirp) improved usage of command line flags. It now accepts paths=import (default), paths=source_relative, module={PREFIX} and works well with multiple --proto_path sources. This makes it fully compatible with the flags used on protoc-gen-go compiler invocation: https://developers.google.com/protocol-buffers/docs/reference/go-generated#invocation
• Update go_package on test proto files to use a fully qualified go import path. This is required by new versions of protoc-gen-go.
• Removed dependency on gogo-protobuf. Twirp still works with it, but requires a dependency with protobuf APIV1.
• Removed generated python code on Go tests, that was cluttering the test folders and did not have any effect on them.
• Simplified Makefile and generate commands, being more explicit makes it easier to know where the binaries are situated.

Update instructions

• The runtime library github.com/twitchtv/twirp does not have any changes.
• Generated clients and services (with protoc plugin github.com/twitchtv/twirp/protoc-gen-twirp) will update their imports from github.com/golang/protobuf/proto (APIV1) to google.golang.org/protobuf (APIV2). Projects that make use of the generated clients or service have to update the imports as well.
• The new google.golang.org/protobuf (APIV2) is mostly backwards compatible, but not completely. Some changes that we found needed in our own tests:
  • In the proto file, the option go_package is mandatory and must include a "/" (it is supposed to be a full import path). If you have to add a full path to the go_package, you may want to generate with the options paths=source_relative. For example: protoc --go_out=. --go_opt=paths=source_relative --twirp_out=. --twirp_opt=paths=source_relative myfile.proto
  • Generated message models (structs) now contain a mutex, your linter may complain if the models are copied by value. The solution is to peass pointers instead, or disable the lint for lines where a copy is made on purpose.
  • Check protobuf go compatibility and their releases for more details.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[marioizquierdo]

This PR will be released on May 3rd (next Monday) as v8.0.0.
We are doing some more testing and completing documentation meanwhile.