As of release 4.0.0, the transitive mode has been completely removed. All compilation now exclusively uses the direct mode.

In previous versions of rules_proto_grpc, the compilation aspect would compile and aggregate all dependent .proto files from any top level target. In hindsight, this was not the correct behaviour and led to many bugs, since you may end up creating a library that contains compiled proto files from a third party, where you should instead be depending on a proper library for that third party’s protos.

Even in a single repo, this may have meant multiple copies of a single compiled proto file being present in a target, if it is depended on via multiple routes. For some languages, such as C++, this breaks the ‘one definition rule’ and produces compilation failures or runtime bugs. For other languages, such as Python, this just meant unnecessary duplicate files in the output binaries.

Therefore, in the 3.0.0 of rules_proto_grpc, there was added an option to bundle only the direct proto dependencies into the libraries, without including the compiled transitive proto files. This is done by replacing the deps attr on lang_{proto|grpc}_{compile|library} with the protos attr. Since this would be a substantial breaking change to drop at once on a large project, the new behaviour was opt-in in 3.0.0 and the old method continued to work throughout the 3.x.x release cycle. As of release 4.0.0, the old transitive mode has been removed completely.

As an additional benefit of this change, we can now support passing arbitrary per-target rules to protoc through the new options attr of the rules, which was a much sought after change that was impossible in the aspect based compilation.

Switching to non-transitive compilation

In short, replace deps with protos on your targets:

# Old
    name = "routeguide",
    deps = ["//example/proto:routeguide_proto"],

# New
    name = "routeguide",
    protos = ["//example/proto:routeguide_proto"],

In applying the above change, you may discover that you were inheriting dependencies transitively and that your builds now fail. In such cases, you should add a lang_{proto|grpc}_{compile|library} target for those proto files and depend on it explicitly from the relevant top level binaries/libraries.