[RFC PATCH 0/6] Use trace2 in commit-reach

As promised, here is the direction I took when applying the trace2 feature to the walking code in commit-reach.c. Hence, this depends on Jeff's trace2 patches and ds/reachable.

There are multiple benefits to the approach I take here:

1. If a user has performance problems, we can rerun the command
   with tracing on and get the region enter/leave notifications
   and the extra data like "num_walked".

2. While I was testing this series against real-world examples,
   I found a number I didn't expect. The numbers for
   can_all_from_reach_with_flags were much higher than I expected.
   Turns out the heuristic I wrote was not working correctly. With
   the trace2 library, I was able to add a "run_and_check_trace2"
   function in test-lib.sh so I could make the number of walked
   commits be a condition we check in the test. Then, the benefit
   we expect is demonstrated by the test suite when I fix the
   bug.

Thanks, -Stolee

P.S. I'm sending this RFC from gmail because I'm having SMTP issues with my work email.

Derrick Stolee (6):
  commit-reach: add trace2 telemetry and walk count
  comit-reach: use trace2 for commit_contains_tag_algo
  commit-reach: use trace2 in can_all_from_reach
  test-tool: start trace2 environment
  test-lib: add run_and_check_trace2
  commit-reach: fix first-parent heuristic

 commit-reach.c        | 32 ++++++++++++++++++++++++++++++--
 t/helper/test-tool.c  |  3 +++
 t/t6600-test-reach.sh |  6 ++++++
 t/test-lib.sh         | 14 ++++++++++++++
 4 files changed, 53 insertions(+), 2 deletions(-)