Expose default attr 'compiler'

[johnskopis]

Not sure if this belongs here or in rules_go. I recently migrated from pubref rules (gogo) to a recent go_rules using this example: https://github.com/weaveworks/cortex/compare/bazel-0.5.4...ianthehat:bazel-0.5.4

I had to make made gazelle generate go_proto_library rules with the compiler attribute set to my gogo_proto compiler. I ran gazelle with -external=vendored -proto=default.

The only issue was in vendor/github.com/golang/protobuf/protoc-gen-go/descriptor/BUILD.bazel: The hacked up gazelle didn't set a different compiler for go_rpc_library but I think that would have fixed it. I just removed compiler and marked the file gazelle: ignore

My compiler had to use external @targets (those didn't specify the compiler attribute)

go_proto_compiler(                                                               
    name = "gogo_proto",                                                         
    deps = [                                                                     
        "@com_github_gogo_protobuf//gogoproto:go_default_library",               
        "//vendor/github.com/gogo/protobuf/proto:go_default_library",            
        "//vendor/github.com/gogo/protobuf/sortkeys:go_default_library",         
        "//vendor/github.com/gogo/protobuf/types:go_default_library",            
    ],                                                                           
    plugin = "@com_github_gogo_protobuf//protoc-gen-gogoslick",                  
    visibility = ["//visibility:public"],                                        
)  

In order for the above to work I depend on external @targets. It's unclear if those targets are maintained by gazelle running with external=vendor. I think I would like gazelle to generate rules for external @targets using external=external mode and everything else using external=vendored mode.

Does that make sense?

Does it make sense to add args to gazelle: --proto_compiler: default proto compiler to use when generating go_proto_library rules (default: @io_bazel_rules_go//proto:go_proto) --rpc_proto_compiler: default proto compiler to use when generating go_rpc_library rules (default: @io_bazel_rules_go//proto:go_grpc)

Thanks

[johnskopis]

After a little bit more thought it probably makes more sense to allow caller to override the implementation of go_proto_library or go_rpc_library instead

[jayconrod]

At the moment go_grpc_library is just a wrapper for go_proto_library with a specific compiler. I'd like to make Gazelle migrate existing instances of go_grpc_library to go_proto_library (see #8).

I think it's reasonable to have an option that explicitly sets the compiler attribute on generated go_proto_library rules though.

FYI, you can use buildozer to make bulk changes like this to rules. Should be easier than forking and modifying Gazelle.

[Globegitter]

It would be nice if this could also be defined for the go_repository, so e.g. I could specify

go_repository(
        name = ".....",
        commit = "....",
        importpath = "...",
        build_file_proto_compiler = "@io_bazel_rules_go//proto:gogofaster_grpc",
    )

But I suppose that is more specific to the rules_go repo. So opened an issue there for it.