Expose a py_proto_library target for build_event_stream.proto so that way the python programs outside the Bazel repo can consume the BEP

Description of the feature request:

Make the src/main/java/com/google/devtools/build/lib/buildeventstream/proto/build_event_stream.proto file publicly visible. Alternatively, export the file with exports_files().

What underlying problem are you trying to solve with this feature?

I have a Python tool that needs to ingest the build event stream, so I’m trying to generate a Python protobuf library for the BES.

I’m using the @com_github_grpc_grpc//py_proto_library rule as such:

py_proto_library(
    name = "build_event_stream",
    deps = ["@io_bazel//src/main/java/com/google/devtools/build/lib/buildeventstream/proto:build_event_stream_proto"],
)

However, since the proto file of interest is in an external workspace, the generated build_event_stream_proto_pb2.py file has the following content which can’t be imported:

from ...io_bazel.src.main.java.com.google.devtools.build.lib.buildeventstream.proto.build_event_stream_pb2 import *

---

The workaround to this is to declare a filegroup with the proto file of interest, manually build a local proto library, and then list that target as a dependency (I’ve verified that this approach works with public proto files such as @io_bazel//src/main/protobuf:extra_actions_base.proto).

# This example should work, but doesn't since build_event_stream.proto is not publicly visible

py_proto_library(
    name = "build_event_stream",
    deps = [":build_event_stream_proto"],
)

proto_library(
    name = "build_event_stream_proto",
    srcs = [":build_event_stream_proto_file"],
)

filegroup(
    name = "build_event_stream_proto_file",
    srcs = ["@io_bazel//src/main/java/com/google/devtools/build/lib/buildeventstream/proto:build_event_stream.proto"],
)

Unfortunately, this workaround does not work for this case because build_event_stream.proto is not publicly visible.

Which operating system are you running Bazel on?

Ubuntu 20.04.4 LTS

What is the output of bazel info release?

release 4.2.2

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What’s the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

Nothing exactly relevant, but there are a bunch of questions about which py_proto_library rule to actually use (I’ve found 3 implementations…).

Any other information, logs, or outputs that you want to share?

No response

[haxorz]

On second thought, there’s already //src/main/java/com/google/devtools/build/lib/buildeventstream/proto:build_event_stream_java_proto with intentionally-public visibility. So that precedent makes me think we don’t need to think about setting a precedent ourselves here.

Therefore I think the proposed change is very reasonable.

[tpudlik]

I too became interested in how py_proto_library is coming along, and found it’s now a PR: https://github.com/bazelbuild/rules_python/pull/832. Looks pretty close to going in!