[tz] tzcode error handling

[Robert Elz]

    Date:        Mon, 11 Dec 2017 17:25:59 -0500
    From:        scs at eskimo.com (Steve Summit)
    Message-ID:  <2017Dec11.1725.scs.0004 at quinine.local>


  | But with all of that said, I suppose that a program that wanted
  | to fail less quietly on misinstalled or misconfigured tz data
  | could, instead of calling this new tz_set_warn_func() first, call
  | a hypothetical new tzset_with_error(&errorinfo) first,

This would be one way, as all the errors/whatever you seem to be
interested in are related to tzset and nothing really related to issues
after tzset has succeeded (when it succeeds) properly.

Alternatively, simply add some error/status info into the internal zone
structure, and then add a function to extract status (much like ferror()
does for stdio - though perhaps with a little more info available).

All in all the second seems like a more useful addition to me, if anything
really needs changing at all (the alternative is simply to create a
tzverify program, which would do what tzset does, but in a user visible way,
so when things are not behaving as they should, the user can just run that
program and see exactly what is happening - when everything is correctly
configured, none of this extra is needed, it is just extra baggage for
most programs, most of the time.)

kre