[PATCH platform2 1/2] common-mk: add goproto_library source_relative opt

[Alyssa Ross <hi@alyssa.is>]

We need this for the go_package changes in protoc-gen-go 1.5.x.  If we
didn't use source-relative paths, the full module path would be
repeated in the output location, so we'd get paths like
src/chromiumos/vm_tools/vm_crash/chromiumos/vm_tools/vm_crash/vm_crash.pb.go.

To avoid the duplication, we either need to set source_relative, or
set proto_out_dir to just go/src.  The latter isn't workable, because
then everything two libraries that both use common.proto will both
generate outputs called "go/src/common.pb.go", which will upset GN.
---
 common-mk/proto_library.gni | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/common-mk/proto_library.gni b/common-mk/proto_library.gni
index fb9fb4231d..23645a134f 100644
--- a/common-mk/proto_library.gni
+++ b/common-mk/proto_library.gni
@@ -225,6 +225,9 @@ template("proto_library") {
 #   proto_lib_dirs (optional)
 #       Directories to search for protos a proto file depends on.
 #       proto_in_dir and "${sysroot}/usr/share/proto" are added by default.
+#   source_relative (optional)
+#       If true, the output file is placed in the same relative directory as the
+#       input file (but under proto_out_dir).
 template("goproto_library") {
   action(target_name) {
     forward_variables_from(invoker,
@@ -254,6 +257,10 @@ template("goproto_library") {
 
     go_plugin_parameters = []
 
+    if (defined(invoker.source_relative) && invoker.source_relative) {
+      go_plugin_parameters += [ "paths=source_relative" ]
+    }
+
     if (defined(invoker.gen_grpc) && invoker.gen_grpc) {
       go_plugin_parameters += [ "plugins=grpc" ]
     }
-- 
2.31.1