Flows do not render with `flow_ids`, as per guide about perfetto HOT 4 CLOSED

Unfortunately the textual dump of the Protobuf trace doesn't tell the whole story.

flow_ids type should be repeated fixed64 (https://cs.android.com/android/platform/superproject/main/+/main:external/perfetto/protos/perfetto/trace/track_event/track_event.proto;l=221;drc=ce102357934e8bf42dc2fcc8a0b145a4faed4a9d), but in your trace it's encoded as repeated fixed64 [packed=true].

Here's how we could fix this problem:

1. How are you encoding your protobufs? Which library are you using? Are you using a library that only supports "proto3" (In proto3 repeated fields are encoded as packed by default)? Can you switch to a library that supports encoding repeated fields as non packed?
2. As a workaround, you could reencode with protoc before passing it to ui.perfetto.dev. Here's a hacky way: protoc --decode=perfetto.protos.Trace -Iperfetto perfetto/protos/perfetto/trace/trace.proto < repro.pb | protoc --encode=perfetto.protos.Trace -Iperfetto perfetto/protos/perfetto/trace/trace.proto > repro2.pb, where perfetto is a directory where you have a checkout of the perfetto repo.
3. Ideally ui.perfetto.dev should accept your trace. https://protobuf.dev/programming-guides/encoding/#packed says

Protocol buffer parsers must be able to parse repeated fields that were compiled as packed as if they were not packed, and vice versa.

Doing 3 requires a non trivial amount of work and I don't think fits nicely with the current parsing architecture, but I'm going to get @LalitMaganti comment on this.

from perfetto.

Doing 3 requires a non trivial amount of work and I don't think fits nicely with the current parsing architecture, but I'm going to get @LalitMaganti comment on this.

Yup agree with everything you say, you're absolutely right that if we follow the spec strictly, we would accept it. However,

• that would introduce a slight slowdown everywhere we parse repeated scalar fields which is in quite a few places
• it would add non-trivial complexity to the parsers

I would not do anything on our side for this issue.

from perfetto.

Thank you both for your help! I was using betterproto as the encoder -- I'll modify the generated bindings to ensure flow_ids are non-packed.

from perfetto.

Thank you both for your help! I was using betterproto as the encoder -- I'll modify the generated bindings to ensure flow_ids are non-packed.

Great!

from perfetto.