Custom Plugins

Custom plugins are supported by rules_proto_grpc, through the use of the proto_plugin Starlark rule and creating of a rule that implements proto_compile_impl for the new plugin.

To add a new plugin, you can generally follow the pattern seen in the multiple language examples in this repository. In short, the basic idea is:

  1. Load the plugin rule: load("@rules_proto_grpc//:defs.bzl", "proto_plugin")

  2. Define the rule, giving it a name, options (not mandatory), tool and outputs. tool is a label that refers to the binary executable for the plugin itself and can be select()’ed based on your platform, for example.

  3. Choose your output type (pick one!):

    • outputs: A list of strings patterns that predicts the pattern of files generated by the plugin. Use this type for plugins that produce one output file per input proto file.

    • out: The name of a single output file generated by the plugin. Use this type for plugins that produce a single output file per call to protoc.

    • output_directory: Set to true if your plugin generates files in a non-predictable way, for example if the output paths depend on the service names within the files.

  4. Create a compilation rule and aspect using the following template, substituting the plugin label where indicated:

load("@rules_proto//proto:defs.bzl", "ProtoInfo")

# Create compile rule
example_compile = rule(
    implementation = proto_compile_impl,
    attrs = dict(
        _plugins = attr.label_list(
            providers = [ProtoPluginInfo],
            default = [
                Label("//<LABEL OF YOUR PLUGIN>"),
            doc = "List of protoc plugins to apply",
    toolchains = [str(Label("@rules_proto_grpc//protobuf:toolchain_type"))],