[PATCH 0/3] repo: add degree-of-concern reporting to structure

"git repo structure" computes a set of statistics that are useful for diagnosing performance issues in a git repository. But for a typical user who hasn't encountered any issues yet, it can be difficult to interpret the data - when should a value be considered concerning?

This patchset introduces a feature to "git repo structure" that reports on how concerning certain measures of storage structure are for a repository. In table mode, concern is displayed as a column containing a number of stars indicating the degree of concern; in line or nul mode, concerns are displayed as additional lines with a numeric value.

To select defaults for the thresholds where a value becomes concern, a (hopefully) representative selection of repositories were analyzed. Based on empirical exploration of the data, the measurement that seemed closest to accurately assessing when a repository's structure becomes concerning was based on the base 2 logarithm of the value. Across all of the sample repositories, for all of the measurements, the point at which things become problematic was when a base 2 logarithm of a value was more than 1 standard deviation from the mean of the log_2 values in the sample set. Based on this, the concern threshold was set for each of the measures.

While this seems like a reasonable approach for setting default thresholds, it's obviously still very ad-hoc. It's likely that over time, the default values will evolve; and in the short term, projects may want to set their own thresholds. So this patchset includes support for configuring the thresholds on a per-reposiry basis.

Overview of the change:

* The first commit adds the command-line option "--concern", and creates the basic implementation of concern reporting.
* The next commit adds configurability for the concern thresholds.
* The final commit update the documentation for the command and
  configuration options.

Signed-off-by: Mark C. Chu-Carroll <markchucarroll@fastmail.com>
---
Mark C. Chu-Carroll (3):
      repo: add level of concern reporting
      repo: make concern thresholds configurable
      repo: add documentation for level-of-concern.

 Documentation/config/repo.adoc |  60 ++++++++
 Documentation/git-repo.adoc    |  27 +++-
 builtin/repo.c                 | 335 ++++++++++++++++++++++++++++++++++++++---
 t/t1901-repo-structure.sh      | 134 +++++++++++++++++
 4 files changed, 535 insertions(+), 21 deletions(-)

--- base-commit: 3bc0341126508f78f5869cbfc0005e987efdf0c7 change-id: 20261019-b4-repo-structure-concern-f1d6f6326095