class SimpleCov::Formatter::JSONFormatter::ResultHashFormatter

def git_commit

doesn't print git's diagnostics to the build.
coverage.json. stderr is captured (not forwarded) so a non-git project
matters most when `source_in_json false` drops the source text from
can recover the exact source a report was generated against, which
project isn't a git checkout or git isn't on PATH. Recorded so tools
Full git commit SHA of `SimpleCov.root`'s HEAD, or nil when the 
def git_commit
  output, status = Open3.capture2e("git", "-C", SimpleCov.root.to_s, "rev-parse", "HEAD")
  status.success? ? output.strip : nil
rescue StandardError
  nil
end