(define (run-git repo command args proc)
  (receive (in out pid err)
      (process* "git" (cons* "--git-dir" repo command args))
    (begin0
     (proc in)
     (receive (_ ok? status/signal) (process-wait pid)
       (unless ok?
         (error 'run-git
                (sprintf "git ~A on ~A terminated abnormally with signal ~A"
                         command
                         repo
                         status/signal)))
       (unless (zero? status/signal)
         (error 'run-git
                (sprintf "git ~A on ~A failed with exit status ~A:~%~A"
                         command
                         repo
                         status/signal
                         (read-all err)))))
     (close-input-port err)
     (close-input-port in)
     (close-output-port out))))