cmd/protoc-gen-go-grpc: Add flag to use separate service package

[qianlongzt]

Fixes: #8233

Release notes for cmd/protoc-gen-go-grpc:

• A new boolean flag named use_separate_service_package has been added to support generating service and message code in separate packages. When this flag is set to true, the service code will import the message package and refer to message symbols using package-qualified names. Since both the service and message code still share the same package names, users must either use the --go-grpc_out flag to place the service code in a different directory or manually move it.

RELEASE NOTES: none

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.19%. Comparing base (080f956) to head (a79e9fb).
Report is 31 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8280      +/-   ##
==========================================
+ Coverage   82.13%   82.19%   +0.06%     
==========================================
  Files         417      417              
  Lines       41385    41385              
==========================================
+ Hits        33991    34018      +27     
+ Misses       5961     5941      -20     
+ Partials     1433     1426       -7     

see 15 files with indirect coverage changes

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[dfawley]

How about something like: name this output_package and make it a string? Then the import path could be file.GoImportPath with everything after the last / stripped and replaced by what's specified here? That would allow more flexibility for how the code is generated.

[qianlongzt]

The import path becomes unnecessary after the file is generated.

#8245.
#8233 (comment)

[arjan-bal]

The package name can't be changed by the gRPC plugin, it is controlled by the Go protobuf compiler. It is usually specified by the go_package option in the .proto file, but there are other ways also (see docs).

Users can place the _grpc.pb.go file in a separate directory by using the different values for --go_out and --go_grpc_out flags. The semantics of the --go_grpc_out flag are the same as --go_out described here. For example, calling the following command:

❯ protoc --go-grpc_opt="use_separate_service_package=true,module=google.golang.org/grpc" --go-grpc_out="service" \
    --go_opt="module=google.golang.org/grpc", --go_out=. "examples/route_guide/routeguide/route_guide.proto"  

will produce the files in the following directories:

examples/route_guide/routeguide/
├── route_guide.pb.go
service/
└── examples/route_guide/routeguide/
    └── route_guide_grpc.pb.go

This means that you can specify a custom path prefix for the generated code. This doesn't help in cases where you want to add a path suffix, e.g: if you want to place oute_guide_grpc.pb.go in examples/route_guide/routeguide/service/ in the example above. For such cases, users can copy the generated code, though it is suboptimal.

[arjan-bal]

I think the most user friendly solution to split package would be to have a proto option like go_grpc_package which has semantics similar to go_package. The probuf complier would then need to handle splitting the service and message code when go_package and go_grpc_package are different.

[dfawley]

Is that something we can do? I thought the options were defined by protobuf. We could propose a go_services_package if so. The Go protobuf team seems to prefer this ideology anyway (generate services and messages into separate packages).

[arjan-bal]

It's possible to change the package name in the generated gRPC service file by setting file.GoPackageName += protogen.GoPackageName(packageSuffix). I found this in connectrpc's codegen.

if packageSuffix != "" {
    if !token.IsIdentifier(packageSuffix) {
        plugin.Error(fmt.Errorf("package_suffix %q is not a valid Go identifier", packageSuffix))
        return
    }
    file.GoPackageName += protogen.GoPackageName(packageSuffix)
    generatedFilenamePrefixToSlash := filepath.ToSlash(file.GeneratedFilenamePrefix)
    file.GeneratedFilenamePrefix = path.Join(
        path.Dir(generatedFilenamePrefixToSlash),
        string(file.GoPackageName),
        path.Base(generatedFilenamePrefixToSlash),
    )
    goImportPath = protogen.GoImportPath(path.Join(
        string(file.GoImportPath),
        string(file.GoPackageName),
    ))
}

With this, we can allow the user to configure a suffix. The grpc code will be placed in a subdirectory with name package_<suffix> and with a package name package_<suffix>.

[dfawley]

This would be my preference, then.

We should think about whether renaming the package completely would be better than just adding a suffix. I'm not sure which one would be better, but either would be better than the previous proposal.

[github-actions]

This PR is labeled as requiring an update from the reporter, and no update has been received after 6 days. If no update is provided in the next 7 days, this issue will be automatically closed.