Description of the problem / feature request:

With protobuf's proto_lang_toolchain, after this change protocolbuffers/protobuf@7b28278 it seems the blacklisted_protos are no longer working correctly and removing that field has no effect on the build.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

See protocolbuffers/protobuf#7046 for a repro case

What operating system are you running Bazel on?

macOS

What's the output of bazel info release?

release 1.2.0 (I also tried with 2.0.0 with no change)

Have you found anything relevant by searching the web?

The protobuf commit linked above referenced this bazel change a5ee2c4

I'm also wondering if the issue is with protobuf's use of strip_import_prefix on the proto_library targets they define: protocolbuffers/protobuf@a03d332