Compiler warnings from protoc can get lost, especially when part of a large build system, and there's no flag—at least, not one that I can find—to upgrade those warnings into fatal errors, like the -Werror flag does for GCC.

It would also be nice to provide plugins with an interface for indicating when a warning has been produced, so that protoc can exit with a failing exit status if -Werror has been passed. Our Go protobuf generator produces some warnings that we'd like to treat as errors, for example: gogo/protobuf/issues/356