Plugin support for protobuf compiler (protoc) targets.

third_party/protobuf/proto_library.gni

Index: third_party/protobuf/proto_library.gni
diff --git a/third_party/protobuf/proto_library.gni b/third_party/protobuf/proto_library.gni
index df9d657bf46aa0366f9681f45db30cc5db87fb42..13a64f930f48dd9a35206c8e4241b4a161b2cc07 100644
--- a/third_party/protobuf/proto_library.gni
+++ b/third_party/protobuf/proto_library.gni
@@ -25,6 +25,9 @@
 #       It is likely you also need to #include a file for the above EXPORT
 #       macro to work. See cc_include.
 #
+#   cc_generator_plugin (optional)
+#       Plugin executable name. Expected .pb.h and .pb.cc as output.

[xyzzyz, 2016/06/20 20:17:46]

If you drop the requirement that the plugin outputs need to be .pb.h and .pb.cc,
I think the code will be both more general and simpler at the same time.

It will be more general, because e.g. gRPC plugin generates .grpc.pb.h and
.grpc.pb.cc files in addition to .pb.h/.pb.cc files generated by regular protoc,
and so the current code will not be usable with gRPC plugin. You will probably
need to add some parameter here to let the GN/GYP know about the desired
extension (and so about desired output artifacts). Also, it looks like your
plugin generates the file with the same as regular "--cpp_out". Is it necessary
in your case? If so, you could also add parameters that would determine if
regular "--cpp_out" is passed.

It will be simpler, because you will not need to make any changes to
protoc_wrapper.py at all -- you will just add an additional "--plugin_out" flag
alongside currently existing "--cpp_out" and "--python_out", conditional on a
plugin being used.

[kraynov, 2016/06/20 20:19:47]

Acknowledged.

+#
 #   cc_include (optional)
 #       String listing an extra include that should be passed.
 #       Example: cc_include = "foo/bar.h"
@@ -100,6 +103,11 @@ template("proto_library") {
       ]
     }
 
+    if (defined(invoker.cc_generator_plugin)) {
+      cc_generator_plugin = invoker.cc_generator_plugin
+    } else {
+      cc_generator_plugin = ""
+    }
     args += [
       "--protobuf",
       "$rel_out_dir/{{source_name_part}}.pb.h",
@@ -107,6 +115,7 @@ template("proto_library") {
       "{{source_dir}}",
       "--proto-in-file",
       "{{source_file_part}}",
+      "--cc-generator-plugin=$cc_generator_plugin",
 
       # TODO(brettw) support system protobuf compiler.
       "--use-system-protobuf=0",
@@ -165,11 +174,14 @@ template("proto_library") {
 
     public_configs = [ "//third_party/protobuf:using_proto" ]
 
-    public_deps = [
-      # The generated headers reference headers within protobuf_lite, so
-      # dependencies must be able to find those headers too.
-      "//third_party/protobuf:protobuf_lite",
-    ]
+    # If using built-in cc generator the resulting headers reference headers
+    # within protobuf_lite, hence dependencies require those headers too.
+    # In case of generator plugin such issues should be resolved by invoker.
+    if (!defined(invoker.cc_generator_plugin)) {
+      public_deps = [
+        "//third_party/protobuf:protobuf_lite",
+      ]
+    }
     deps = [
       ":$action_name",
     ]