Merged. Thanks!

I wasn't sure how to add tests for either.

Add a test to test crate which adds a proto3 message with repeated primitive, and checks that serialized as packed.

However, given that the crate is in low maintenance mode, I accept this as is.

I didn't see a way to distinguish which syntax was being used in a test.

Test codegen can be modified to emit this information. Or proto version can be obtained from reflective API.

I didn't see a way to have an invalid proto in a test

I think the project does not have a lot of tests for errors.

There's also no line/column number, but I'm not sure if that's expected.

When the crate was implemented, I did not know how to do errors properly. Now I know, but as I said, crate is in low maintenance.

Wait, I'm reverting this commit. I believe it is implemented incorrectly. I suspect the problem is in pure rust proto parser. I suspect protoc-based parser populates this field, but pure parser is not:

field.field.proto().options.get_or_default().packed()

Also, let's add a test.

Thanks for the review! I've added a test. I don't follow what you're saying about the pure parser not setting the packed field. I think the pure parser handles options here, and the existing tests show that packed=true/packed=false work for both protoc and pure.
Was there a bug you saw when this merged?

I don't follow what you're saying about the pure parser not setting the packed field

I suspect protoc parser already sets this field by default, and pure parser does not.

https://github.com/protocolbuffers/protobuf/blob/94ab406bcf048146ac494335e3b8ad9ef22fdabb/src/google/protobuf/descriptor.proto#L661

So my hypothesis is, we need to patch pure parser instead of patching codegen.

$ protoc test-crates/protobuf-codegen-protoc-test/src/common/v2/test_repeated_packed_pb.proto -I test-crates/protobuf-codegen-protoc-test/src/common/v2/ -o /tmp/descriptor
$ protoc --decode=google.protobuf.FileDescriptorSet google-protobuf-all-protos/protobuf/protobuf-git/src/google/protobuf/descriptor.proto  -I google-protobuf-all-protos/protobuf/protobuf-git/src/google/protobuf  < /tmp/descriptor > /tmp/descriptor.txt

descriptor.txt

That looks to me like protoc is not setting the field by default, which makes sense, since the field is optional:

  message_type {
    name: "TestIssue281"
    field {
      name: "values"
      number: 1
      label: LABEL_REPEATED
      type: TYPE_FIXED32
      options {
        packed: true
      }
      json_name: "values"
    }
  }
  message_type {
    name: "TestPackedDefault"
    field {
      name: "varints"
      number: 1
      label: LABEL_REPEATED
      type: TYPE_UINT32
      json_name: "varints"
    }
  }

So I think both parsers treat packed as optional, and the codegen needs to handle the field not being set.