Add built-in support for gpb for building proto files

When gpb is found in DEPS or BUILD_DEPS then it is used
instead of erlang_protobuffs.

plugins/protobuffs.mk

@@ -28,14 +28,27 @@ $(ERLANG_MK_TMP)/last-makefile-change-protobuffs: $(filter-out $(PROJECT).d,$(MA
 $(PROJECT).d:: $(ERLANG_MK_TMP)/last-makefile-change-protobuffs
 endif
 
+ifeq ($(filter gpb,$(BUILD_DEPS) $(DEPS)),)
 define compile_proto.erl
 	[begin
-		protobuffs_compile:generate_source(F,
-			[{output_include_dir, "./include"},
-				{output_src_dir, "./src"}])
+		protobuffs_compile:generate_source(F, [
+			{output_include_dir, "./include"},
+			{output_src_dir, "./src"}])
 	end || F <- string:tokens("$1", " ")],
 	halt().
 endef
+else
+define compile_proto.erl
+	[begin
+		gpb_compile:file(F, [
+			{include_as_lib, true},
+			{module_name_suffix, "_pb"},
+			{o_hrl, "./include"},
+			{o_erl, "./src"}])
+	end || F <- string:tokens("$1", " ")],
+	halt().
+endef
+endif
 
 $(PROJECT).d:: $(PROTO_FILES)
 	$(verbose) mkdir -p ebin/ include/

test/plugin_protobuffs.mk

@@ -40,6 +40,38 @@ protobuffs-compile: build clean
 		{ok, [empty_pb, simple_pb]} = application:get_key($(APP), modules), \
 		halt()"
 
+protobuffs-compile-with-gpb: build clean
+
+	$i "Bootstrap a new OTP library named $(APP)"
+	$t mkdir $(APP)/
+	$t cp ../erlang.mk $(APP)/
+	$t $(MAKE) -C $(APP) -f erlang.mk bootstrap-lib $v
+
+	$i "Add gpb to the list of dependencies"
+	$t perl -ni.bak -e 'print;if ($$.==1) {print "BUILD_DEPS = gpb\n"}' $(APP)/Makefile
+
+	$i "Download two proto files"
+	$t mkdir $(APP)/src/proto/
+	$t curl -s -o $(APP)/src/proto/empty.proto $(PROTOBUFFS_URL)/proto/empty.proto
+	$t curl -s -o $(APP)/src/proto/simple.proto $(PROTOBUFFS_URL)/proto/simple.proto
+
+	$i "Build the application"
+	$t $(MAKE) -C $(APP) $v
+
+	$i "Check that an Erlang module was generated and compiled"
+	$t test -f $(APP)/src/empty_pb.erl
+	$t test -f $(APP)/src/simple_pb.erl
+	$t test -f $(APP)/include/empty_pb.hrl
+	$t test -f $(APP)/include/simple_pb.hrl
+	$t test -f $(APP)/ebin/empty_pb.beam
+	$t test -f $(APP)/ebin/simple_pb.beam
+
+	$i "Check that the generated modules are included in .app file"
+	$t $(ERL) -pa $(APP)/ebin/ -eval " \
+		ok = application:load($(APP)), \
+		{ok, [empty_pb, simple_pb]} = application:get_key($(APP), modules), \
+		halt()"
+
 protobuffs-makefile-change: build clean
 
 	$i "Bootstrap a new OTP library named $(APP)"