Re: [PATCH 0/4] trace2: add macOS and Windows process ancestry tracing

[Derrick Stolee <stolee@gmail.com>]

On 2/5/2026 11:05 AM, Matthew John Cheetham via GitGitGadget wrote:
> In 353d3d77 (trace2: collect Windows-specific process information)
> Windows-specific process ancestry information was added as a data_json event
> to TRACE2. Furthermore in 2f732bf1 (tr2: log parent process name) similar
> functionality was added for Linux-based systems, using procfs.
> 
> Let's teach Git on macOS to also gather process ancestry information, and
> emit it as a cmd_ancestry TRACE2 event.

This is done in patches 1-2. I notice that there are no tests validating
that this works.

I see that in t/t0210-trace2-normal.sh there is a scrub_normal() helper
that removes the cmd_ancestry event due to compatibility reasons.

I'd be interested to see if we could enable these tests to demonstrate
your changes here. Of course, Windows, Linux, and macOS are not the _only_
platforms we support. They are the only ones we check in CI, though.

> Furthermore, let's refactor the Windows implementation to align with the
> Linux and macOS versions - by emitting the ancestry information as a
> cmd_ancestry event. We keep the older, custom data_json event type on
> Windows for compatibility for consumers of the TRACE2 data that use the
> older event.

I appreciate this compatibility approach. I mention in my patch-by-patch
review that we should eventually drop the old mechanism, say in two major
versions.

The code looks good to me, just a question about the testing and some very
minor nitpicks around recursion and strvecs.

Thanks,
-Stolee