bazel rules for the protobuf C++ compiler

Question

I'm using Bazel and Google's protocol buffers. I want to add a Bazel rule so I can generate the C++ API from the .proto files. In GNU make, I would do (simplified example):

%.h: %.cc
%.cc: %.proto
    protoc --cpp_out=. $<

How can I accomplish the same (i.e. generate the API whenever mymessage.proto changes) using Bazel?

Answer 1

Native support for cc_proto_library has recently landed in Bazel: http://bazel.build/blog/2017/02/27/protocol-buffers.html.

tl;dr, after setting your WORKSPACE file once,

cc_proto_library(
    name = "person_cc_proto",
    deps = [":person_proto"],
)

proto_library(
    name = "person_proto",
    srcs = ["person.proto"],
    deps = [":address_proto"],
)

...

Then,

$ bazel build :person_cc_proto

---

There's an example at https://github.com/cgrushko/proto_library.

The gist is that you define a proto_library to "import" you .proto file into Bazel, and cc_proto_library to compile it to C++. The protocol buffer compiler and runtimes are taken by default from @com_google_protobuf//:protoc and @com_google_protobuf_cc//:cc_toolchain, respectively.

The reason for this separation is to enable large proto graphs that need to be compiled to multiple languages.