Treat protoc warnings as errors (#3113)

CONTRIBUTING.md

@@ -11,7 +11,7 @@ This doc is for contributors to Temporal Server (hopefully that's you!)
   - Install on Ubuntu with `sudo apt install golang`.
 * [Protocol buffers compiler](https://github.com/protocolbuffers/protobuf/) (only if you are going to change `proto` files):
   - Install on macOS with `brew install protobuf`.
-  - Install on Ubuntu with `sudo apt install protobuf-compiler`.
+  - Download all other versions from [protoc release page](https://github.com/protocolbuffers/protobuf/releases).
 * [Temporal CLI tctl](https://github.com/temporalio/tctl)
   - Homebrew `brew install tctl`
   - Go install `make update-tctl`

Makefile

@@ -150,7 +150,7 @@ protoc: $(PROTO_OUT)
 	@printf $(COLOR) "Build proto files..."
 # Run protoc separately for each directory because of different package names.
 	$(foreach PROTO_DIR,$(PROTO_DIRS),\
-		protoc $(PROTO_IMPORTS) \
+		protoc --fatal_warnings $(PROTO_IMPORTS) \
 		 	--gogoslick_out=Mgoogle/protobuf/descriptor.proto=github.com/golang/protobuf/protoc-gen-go/descriptor,Mgoogle/protobuf/duration.proto=github.com/gogo/protobuf/types,Mgoogle/protobuf/wrappers.proto=github.com/gogo/protobuf/types,Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,plugins=grpc,paths=source_relative:$(PROTO_OUT) \
 			$(PROTO_DIR)*.proto \
 	$(NEWLINE))