[ggj][bazel] fix: fail early if bazel lacks a grpc_service_config.jso…

…n file (#541)

* fix: align resname ctors with superclass variants

* fix: avoid type collisions - refactor {Concrete,Vapor}Ref into AstNodes

* fix: better message null checks in Parser

* fix: map proto.Empty RPC types to void in ServiceClient

* fix: improve import(shortName) state-keeping in ImportWriterVisitor

* fix: fix stub pkg for all ServiceSettingsStub usages

* fix: handle older protos with javaMultipleFiles=false

* fix: gate isPaged on all fields for monolith back-compat

* fix: fail early if bazel lacks a grpc_service_config.json file

rules_java_gapic/java_gapic.bzl

@@ -93,6 +93,8 @@ def java_gapic_library(
 
     if grpc_service_config:
         file_args_dict[grpc_service_config] = "grpc-service-config"
+    else:
+        fail("Missing a gRPC service config file")
 
     if gapic_yaml:
         file_args_dict[gapic_yaml] = "gapic-config"