.. _module-pw_protobuf_compiler:

--------------------
pw_protobuf_compiler
--------------------
The Protobuf compiler module provides build system integration and wrapper
scripts for generating source code for Protobuf definitions.

Generator support
=================
Protobuf code generation is currently supported for the following generators:

+-------------+----------------+-----------------------------------------------+
| Generator   | Code           | Notes                                         |
+-------------+----------------+-----------------------------------------------+
| pw_protobuf | ``pwpb``       | Compiles using ``pw_protobuf``.               |
+-------------+----------------+-----------------------------------------------+
| Nanopb      | ``nanopb``     | Compiles using Nanopb. The build argument     |
|             |                | ``dir_pw_third_party_nanopb`` must be set to  |
|             |                | point to a local nanopb installation.         |
+-------------+----------------+-----------------------------------------------+
| Nanopb RPC  | ``nanopb_rpc`` | Compiles pw_rpc service and client code for   |
|             |                | nanopb. Requires a nanopb installation.       |
+-------------+----------------+-----------------------------------------------+
| Raw RPC     | ``raw_rpc``    | Compiles raw binary pw_rpc service code.      |
+-------------+----------------+-----------------------------------------------+
| Go          | ``go``         | Compiles using the standard Go protobuf       |
|             |                | plugin with gRPC service support.             |
+-------------+----------------+-----------------------------------------------+
| Python      | ``python``     | Compiles using the standard Python protobuf   |
|             |                | plugin, creating a ``pw_python_package``.     |
+-------------+----------------+-----------------------------------------------+

GN template
===========
The ``pw_proto_library`` GN template is provided by the module.

It defines a collection of protobuf files that should be compiled together. The
template creates a sub-target for each supported generator, named
``<target_name>.<generator>``. These sub-targets generate their respective
protobuf code, and expose it to the build system appropriately (e.g. a
``pw_source_set`` for C/C++).

For example, given the following target:

.. code-block::

  pw_proto_library("test_protos") {
    sources = [ "test.proto" ]
  }

``test_protos.pwpb`` compiles code for pw_protobuf, and ``test_protos.nanopb``
compiles using Nanopb (if it's installed).

Protobuf code is only generated when a generator sub-target is listed as a
dependency of another GN target.

**Arguments**

* ``sources``: List of ``.proto`` files.
* ``deps``: Other ``pw_proto_library`` targets that this one depends on.

**Example**

.. code::

  import("$dir_pw_protobuf_compiler/proto.gni")

  pw_proto_library("my_protos") {
    sources = [
      "foo.proto",
      "bar.proto",
    ]
  }

  pw_proto_library("my_other_protos") {
    sources = [
      "baz.proto",  # imports foo.proto
    ]

    # Proto libraries depend on other proto libraries directly.
    deps = [ ":my_protos" ]
  }

  source_set("my_cc_code") {
    sources = [
      "foo.cc",
      "bar.cc",
      "baz.cc",
    ]

    # When depending on protos in a source_set, specify the generator suffix.
    deps = [ ":my_other_protos.pwpb" ]
  }